bob@ns.UUCP (Bob Mathias) (02/09/91)
One of the bbs's that I use just upgraded to the new USR Dual Standard modem (V32.bis capable). Finally I would get a chance to see how much faster V32.bis is to HST. I downloaded a number of files using Ymodem-G with both V32.bis and HST. And lo and behold, HST proved to be faster. On a 300k zipped files I got 1727cps for HST and only 1682cps for V32.bis. I wouldn't have been too surprised if the transfer rate were the same since file transfers on PC bbs's using Ymodem-G have the data flowing at the 14.4 rate in one direction (thus not taking advantage of V32.bis ability of transferring data at 14.4 in both directions). But why would it be slower? -- Bob Mathias uucp: ...!uunet!ccicpg!uis-oc!ns.UUCP!bob Unisys Corporation voice: (714) 727-0323 A and V Series Systems Engineering fax: (714) 727-0350 Irvine, California
tnixon@hayes.uucp (02/12/91)
In article <65@ns.UUCP>, bob@ns.UUCP (Bob Mathias) writes: > One of the bbs's that I use just upgraded to the new USR Dual Standard modem > (V32.bis capable). Finally I would get a chance to see how much faster > V32.bis is to HST. I downloaded a number of files using Ymodem-G with > both V32.bis and HST. And lo and behold, HST proved to be faster. On > a 300k zipped files I got 1727cps for HST and only 1682cps for V32.bis. Did you repeat this multiple times, and are these the average of several attempts? Or did you just try one time for each modulation? The reason I ask is that these figures are in fact the same within +/- 22 cps; this is only +/- 1.3%. The CPS calculations of most comm programs can easily vary by this much, since most are based on full-second increments (which, on a 300k file transmitted at 1704cps, could easily put you off by +/- 1% by itself). Another, actually more likely, explanation is that USR is using 256-byte frames in HST mode (the default for their modified MNP4), and 128-byte frames in V.32bis mode (the default for V.42 LAPM). With 256-byte frames, the maximum throughput of a 14,400bps modem is about 1722cps (including 7 bytes of overhead per frame, and the typical 1 bit inserted every 64 for transarency purposes); with 128-byte frames the maximum throughput is about 1678cps (excluding data compression in both cases). This aligns closely with the figures you see. The benefit of using the smaller frame size is that you recover faster when there is line noise, but pay a small throughput penalty otherwise. If you configured the modem to negotiate to a 256-byte frame size in LAPM, the throughputs would be identical. Another factor could be some anomaly in USR's inplementation that causes them to have slightly less throughput in V.32bis than in HST. There two modulations provide a 14,400bps pipe, so there's no reason for them to have different throughput, all other conditions being equal. -- Toby -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
wallach@motcid.UUCP (Cliff H. Wallach) (02/16/91)
In article <3774.27b7e5c6@hayes.uucp> tnixon@hayes.uucp writes: -In article <65@ns.UUCP>, bob@ns.UUCP (Bob Mathias) writes: - -> One of the bbs's that I use just upgraded to the new USR Dual Standard modem -> (V32.bis capable). Finally I would get a chance to see how much faster -> V32.bis is to HST. I downloaded a number of files using Ymodem-G with -> both V32.bis and HST. And lo and behold, HST proved to be faster. On -> a 300k zipped files I got 1727cps for HST and only 1682cps for V32.bis. - -Another, actually more likely, explanation is that USR is using -256-byte frames in HST mode (the default for their modified MNP4), -and 128-byte frames in V.32bis mode (the default for V.42 LAPM). -With 256-byte frames, the maximum throughput of a 14,400bps modem is -about 1722cps (including 7 bytes of overhead per frame, and the -typical 1 bit inserted every 64 for transarency purposes); with -128-byte frames the maximum throughput is about 1678cps (excluding -data compression in both cases). This aligns closely with the -figures you see. The benefit of using the smaller frame size is -that you recover faster when there is line noise, but pay a small -throughput penalty otherwise. If you configured the modem to -negotiate to a 256-byte frame size in LAPM, the throughputs would be -identical. - -- Toby - Much of the code is common to both modes of operation. The throughput differences are a result of the smaller frame size in LAPM mode. Buffer space is an issue; MNP4 requires 8*256 bytes, LAPM 15*128 bytes. Pre-V42 HST modems only had 8k of ram, and I had planned for an easy field upgrade to V42. This didn't happen after I left US Robotics. Cliff Wallach ...uunet!motcid!wallach