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Chapter 8 ZMODEM Protocol 18 |
serial number of the receiving program, or 0. |
8.2 FFFFiiiilllleeee TTTTrrrraaaannnnssssmmmmiiiissssssssiiiioooonnnn |
The sender then sends a ZZZZFFFFIIIILLLLEEEE header with ZMODEM Conversion, Management, |
and Transport options[3] followed by a ZCRCW data subpacket containing the |
file name, file length, modification date, and other information identical |
to that used by YMODEM Batch. |
The receiver examines the file name, length, and date information provided |
by the sender in the context of the specified transfer options, the |
current state of its file system(s), and local security requirements. The |
receiving program should insure the pathname and options are compatible |
with its operating environment and local security requirements. |
The receiver may respond with a ZZZZSSSSKKKKIIIIPPPP header, which makes the sender |
proceed to the next file (if any) in the batch. |
If the receiver has a file with the same name and length, |
it may respond with a ZZZZCCCCRRRRCCCC header, which requires the |
sender to perform a 32 bit CRC on the file and transmit the |
complement of the CRC in a ZZZZCCCCRRRRCCCC header.[4] The receiver |
uses this information to determine whether to accept the |
file or skip it. This sequence is triggered by the ZMCRC |
Management Option. |
A ZZZZRRRRPPPPOOOOSSSS header from the receiver initiates transmission of the file data |
starting at the offset in the file specified in the ZZZZRRRRPPPPOOOOSSSS header. |
Normally the receiver specifies the data transfer to begin begin at |
offset 0 in the file. |
The receiver may start the transfer further down in the |
file. This allows a file transfer interrupted by a loss |
or carrier or system crash to be completed on the next |
connection without requiring the entire file to be |
retransmitted.[5] If downloading a file from a timesharing |
system that becomes sluggish, the transfer can be |
interrupted and resumed later with no loss of data. |
The sender sends a ZZZZDDDDAAAATTTTAAAA binary header (with file position) followed by |
one or more data subpackets. |
__________ |
3. See below, under ZFILE header type. |
4. The crc is initialized to 0xFFFFFFFF. |
5. This does not apply to files that have been translated. |
Chapter 8 Rev 10-27-87 Typeset 10-27-87 18 |
Chapter 8 ZMODEM Protocol 19 |
The receiver compares the file position in the ZZZZDDDDAAAATTTTAAAA header with the |
number of characters successfully received to the file. If they do not |
agree, a ZZZZRRRRPPPPOOOOSSSS error response is generated to force the sender to the |
right position within the file.[6] |
A data subpacket terminated by ZZZZCCCCRRRRCCCCGGGG and CRC does not elicit a response |
unless an error is detected; more data subpacket(s) follow immediately. |
ZZZZCCCCRRRRCCCCQQQQ data subpackets expect a ZZZZAAAACCCCKKKK response with the |
receiver's file offset if no error, otherwise a ZZZZRRRRPPPPOOOOSSSS |
response with the last good file offset. Another data |
subpacket continues immediately. ZZZZCCCCRRRRCCCCQQQQ subpackets are |
not used if the receiver does not indicate FDX ability |
with the CCCCAAAANNNNFFFFDDDDXXXX bit. |
ZZZZCCCCRRRRCCCCWWWW data subpackets expect a response before the next frame is sent. |
If the receiver does not indicate overlapped I/O capability with the |
CCCCAAAANNNNOOOOVVVVIIIIOOOO bit, or sets a buffer size, the sender uses the ZZZZCCCCRRRRCCCCWWWW to allow |
the receiver to write its buffer before sending more data. |
A zero length data frame may be used as an idle |
subpacket to prevent the receiver from timing out in |
case data is not immediately available to the sender. |
In the absence of fatal error, the sender eventually encounters end of |
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