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cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.3 Base-Band (BB) Header | The Base-Band (BB) frame header (BBHEADER) is transmitted in the clear. The content of the BBHEADER should not allow reliable inferences about traffic activity when traffic obfuscation is enforced. For these reasons, and others explained later, the BBHEADER should have settings as follows. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 117 Table 8.8: BBHEADER settings BBHEADER Field Applicable variants Value MATYPE Field TS/GS Generic Stream 01 SIS/MIS Multiple Input Streams 0 CCM/ACM CCM or ACM, as appropriate 0 or 1 ISSYI (not used) 0 NPD (not used) 0 RO As appropriate for the Roll-Off Used ISI (2nd byte of MATYPE) Distinguishes channels (see clause 8.3.4.4) UPL 0 DFL Always use max feasible size for the DFL of the frame SYNC Indicates encrypted BB payload (see clause 8.3.4.6) w or w/o NCR SYNCD 00 CRC-8 Calculated as normal These settings are within the normal DVB-S2 operation contour. No customization of the BBHEADER syntax or semantics is required. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.4 Acquisition and Protected Channels on the Forward Link | The Acquisition Channel and the Protected Channel on the Forward Link are created using the following fields in the BBHEADER: • ISI byte (Input Stream Identifier, as available with Multiple Input Streams) • SYNC byte (as is available with Continuous Generic Streams) The ISI byte is used here to indicate the Acquisition Channel vs. the Protected Channel. The Professional profile could specify a default value for the ISI for the Acquisition Channel to promote interoperability. The ISI byte value for the Protected Channel can be specified via signalling from the NCC, via the Acquisition Channel. The SYNC byte is used to identify whether DVB-RCS encryption is used or not on the Acquisition Channel. The SYNC byte values for indicating this should be taken from the private range (0xB9 to 0xFF) currently allowed for the SYNC byte, and effort should be made to append to the standardized values. Two values are needed to cover two cases: • BBFRAME payload holds an encrypted block (header and payload) • The NCR (encapsulated in GSE and in-the-clear) immediately follows the BBHeader, and is followed by an encrypted block (header and payload) The recommended values, to facilitate appending these to standard values are: 0xB9 and 0xBA respectively. (For both formats the encrypted payload of the BBFrame should fill-out the rest of the frame to its maximum feasible DFL value (given the PL layer parameters for that PL frame), leaving room for only a CRC-32 field at the very end of the BBFRAME. This field is split in two, where the first half is used for an encrypted CRC-16 covering the encrypted payload, whereas the last part is used for a cleartext CRC-16 covering the whole BBFRAME, including the header. Where encrypted, the encryption applies to the content (i.e. the payload) of the BBFRAME. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.5 Acquisition and Protected Channels on the Return Link | Implementation of these channels on the Return Link may be accomplished means of resources for the Acquisition Channel and resources for the Protected Channel. An RCST on the Acquisition Channel Forward Link will receive only the signalling applicable to the Return Link for the Acquisition Channel. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 118 An RCST on the Protected Channel Forward Link will receive the signalling from this channel and will stop receiving anything else than the NCR from the Acquisition Channel. To implement this, some SI that might in unprotected systems be sent as one table, will have to be sent as two tables, one variant in the Acquisition Channel and another variant in the Protected Channel. The resources may be organized to obfuscate the traffic patterns on the carriers used for the Acquisition Channel and the carriers used for the Protected Cannel, by overlapping these channels on shared carriers. The encrypted payload of the frame should fill-out the rest of the frame to its maximum feasible value, leaving room for only the CRC-32 field at the very end of the RLE packet. This field is split in two, where the first half is used for an encrypted CRC16 covering the encrypted payload, whereas the last part is used for a cleartext CRC-16 covering the whole RLE packet, including the header. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.6 AES-CTR-256 for Link Encryption | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.6.0 General | The Professional profiles use AES-256 in Counter (CTR) mode (AES-256-CTR). This allows for variable length blocks of data to be encrypted without compromising security. That results in greater overall network efficiency. Different variations of this method can be applied to the Protected Channels on the Forward (and Regenerative Mesh), Return (and Transparent Mesh) Link carriers, and the Acquisition Channel on Forward and Return Link. In particular, the application to regenerative mesh systems imposes special constraints (as described in clause 8.3.4.6.2). |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.6.1 Transparent Operation | For the Forward Link, the cleartext NCR, with an extension method applied, is proposed used as the counter and may be combined with the network PASSPHRASE and other bit string in the application of CTR mode. The native broadcasted DVB-RCS NCR wraps in less than 46 hours and is not sufficient alone. This design utilizes a counter that is already well established in DVB-RCS and avoids including other explicit counters that should be maintained and trusted for the CTR counter purpose. The NCR extension method is proposed to be a synthesis by a well-known algorithm from the knowledge of the security system Time of Day (TOD), and then aligned with the standard broadcasted NCR at a suitable resolution. Entering the security system TOD with a precision of a couple of minutes should be operationally feasible and should also be sufficient to acquire the link. Better accuracy in entered TOD than that should probably not be required. One selected byte (the Crypto Block Header) of the NCR is attached to the encrypted data block as header as an explicitly signalled part of the counter to help resolve NCR ambiguity due to uncertainty in NCR reconstruction. The encryption unit chooses one value of NCR from its own NCR counter, and the decryption unit chooses a value of the NCR from its own regenerated NCR as assumed used by the encryption unit (referring to the satellite position). These NCR values are likely to be close but also likely to be slightly different when operating with the required resolution of the NCR section to be used in the counter value. For the Return Link, the AES-256 counter should be based on an extended superframe counter, combined and other SI table numbers (e.g. timeslot_number, frame_number, superframe ID). The sizes of the bit fields used to form this counter should anticipated future expansion of the frame_number and timeslot_counter to at least full bytes (e.g. 1 and 2 bytes, respectively). Different keys may be used for the Forward Link vs. Return Link directions at security policy discretion. Market demand for this exists today, as it enhances security and allows some added flexibilities, at the expense of distributing more keys. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 119 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.6.2 Regenerative Mesh Operation | When considering the Regenerative Mesh return link, the use of the implicit cryptographic synchronization techniques like the extended superframe counter is problematic, because when data is demodulated on-board the satellite, the extended superframe counter meaning is lost during multiplexing and re-modulating the data on the processed DVB-S2 downlink. An alternative method for the regenerative return link is to use explicit cryptographic synchronization vector (embedded in the RLE packet), such as a variant of NCR extension (used on the transparent forward link). In this regenerative variant, a shared secret Initialization Vector (IV) is used to extend the NCR. This IV can be provisioned in all RCST. The operator may decide to have a common IV for all RCSTs in the network, or per SVN, or even one IV per each RCST pair communicating. Another possibility for systems that support DCP is to dynamically negotiate the IV using specific TRANSEC protocol DCP messages. This negotiation is implemented with NCC intervention to maintain the secret and an authenticated and trusted IV. The NCC DCP Link Service Establishment_Responses may contain an additional IE with a random IV that would be used for each RCST connectivity link. DCP messages should be encrypted, and therefore the secret is assured. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.4.7 Encryption Used at higher layers | For the IPsec tunnel between SRM and SGW, the following encryption methods are required: • a digital signature method, e.g. from [i.22]; • a symmetric key encryption method, e.g. from [i.22]. For encryption of the key pair the following methods are required supported: • an asymmetric encryption method, e.g. from [i.21]. For key distribution from CA/KG, an asymmetric encryption method, e.g. from [i.21]. For key distribution from Key Generator device, a symmetric encryption method e.g. from [i.21]. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.5 Traffic Obfuscation | On the forward link, traffic obfuscation is achieved by filling of any unoccupied DVB-S2 frames with "chaff" packets. Operator discretion should be supported regarding the desired level traffic obfuscation on Return/Mesh carriers. To accomplish full obfuscation it would be necessary to use Constant Rate Assignments (CRA) exclusively, and/or use FCA systematically to complement Bandwidth-on-Demand, and to rule out contention-based SYNC and logon bursts for signalling. This will usually cause a large reduction in usage efficiency, which could have an impact of the cost of operations. This mode also limits flexibility, as terminals cannot easily get significantly more bandwidth in times of sudden need, which could impair accomplishing the mission at a critical time. It is therefore reasonable to support conditional obfuscation within the context of the Professional profile, to be implemented selectively by network operator. An enhanced NCC, using robust assignment algorithms and input on current obfuscation policy by terminal, can enforce the necessary rules for traffic activity obfuscation on TDMA carriers using standard DVB-RCS signalling. Thus, there is no need here for a separate security profile to allow selective relaxation on traffic activity obfuscation, and no issues affecting inter-operability. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6 Regenerative Mesh Extension | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6.0 Introduction | Mesh Interactive Satellite Systems use the Professional profile as the standard TRANSEC implementation. This clause describes explicitly some extensions needed to implement TRANSEC in conjunction with dynamic connectivity and the DCP protocol. The mesh extension permits also to establish Protected Channels without HSM interaction. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 120 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6.1 Encrypted Communications Channels, layered architecture and NCR | Regenerative Mesh Systems follow the same architecture and procedures as stated in clauses 8.3.2.1, 8.3.2.2, and 8.3.2.3 with the noted exception for mesh. Additionally professional mesh RCST can establish protected channels with other RCSTs. Figure 8.5 illustrates mesh extension possible channels. Figure 8.5: Mesh extension in the professional profile |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6.2 Authentication and Key Management | Mesh Systems follow the same procedures as stated in clause 8.3.3 with the noted exception for mesh. These procedures are used to achieve the "System Logon" The DCP Logon and RCST to RCST or RCST to NCC/GW dynamic link establishments are specified in following subsections. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6.3 DCP Logon | DCP Logon (see the DVB RCS2 HLS [i.4], annex E) should be performed over the protected channel with the NCC. The NCC maintains one protected channel (and one session key) per logged-in RCST. This channel is used for synchronization maintenance and for DCP connection establishment. When the RCST communicates with other RCST a new protected channel is established and the RCSTs communicate using a new session key. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.3.6.4 RCST to RCST Dynamic Link establishment | This clause describes the connection establishment and the RCST protected channel acquisition with other RCST as per the following procedure using DCP (the DVB RCS2 HLS [i.4], annex E): 1) The RCST starts a communication sending a (bi-directional) Link Service Establishment Request by sending a RCST DCP message to the NCC, using the protected channel. This channel has been obtained using an authentication procedure, so this exchange is considered authenticated and secure. 2) The NCC receives the message and decodes it using the protected channel key. 3) The NCC performs the following functions: a) The NCC checks the connection parameters and approves the connection. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 121 b) The NCC creates the session key. This is an AES 256 key formed from random bytes. c) The NCC extracts the destination and source RCSTs X.509 certificates from the NMC database. d) The NCC creates two versions of the session key coded with: - the destination RSA public key; and - the source RSA public key. 4) The NCC sends the Link Service Establishment Request by sending the NCC DCP message to the called RCST, containing, the Connection Control_Descriptor containing an Information Element (IE) with the session key encrypted with the called RCST public key. This entire message is encrypted with the peer RCST protected key, shared with the NCC so it is also authenticated. 5) The Called RCST decrypts the message with the protected channel key, obtains the connection information and approves the connection. Finally obtains the session key decrypting the IE with its private key. 6) The Called RCST sends the Link Service Establishment Response by sending the RCST DCP message to the NCC using the protected channel. 7) The NCC sends the Link Service Establishment Response by sending the NCC DCP message to the Calling RCST, with an information element (IE), with the session key encrypted with the calling RCST public key. This entire message is encrypted with the peer RCST protected key, shared with the NCC so it is also authenticated. 8) The Calling RCST decrypts the message with the protected channel key, obtains the connection information and approves the connection. Finally, it obtains the session key by decrypting the Information Element (IE) with its private key. 9) All messages between the RCSTs are exchanged using the session key. The session has been authenticated (as both RCSTs obtained the session key, using its private key, and the NCC is an authenticated entity they trust) and is secure as AES-256 is used. This case is the most generic one. Other dynamic link establishment types (e.g. uni-directional, NCC initiated) should follow the same procedure of establishing protected channels. Note that traffic dynamic links are established using an AES session key per traffic connection. