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00 0100FF62 62637363 6865642E 74787400 |...bbcsched.txt.|
10 36333437 20333331 34373432 35313320 |6347 3314742513 |
20 31303036 34340000 00000000 00000000 |100644..........|
30 00000000 00000000 00000000 00000000
40 00000000 00000000 00000000 00000000
50 00000000 00000000 00000000 00000000
60 00000000 00000000 00000000 00000000
70 00000000 00000000 00000000 00000000
80 000000CA 56
Figure 6. YMODEM Header Information and Features
_____________________________________________________________
| Program | Length | Date | Mode | S/N | 1k-Blk | YMODEM-g |
|___________|________|______|______|_____|________|__________|
|Unix rz/sz | yes | yes | yes | no | yes | sb only |
|___________|________|______|______|_____|________|__________|
|VMS rb/sb | yes | no | no | no | yes | no |
|___________|________|______|______|_____|________|__________|
|Pro-YAM | yes | yes | no | yes | yes | yes |
|___________|________|______|______|_____|________|__________|
|CP/M YAM | no | no | no | no | yes | no |
|___________|________|______|______|_____|________|__________|
|KMD/IMP | ? | no | no | no | yes | no |
|___________|________|______|______|_____|________|__________|
5.1 KMD/IMP Exceptions to YMODEM
KMD and IMP use a "CK" character sequence emitted by the receiver to
trigger the use of 1024 byte blocks as an alternative to specifying this
option to the sending program. Although this two character sequence works
well on single process micros in direct communication, timesharing systems
and packet switched networks can separate the successive characters by
several seconds, rendering this method unreliable.
Sending programs may detect the CK sequence if the operating enviornment
does not preclude reliable implementation.
Instead of the standard YMODEM file length, KMD and IMP transmit the CP/M
record count in the last two bytes of the header block.
Chapter 6 XMODEM Protocol Enhancements
X/YMODEM Protocol Reference 10-27-87 17
6. YMODEM-g File Transmission
Developing technology is providing phone line data transmission at ever
higher speeds using very specialized techniques. These high speed modems,
as well as session protocols such as X.PC, provide high speed, nearly
error free communications at the expense of considerably increased delay
time.
This delay time is moderate compared to human interactions, but it
cripples the throughput of most error correcting protocols.
The g option to YMODEM has proven effective under these circumstances.
The g option is driven by the receiver, which initiates the batch transfer
by transmitting a G instead of C. When the sender recognizes the G, it
bypasses the usual wait for an ACK to each transmitted block, sending
succeeding blocks at full speed, subject to XOFF/XON or other flow control
exerted by the medium.
The sender expects an inital G to initiate the transmission of a
particular file, and also expects an ACK on the EOT sent at the end of
each file. This synchronization allows the receiver time to open and
close files as necessary.
If an error is detected in a YMODEM-g transfer, the receiver aborts the
transfer with the multiple CAN abort sequence. The ZMODEM protocol should
be used in applications that require both streaming throughput and error
recovery.
Figure 7. YMODEM-g Transmission Session
SENDER RECEIVER
"sb foo.*<CR>"
"sending in batch mode etc..."
G (command:rb -g)
SOH 00 FF foo.c NUL[123] CRC CRC
G
SOH 01 FE Data[128] CRC CRC