Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!texsun!texbell!vector!telecom-gateway From: INTERMAIL@a.isi.edu (Robert Gutierrez / MCI ID: 367-9829) Newsgroups: comp.dcom.telecom Subject: Re: Modems and LD Carriers Message-ID: Date: 17 May 89 06:57:55 GMT Sender: news@vector.Dallas.TX.US Lines: 65 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 168, message 2 of 8 From: westmark!dave@rutgers.edu (Dave Levenson) >In article , gould@pilot.njin.net >(Brian Jay Gould) writes: > I have seen numerous comparisons by carriers, of their noise levels >(dropping pins and such). The modem manufacturers specify data rates based >upon noise free lines. > So... has anyone ever attempted to chart data rate versus carrier? > (for several modem types) >We have used three different LD carriers in recent years. Our >experience is that each of these (SBS Skyline, MCI, and AT&T) shows >significant variation between different calls to the same place, >using the same carrier. The variation in data transmission quality >varies even more among calls placed over the same carrier to >different destinations. The variation between these carriers was no >more than the variation between different calls using the same >carrier. I could not agree more. Even at MCI, the circut quality could even depend on the time of day you call. Scenaro: You call from San Francisco to New York. If you called at 9pm, your call would travel over our backbone fiber that runs between San Francisco and Washington DC, then via digital radio to New York (over-simplification here), but it is possible that you try at 9AM instead, and all trunks are busy on that fiber route, then we have to find an alternate route for you call to terminate in New York. So, lets see, we send you to Los Angeles first, then Phoenix, Arizona, then Dallas, Texas, then St. Louis, Missouri, then......you get the picture. Then there is unexpected problems that can contribute, like "backhoe fade"....:-) >We also find plenty of noisey intra-lata calls. If the local >carrier cannot deliver a clean dial-up circuit across town, how can >they be expected to provide a uniformly clean interface to any of >the inter-lata carriers? It doesn't matter much how good the toll >carrier is if the local carrier is bad. A given circuit is as good >as its weakest link, isn't it? Ahhh yes, the local carrier lines. I have a problem in that regard. I am on Portal (cup.portal.com) in Cupertino, California. I call from Hayward, California, so, it is intralata. I am calling from a 1AESS to a DMS-100, distance: 25 miles. I would hope to think that there are directs between HYWRCA11CG0 (Hayward C.O.) and SNJSCA12CG0 (San Jose C.O. serving Cupertino). When I call Cupertino at 2400 baud, I always get a bunch of curly characters at the beginning of the transmission, usually going away after repeated 's (or, during retraining/equalization). This usually points towards frame errors/slips on a T-1 carrier, a common problem on the DMS-100, but I have also gotten this while calling through MCI which we have direct circuts to that C.O., but not from work, where we route through San Francisco instead (I think it's San Francisco 10 or 12 were on). I searched my own calls from work, and they terminate directly into SNJS/12, but I have no way of searching my intralata calls to see if I hit the tandem on their end (Santa Clara) or my end (Oakland), and see if one of the tandems is screwing this up. Of course, trying to explain all this to repair (611), and they usually say "huh?". Let us know if you do proceed with the modem experiments, and the results and problems you encounter. Robert Gutierrez MCI Telecommuncations Western Region Trouble Management Center Hayward, California.