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4 Government Profile | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.1 Introduction | This clause presents a transmission security (TRANSEC) feature implementation for DVB-RCS2. The scheme is based on an existing, approved and tested implementation which is deployed on a point-to-multipoint VSAT system that has many characteristics in common with DVB-RCS(2), including a shared forward link based on DVB-S2 and an MF-TDMA return link. Modifications have been made to the extent required for the TRANSEC scheme to fit in the DVB-RCS2 framework. Equipment incorporating the scheme on which this proposal is based has been certified in accordance with FIPS 140-2 level 2 [i.34]. The security features offered by this scheme include authentication, link layer encryption and traffic obfuscation. Authentication is based on Public Key Infrastructure (PKI) and X.509 certificates [i.24]. This is considered sufficient for RCST Authentication and Encryption Key Exchange, as well as for protection against cloning, hub faking and replay attacks. The link layer encryption employs AES-256 in approved modes of operation; the security architecture is arranged such that no element of signalling or traffic ever traverses the satellite link unencrypted. The traffic obfuscation feature ensures that all frames in the forward link are filled with encrypted data, so that actual traffic activity cannot be determined by observing the signal. It also ensures that all traffic time slots in the return link are filled with bursts. The occupancy of logon and control slots masks the real logon and synchronization maintenance activity in the network. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 122 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.2 Security Architecture | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.2.0 General | This clause describes the functional architecture of the security system. Other than the separation into Network Control Centre (NCC) and RCST, this architecture does not make any assumptions about the physical implementation of the functional elements. The nature of this clause is informative; specific requirements are introduced in later clauses that deal with the individual security features in more detail. The architecture is based on the use of two bi-directional, logical channels. These are known as the Acquisition Ciphertext Channel (ACC) and Dynamic Ciphertext Channel (DCC), respectively. These channels are encrypted using separate keys. The DCC is preferred and is used for all unicast and multicast traffic as well as for the majority of signalling exchanged with RCST's that are fully synchronized and authenticated in the network. The Acquisition Ciphertext Channel is used for initial logon, authentication and to exchange keys for the Dynamic Ciphertext Channel. It is also used for any information that needs to be sent to logged-off terminals. The rationale for this arrangement is that, in the event the ACC key becomes compromised; only information about the acquisition process is exposed. The network can continue to operate while a new ACC key is established. Because the DCC key is protected by the RSA public/private keys, possession of the ACC key does not allow an attacker to recover the DCC key. At the same time, this arrangement allows all signalling information to be encrypted, even when exchanged with RCST's that are not logged on. The air interface used to transport the two channels is described in more detail in clause 8.4.4. For the purpose of this architectural description, it suffices to note that each frame of the DVB-S2 forward link can contain data for either or both logical channels, while each burst in the return link contains data for only one logical channel. The architecture is described in more detail in the following sub-clauses. Internal interfaces between the functional units are not defined in detail; these interfaces are implementation-specific and can be assumed to carry all necessary side information, such as addressing, priorities, MODCOD selection and choice of logical channel. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.2.1 NCC Security Architecture | The NCC security architecture is shown in Figure 8.6. The architecture works for CCM, VCM and ACM. The functions of the elements are as follows: 1) The external network as shown here encompasses both red and black networks; the interface is thus shown inside a possible convergence router. 2) The firewall may or may not be present in this location, depending on the red-black network configuration. However, this does not affect the TRANSEC architecture significantly. 3) The edge router is the main, bi-directional interface point of the satellite network. As indicated, actual user traffic for the forward link will normally be carried in the DCC. 4) The encapsulation and mode adaptation unit operates in a manner similar to that used in non-TRANSEC operation, whether in CCM, VCM or ACM mode. Its main purpose is to create the payloads of BBFRAME's from the incoming IP traffic and signalling. The unit does however have a number of additional features, in particular: - The ability to create place-holders for a number of fields associated with the encryption. - The ability to create place-holders for dummy or "chaff" GSE packets to fill any portion of a BBFRAME that cannot be filled with real traffic. - The ability to create complete frames filled with chaff packets, so that the transmission of DVB-S2 dummy frames is avoided. The air interface is described in more detail in clause 8.4.4. There are logically separate outputs from this unit for the ACC and DCC portions of the frame payload. 5) The ACC "stamping" module performs NCR re-stamping in accordance with the standard, based on SOF time stamps as indicated. It also inserts the Initialization Vector (IV) value for the encryption in the place-holder provided and fills any chaff packets with pseudo-random data. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 123 6) The stamping module for the DCC is functionally identical to that for the ACC, except that it does not perform IV stamping or NCR re-stamping. 7) Encryption of the ACC is performed independently, using the appropriate key. As indicated, the IV for subsequent encryption operations depends on the output of previous operations. 8) Encryption of the DCC is performed independently, using the appropriate key. As indicated, the IV for subsequent encryption operations depends on the output of previous operations. 9) Construction of the BBFRAME encompasses insertion of the BBHEADER, concatenation of the elements of the frame resulting from the ACC and DCC encryption, and addition of the BBFRAME Cyclic Redundancy Check (CRC) in accordance with the standard. 10) The DVB-S2/S2X modulation includes all functions defined in ETSI EN 302 307 [i.2] and [i.80] from the mode adaptation interface onwards. The resulting transmission is fully DVB-S2 compliant. 11) The DVB-RCS demodulator recovers encrypted return link burst payloads from the IF interface. A practical system usually has several return link carriers. 12) The decryption device recovers the plaintext from each burst payload. Since each burst carries only one logical channel, there is no need for parallel decryption. The channel used is indicated in encrypted form within the burst itself, as described in clause 8.4.4.2. 13) The burst processing function separates traffic, in-band signalling and payloads from logon and control bursts. It directs them to the signalling and traffic processors as appropriate. This function is identical to that found in non-TRANSEC systems. 14) The signalling processing is similar to that found in non-TRANSEC systems; however, it has a number of additional functions necessitated by TRANSEC. The functions of this element include: - Generation of "static" signalling for the forward link; this will be carried in the ACC. - Processing of signal level, timing and frequency offset measurements passed on from the demodulator, to generate appropriate RCST control messages. These will be passed back to the RCST in either the ACC or DCC, as described later. - Handling of initial terminal synchronization and MAC layer logon, as per the standard. This is usually carried out in conjunction with the Network Management System. Following completion of this process (i.e. when the RCST is in the "TDMA Sync" state), the Security Management System is alerted to initiate the Authentication Process. - Processing of in-band and out-of-band capacity requests to generate the Terminal Burst Time Plan (TBTP2) for traffic. The TBTP2 differs from that in a non-TRANSEC system in that all traffic slots are always assigned, even in a lightly loaded system. This is part of the traffic obfuscation that hides the actual traffic activity in the overall network and per-RCST. The TBTP2 is separated into two parts; that for the ACC is sent in the ACC; that for the DCC is sent in the DCC. - Generation of slot assignments for logon and control bursts in a manner that obfuscates the actual activity pattern, as described later. 15) The traffic processing operates almost identically to non-TRANSEC systems. Its main purpose is to re-assemble layer-3 (IP) packets from the fragments received in burst payloads. Normal user traffic is forwarded to the edge router. However, any TRANSEC-related messages (e.g. elements of the authentication exchanges) are forwarded to the Security Management System; they never appear on external interfaces. 16) The Security management System is unique to a TRANSEC-enabled network. The main functions of this unit are: - Generation of public and private encryption keys and security certificates or, alternatively, interfacing to external key foundries and/or certificate authorities to obtain these over a secure link. The choice of method is system-specific. The external interface is required for multi-beam systems that support mobile terminal roaming, in order to facilitate handover of RCST's between beams. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 124 - Distribution of keys within the system (within the NCC and over-the-air to RCST's) and control of key roll-over. Internal distribution is not shown in the diagram, to reduce clutter. In order to support handover of mobile RCST's, an external interface for transmitting or receiving key roll-over commands is required. - Management of RCST authentication at logon, communicating directly with the RCST. - Informing the network management system of the outcome of the authentication. - Operator interface for configuration of all security-related parameters, zeroising compromised RCST's, etc. 17) The Network Management System operates in a manner very similar to that in a non-TRANSEC network, including management of QoS, etc., which are not security-related. The NMS will however not enable an RCST for regular operation in the Signalling Processing unit until it has passed the authentication process. Should the authentication process fail, the RCST will be logged off immediately. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 125 Edge Router Firewall External Network Encapsulation Mode Adaptation DCC Stamping ACC DCC Stamping Encryption Encryption BBFRAME Construction DVB-S2 Modulation SOF TX IF Signalling Processing Traffic Processing Decryption DVB-RCS Demodulation RX IF Network Management System Security Management System Optional secure link To external CA, key foundry 1 2 3 4 5 6 7 8 9 10 11 12 14 15 16 IV IV Burst Processing 17 Mode Adaptation Interface 13 Figure 8.6: NCC security architecture ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 126 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.2.2 RCST Security Architecture | The RCST security architecture is shown in Figure 8.7. The architecture applies to CCM, VCM and ACM in the forward link and to static as well as adaptive return links. Since the BBHEADER is not encrypted, the scheme is fully DVB-S2 compliant. The functions of the elements are as follows: 1) The DVB-S2 demodulator operates in the same manner as in a non-TRANSEC network. It delivers all the BBFRAME's that it is able to demodulate correctly, based on the BBFRAME CRC check. 2) The stream filter can remove streams in the forward link carrier that are known not to be relevant, based e.g. on the ISI value in the BBHEADER (the BBHEADER is not encrypted). This part of its function is identical to what it does in non-TRANSEC networks. Furthermore, based on information obtained from a partial decryption of the frame using the ACC key, the stream filter separates the frame payload into parts that need to be completely decrypted using the ACC and DCC keys, respectively. It also extracts the IV to be used for decryption. 3) The ACC decrypter operates twice per frame; first to recover plaintext information about the amounts of AC and DC data contained, and subsequently to decrypt the ACC data proper. The DCC decrypter recovers plaintext data for the DCC channel. 4) The output of the decrypters are GSE PDU fragments and/or complete packets. These are provided to the de-encapsulators. The de-encapsulation process is essentially identical to that in non-TRANSEC networks. It re-assembles IP packets from the GSE PDU's and extracts signalling information. It operates separately on PDU's from the ACC and DCC. 5) The signalling processing is identical to that for non-TRANSEC networks, except that it needs to handle TRANSEC-specific signalling elements. These are carried in the normative "hooks". 6) The IP processing is largely identical to that in non-TRANSEC networks. Any IP packets destined for the security management functions (this is not used in the current implementation) are routed internally and never appear on the external interface. As in non-TRANSEC networks, incoming data are sent to the queues/buffers for transmission in the return link. 7) The local (site) network encompasses all local connectivity; specifically, this interface is considered to be inside any separation between black and red networks. 8) The security management function is specific to TRANSEC networks; essentially it is the counterpart of the Security Management System in the NCC. It handles the following: - Protocols for all exchanges of certificates and key updates, including generation of security-related messages to be carried in the return link. - Zeroising, status reporting (not part of current implementation). - Encryption and decryption of messages encrypted using the public-key scheme. - Distribution of keys to the encryption and decryption units in the RCST and key roll-over (not shown in the diagram to reduce clutter). 9) The traffic processing subsystem has the functions also found in non-TRANSEC systems, including separation into traffic/request classes, fragmentation and encapsulation. The encapsulation process is altered slightly, to account for burst payload sizes being modified to allow room for encryption-related parameters. The buffering function contains the necessary classification to separate packets to be sent using the ACC and DCC respectively. It should be noted that it will in general not be necessary to replicate the complete set of QoS classifications in the ACC: This channel is never used for actual user traffic, and its use is limited as soon as the authentication is complete and the keys have been established for the DCC. 10) Capacity requests are generated as in non-TRANSEC systems; the only difference being that the request generation needs to consider also traffic queued in the ACC. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 127 11) The burst formatting function generates bursts in all time slots assigned in the TBTP2. If there is no actual content to transmit, a "chaff" payload is generated. This function also includes insertion of encryption-related parameters and in-band capacity requests. The channel (ACC or DCC) to use is determined by the source of the burst payload at the head of the queue in the buffering sub-system. 12) The complete burst payload is encrypted using the appropriate key(s), as described in detail in clause 8.4.4.2. 13) The modulation function is identical to that in non-TRANSEC networks. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 128 DVB-S2 Demodulation RX IF Stream Filter Decryption ACC Decryption DCC Decaps. IP Processing Signalling Processing NCR, Control, Time Plans, ... Security Management Traffic Processing DCC Capacity Requests Encryption Burst Formatting Modulation TX IF 1 2 3 6 8 10 12 13 11 Site Network Frame layout 9 TBTP2 Decaps. 