Xref: utzoo comp.dcom.modems:7660 comp.sys.mac.comm:1911 Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!ncar!ames!ads.com!jtn From: jtn@ADS.COM (John T. Nelson) Newsgroups: comp.dcom.modems,comp.sys.mac.comm Subject: How to increase throughput on 9600 bps modem? Message-ID: <9PF^W}#@ads.com> Date: 13 Dec 90 05:21:44 GMT Sender: usenet@ads.com (USENET News) Organization: Advanced Decision Systems, Mtn. View, CA (415) 960-7300 Lines: 40 Thanks to all who responded to my query about the Racal Vadic 9632 VP modem. I've got ZMODEM running now (without hardware handshake!) but looking at the throughput I have even MORE questions! Most binary files transfer from my Mac IIcx through the 9600 V.32 modem to the remote site (Telebit T2500) at about 300 bps -> 600 bps. Text files (like Macintosh HQX files) transfer at around 900 bps. ZMODEM claims that 900 bps is 98 percent effeciency. Ok... let's assume ZMODEM is telling the truth when it says that 1000 bps is the best I can expect. Why is it that binary files are doing the snail's pace of 300? There's more to it than that actually. Very often the performance gets as low as 60 bps! This is apparently because the transmissions are very "bursty" in character. There will be a sudden burst of characters to the remote modem and then a LONG 5 second delay of dead air and then a little more traffice and then another LONG delay of say 10 seconds and so on ad nauseum. Is this because ZMODEM is getting NAK packets of some kind back and retransmitting? Why the LONG delays? Here's another fun bit of info. Transfers from the remote machine TO my Mac are FAST! Always. Binary and ascii data crank at 98 percent effeciency all the time. Now why in the world would reception be faster than transmission? At least it works. I disable ALL flow control and use the latest copy of "rz" from mpace.cs.purude.edu (I think that's the place) and use the full 8 bit data path. Enjoy. -- ORGANIZATION: Advanced Decision Systems GEOGRAPHIC: Arlington, VA UUCP: kzin!speaker@mimsy.umd.edu INTERNET: jtn@potomac.ads.com SPOKEN: John T. Nelson PHONE: (703) 243-1611 PROJECT: Macintosh hacking -- "Love the Machine... Hate the Company"