Path: utzoo!attcan!uunet!samsung!uakari.primate.wisc.edu!uwm.edu!wuarchive!texbell!vector!telecom-gateway From: gronk!johnl@uunet.uu.net (John Limpert) Newsgroups: comp.dcom.telecom Subject: Re: Need Information on "Bit Slippage" Message-ID: Date: 16 Nov 89 18:22:47 GMT Sender: news@vector.Dallas.TX.US Reply-To: John Limpert Organization: BFEC/GSFC Greenbelt, Maryland Lines: 34 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 516, message 11 of 11 In article johnk@opel.UUCP (John Kennedy) writes: >A coworker is experiencing a problem while using a 1200-baud dialup >modem, where he is seeing periodic "}" symbols, and characters 0x255 >and 0x251. >When I was having a similar problem at another company, the phone >gurus there told me this was a phenomenon known as "bit slippage", >whereby two switches were losing sync on the digital connection >between them. I have heard the same explanation of the periodic '}' problem. The '}' is produced when a T1 (1.5 mbps) link loses synchronization and loses/mangles a frame. Each end of the T1 link is supplied with its own clock source. If there is a discrepancy in the clock frequencies the link will lose synchronization periodically. The phone company has a hierarchal timing distribution system that is supposed to provide an accurate clock to the T1 equipment. I have been told that the clock frequency error may be caused by two problems. One, the local clock distribution system fails and the T1 equipment switches to an internal clock source when it detects the failure. It may be a long time before anyone notices the failure and corrects the problem. Alarms only work if someone checks them. Two, someone has installed some T1 equipment without providing an accurate clock source. This can be out of ignorance or unwillingness to pay for a quality timing distribution system. This information is what I have been told by others, please correct me if it is wrong. John Limpert johnl@gronk.UUCP uunet!n3dmc!gronk!johnl