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Chapter 16 Rev 10-27-87 Typeset 10-27-87 40
Chapter 16 ZMODEM Protocol 41
17. FFFFUUUUTTTTUUUURRRREEEE EEEEXXXXTTTTEEEENNNNSSSSIIIIOOOONNNNSSSS
Future extensions include:
o+ Compatibility with 7 bit networks
o+ Server/Link Level operation: An END-TO-END error corrected
program to program session is required for financial and other
sensitive applications.
o+ Multiple independent threads
o+ Encryption
o+ Compression
o+ File Comparison
o+ Selective transfer within a file (e.g., modified segments of a
database file)
o+ Selective Retransmission for error correction
18. RRRREEEEVVVVIIIISSSSIIIIOOOONNNNSSSS
10-27-87 Optional fields added for number of files remaining to be
sent and total number of bytes remaining to be sent.
07-31-1987 The receiver should ignore a ZEOF with an offset that
does not match the current file length. The previous action of
responding with ZRPOS caused transfers to fail if a CRC error
occurred immediately before end of file, because two retransmission
requests were being sent for each error. This has been observed
under exceptional conditions, such as data transmission at speeds
greater than the receiving computer's interrupt response capabilitiy
or gross misapplication of flow control.
Discussion of the Tx backchannel garbage count and ZCRCW after error
ZRPOS was added. Many revisions for clarity.
07-09-87 Corrected XMODEM's development date, incorrectly stated as
1979 instead of the actual August 1977. More performance data was
added.
05-30-87 Added ZMNEW and ZMSKNOLOC
05-14-87 Window management, ZACK zshhdr XON removed, control
character escaping, ZMSPARS changed to ZXPARS, editorial changes.
04-13-87 The ZMODEM file transfer protocol's public domain status
is emphasized.
04-04-87: minor editorial changes, added conditionals for overview
version.
03-15-87: 32 bit CRC added.
12-19-86: 0 Length ZCRCW data subpacket sent in response to ZPAD or
Chapter 18 Rev 10-27-87 Typeset 10-27-87 41
Chapter 18 ZMODEM Protocol 42
ZDELE detected on reverse channel has been changed to ZCRCE. The
reverse channel is now checked for activity before sending each
ZDATA header.
11-08-86: Minor changes for clarity.
10-2-86: ZCNL definition expanded.
9-11-86: ZMPROT file management option added.
8-20-86: More performance data included.