caf@omen.UUCP (Chuck Forsberg WA7KGX) (11/05/88)
A recent report comparing file transfer speeds of various protocols in a Telenet environment has prompted some discussion. A number of ZMODEM users have commented that the results given for ZMODEM in the report are not representative of their results obtained over PC Pursuit. Recent discussions have shed more light on this issue. It is becoming understood that the XON/XOFF flow control provided by PC Pursuit causes throughput to suffer somewhat. We can look forward to more efficient operation in the future. In the meantime some band aids can be applied when necessary. DOWNLOADS: To speed downloads, set parameter 64 in your PAD to a value between 4 and 7. The command is "set 0:0,64:7" and must be given to the "@" prompt AFTER connecting to the modem in the distant city. Please note that the DSZ, ZCOMM and Professional-YAM documentation failed to include the "0:0" which is a magic cookie that allows one to set the special Telenet parameters. With PC Pursuit, do not set the other PAD parameters, only set parameter 64. If possible, the sending program should set its ZMODEM window size to 3072 (this value may be experimented with). "z pw3072" UPLOADS: As above, but the ZMODEM window size should be lower, 2048 or even 1532. An apparent problem in the Telenet software prevents the caller from setting parameter 64 in the distant PAD. Uploading throughput still leaves much to be desired, with a small window slowing transmission and a larger window allowing Telenet buffer overruns. New versions of ZCOMM and Professional-YAM will be available soon with special code to recognize this problem and expedite error recovery under these conditions. The particular system used for some of the ZMODEM upload tests had a particular problem not related to the Telenet network: the Alloy disk system increased interrupt latency, causing loss of data at 2400 bps (!). Alloy products are (in)famous for disrupting concurrent commmunications as slow as 2400 bps. Chuck Forsberg WA7KGX ...!tektronix!reed!omen!caf Author of YMODEM, ZMODEM, Professional-YAM, ZCOMM, and DSZ Omen Technology Inc "The High Reliability Software" 17505-V NW Sauvie IS RD Portland OR 97231 503-621-3406 TeleGodzilla BBS: 621-3746 CIS: 70007,2304 Genie: CAF