5 4 7 Figure 8.7: RCST security architecture ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 129 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3 Authentication and Key Management | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.1 Authentication of RCST's and Hubs | The following steps constitute the complete logon and authentication process for RCST's. While most of the authentication takes place following the physical/MAC layer log-on and synchronization, certain actions are taken in advance in order to protect the corresponding information: 1) The NCC generates 2 TBTP2's per superframe. One of these is the normal time plan used to indicate to RCST's the slots in which they may transmit. This TBTP2 plan is always encrypted using the active DCC key. The second TBTP2 is encrypted using the network acquisition (ACC) key. It contains assignments of logon slots (if used) and also of other selected slots used for authentication purposes. The union of the two TBTP2's covers all slots within a superframe. 2) The TBTP2's are forwarded and broadcast in the normal manner. RCST's that are not yet acquired receive the time plan via the ACC and identify a suitable logon slot to initiate the physical-layer log-on. This can be a random-access or an assigned slot as defined in ETSI EN 301 545-2 [i.1]. 3) The RCST acquires the return link in the normal fashion, using a sequence of logon and control slots. All assignments for these slots are carried in the TBTP2 and/or TIM contained in the ACC. 4) Once the RCST has reached the "TDMA Sync" state, it should follow the steps of the key distribution protocol described in clause 8.4.3.2 before it is trusted by the network, and for it to trust the network. All communications associated with this are carried in the ACC. Hence, RCST's in this state will request capacity normally and will be granted TDMA slots required for the key distribution exchanges. During this step, the hub and RCST exchange key negotiation messages in the ACC. Three message types exist: solicitations, certificate presentations and key updates. Solicitation messages are used to synchronize, request, inform, and acknowledge the peer. Certificate presentations contain X.509 certificates. Key updates contain AES key information, signed and encrypted with RSA-2048 [i.25]. The RSA encryption is done using the RCST's public key and the signature is created using the NCC's private key. The protocol messages are defined in clause 8.4.3.4. 5) Once authentication is complete, the key update message should also complete in the ACC. The actual symmetric keys are encrypted using the RCST's public key information obtained in the exchanged certificates. 6) Once the symmetric key is exchanged, the RCST enters the network as a trusted entity and begins normal operation, using the DCC for all traffic and signalling. The admission procedure outlined above ensures that neither control information nor actual traffic is ever allowed to traverse the air interface unencrypted. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.2 Key Management | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.2.0 Introduction | The key management protocol defined in this clause meets FIPS 140-2 requirements for PKI-based key management protocols that use X.509 [i.24] certificate authentication. When the present TRANSEC implementation is employed, this protocol is mandated for authentication of RCST's, and is recommended also for all other key management operations within the system - for example, the transfer of keying material between the Security Management System and the actual encryption devices within the gateway, or exchanges with external certificate authorities and key foundries. There are three elements of this protocol: Key distribution, Key rollover and Host Keying. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 130 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.2.1 Key Distribution | The key distribution protocol is illustrated in Figure 8.8. This protocol assumes that, upon receipt of a certificate from a peer, the host is able to validate and establish a chain of trust based on the contents of the certificate. This allows the NCC to authenticate the RCST, and also allows the RCST to authenticate the NCC, thus preventing it from being "hijacked" by a hostile NCC. Certificate formats and methodologies to verify the peer's certificate are in accordance with X.509 [i.24]. When used as part of the authentication of an RCST, the first certificate solicitation will normally be initiated by the NCC (specifically, the Security Management System). When the present TRANSEC implementation is employed, the key update is a mandatory part of the protocol when used as part of the authentication of an RCST. Key updates may also be initiated by either peer at any time. Details of the protocol are defined in clause 8.4.3.4. Figure 8.8: Key distribution protocol |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.2.2 Key Update and Rollover | A peer may initiate a key update in an unsolicited fashion as needed. The data structure used to complete a key update is illustrated in Figure 8.9. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 131 Figure 8.9: Key ring This data structure conceptually consists of a set of pointers (Current, Next, Fallow), a 2 bit identification field (utilized in the Encryption Headers as described in clause 8.4.4), and the actual symmetric keys themselves. A key update consists of generating a new key, placing it in the last fallow slot just prior to the Current pointer, updating the next pointers and current pointers in a circular fashion, and generating a Key Update message reflecting these changes. The key update mechanism allows for multiple keys to be "in play" simultaneously, so that seamless key rollovers can be achieved. A seamless key rollover is ensured by always transmitting the 2-bit identification field ("key ring position") which identifies the key used for encryption. The NCC can carry out the key rollover at any time after the key update has been completed, simply by starting to use the "next" key. In the inbound, the RCST carries out the key rollover as soon as a key rollover in the forward link has been detected. It is the responsibility of the NCC to ensure that the appropriate keys are available before carrying out a key rollover. When the present TRANSEC implementation is employed, this key rollover mechanism is mandated for maintenance of the ACC and DCC keys in the RCST. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.2.3 Host Keying | The host keying protocol is defined in Figure 8.10. This protocol defines how any host is originally provided an X.509 certificate from a Certificate Authority. The Certificate Authority Foundry can be part of the Security management System in the NCC or can be a remote entity accessed through a secure protocol. The messages that constitute this protocol are defined in Recommendation ITU-T X.509 [i.24]. The messages are exchanged using TCP. Following completion of the initial certificate exchange shown in Figure 8.9, the hub will transmit the network acquisition key to the host. The network acquisition key is encrypted with the host public key before being transmitted to the host. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 132 Figure 8.10: Host keying protocol |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.3 Key Management for Acquisition Ciphertext Channel | The ACC key is provided by the NCC. It is never exposed in the clear. When transferred, it is always encrypted with the host's public key. NOTE: Because an RCST cannot enter the network without the current ACC key, an RCST that is out of the network for the entire period between the time a new key is pushed and the time it is activated will be unable to join the network until a new key is entered by other means, as defined in clause 8.4.6.2. Because of this, the operator should select a crypto-period which balances the operational needs of the network against preserving the theoretical strength of the ACC key. The key roll operates in a manner similar to the dynamic key rollover: 1) When an RCST first enters the network, it is given the "current" ACC Key and the "next" ACC key. The "next" key is the one that will be used after the next key roll. 2) In the return direction, RCST carries out a key rollover when one is detected in the forward link. 3) When the key rollover occurs, the remote uses the "next" ACC KEY. 4) After the key rollover, a new "next" key is generated by the NCC. 5) The new current/next key pair is pushed to all RCST's. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 133 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4 Authentication and Key Management Protocol Messages | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4.0 Overview | This clause defines the method for exchanging key management protocol messages and the contents of these messages. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4.1 Certificate Solicitation Message | The format of the certificate solicitation message is shown in Table 8.9. Table 8.9: Syntax of certificate solicitation message Syntax No. of bits Information Mnemonic Reserved Information certificate_solicitation_message() { RCST_MAC_address 48 uimsbf interactive_network_ID 16 uimsbf rx_session_id 32 uimsbf peer_tx_session_id 32 uimsbf tx_session_id 32 uimsbf peer_rx_session_id 32 uimsbf rx_session_state 3 2 uimsbf tx_session_state 2 uimsbf rx_certification_state 1 bslbf rx_certificate_id 32 see text tx_certificate_id 32 see text algorithm_length 4 4 uimsbf for (i=0; i< algorithm_length; i++) { Algorithm 16 uimsbf } transport_set_count 8 uimsbf for (i=0; i< transport_set_count; i++) { transport_set_start 4 uimsbf transport_set_end 4 uimsbf } message_length 8 uimsbf for (i=0; i< message_length; i++) { message_byte 8 } } Semantics for certificate_solicitation_message: RCST_MAC_address: RCST hardware address as per IEEE 802.3 [i.26]. interactive_network_id: This 16 bit field gives the label identifying the network_ID for the interactive network. rx_session_id: This field defines the transmitting node's ID for incoming exchanges. The initial value is set to a random number when the node is initialized. Thereafter the value is incremented once every constant time period (e.g. every fifteen minutes). The time period is configured during system installation. peer_tx_session_id: If there have been no exchanges from the peer receiving this message, then this field has a value of zero. Otherwise the value of the tx_session_id most recently received from the peer is copied into this field. tx_session_id: This field defines the transmitting node's ID for outgoing exchanges. The initial value is set to a random number when the node is initialized. Thereafter the value is incremented once for each Key Update. NOTE: If the link goes down and the RCST needs to re-acquire, there will be a Key Update as part of that activity; thus this value will also be incremented in that case. peer_rx_session_id: If there have been no exchanges from the peer receiving this message, then this field has a value of zero. Otherwise the value of the rx_session_id most recently received from the peer is copied into this field. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 134 rx_session_state: This field defines the status of the session from the receiving peer to the transmitting node. The allowed values are defined in Table 8.10. Table 8.10: Values for rx_session_state and tx_session_state Value State 0 Session up 1 Session down 2 Session opening 3 Reserved tx_session_state: This field defines the status of the session from the transmitting to the receiving node of the present message. The allowed values and their interpretation are the same as for rx_session_state (Table 8.10). rx_certification_state: This field defines the status of a certificate received from the peer receiving this message. It takes the value '1' if a certificate has been received and '0' otherwise. rx_certificate_id: If there have been no exchanges from the peer receiving this message, then this field has a value of zero. Otherwise it is set as follows: The 20-byte ASN.1 digest [i.27] of the peer's certificate is computed. The first four bytes (0..3) of this are placed into the field, with byte 0 being placed in the least significant eight bits, through byte 3 being placed in the most significant eight bits. tx_certificate_id: This field is set as follows: The 20-byte ASN.1 digest [i.27] of the node's certificate is computed. The first four bytes (0..3) of this are placed into the field, with byte 0 being placed in the least significant eight bits, through byte 3 being placed in the most significant eight bits. algorithm_length: This field defines the number of encryption algorithms that the transmitting node is capable of using. algorithm: This field contains the identifying number of an algorithm which the node is capable of using. The allowed values are defined in Table 8.11. Table 8.11: Encryption algorithm identifying numbers Algorithm Number RSA-2048 500 AES-256 CBC 507 AES-256 CFB 508 AES-256 CTR 509 NOTE 1: The AES-256 algorithm is also used in ECB mode, but only for computation of initialization vectors, not for actual data encryption. NOTE 2: The transport_set_count, transport_set_start and transport_set_end fields are included for future enhancement. There is currently one transport_set defined, with fixed values. In general, transport_sets define the keys usable for TRANSEC certificates. transport_set_count: This field is set to 1. transport_set_start: This field is set to 2. transport_set_end: This field is set to 3. message_length: This field is set to the length, in bytes, of the optional text message field. if no message is included, this field is set to 0. message_byte: One byte of an optional text message field. The presence, contents and usage of this message are all unspecified. In the forward link, the solicitation message is transported in the TIM in a TRANSEC_ message_descriptor with a transec_message_type value of 0x02. The transec_message_byte sequence contains the certificate_sollicitation_message formatted according to Table 8.9. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 135 In the return link, the message is transported in a PDU using the TRANSEC_certificate protocol type. The format of the PDU is as specified in Table 8.12. The message_type field is set to the value 0x02 for a certificate_solicitation message. Table 8.12: PDU format for certificate solicitation messages Syntax No. of bits Mnemonic Certificate_message(){ message_type 8 uimsbf certificate_solicitation_message see text } |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4.2 Certificate Presentation Message | The certificate is formatted in accordance with the X.509 standard [i.24]. In the forward link, it is transported in the TIM, in a TRANSEC_message_descriptor with a transec_message_type value of 0x03. The transec_message_byte sequence contains the certificate, formatted according to [i.24]. In the return link, the certificate is transported in a PDU using the TRANSEC_certificate protocol type. The format of the PDU is as specified in Table 8.13. The message_type field is set to the value 0x03 for a certificate presentation message. Table 8.13: PDU format for certificate presentation messages Syntax No. of bits Mnemonic Certificate_message(){ message_type 8 uimsbf Certificate As per [i.24] } |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4.3 Key Update Message | In the forward link, they key update message is transported in the TIM, in a TRANSEC_message_descriptor with a transec_message_type value of 0x03. The transec_message_byte sequence contains the key update message, formatted according to Table 8.14. Table 8.14: Syntax of key_update_message Syntax No. of bits Information Mnemonic Reserved Information key_update_message() { message_type 16 uimsbf payload_length 8 uimsbf for (i=0; i< payload_length; i++) { payload_byte 8 see text } algorithm_length 3 5 uimsbf for (i=0; i<algorithm_length; i++) { algorithm_byte 8 see text } for (i=0; i< AF; i++) { 8 filler_byte 8 uimsbf } signature_length 8 uimsbf for (i=0; i< signature_length; i++) { signature_byte 8 see text } interactive_network_id 16 uimsbf } ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 136 Semantics for key_update_message: message_type: This field identifies the message type. It is set to "1012" (decimal). payload_length: This field defines the number of bytes contained in the payload field. payload_byte: Each instance of this field contains one byte of the encrypted contents of the Key Update Command. Each instance of the field has been encrypted first with the RCST's public RSA key, and secondly with the NCC's private RSA key. The format of the overall payload field is defined in clause 8.4.3.4.3.1. algorithm_length: This field defines the number of bytes in the algorithm field. algorithm_byte: Each instance of this field contains one byte of the name of the encryption algorithm used. Valid names are listed in Table 8.15. Table 8.15: Permitted encryption algorithm names Algorithm "ALG_AES_CBC" "ALG_AES_CFB" "ALG_AES_CTR" filler_byte: Unused byte; the number AF of these bytes is such that AF+algorithm_length is an integer multiple of 4. signature_length: This field defines the number of bytes in the signature field. signature_byte: Each instance of this field contains one byte of the signature field. The signature consists of the first twenty bytes of the new key, encrypted first by the destination RCST's Public RSA key, and secondly by the NCC's Private RSA key. interactive_network_id: This 16 bit field gives the label identifying the network_ID for the interactive network. 