Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!husc6!mit-eddie!gatech!hao!ames!ucbcad!ucbvax!SIMTEL20.ARPA!W8SDZ From: W8SDZ@SIMTEL20.ARPA (Keith Petersen) Newsgroups: comp.dcom.modems Subject: help!! DMS100 Message-ID: Date: Tue, 5-May-87 20:35:00 EDT Article-I.D.: SIMTEL20.KPETERSEN.12300065008.BABYL Posted: Tue May 5 20:35:00 1987 Date-Received: Thu, 7-May-87 06:05:55 EDT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 26 The 1200/2400 bps modem "noise" problems with the Northern Telecom DMS100 digital switch are well known by your vender. If they are not telling you about them, ASK! There are 25-30 software revisions for the digital switch software which must be installed to help eliminate this problem. There are also some hardware modifications to the DMS100 which involve synchronizing all the oscillators in each frame and locking them together to a master oscillator - which itself must be locked to a master that services other exchanges in your area. The problem is caused by the fact that the "switch" your call goes through is a multiplex switch. That means it's "chopping" the signal (at an 8 KiloHertz rate). This causes little holes in your modem tones. Normally these will be smoothed out by the characteristics of the subscriber local loop. The problem comes when your call goes through two switches which are not synchonized. The result is that the holes produced by each switch have random coincidence with each other. The result - pulse width modulation. This really messes up the 1200 and 2400 bps modems! --Keith Petersen Arpa: W8SDZ@SIMTEL20.ARPA Uucp: {bellcore,decwrl,harvard,lll-crg,ucbvax,uw-beaver}!simtel20.arpa!w8sdz GEnie Mail: W8SDZ RCP/M Royal Oak: 313-759-6569 (300, 1200, 2400 bps)