ege@scs.fiu.edu (Dr. Raimund K. Ege) (02/27/91)
When connecting to a Intel 9600ex with a Microcom AX/2400c
I get a strange behavior: while the connection seems to
be established at MNP level 5 (it says: connect 2400/rel),
the communication seems to be some kind of a burst mode.
For example, to redraw a screen in emacs, it needs three fast
bursts of data. Is there any way to set the Intel or Microcom
modem to avoid this behavior ?
Any help is appreciated.
--
Raimund K. Ege School of Computer Science
Florida Int'l University
ege@scs.fiu.edu (305) 348-3381 University Park
ege@servax.bitnet FAX (305) 348-3549 Miami, FL 33199tnixon@hayes.uucp (02/28/91)
In article <2634@kluge.fiu.edu>, ege@scs.fiu.edu (Dr. Raimund K. Ege) writes: > When connecting to a Intel 9600ex with a Microcom AX/2400c > I get a strange behavior: while the connection seems to > be established at MNP level 5 (it says: connect 2400/rel), > the communication seems to be some kind of a burst mode. > For example, to redraw a screen in emacs, it needs three fast > bursts of data. Is there any way to set the Intel or Microcom > modem to avoid this behavior ? The reason you see "burstiness" is that you are running the speed between the local PC and modem at higher than the rate on the phone line. The data is continuously streaming in on the phone line, but at only 2400bps. In order to have the opportunity to correct errors, the modem must buffer up an entire frame of data (256 bytes in MNP4, more with MNP5 compression) to check for errors before it can begin forwarding it to the PC. When it does receive an entire frame, it then sends it on to the PC -- at 9600 or more. In the meantime, the next frame is being received -- at 2400. Of course, the first frame is forwarded to the PC much faster than the next frame is received, so you see a "pause" -- but this pause is NOT indicative of any pause in the data flow on the phone line, just on the interface between the modem and your PC. The only way to eliminate this burstiness is to slow down the interface speed between the modem and local PC to more closely match the speed on the phone line -- using 4800 will be less "bursty" than 2400, but you'll still see some pauses. You COULD eliminate the pauses entirely by lowering the PC-to-modem speed to be the same as the line speed -- 2400 -- but this also completely eliminates any benefits of data compression. Most people would prefer to have SOME burstiness and higher throughput. All new users of error control modems wonder about this burstiness, but you get used to it pretty quickly. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 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