8.4.3.4.3.1 Key Update Payload Format The cleartext of the payload field is formatted as defined in Table 8.16. Table 8.16: Syntax of key update payload field Syntax No. of bits Information Mnemonic Reserved Information key_update_payload() { tx_session_id 32 uimsbf rx_session_id 32 uimsbf command_count 8 uimsbf for (i=0; i< command_count; i++) { transport_id 8 uimsbf active_key_index 6 2 uimsbf new_key_count 8 uimsbf for (j=0; j< new_key_count; j++) { key_ring_index 5 2 uimsbf valid 1 bslbf key_length 8 uimsbf for (k=0; k<key_length; k++) { key_byte 8 see text } } } } Semantics for key_update_payload: tx_session_id: The semantics for this field are the same as for the synonymous field in the certificate_solicitation_message (clause 8.3.4.1); ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 137 rx_session_id: The semantics for this field are the same as for the synonymous field in the certificate_solicitation_message (clause 8.3.4.1); command_count: This field defines the number of key update commands that follow; transport_id: This field identifies the purpose of the command. Allowed values are 2 for "TRANSEC Master TX Netkey" (hub-to-remote) and 3 for "TRANSEC master RX Netkey" (remote-to-hub); active_key_index: Identifies the key ring position of the currently active key; new_key_count: This field identifies the number of new keys that follow; key_ring_index: The index to the RCST's key ring position where the key is to be stored; valid: Validity of the new key. This field should always be set to '1'; key_length: This field identifies the length of the key in bytes; key_byte: Each instance of this field contains one byte of the actual key. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.3.4.4 Key Update Acknowledgement | This message is sent only in the return link. The format of this message is identical to the Certificate solicitation message (clause 8.3.4.1). If the message is being used as a Certificate Solicitation message, then either the peer_tx_session_id, the peer_rx_session_id, or both, will be zero. This indicates that a Certificate has not been received and successfully processed. If both of these fields do have values, and if these values match what the NCC expects to see from this RCST, then the message is a Key Update Acknowledgement. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4 Encryption | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.1 Forward Link | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.1.0 Frame Structure | Each DVB-S2/S2X frame in the forward link is encrypted using AES-256 in CBC mode, as defined in this clause. The CBC operation is defined in clause 8.4.3.1. The organization of a BBFRAME with TRANSEC is illustrated in Figure 8.11. Figure 8.11: DVB-S2 BBFRAME with TRANSEC Encrypted GSE Packet(s) The fields in this frame are as follows: • The BBHEADER is as per the DVB-S2/S2X standard and is sent unencrypted. The DFL indicates the payload length from the start of the ACC EC field to the end of the CRC-32. The SYNC field within the BBHEADER is set to indicate the use of Generic Stream Encapsulation with CRC, as per [i.28]. • The ACC EC field is sent unencrypted. It is a one-byte field that describes the ACC encryption in the current frame. The format of this field is defined in Table 8.17. Table 8.17: ACC EC field Bits Description 7 (MSB) IV presence indicator. Should be set to 1. 6:2 Reserved (set to 1) 1:0 ACC key index ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 138 • The 16-byte Initialization Vector (IV) is sent unencrypted. At system start-up, the initial IV should be the result of one of the Known Answer Tests defined for the AES encryption algorithm. For each subsequent BBFRAME, the last 16 bytes of encrypted data are used as the initial IV for the following BBFRAME. NOTE: Since an initial IV is transmitted in each BBFRAME, this method works even in situations where only some frames can be demodulated by a particular RCST; for example in ACM systems. • The #ACC field is a one-byte field. It indicates the number of 16-byte chunks that are encrypted using the ACC key. Since the first chunk is always ACC encrypted, this number is always at least equal to 1. It is itself encrypted using the ACC key, as described below. • The DCC EC field is a one-byte field that describes the DCC encryption in the current frame. The format of this field is defined in Table 8.18. It is encrypted using the ACC key, as described below. Table 8.18: DCC EC field Bits Description 7 (MSB) IV presence indicator. Should be set to 1. 6:2 Reserved (set to 1) 1:0 DCC key index • The #DCC field is a one-byte field. It indicates the number of 16-byte chunks that are encrypted using the DCC key. It is itself encrypted using the ACC key, as described below. • The GSE packets constitute the actual information payload of the frame. They are encrypted using the ACC and DCC keys as described below. • The CRC-32 is a 4-byte field. It is computed over the frame content in the same manner as for non-TRANSEC implementations, in accordance with [i.28]. • Padding is appended as required to fill the BBFRAME, as per the DVB-S2 standard. The complete, encrypted BBFRAME is forwarded to the mode adaptation interface of the DVB-S2 modulator. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.1.1 Encryption Process | Each frame contains at least one chunk encrypted using the ACC key. As illustrated in Figure 8.11, this chunk contains the #ACC, DCC EC and #DCC fields, plus the first 13 bytes of actual ACC data. This is followed by #ACC-1 further chunks of ACC-encrypted data and #DCC chunks of DCC-encrypted data. The Cipher Block Chaining process is carried over from the ACC to the DCC, as illustrated in Figure 8.12. Figure 8.12: Cipher block chaining process The ACC and DCC each consist of an integer number of 16-byte chunks. Unused space at the end of each channel should be filled by a chaff packet. If the amount of unused space is insufficient for the insertion of a chaff packet, it should be filled with pseudo-random data from the Chaff Packet generator's RNG (clause 8.4.5.6). It is the responsibility of the receiver to detect this condition and discard the excess bytes. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.1.2 Decryption Process | The decryption process is the inverse of the encryption. It proceeds as follows: • Physical-layer recovery of the frame is performed, including the CRC-32 check and stream filtering to discard irrelevant frames. • The IV is loaded into the AES engine and the first chunk is decrypted using the ACC key indicated in the ACC EC field. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 139 • The number of subsequent ACC chunks and the total number of DCC chunks are determined from the decrypted fields. • Remaining ACC chunks are decrypted; chaff packets and any trailing random data are discarded and the recovered GSE packets forwarded to the de-capsulation. • DCC chunks are decrypted; chaff packets and any trailing random data are discarded and the recovered GSE packets forwarded to the de-capsulation. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.2 Return Link and Mesh Transmissions | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.2.0 Frame Structure | Each burst in the return link and mesh links are encrypted using AES-256 in CFB mode, as described in this clause. The CFB mode is defined in clause 8.4.4.3.2. Each burst serves only the ACC or DCC. The encryption process ensures that the actual channel used can be inferred from the encrypted burst only by the intended recipient. The organization of a TRANSEC burst payload is illustrated in Figure 8.13. Figure 8.13: Burst with TRANSEC encryption The fields in this are as follows: • The EC2 field is sent unencrypted. It is a one-byte field which describes the key used to encrypt the EC1 field. The format of this field is defined in Table 8.19. Table 8.19: EC2 field Bits Description 7:3 (MSB) Reserved (set to 1) 2 Key selector. Should be set to 1 to denote ACC. 1:0 Key index • The EC1 field is a one-byte field which describes the key used to encrypt the payload and CRC-16. The format of this field is defined in Table 8.20. Table 8.20: EC1 field Bits Description 7:3 (MSB) Reserved (set to 1) 2 Key selector. (0=DCC, 1=ACC). 1:0 Key index • The payload field constitutes the actual information content of the burst. It is encrypted using the ACC or DCC key as indicated by the EC1 field. For TRANSEC purposes, the number of bytes k in this field can be any value greater than or equal to 29. • The CRC-16 is a two-byte field. It is computed over the entire, unencrypted and unscrambled content of the burst, from the EC2 field to the end of the payload. When this CRC is used, no other burst CRC should be used. The polynomial for this CRC is 1 + x5 + x12 + x16. The complete, encrypted burst payload is forwarded to the scrambling, FEC encoding and modulation function. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 140 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.2.1 Encryption Process | The encryption process consists of the following steps, as illustrated in Figure 8.14: • The CRC-16 is computed. • The k+2 bytes of the payload and CRC-16 are encrypted using CFB mode; using the appropriate key as identified in the EC1 field and an initial IV computed according to the provisions in clause 8.4.4.2.3. • The EC1 field and the first 15 bytes of the encrypted payload-plus-CRC are encrypted using CBC mode; using the ACC key identified in the EC2 field and using as IV the next 16 bytes (bytes 16 - 31) of the ciphertext resulting from the encryption of the payload and CRC-16. • The EC2 field is transmitted in cleartext. Figure 8.14: Burst Encryption Process |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.2.2 Decryption Process | The decryption process is the inverse of the encryption. It proceeds as follows: • Physical-layer recovery of the burst is performed. • The EC1 field and the first 15 bytes of the encrypted payload-plus-CRC are decrypted using the ACC key identified in the EC2 field; using as IV the next 16 bytes of the encrypted payload-plus-CRC. • The key to be used for decryption of the payload is determined from the EC1 field. • The payload and CRC-16 are decrypted using the key identified in the EC1 field and an initial IV computed according to the provisions in clause 8.4.4.2.3. • The CRC-16 is checked. This not only provides payload integrity, but also ensures that consistent keys have been used in the encryption and decryption. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.2.3 initialization Vectors for Burst Transmission | Initialization Vectors for encryption of the first block of each burst transmission are not transmitted over the air, but are generated at both ends of the link in a synchronized manner. The IV is obtained by encryption of a 128-bit string, using AES-256 in ECB mode and the current ACC key. The composition of the 128-bit string is shown in Table 8.21. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 141 Table 8.21: Burst IV plaintext composition Bits Description 69 (MSB) Random number 8 Superframe_sequence 16 Superframe_Count_Extension 16 Superframe_Count 8 frame_number 11 (LSB) Timeslot_Number Values for these fields are obtained as follows: • The random number is generated by the NCC and communicated periodically to the RCST's using the TRANSEC_message_descriptor. This version of the TRANSEC_message_descriptor is sent at regular intervals in the TIM; it includes identification of the superframes to which it applies: - The superframe_sequence is the normal DVB-RCS2 identifier of the superframe sequence to which the RCST is logged in. - The 16-bit Superframe_Count_Extension is an extension of the conventional Superframe_Count. Its value is communicated periodically to the RCST's using the TRANSEC_message_descriptor in the TIM. Once set, the RCST increments the Superframe_Count_Extension whenever the regular Superframe_Count rolls over from 65 535 to 0. - Superframe_Count, frame_number and Timeslot_Number are the conventional DVB-RCS2 identifiers of the time slot in which the transmission takes place. In order to avoid re-setting, the Superframe_Count_Extension should be set at system re-boot to the number of Superframe_Count wrap-around periods elapsed since January 1, 1970 00:00 UTC, modulo 65 536. The NCC may renew the value of the random number as desired. The new value is communicated using the TRANSEC_message_descriptor with a transec_message_type value of 0x01 and including the random number. The transec_message_byte sequence is formatted in accordance with Table 8.22. Table 8.22: Return / mesh link IV descriptor sub-type Syntax No. of bits Information Mnemonic Reserved (see note) Information return_link_IV_update(){ superframe_loop_count 8 Uimsbf for (i=0; i<= superframe_loop_count; i++) { random_present 7 1 if (random_present ==1) { random_number 3 69 Uimsbf } superframe_sequence 8 Uimsbf superframe_count_extension 16 Uimsbf superframe_count 16 Uimsbf } Uimsbf } The semantics for the return_link_IV_update are as follows: superframe_loop_count: This is an 8-bit field indicating one less than the number of iterations of the loop that follows. A zero count indicates one iteration. random_present: This flag indicates the presence or absence of the random_number field. The value is set to 1. random_number: This is a 72-bit field that contains bits that may be used as the MSB's of the IV for the first block of each burst payload. The value applies to the superframe identified by superframe_ID and takes effect from the superframe identified by the superframe_count_extension and superframe_count. If that time is in the past, the value takes effect immediately. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 142 superframe_sequence: This 8-bit field identifies the superframe sequence to which the parameters apply. superframe_count_extension: This 16-bit field defines the value of superframe_count_extension in force in combination with superframe_count. The RCST increments its local value of superframe_count_extension whenever superframe_count rolls over from 65535 to 0. superframe_count: This 16-bit field identifies the modulo-65536 superframe count to which the descriptor entry applies. