dyer@spdcc.com (Steve Dyer) (11/10/88)
In article <telecom-v08i0166m05@vector.UUCP> lars%acc.arpa@bu-cs.BU.EDU writes: >The bandwidth of a metallic circuit is probably more like one megabit; >this is why we are moving towards IDSN: 2 twisted pairs is 1544 kbps = >24 voice channels. OK. Here's my situation. I've got a metallic (LADS) circuit between my house and my Internet site. I am presently running at 19.2kb with a pair of Gandalf LDS309a limited distance modems. What are my chances of ekeing any additional bandwidth out of this line, and what technology would be necessary to take advantage of it? I have seen ads for 56kb DSUs which are also claimed to work on twisted pair, but they seem to refer to in-house private twisted pair and not metallic lines from the TelCo. Just what is the theoretical and practical maximum bandwidth of a LADS circuit? -- Steve Dyer dyer@harvard.harvard.edu dyer@spdcc.COM aka {harvard,husc6,linus,ima,bbn,m2c,mipseast}!spdcc!dyer
roy@phri (Roy Smith) (11/16/88)
> I've got a metallic (LADS) circuit between my house and my Internet site. > I am presently running at 19.2kb with a pair of Gandalf LDS309a limited > distance modems. What are my chances of ekeing any additional bandwidth > out of this line We have a LADC (is that the same as LADS?) circuit. About a mile total loop length of 26 gauge wire (2 pairs). Using either Black Box V.35-LDM's or Rad ASM-20's we manage to run 56 kbps with no problems (well, no problems after many fights with NY Tel to get the bugs out of the line, which included 2 bad house pairs and a pair with polarity not observed). Actually, I think the LDM's are running at 64 kbps. Rad supposedly has a flavor of the ASM-20 which will run at 128 kbps, as does Black Box. VIR has a modem whch will supposedly do 230 kbps over that line, but we havn't gotten it to work at anything faster than 19.2 kbps. Most of the units I mentioned are V.35 modems, but that's a trivial problem. I'm sure they can be bought with RS-232 interfaces, and if not, RS-232 to V.35 converters are trivial. All the above-mentioned modems are about $600-700 each. -- Roy Smith, System Administrator Public Health Research Institute {allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net "The connector is the network"
roy@phri (Roy Smith) (11/20/88)
To update what I said earlier: > VIR has a modem whch will supposedly do 230 kbps over that line, but we > havn't gotten it to work at anything faster than 19.2 kbps. We tried the VIRs on another loop which is much shorter (we figure about 2-3000 feet) and it seems to work fine at 144 kbps, but we still can't get it to work at 230 kbps over any appreciable amount of wire. VIR admits that there is a problem with the modem (they have already modified it a couple of times, although I have no idea what they did to it). In fact, on of the engineers at VIR admitted that RAD makes the best modems! VIR says they will have a redesign of theirs out in a few months which really should work at 230 kbps over 1-mile loops. To be fair, VIR has been very good to us. They lent us 2 BERTs for a few weeks so we could test the lines and help us convince NY Tel that there really was something wrong. -- Roy Smith, System Administrator Public Health Research Institute {allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net "The connector is the network"