Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!killer!vector!chip From: chip@vector.UUCP (Chip Rosenthal) Newsgroups: comp.dcom.lans Subject: Re: Ethernet bridges above 56Kb Message-ID: <475@vector.UUCP> Date: 31 Jul 88 14:41:40 GMT References: <9392@dartvax.Dartmouth.EDU> <116@ernie.NECAM.COM> <4399@cos.com> Reply-To: chip@vector.UUCP (Chip Rosenthal) Organization: Dallas Semiconductor Lines: 49 In article <4399@cos.com> howard@cos.com (Howard C. Berkowitz) writes: >The original T1 system used repeaters every 6000 wire feet on >24 AWG or larger cables; They still are. That's why the suggestions of running something other than 1.544MHz seem a little silly to me. There are two types of T1 lines: private and public. You can use any kind of framing format you want on private lines, but in either case you must meet the signal requirements of the FCC and your carrier. AT&T requires 1.544MHZ+-50ppm. I believe ANSI (and possibly Belcore) is moving to 30ppm. >These repeaters needed the following >rules to be followed to assure adequate zero-crossing signals: > 1. At least 3 one bits in every 24 time slots > 2. No more than 15 consecutive zeroes > 3. One bits sent with "alternate mark inversion:" Close. The actual one's density requirement is no more than 15 consecutive zeros, and in every window of (N+1)*8 bits there must be N ones, where N is between 2 and 23 (or is that 24?). >Additional constraints have been added for network management >and signal quality monitoring. I don't remember all of the >details, but, from memory, the Extended Superframe Format calls >for something like every 2047th bit to be a one. Someone with >the ESF references handy can correct this. OK...the ESF framing format replaces D4. Both of these formats group 193-bit frames into superframes. ESF has 24 frames per superframe, D4 has 12. Under D4, the 12 framing bits a fixed pattern for alignment to the superframe. Under ESF, the 24 framing bits contain 6 bits for frame alignment, 6 bits as a CRC on the previous superframe, and 12 bits as a facilities data link (FDL). The FDL is what was referred to. It is a 4Kbps communication channel for configuration commands (loopback, yellow alarm, etc.) and status reports (errored seconds, severely errored seconds, etc.). But, the electrical signal requirements are no different between ESF and D4. Unfortunately...I don't think this helps the original poster who wanted to connect to networks together. I don't know offhand if any muxes allow you to allocate several channnels for a data channel. If you are interested in making some phone calls, I could probably pull together a list of mux vendors from my files. As a side issue, this is one of the Great Promises of ISDN. Under 23B+D primary rate, you are supposed to be able to allocate as many 64Kbps B channels as required for your data stream. -- Chip Rosenthal /// chip@vector.UUCP /// Dallas Semiconductor /// 214-450-0400 {uunet!warble,sun!texsun!rpp386,killer}!vector!chip I won't sing for politicians. Ain't singing for Spuds. This note's for you.