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.3 AES-256 Operational Modes | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.3.0 Introduction | This clause defines the block cipher operation modes in which the AES-256 algorithm is used in the system. Figure 8.15 to Figure 8.19 are obtained from Wikipedia.org and are placed in the public domain by their author by the statement: "This image has been released into the public domain by its author, Lunkwill. This applies worldwide." |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.3.1 Cipher Block Chaining (CBC) Mode | CBC is the preferred operational mode from a security perspective and is the mode applied in the forward link. CBC encryption is illustrated in Figure 8.15. Each block of 256 bits of plaintext is excusive-or'ed with the Initialization Vector (IV). The encryption algorithm is applied to the result, using the appropriate key. The result of this is the ciphertext. The first block in a frame uses the IV supplied in the frame. The ciphertext resulting from each encryption operation is used as IV for the encryption of the subsequent block. Figure 8.15: CBC Encryption The corresponding decryption is shown in Figure 8.16. The decryption algorithm is applied to each 256-bit block of ciphertext, using the appropriate key. The result is exclusive-or'ed with the IV to produce the plaintext block. The first block in a frame uses the IV supplied in the frame. Each subsequent block uses the ciphertext of the preceding block as IV. Figure 8.16: CBC Decryption |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.3.2 Cipher Feedback (CFB) Mode | This mode is also acceptable from a security perspective; it is applied for burst transmission in the return link and for mesh. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 143 Encryption is shown in Figure 8.17. The Initialization Vector (IV) is encrypted using the AES-256 algorithm, using the appropriate key. The result is exclusive-or'ed with the plaintext to form the ciphertext. The first block in a frame uses the IV supplied externally. The ciphertext resulting from each encryption operation is used as IV for the encryption of the subsequent block. Since the last block of ciphertext is not used as a subsequent IV, it is acceptable for this to be shorter than 256 bits. Such a shortened ciphertext block is produced by exclusive-or'ing the initial output bits from the encryption operation with corresponding plaintext bits. Figure 8.17: CFB encryption The corresponding decryption is shown in Figure 8.18. The Initialization Vector (IV) is encrypted by the AES-256 algorithm, using the appropriate key. The result is exclusive-or'ed with the ciphertext to form the plaintext. The first block in a frame uses the IV supplied externally. Each block of ciphertext also serves as IV for decryption of the subsequent block. Since the last block of ciphertext is not used as a subsequent IV, it is acceptable for this to be shorter than 256 bits. In this case, the plaintext block is produced by exclusive-or'ing the initial output bits from the encryption operation with corresponding ciphertext bits. Figure 8.18: CFB decryption |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.3.3 Electronic Code Book (ECB) Mode | This mode is used only to randomize vectors internally in equipment. Encryption is shown in Figure 8.19. Each block of plaintext is encrypted individually, using the appropriate key. ECB decryption is not used in this application. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 144 Figure 8.19: ECB encryption |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.4.4 Public-Key Encryption | Public-key encryption and decryption are carried out using RSA-2048 [i.25]. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5 Traffic Activity Obfuscation | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.1 Forward Link Chaff Packets and Fill Frames | Any part of a forward link frame that cannot be filled with actual data is filled with chaff packets. This packet is an un-fragmented GSE packet transmitted in broadcast mode; i.e. with no address label and using the TRANSEC_chaff protocol type. The packet payload is random data. Use of the random number generator specified in clause 8.4.5.6 is recommended. If the part of the frame to be filled is too small for a complete GSE packet with minimal header, it should be filled with random data. DVB-S2 dummy frames are not transmitted. If there is no data to transmit in a frame, is filled entirely with chaff packets. These can be transmitted in the ACC and DCC as desired, following the normal rules. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.2 Dummy Demand-Assigned Traffic Bursts | All demand-assigned traffic slots in the MF-TDMA frame are assigned to RCST's unless prevented by fundamental hardware constraints such as the single-carrier nature of the transmitter. An RCST always transmits in an assigned traffic slot. If the RCST has no useful data to transmit, the burst payload is filled with random "chaff" data. Use of the random number generator specified in clause 8.4.5.6 is recommended. The random payload is encrypted using the DCC key. The slot assignments are made in such a way that the long-term average of the number of bursts transmitted by all RCST's per unit of time is approximately equal, while respecting the actual capacity demands of the individual RCST's. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.3 Logon Burst Assignment and Randomization | The use of assigned logon transmissions is preferred to contention-based transmission. The procedure defined in this clause is used to obfuscate the actual logon activity in the network. Each logon slot in the superframe is used in one of three ways: As a dummy slot assigned to an already-logged on RCST, as an actual logon slot, or unused. A logged-on RCST always transmits in an assigned logon slot. The payload of the burst is random "chaff" data. Use of the random number generator specified in clause 8.4.5.6 is recommended. The random payload is encrypted using the ACC key. The transmit power is the same as that used for actual logon transmissions. The burst transmit instant is chosen randomly in such a manner that the burst arrival time is uniformly distributed over the logon slot at the NCC, but contained entirely within this slot. The burst transmit frequency is offset from the nominal value by a random quantity, chosen uniformly in an interval corresponding to the system's frequency tolerance for logon bursts. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 145 An RCST that is not logged on transmits a conventional logon burst in an assigned slot. No transmissions take place in unused slots. The use of each logon slot in each superframe is chosen randomly, with probabilities as given in Table 8.23. Use of the random number generator specified in clause 8.4.5.6 is recommended. Table 8.23: Logon slot assignment probabilities Slot usage Probability Dummy N M P / 1 − Actual 2 P Unused ( ) N M P P / 1 2 1 + − − Each time an actual logon burst is detected, the NCC starts a counter which is initialized to N and is decremented for each superframe by the total number of logon slots in the superframe. The counter is deactivated when it reaches 0. M is the number of active counters in any given superframe. The probabilities P1 and P2 are system design parameters, chosen such that P1+ P2 < 1. NOTE: The choice of P1 and P2 and N are a trade-off between on the one hand the degree to which the actual activity can be hidden and on the other hand the amount of capacity set aside for this purpose. Typical values are P1 = 0,5, P2 = 0,25 and N equal to the total number of logon slots in 100 seconds. Assignment of dummy slots to the logged-on RCST population are randomized but such that the average number of dummy transmissions is approximately equal for all RCST's. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.4 Control Burst Transmissions | The use of assigned control burst transmissions is preferred to contention-based transmission. All control slots in the MF-TDMA frame should be assigned to RCSTs unless prohibited by hardware constraints such as the single-carrier nature of the transmitter. An RCST always transmits in an assigned control slot. The control slot assignments are made in such a way that the average interval between the corresponding transmissions is approximately equal for all active RCST's. The slot positions for individual RCST's are randomized. Use of the random number generator specified in clause 8.4.5.6 is recommended. It is recommended to assign the slots through the TBTP2, rather than through the control assign descriptor. Power setting, timing offset and frequency offset of dummy control transmissions are made in the same manner as that defined for logon transmissions in clause 8.4.5.3. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.5 Contention-based Control and Logon Transmission | Contention-based transmission of traffic slots should not be used. The use of contention-based transmission logon and control burst transmissions is not recommended. If this method is nevertheless used, the process defined in this clause can be used to obfuscate the actual activity. For the purpose of this clause, the term "slot" means a logon or control slot used for contention-based access. Each slot is used in one of three ways: As a dummy slot assigned to an already-logged on RCST, as an actual contention slot, or unused. A logged-on RCST always transmits in an assigned slot. A control burst transmission is in accordance with the normal rules for assigned control slots. A logon transmission made by a logged-on RCST in an assigned slot is in accordance with the corresponding provisions of clause 8.4.5.3, including the randomization of timing and frequency. Actual contention slots can be used by RCSTs for contention access in accordance with the normal rules. Unused slots are identified in the TBTP2 by assigning them to a non-existent RCST. The use of each contention slot in each superframe should be chosen randomly, using the probability distribution defined in clause 8.4.5.3. Separate counter sets should be maintained for control and logon slots. Assignment of dummy contention slots to the logged-on RCST population should be randomized but such that the average number of dummy transmissions is approximately equal for all RCST's. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 146 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.5.6 Random Number Generation | The following method (from [i.29]) is recommended for generation of pseudo-random data. The algorithm has 4 state variables: x, y, z, w (all are 32-bit unsigned values). The state variables are initialized to x = 123456789; y = 362436069; z = 521288629; w = 88675123. Initialization should take place at system re-boot only. Following initialization, the random number generator is exercised a random number of times and the corresponding values discarded. The number should not be less than 1 000 and be derived from the date and time obtained from an NTP server. Computation of the next pseudo-random number w is carried out as follows: t = x ^ (x << 11); x = y; y = z; z = w; w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)) Where "^" denotes bit-wise exclusive-or (modulo-2 addition), "a << b" indicates a left-shifted by b bit positions and "a >> b" indicates a right-shifted by b bit positions. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.6 Special Considerations | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.6.1 Beam Handover in Mobile Systems | In order to facilitate beam handover and initial entry of mobile terminals in a TRANSEC-secured system that employs multiple beams and even multiple satellites and gateways, it is necessary that the same ACC keys are used in all forward links. One security management system will be responsible for generating these keys and for initiating simultaneous roll-overs. Responsibility for this function may be with the security management system of one of the networks, or with an external entity. The keys and roll-over commands are communicated to the security management systems of the affected networks using a secure link. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.4.6.2 Manual Key Entry | For initial commissioning, it should also be possible to enter a network acquisition key manually, before the RCST has generated an X.509 certificate. The key is protected by a user-generated passphrase of any desired length. Transmitting the key to the RCST is done outside of the system, either verbally (e.g. over a phone line) or in a file transfer. This procedure can also be used to bring in an RCST which has missed the ACC key rollover twice. The procedure is as follows: 1) The operator of the Security Management System enters a key generation command which includes the desired passphrase and the hardware MAC address of the RCST. The passphrase is a UTF-8 [i.30] string of any length. 2) The Security Management System takes the RCST hardware address (48-bit IEEE MAC address as per [i.5]), passphrase, and appends a 64 bit random number ("salt") to form a string. This is turned into a 256 bit key using PBKDF2 as described in [i.31]. The iteration count should be 1 000. 3) The key generated in the previous step is used to encrypt the ACC key using AES-256 in ECB mode. The 310 bits result, consisting of 256 encrypted key bits + 64 salt bits are transmitted to the operator of the RCST. They are encoded for ease of transmission as follows. For this process, the term "checksum" means SHA-512 hash [i.32] truncated to use only the bits at the beginning. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 147 4) The Security Management System presents three strings which contains information to be transmitted to the remote. The three strings can be encoded using either base-32 or base-64 encoding in accordance with [i.33]. The strings are constructed as illustrated in Figure 8.20 and described in the following: a) String 1 consists of the following elements: i) A five-bit header, which is formatted as follows: 1) One reserved bit. 2) Two bits indicating the key ring position of the key. 3) One reserved bit. 4) One bit indicating the main encoding scheme used ('0' indicates base-64, '1' indicates base-32). This header is itself base-32 encoded to occupy one byte. ii) The first 14 bytes (1 - 14) of the AES-encrypted ACC key. iii) Chsum1, which is a 2 byte checksum computed over the preceding 15 bytes. The concatenation of (ii) and (iii) are encoded according to the selected scheme. The complete string contains either 23 or 27 bytes, depending on the encoding. b) String 2 consists of the following elements: i) 15 bytes (15-29) of the AES-encrypted ACC key. ii) Chsum2, which is a 2 byte checksum computed over the preceding 15 bytes. The concatenation of (i) and (ii) are encoded according to the selected scheme. The complete string contains either 23 or 28 bytes, depending on the encoding. c) String 3 consists of the following elements: i) The last 3 bytes of the AES-encrypted ACC KEY. ii) The 8 bytes "salt". iii) Chsum 3, which is a 2 byte checksum computed over the concatenation of the entire encrypted ACC key and the "salt". iv) Chsum4, which is a 2 byte checksum computed over the concatenation of the entire encrypted ACC key, the "salt", the passphrase and the RCST's MAC address. v) Chsum5, which is a 2 byte checksum computed over the concatenation of (i), (ii), (iii) and (iv). The concatenation of items (i) through (v) are encoded according to the selected scheme. The complete string contains either 23 or 28 bytes, depending on the encoding. 5) These three strings are transmitted to the RCST operator (e.g. read over the telephone or by file transfer). 6) On the RCST console, these three strings are entered. When base-32 encoding is used, the RCST should treat uppercase and lowercase as equivalent. If a string fails checksum, the operator is prompted to re-enter it. 7) Once the three strings are entered, the RCST operator is prompted for the passphrase. Operator enters passphrase. If the checksum fails, the operator is prompted to re-enter. 8) The AES key is determined and the ACC key is decrypted. 9) The RCST joins the network. At this point it receives the "next" ACC KEY in the normal way. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 148 Figure 8.20: Formatting And Encoding Of Manual Key Entry Strings ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 149 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.5 Summary | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.5.1 Profiles Compared | Table 8.24 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 8.5.2 TRANSEC Hooks Used | Table 8.25: SUMMARY OF TRANSEC HOOKS USED ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 150 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9 RCST Deployment Guidelines | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.0 Overview | This clause provides guidelines material for the overall architecture and deployment of the RCST. Examples of frequency bands uses for transmit/receive, regulatory aspects as well as antenna alignment procedures and requirements are presented. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.1 Example of RCST Architecture | The RCST typically complies with the architecture outlined in Figure 9.1. An RCST may conceptually consist of the Outdoor Unit (ODU), the Interfacility Link (IFL), and the Indoor Unit (IDU). The ODU is composed of the following subsystems: Antenna Subsystem (ANT), Transceiver (TRx), and Mechanical Subsystem (MECH). The Interfacility Link (IFL) is a cable assembly, which interconnects the IDU with the ODU. The ANT consists of the reflector(s) and a combined transmit/receive feed. Optionally the ANT may also include an additional receive feed for receiving from a satellite at a different orbital location. The receive (Rx) part of the TRx includes the Low Noise amplifier(s), frequency downconversion and polarization as well as frequency band selection. The transmit part (Tx) of the TRx performs frequency upconversion as well as power amplification. The MECH attaches the ODU to a firm structure and provides means for accurate pointing. The IDU consists of the following subsystems: Network Interface Unit (NIU), User Interface Unit (UIU), Power Supply Unit (PSU) and Packaging. These subsystems can be implemented e.g. in a standalone IDU, within a desktop PC or Set Top Box. The UIU is the interface between all receive/transmit elements of the IDU and the user device. The NIU is constituted of at least one forward link receiver for reception of the forward link signalling (and the Traffic sent on the same carrier), a transmit chain for transmission of Traffic and forward link signalling to the ODU, and all the necessary controlling elements. If only one forward link receiver is available Traffic and forward link signalling should be received from the same carrier. Additional forward link receivers allow the transmission of Traffic and forward link signalling on different carrier. This results in significant improvement of operational flexibility and should be the preferred solution. The number of available forward link receivers is a parameter exchanged between the RCST and the NCC during RCST logon. It should be noted that the conceptual split between IDU and ODU functionality as described above, and specified in the present document represents only one possible separation of functions. There may be also different approaches providing the same overall functionality. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 151 Rx unit Tx unit Additional Rx units Network Interface Unit User Interface Unit Power Supply Unit Packaging Inter- Facility Link Rx: 950 - 2 150 GHz / EN 61319-1 Mechanical Subsystem Optional additional cable(s) for L-band Tx interface and/or multi-satellite reception Antenna Subsystem (inc feed) Transceiver ODU IDU Figure 9.1: Conceptual RCST architecture 9.2 Frequency ranges and regulatory constraints envelope for Fixed RCST |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.2.1 Examples of used frequency bands for FSS | The following frequency bands are typically used: • Reception is in one or several of the frequency bands of the Fixed Satellite Service (FSS) or Broadcast Satellite Service: 10,70 GHz to 11,70 GHz. 11,70 GHz to 12,50 GHz. 12,50 GHz to 12,75 GHz. 17,70 GHz to 19,70 GHz. 19,70 GHz to 20,20 GHz. 21,40 GHz to 22,00 GHz. • Transmission is in one of the frequency bands allocated to FSS: 14,00 GHz to 14,25 GHz. 27,50 GHz to 29,50 GHz. 29,50 GHz to 30,00 GHz. Other bands are also envisaged. Regulation of usage of frequency bands is covered by other bodies. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 152 Linear or circular polarization is used for transmission and reception. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.2.2 Regulatory Aspects | There are four main sources of applicable regulatory documents: • ITU-R, in the form of the Radio Regulations and specific recommendations. • ETSI, which is not a regulatory body as such, but produces normative documents (EN's) that are adopted by reference in actual regulations. • The FCC, which issues the regulations for the United States. • CEPT, which issues common regulations for its (European) member states. These are sometimes, but not always, based on ETSI documents. The regulations of most interest to the VSAT community deal with three subject areas: • Interference limitation and co-existence. • Electromagnetic compatibility. • Blanket licensing. The present document should not be used to justify the fulfilment of the essential requirements under article 3.2 of the Radio Equipment Directive [i.43]. Requirements for Electro Magnetic Compatibility (EMC) under article 3.1b of the RED [i.43] are given in ETSI EN 301 489-12 [i.16]. Harmful interference is limited by requiring a minimum set of Control and Monitoring Functions (CMF) as well as specifying limits for on-axis radiation, off-axis spurious radiation, carrier suppression, off-axis EIRP emission density and pointing accuracy. These specifications are in general depending on the transmit frequency, regulatory authority and type of terminal. For example, for systems operating in Europe, ETSI EN 301 428 [i.7] applies in Ku-band and ETSI EN 301 459 [i.6] applies in Ka-band. The RF parameters of the RCST have been selected to comply with the conditions identified in the ECC decisions ECC/DEC(06)02 [i.36] and ECC/DEC(06)03 [i.37] related to Exemption from Individual Licensing of High- and Low-EIRP Satellite Terminals. These ECC decisions make reference to the Harmonised Standards ETSI EN 301 459 [i.6] and ETSI EN 301 428 [i.7]. Furthermore, these ECC decisions add the following constraints: • For low-EIRP terminals, EIRP not to exceed 34 dBW. • For high-EIRP terminals: - EIRP less than or equal to a nationally defined limit, which can be in the range 50 - 60 dBW. - A coordination distance from airport perimeter fences that depends on the EIRP and station latitude; it varies between 500 and 3 900 m. When operating at the nominal EIRP, the spectral regrowth should not exceed 20 dB. Spectral regrowth is defined as the ratio of the power in an adjacent channel of bandwidth (1+α) × symbol rate to the power in an equivalent bandwidth centred on the transmit carrier. It should be noted that the frequency separation between the adjacent channel and transmit channel is system dependent. 9.3 Frequency ranges and regulatory constraints envelope for Mobile RCST |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.0 Overview | Operation of an RCST in a mobile environment is usually permissible under different regulatory and licensing conditions to those for the fixed or nomadic use. The regulatory conditions for mobile operation will, in general, impose constraints on the frequency bands employed, operational geographical area and off-axis emissions of the terminal. Furthermore, interference constraints may be imposed and require careful consideration. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 153 This clause addresses the regulatory constraints for the use of mobile terminals, in particular terminals with small size antennas. It focuses on the earth-to-space direction, since on the space-to-earth direction, the necessary protection against FSS/FS interferences will be very dependent on the coordination situation and the adjacent systems characteristics, leading to specific constraints on the terminal sizing. Within the ITU-R Radio Regulations, the following bands are allocated to the Mobile Satellite Service (MSS) in the earth-to-space direction and are thus of interest for DVB-RCS mobile applications: 5 925 - 6 425 MHz The Radio Regulations contain two footnotes (5.457A and 5.457B) concerning the use of ESV's and Resolution 902 (WRC-03) contains provisions relating to ESV's which operate in fixed-satellite service networks. NOTES: 5.457A: In the bands 5 925 - 6 425 MHz and 14 - 14,5 GHz, earth stations located on board vessels may communicate with space stations of the fixed-satellite service, in accordance with Resolution 902 (WRC-03). 5.457B: In the bands 5 925 - 6 425 MHz and 14 - 14,5 GHz, earth stations located on board vessels may operate with the characteristics and under the conditions contained in Resolution 902 (WRC-03) in Algeria, Saudi Arabia, Bahrain, Comoros, Djibouti, Egypt, United Arab Emirates, the Libyan Arab Jamahiriya, Jordan, Kuwait, Morocco, Mauritania, Oman, Qatar, the Syrian Arab Republic, Sudan, Tunisia and Yemen, in the maritime mobile-satellite service on a secondary basis, in accordance with Resolution 902 (WRC-03). 14,0 - 14,5 GHz Secondary allocation in all three ITU-R Regions (earth-to-space). 29,5 - 29,9 GHz Primary allocation in Region 2 (earth-to-space). Secondary allocation in Region 1 & 3 (earth-to-space). 29,9 - 31,0 GHz Primary allocation in all three Regions (earth-to-space), typically for government use only. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1 Regulatory constraints applicable to the Ku-band allocations | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1.0 General | Within the Ku-band, only the sub-band 14,0 - 14,5 GHz is allocated to mobile satellite service on a secondary basis and covers the three types of utilization of the mobile services: • Land Mobile Satellite Service (LMSS) • Aeronautical Mobile Satellite Service (AMSS) • Maritime Mobile Satellite Service (MMSS) The transmissions from the Mobile Earth Station to the Satellite in the 14 - 14,5 GHz band falling under a secondary allocation, the transmissions should not cause harmful interference to primary services (e.g. the Fixed Satellite Service (FSS)) and at the same time cannot claim protection from harmful interference from those services. In addition to FSS, some other terrestrial based services are using part of 14 - 14,5 GHz Ku frequency band including the Fixed Services (FS) (in Regions 1 and 3), Radio Astronomy Services (RAS), and the Space Research Service (SRS) and these require appropriate protection from the mobile RCST emissions. The use of this 14 - 14,5 GHz allocation was extended to the aeronautical mobile satellite service at the World Radiocommunications Conference in July 2003. This conference has also detailed the use of this band by ESV (Earth Station on board Vessels) through a new recommendation (Rec 37) and a new resolution (Res 902). Within Europe, ETSI has developed several standards: • ETSI EN 301 427 [i.8], harmonised EN for low data rate Mobile satellite Earth Stations (MESs) except aeronautical mobile satellite earth stations, operating in the 11/12/14 GHz bands. • ETSI EN 302 186 [i.9], harmonised EN for satellite mobile Aircraft Earth Stations (AESs) operating in the 11/12/14 GHz bands. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 154 • ETSI EN 302 340 [i.10], harmonised EN for satellite Earth Stations on board Vessels (ESVs) operating in the 11/12/14 GHz frequency bands allocated to the Fixed Satellite Service (FSS). • ETSI EN 302 448 [i.11], harmonised EN for satellite Earth Stations on Trains (ESTs) operating in the 11/12/14 GHz frequency bands allocated to the Fixed Satellite Service (FSS). • ETSI EN 302 977 [i.12], harmonised EN for Vehicle-Mounted Earth Stations (VMES) operating in the 12/14 GHz frequency bands. These documents specify the minimum technical performance requirements of Mobile Station equipment with both transmit and receive capabilities for provision of mobile satellite service in the frequency bands given in Table 9.1. Table 9.1: Frequency bands for the equipment specified in the standards Mode of Operation Frequency Band Transmit 14 - 14,50 GHz Receive 10,70 - 11,70 GHz Receive 12,50 - 12,75 GHz Regulations regarding the USA: due to the adoption of 2 degree satellite spacing in the orbital arc over the USA the FCC has introduced regulations that are somewhat more stringent than the ETSI ones. The reader is referred to [i.13], Part 25 (Satellite Communications) of the USA Code of Federal Regulations (47: Telecommunications). In addition, the FCC 04-286 report and order provides some further background. Within the ITU, Recommendation ITU-R M.1643 [i.14] is also of interest. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1.1 Off-axis EIRP limits | Considering the appropriate ETSI regulatory documents it can be seen that for directional antennas, the maximum EIRP in any 40 kHz band from any Mobile satellite Earth Station in any direction φ degrees from the antenna main beam axis should not exceed the following limits within 3° of the geostationary orbit: 33 - 25 log (φ + δφ) - 10 log (K) dBW/40 kHz where 2,5° ≤ φ + δφ ≤ 7,0°; +12 - 10 log (K) dBW/40 kHz where 7,0° < φ + δφ ≤ 9,2°; 36 - 25 log (φ + δφ) - 10 log (K) dBW/40 kHz where 9,2° < φ + δφ ≤ 48°; -6 - 10 log (K) dBW/40 kHz where 48° < φ + δφ ≤ 180°; where K is the number of simultaneous transmissions (K=1 for MF-TDMA system). NOTE: These limits apply to satellites spaced at 3° apart. In the case of 2° spacing (reflected in Recommendation ITU-R S.728.1 [i.73]), a more constraining requirement - 8 dB less EIRP density- may be applied. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1.2 Particular constraints applicable to MMSS | The ESV terminal should have an antenna aperture greater than 1,2 meter (possibly 0,6 meter if agreed by the concerned licensing administrations). |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1.3 Particular constraints applicable to AMSS | In region 1 (Europe) as well as Region 2 and 3, some countries operate Fixed Service (FS) links in the band 14,25 - 14,50 GHz (shared band with FSS) on a primary basis. Since AES operation in the band 14 - 14,50 GHz is on a secondary basis, there is a requirement for protection of Fixed Service (FS) systems in the band 14,25 - 14,50 GHz from in-band and out-band emissions from AES operating in the band 14 - 14,5 GHz. The specification of protection of FS systems in the band 14,25 - 14,50 GHz is based on the Power Flux Density (PFD) limits per AES. These limits are of a regulatory nature and only a small number of countries are employing FS systems in the band 14,25 - 14,50 GHz. This requirement is applicable when the AES is in line of sight of a country employing FS systems, and could be relaxed if the operator of the AES network has an agreement with the Administration of that country. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 155 When the AES should limit its PFD at the surface of the Earth, then in any 1 MHz bandwidth in the band 14,25 - 14,5 GHz, the PFD at the surface of the Earth should not exceed the following limits: -132 + 0,5 × θ dB(W/m2), where 0° ≤ θ ≤ 40° -112 dB(W/m2), where 40° < θ ≤ 90° where θ (in degrees) is the angle of arrival at the Earth surface of the radio-frequency wave from the AES. In addition, the AMSS being secondary to the Radio Astronomy service and to the SRS service (secondary in 14 - 14,3 GHz) according to Recommendation ITU-R M.1643 [i.14], protection of some specific Radio Astronomy stations in specific locations should also be considered. Frequency management techniques using RAS/FS/SRS location knowledge may be used to perform active detection and mitigation of interferences. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.1.4 Illustration of the impact of the off-axis EIRP constraint | It is believed that the main constraint for small size mobile terminals will come from the off-axis EIRP limit. This constraint is illustrated in Figures 9.2 and 9.3. Assuming a theoretical Bessel shape antenna pattern, corresponding to uniform aperture illumination, it is possible to determine the maximum on-axis EIRP of the MES terminal as a function of the antenna diameter under the limitation of the off-axis EIRP described earlier. Figure 9.2: Off-axis EIRP density for large antennas 0 5 10 15 20 25 30 35 40 45 0 3 6 9 12 15 off-axis angle, degs EIRP density in any 40 kHz EIRP density (1.0m dia) EIRP density (0.8m dia) EIRP density (0.5m dia) EIRP density limit ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 156 Figure 9.3: Off-axis EIRP density for small antennas This EIRP off-axis mask is a significant constraint, since in order to close the link budget, the small size of the antenna cannot be compensated by an increase of RF power. Using tapered aperture illumination may, however, ameliorate the situation. Figure 9.4 illustrates the evolution of the EIRP density as a function of the antenna diameter (assuming a theoretical antenna pattern as previously illustrated) under the constraints of not exceeding the EIRP off-axis mask limits. Figure 9.4: Evolution of the on-axis EIRP density as a function of the antenna diameter As a reference, the EIRP density (in dBW/40 kHz) is provided in Figure 9.4 (i.e. 31,9 dBW/40 kHz) as well as the reference antenna size for this budget (80 cm). As a reference, the EIRP density (in dBW/40 kHz) extracted from reference link budgets is provided in Figure 9.4 (i.e. 31,9 dBW/40 kHz) as well as the reference antenna size for this budget (80 cm). It can be shown that in case small compact terminals (below 40 cm) are necessary, and for less favourable satellite coverage performances than the ones (resulting from higher terminal EIRP requirement), a reduction of the on-axis EIRP density may be necessary. In addition a small antenna size will require additional protection from receiving interference from adjacent satellite transmissions. 0 5 10 15 20 25 0 5 10 15 off-axis angle, degs EIRP density in any 40 kHz EIRP density (0.3m dia) EIRP density (0.2m dia) EIRP density (0.1m dia) EIRP density limit On-axis EIRP density 0 5 10 15 20 25 30 35 40 45 50 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 Antenna Diameter (m) EIRP Density (dBW/40kHz) ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 157 For those specific applications, the utilization of low code rate, or additional terminal return path and gateway forward path signal spreading may be considered. The latter option in particular is however clearly outside the provisions of the present document. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.3.2 Regulatory constraints applicable to the Ka-band allocations | No known regulations are applicable specifically to mobile applications in the Ka-band. The only known applicable standards are the following ETSI standards which relate to terminals in general: • ETSI EN 301 358 [i.15] • ETSI EN 301 459 [i.6] A regulation for terminals on mobile platforms is in preparation; this will be published as ETSI EN 303 978 [i.74]. These standards state that the maximum EIRP in any 40 kHz band within the nominated bandwidth of the co-polarized component in any direction φ degrees from the antenna main beam axis should not exceed the following limits: 19 - 25 log φ - 10 log N dBW for 1,8° ≤ φ ≤ 7,0°; -2 - 10 log N dBW for 7,0° < φ ≤ 9,2°; 22 - 25 log φ - 10 log N dBW for 9,2° < φ ≤ 48°; -10 - 10 log N dBW for φ > 48°. where N is the number of simultaneous transmissions (N=1 for MF-TDMA system). The corresponding FCC regulation (FCC 25-138 [i.13]) is approximately 0,5 dB more stringent. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4 Interfaces | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.0 Overview | This clause describes examples of bidirectional communications used between the IDU and the ODU as Inter Facility Link (IFL). For fixed satellite services the IFL usually takes the form of a pair of coaxial cables. Examples of implementation protocols using coaxial cables are described in clause 9.4.1 and annex G. Particular VSAT systems may have the need for additional control protocols. For example, Mobile applications have the needs for control communications between the modem and the antenna, and will benefit from using TCP/IP over Ethernet. The control protocol may include features such as: • Robust control interconnection of modem and antenna by using TCP • Configuration of the antenna, particularly in the context of automatic beam switching • Antenna position updates from the antenna (as an alternative for example to NMEA-0183) • Communicating antenna status data and monitoring data (e.g. SNR, modem lock, TX power, blocking conditions) Examples of such control protocols using Ethernet are outlined in clause 9.4.2. Other ways of implementing the interface and control protocols than described here are also possible. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1 Coaxial Cable IFL | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.0 General | An example of the IFL protocol the Eutelsat DiSEqC™ bus specification [i.20]. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 158 In order to facilitate the use of RCST for individual or collective installation, the signals and the frequencies supporting those communications needs to be compliant with the EN 50083 [i.19] series and EN 61319-1 [i.18] if applicable. Performance figures in this clause are not necessarily optimized in terms of the requirements of ETSI EN 301 545-2 [i.1] for all potential implementations. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.1 RX IFL | The RX IFL system interfaces between LNB and IDU. The definition is directly derived from ETSI ETS 300 784 [i.17] and EN 61319-1 [i.18] for "Universal" DBS/DTH terminals. Table 9.2 shows the IFL parameters. Table 9.2: IFL parameters Parameter Value Unit Note Frequency scheme no spectral inversion IF frequency input range, low band See Table 9.3 IF frequency input range, high band See Table 9.3 IF impedance 75 Ohm Return loss LNB & modem > 8 dB Connector type F-type Connector & cable color code blue Cable loss @ 2 150 MHz < 40 dB/100 m LNB band switch tone command according to EN 61319-1 [i.18] Low band selected 0,0 - 0,2 Vpp 18 - 26 kHz High band selected 0,4 - 0,8 Vpp Polarization fixed linear, orthogonal with TX (see note) DC supply voltage 11 - 19 V on the LNB DC supply current < 300 mA NOTE: If dual-polarization reception is supported then the voltage (13/17 V) switching command as specified in [i.18]. Typical IDU IFL frequency input ranges includes the ones shown in Table 9.3. Table 9.3: IFL Rx frequency Frequency Band RF [GHz] LO [GHz] IF [MHz] C-Band 3,7 - 4,2 5,15 950 - 1 450 Ku-band - Low band 10,7 - 11,7 9,75 950 - 1 950 Ku-band - High band 11,7 -12,75 10,6 1 100 - 2 150 Ka-band 19,7 - 20,2 950 - 1 450 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.2 TX IFL | The TX IFL system interfaces between IDU and BUC. A single coaxial cable typically carries: • The TX IF signal in L-band • The TX LO frequency reference signal • A low frequency sub-carrier for DiSEqC™ signalling • The DC power supplying the BUC In general L-band is recommended for all RCS terminals according to following scheme, with no spectral inversion, given in Table 9.4. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 159 Table 9.4: IFL Tx frequency Band RF [GHz] LO [GHz] IF [MHz] Ku-band 14,00 - 14,50 13,05 950 - 1 450 Extended Ku-band 13,75 - 14,25 12,80 950 - 1 450 Full extended Ku-band 13,75 - 14,50 12,80 950 - 1 700 Ka-band 29,50 - 30,00 28,55 950 - 1 450 It might be desired to ease installation by having the IDU automatically set the IDU output level to compensate for different cable attenuations and BUC gains. It is then recommended to use measured RF power from the BUC supported by the IFL protocol defined in annex G. An alternative common method is to have a fixed cable loss IFL system and a fixed gain BUC. This method utilizes a standard level at the IDU output, a utilizing a well-known cable attenuation and well-known BUC gain. The IDU output level can also be calibrated for IFL cable loss and slope at the installation of the terminal by setting an applicable output level value in the IDU. Cable loss as well as the BUC gain are well known parameters that do not change over operational conditions or life-time of the terminal. Typical IFL cable characteristics are shown in Table 9.5. Table 9.5: IFL cable characteristics Parameter Value Unit Note IF drive level set once during modem installation IF impedance 75 Ohm Return loss at BUC and IDU > 13 dB Return loss cable > 16 dB Connector type F-type Connector & Cable color code Red Cable attenuation @ 1 700 MHz < 30 dB/100 m Cable attenuation uniformity < 0,3 dB/MHz Cable length < 50 m Recommended characteristics of the IDU LO reference are given in Table 9.6. Table 9.6: IDU LO reference characteristics Parameter Value Unit Remarks Reference type frequency synchronous Frequency 10 MHz sinusoidal Frequency tolerance < ±25 ppm Overall (see note) Level 0 ± 5 dBm Spurious level < 30 dBc 0,01 - 20 MHz Phase Noise @ 10 Hz -86 dBc/Hz Phase Noise @ 100 Hz -124 dBc/Hz Phase Noise @ 1 kHz -134 dBc/Hz Phase Noise @ 10 kHz -144 dBc/Hz Phase Noise @ 100 kHz -152 dBc/Hz NOTE: The actual reference signal applied when the RCST has acquired NCR synchronization is derived from the NCR of the forward link, therefore it is highly accurate. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.3 ODU control signal | 9.4.1.3.0 DiSEqC™ IFL Signalling Description DiSEqC™ IFL signalling between IDU and BUC enables a number of advanced applications and features. The signalling from IDU to ODU can be implemented by on/off voltage modulation, shown in Table 9.7. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 160 Table 9.7: IFL signals Parameter Value Unit Note Carrier frequency 22 ± 4 kHz According to EN 61319-1 [i.18] Modulation type on/off using voltage superimposing Carrier level, logical 0/1 0 / 0,6 Vpp |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.3.1 Concept of the 22 kHz Pulse Width Keying (PWK) Bus | The low data rate communication between the IDU and the ODU is based on a 22 kHz PWK signal as used by DiSEqC™ [i.20]. The impedance of the bus at 22 kHz should be 15 Ω. A parallel inductor of 270 µH can be used to support a DC. power supply current. In this case a capacitor to ground should be supplied to shape the 22 kHz signal. The DC feeding point is grounded for 22 kHz with a capacitor. If a DC is not needed for powering peripheral devices, then in order to maintain correct operation of the DiSEqCTM bus, there should be a minimum of 10 V bias applied, but the inductor and capacitor can be omitted. The control signal from every device on the bus is produced by a 43 mA current shunt producing a 650 mV signal which is monitored by every device. This amplitude of the DiSEqCTM carrier tone on the bus is normally too small to detect directly on a "TTL" or "CMOS" compatible pin on a microcontroller, so usually a "comparator" input, or a simple external (one transistor) amplifier, is required. In any case, it is important not to make the input too sensitive to small amplitude signals which may be "noise" or interference. It is recommended that the smallest amplitude normally detected is about 200 mV peak to peak. This can be achieved either with hysteresis (positive feedback applied around the comparator/amplifier) or with a DC bias offset (equivalent to about 100 mV) applied to the input of the amplifier/comparator. Hysteresis (if symmetrical) can maintain a reasonably constant 50 % duty cycle for the detected carrier tone, whilst the DC offset method may generate a less desirable asymmetric (pulse) waveform when the carrier amplitude approaches the lower limit. All devices are connected in parallel on the bus and should therefore have a high impedance. The PWK circuit specification is given in Table 9.8. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 161 ODU Rr > 10 000 Ω U22 kHz RB = 15 Ω LB = 270 μH CB = 470 nF typically Bias Voltage > 10 V IDU1 Rr > 10 000 Ω U22 kHz IDUn Rr > 10 000 Ω U22 kHz Cr Cr Cr 43 mA 43 mA 43 mA Figure 9.5: 22 kHz PWK bus concept ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 162 Table 9.8: PWK circuit specification Parameter Value Unit Note Carrier frequency 22 kHz ±20 % Bus load impedance RB 15 Ω ±5 % DC supply Bus load inductance LB 270 μH ±5 % Bus load capacitance CB 470 nF typical Current source current amplitude 43 mA ±10 % source impedance > 10 kΩ 22 kHz carrier detection device resistance Rr 5 to 10 kΩ typical DC block capacitor Typically a few nF, but depends on the value Rr, it should be chosen so as to give a time constant of around 100 μs Bit definition timing base 0,5 ms ±0,1 bit length 1,5 ms "0" 1,0 ms burst + 0,5 ms pause "1" 0,5 ms burst + 1,0 ms pause |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.4 Control functions from the IDU | The following functions should be available: • SSPA ON/OFF (relates to disabled state as described in ETSI EN 301 459 [i.6]. • Tx Unit power off. The following functions may be available: • Frequency tuning within the wide frequency range of the slow frequency agility (if applicable). • Software update of the ODU. • Tx Frequency band selection (select different Local Oscillators). • Modulation ON/OFF (transmit Continuous Wave). • Set Transmit output power level. • Get ODU location data (latitude and longitude). • Full Reset. • Software Reset. • Password Reset. The transmit control signal level at the output of the IDU should comply with the clause 5.3.2 of EN 50083-10 [i.19]. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.5 Monitoring functions (from ODU on request) | The following functions should be available: • SSPA ON/OFF status. • Phase lock oscillator status. • Power supply status. • Device status. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 163 • ODU manufacturing information. The following functions may be available: • ODU temperature information for compensation. • ODU output power level for compensation. • ODU RF calibration parameters for RF level detector compensation. • LNB status (in the case the LNB or a part of the LNB is controlled by the ODU control bus). • Get ODU location data (latitude and longitude). • Authentication information exchange between the ODU and the IDU. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.1.6 Control and Monitoring protocol description | An example of the protocol description is provided in annex G. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.4.2 Control Interface using Ethernet | Many mobile applications have needs for communication between the modem and antenna controller that are more sophisticated than what is commonly used for FSS. Such communications can serve a number of purposes. One important element is facilitation of compliance with regulatory requirements, such as reporting of mispointing and fault conditions and the transfer of logged parameter values. Another important aspect of this communication is the ability to instruct the modem to cease transmission when the antenna controller has detected a situation where this is required - it is typically the antenna controller that will have position information etc. for making these types of decisions. Other elements of this communication can facilitate installation and optimal operation, such as informing the modem about transmitted power, antenna pattern and polarization skew. It is not always practical to carry this communications over the coaxial IFL cables. There are alternative industry-standard interfaces available, which typically use dedicated serial lines or Ethernet connections. One such protocol is the VSAT Antenna Control Protocol (VACP™) that is supported by several antenna vendors. Another protocol is OpenAMIP™, also adopted by several manufacturers of mobile antenna units. OpenAMIP™ is freely available through the Internet (https://www.idirect.net/technology/openamip/). It has also been incorporated in the ARINC-791 standard for aeronautical terminals (see www.arinc.com). |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.5 ODU environmental conditions | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.5.1 Operational environment | There should be no significant degradation of the specified system and subsystem performance when operating under the following environmental conditions: Temperature: -30 °C to +50 °C. Solar Radiation: 500 W/m2 max. Humidity: 0 % to 100 % (condensing). Rain: up to 40 mm/h. Wind: up to 45 km/h. The ODU mechanical construction should make sure there are no random vibrations during wind conditions which cause any significant performance degradation. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 164 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.5.2 Survival conditions | The ODU is allowed to degrade in performance, but should maintain pointing accuracy and suffer no permanent degradation under the following environmental conditions: Temperature: -40 °C to +60 °C. Solar Radiation: 1 000 W/m2. Humidity: 0 % to 100 % (condensing). Precipitation: up to 100 mm/h of rain or 12 mm/h of freezing rain or 50 mm/h of snowfall. Static load: 25 mm of ice on all surfaces. Wind: up to 120 km/h. Storage and Transportation Temperature: -40 °C to +70 °C. Shock and Vibration: as required for handling by commercial freight carriers. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6 RCST Antenna Alignment Guidelines | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.0 Introduction | ETSI EN 301 545-2 [i.1] provides some signalling support that may be used to establish the necessary information exchange between the RCST and the NCC to facilitate manual and automated alignment of the RCST antenna as summarized below. The antenna alignment is composed of forward link alignment and return link alignment processes. The return link alignment starts only after the forward link alignment is completed with a level of accuracy that is specified by the NCC. The subject level of accuracy is periodically broadcast by the NCC as minimum forward link SNR value before the return link transmitter can be activated. The return link alignment process uses probing signals on the return link. These probes may be in the form of Continuous Wave (CW) transmissions or Installation Burst (IB) transmissions. The NCC periodically broadcasts the types of return link alignment methods that it supports. The RCST indicates in the initial Logon SDU the types of return link alignment methods that it can perform. The NCC selects and indicates in the Logon Response the alignment method that the RCST should implement during the return alignment process. In addition, the NCC may indicate to the RCST an alignment population ID that is different from the RCST's operational population ID. The alignment population ID is used by the RCST together with the RMT signalling table so as to identify the Forward Link Signalling (FLS) the RCST should tune to during the alignment process. The NCC sends unicast feedback and commands to the RCST in response to return link alignment probes. The feedback may include CNR measurement, cross-polar and co-polar measurements, cross-polar and co-polar thresholds, and alignment status {Failure, Success, In-progress}. The commands may include configuration information in regard to the return link alignment probes. • For CW alignment, configuration includes transmission frequency, start time, duration of transmission, and transmission EIRP. Note that the NCC may exclude EIRP configuration if dynamic EIRP is not used. If the RCST is a fixed-EIRP device and if the NCC dictates dynamic updates on the EIRP, the RCST should terminate the alignment procedure with failure. • For IB alignment, configuration includes the bit pattern that the RCST should use in the Installation Burst. Note that CW transmission configuration also conveys resource allocation information in the form of {frequency, start time, duration} configuration. In contrast, in the case of IB alignment, configuration and resource allocation take place in different signalling tables. The installation bursts are to be transmitted in dedicated access logon slots, and the NCC allocates such slots to the RCST in the burst time plan (SCT/FCT2/BCT/TBTP2 tables). ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 165 • For both IB alignment and CW alignment, the NCC may set a remaining duration timer in RCST at the expiry of which the RCST should terminate the return link alignment process. This is a safety precaution to preclude the possibility that the RCST ends up in a state where it transmits on the return link indefinitely. If necessary, the NCC may send a new remaining duration value to restart this timer in the RCST. The NCC is in complete control of the return alignment process. Hence, the NCC may deny, terminate, re-start, and modify the return alignment process if necessary. The NCC may also broadcast contact information in ASCII format of a Network Operations Centre for assistance during the alignment process. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.1 Motorised antenna control for automated alignment | It is possible to develop intelligent search algorithms to calculate the elevation and azimuth of the RCST antenna as a function of feedback received from the NCC - in both CW and IB-based return link alignment. Such search algorithms may minimize installation duration and may remove the need for manual installation when combined with motorised antenna control equipment. It should be noted that there is a master-slave relation between the NCC and the RCST during return link alignment. RCST-side protocols that may drive the return link alignment procedure should only transmit on the return link when Pointing Alignment Support descriptors from the NCC command so. There may be timers included in these protocols, at the expiry of which the RCST goes into the initial state (power-down), wait for a random period, and retry the whole alignment procedure from power-up. |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.2 RCST Alignment Accuracy | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.2.1 Required Forward Link alignment accuracy | |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.2.1.0 General | Before starting the return link alignment procedure it is necessary to achieve the required minimum pointing accuracy through the forward link alignment procedure. The term "alignment" here includes two different aspects: • alignment of the antenna bore sight towards the satellite (both circular and linear polarizations); • alignment of the feed to the correct tilt angle (linear polarization only). Two constraints apply to the forward link pointing accuracy requirement: • it has to ensure that the installation burst transmission does not cause harmful interference to other systems; • it has to allow the RCST correctly performing the MAC logon, in the worst ST condition (at the EoC). The radiation pattern of the User Terminal antenna is modelled analytically as a paraboloidal reflector. The resulting radiation pattern is given by: ( ) ( ) ( ) ⋅ ⋅ ⋅ + ⋅ − ⋅ = + + 1 1 1 0 2 ! 2 1 2 n n n y u u J n A u u J A E a f π , where: • a is the antenna radius, • A is the Tapering Amplitude; A = 0,6838 in this analysis (corresponding to an Edge Taper of 10 dB), • n is the roll off depending on the feed radiation pattern; n=1 is considered in this analysis, • Jj is the Bessel function of the first kind and order j. Concerning the cross-polar off-axis EIRP the analysis aims to identify a requirement on the feed rotation accuracy achieved after the forward link alignment procedure. ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 166 The constraints associated to such a requirement are two: • the polarization mismatch loss, affecting the link budget during the logon and return link alignment procedures; • the regulatory constraints on the cross polar EIRP emission. To assess the impact of the feed rotation error, it has been assumed that the terminal antenna is perfect, therefore all the contribution to the cross polar component depends just on the rotation error. Under this assumption, the power on the cross-polar component can be related to the rotation error τ through the following equation: ( ) ( ) τ 2 cos 1 − ⋅ = G G cross Where G is the antenna pattern under perfect rotation conditions. On the other end, the loss due to the polarization mismatch on the cross-polar component is evaluated as: ( ) τ 2 cos = on polarizati Loss Apart from the regulatory constraints, it is worth mentioning that in case the network itself is planned to exploit the two orthogonal linear polarizations, then the feed rotation accuracy should be specified according to the required Cross Polarization Discrimination (XPD) performance. A typical XPD value for a commercial antenna with perfect alignment is in 20 - 25 dB range. Using a simple analytical model it can be derived that the XPD due to the feed rotation accuracy is proportional to the squared tangent of the rotation error. Figure 9.6: XPD due to feed rotation error Therefore assuming to tolerate a degradation of 0,5 dB in the XPD due to the rotation error (assuming an XPD of 25 dB in perfect alignment conditions), the XPD due to the rotation error should be kept higher than 34 dB, corresponding to a feed rotation error lower than 1,1 degrees. Terminal XPD due to misalignment -10 0 10 20 30 40 50 60 70 80 0 5 10 15 20 25 30 35 40 45 Feed rotation error [degrees] XPD due to rotation error [dB] ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 167 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.2.1.1 Ku Band System Scenario | In the Ku-band uplink scenario two terminal types are considered: a consumer terminal, with a 0,96 m antenna dish size and a BUC with 2 W maximum output power, and a professional terminal with a 1,2 m dish and a BUC with 3 W maximum output power. Figure 9.7 shows the radiation pattern of the two antennas at 14 GHz. Figure 9.7: Analytical Radiation Pattern vs φ − Ku band terminals The symbol rate of the installation burst is set to 64 ksymbols/s, and the G/T at the EoC is -4 dB/K. The feed rotation accuracy is assumed to be better than 15 degrees. Starting from this system scenario, the operating point of the power amplifier, i.e. the Output Back Off (OBO) is derived ensuring to meet the Off-axis EIRP emission density limit within the band. Figure 9.8 shows the off-axis EIRP for the two terminal types described above with perfect alignment. Figure 9.8: Off-axis EIRP, Ku band terminals - perfect alignment Figure 9.9 shows the OBO settings (the back-off with respect to the nominal operating point, that is the saturated power minus a nominal Back Off of 0,5 dB). 0 1 2 3 4 5 6 7 8 9 10 -80 -70 -60 -50 -40 -30 -20 -10 0 Offset angle [deg] relative gain [dB] Antenna size 0.96m Antenna size 1.2m Ku band - EIRP density in 40 kHz band -40.00 -30.00 -20.00 -10.00 0.00 10.00 20.00 30.00 -5.00 -4.60 -4.20 -3.80 -3.40 -3.00 -2.60 -2.20 -1.80 -1.40 -1.00 -0.60 -0.20 0.20 0.60 1.00 1.40 1.80 2.20 2.60 3.00 3.40 3.80 4.20 4.60 5.00 φ (deg) EIRP in 40 kHz (dBW) ETSI off axis EIRP limit (40 kHz Band) 0.96 m Antenna 1.2 m Antenna ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 168 Figure 9.9: OBO settings - Ku band system scenario Figures 9.10 and 9.11 show the resulting co-polar EIRP (in the worst 40 kHz band) for the two terminals, for a forward link alignment accuracy of 1, 0,7 and 0,5 degrees. Figure 9.10: Off-Axis EIRP in 40 kHz, 0,96 m Ku band antenna Installation OBO vs FL pointing accuracy -0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 FL Pointing Accuracy [deg] OBO [dB] 0.96m Ant 1.2m Ant 0.96 m Antenna - EIRP in 40 kHz band -40.00 -30.00 -20.00 -10.00 0.00 10.00 20.00 30.00 -5.00 -4.55 -4.10 -3.65 -3.20 -2.75 -2.30 -1.85 -1.40 -0.95 -0.50 -0.05 0.40 0.85 1.30 1.75 2.20 2.65 3.10 3.55 4.00 4.45 4.90 φ (deg) EIRP in 40 kHz (dBW) ETSI off axis EIRP limit (40 kHz Band) Pointing Error = 1 deg Pointing Error = 0.7 deg Pointing Error = 0.5 deg ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 169 Figure 9.11: Off-Axis EIRP in 40 kHz, 1,2 m Ku band antenna Applying these OBO settings derived from the co-polar EIRP limit, the cross-polar EIRP is estimated as shown in Figures 9.12 and 9.13 for the 0,96 and 1,2 m antenna terminals respectively. Figure 9.12: Cross-polar Off-Axis EIRP in 40 kHz, 0,96 m Ku band antenna 1.2 m Antenna - EIRP in 40 kHz band -40.00 -30.00 -20.00 -10.00 0.00 10.00 20.00 30.00 -5.00 -4.55 -4.10 -3.65 -3.20 -2.75 -2.30 -1.85 -1.40 -0.95 -0.50 -0.05 0.40 0.85 1.30 1.75 2.20 2.65 3.10 3.55 4.00 4.45 4.90 φ (deg) EIRP in 40 kHz (dBW) ETSI off axis EIRP limit (40 kHz Band) Pointing Error = 1 deg Pointing Error = 0.7 deg Pointing Error = 0.5 deg 0.96 m Antenna - EIRP in 40 kHz band -40.00 -30.00 -20.00 -10.00 0.00 10.00 20.00 -5.00 -4.55 -4.10 -3.65 -3.20 -2.75 -2.30 -1.85 -1.40 -0.95 -0.50 -0.05 0.40 0.85 1.30 1.75 2.20 2.65 3.10 3.55 4.00 4.45 4.90 φ (deg) EIRP in 40 kHz (dBW) ETSI off axis EIRP limit (40 kHz Band) Pointing Error = 1 deg Pointing Error = 0.7 deg Pointing Error = 0.5 deg ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 170 Figure 9.13: Cross-polar Off-Axis EIRP in 40 kHz, 1,2 m Ku band antenna Therefore also the cross-polar mask is respected, as the co-polar limitation turns out to be the most stringent one. As shown in Figure 9.6, 15 degrees feed rotation error corresponds to an XPD of around 11 dB. Since the off-axis EIRP mask for the cross polar component is 10 dB lower than that of the co-polar component, the cross polar mask is automatically fulfilled when the co-polar is respected. Figure 9.14 shows the link budget results in terms of Link Margin. The installation burst is transmitted with QPSK modulation, and FEC rate 1/3 turbo code. For both terminals, it is possible to successfully perform the MAC logon and meet the off-axis EIRP limits with a pointing error up to 1 degree after the forward link alignment procedure is completed. Figure 9.14: Link Margin versus forward link alignment accuracy 1.2 m Antenna - EIRP in 40 kHz band -40.00 -30.00 -20.00 -10.00 0.00 10.00 20.00 -5.00 -4.55 -4.10 -3.65 -3.20 -2.75 -2.30 -1.85 -1.40 -0.95 -0.50 -0.05 0.40 0.85 1.30 1.75 2.20 2.65 3.10 3.55 4.00 4.45 4.90 φ (deg) EIRP in 40 kHz (dBW) ETSI off axis EIRP limit (40 kHz Band) Pointing Error = 1 deg Pointing Error = 0.7 deg Pointing Error = 0.5 deg Link Margin vs Pointing Error 0.00 2.00 4.00 6.00 8.00 10.00 12.00 0.5 0.7 1 φ [deg] Link Margin [dB] 0.96m Antenna 1.2m Antenna ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 171 |
cb3dadab4f22493b63142dd0ebb828dd | 101 545-4 | 9.6.2.1.2 Ka Band System Scenario | Three different antenna diameters are considered: 0,45, 0,6 and 1,2 m. Figure 9.15 shows the resulting radiation patterns. Figure 9.15: Analytical Radiation Pattern vs φ − Ka band terminals The symbol rate of the installation burst is set to 160 ksymbols/s, and the G/T at the EoC is 15,2 dB/K. As in the previous analysis, the off-axis EIRP for the three considered terminals in case of perfect alignment is used to derive the OBO settings. Note that if a terminal exceeds the EIRP mask, than it cannot boost all the power on 160 Ksymbols/s carriers. As for the Ku band scenario, the feed rotation accuracy is assumed to be better than 15 degrees. With the derived OBO settings, the resulting EIRP (in the worst 40 kHz band) for the three antenna sizes, meets condition 1. The same conclusion applies for the cross-polar pattern, as for the Ku band scenario. Figure 9.16 shows the link budget results in terms of Link Margin. The logon burst is transmitted with QPSK modulation, and FEC rate 1/3 turbo code. These results are independent of the carrier symbol rate, as long as the OBO setting is greater than zero. 0 1 2 3 4 5 6 7 8 9 10 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 Offset angle [deg] relative gain [dB] Antenna size 0.6m Antenna size 1.2m Antenna size 0.45m ETSI ETSI TR 101 545-4 V1.2.1 (2026-01) 172 Figure 9.16: Link Margin versus forward link alignment accuracy It can be seen that for forward link alignment accuracies better than 0,5 degrees, the link budget can be closed with a margin larger than 5 dB for all of the three antenna types. For the 1,2 m reflector, the lower accuracies are not considered as they would exceed the 3 dB beam width θ3dB (as a rule of thumb it also correspond to the angle between the boresight and the first null). This could cause a wrong alignment to the closest secondary lobe. At 0,7 degrees misalignment, the 0,6 m terminal can still close easily the link, while the 0,45 m terminal has a margin slightly lower than 0 dB. The requirements of the forward link alignment accuracy can be relaxed by introducing burst repetition. For example, it would be possible to tolerate 1 degree pointing accuracy for the 0,45 and 0,6 m antenna transmitting the installation burst 7 and 15 times respectively. |
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