Cisco 857 and BT line - no go :(

[g0at]

Hi, this is more of a work peev that's really getting to me, just wondering as to whether anyone could help me out / suggest anything.

At work there's 3 ADSL lines, 2 of which are using cisco routers, the 3rd using a crappy netgear router. I've just configured the 3rd cisco router and plugged it in - not getting a carrier detect. The settings are exactly the same as on the netgear router (vci / vpi - PPPoA - tried both variations of it). Are there any reasons off the top of your head as to why the netgear will work fine and the cisco will not? on a side note i've tried changing the routers around (i.e trying the new cisco router on the old lines - works fine, and the old cisco routers on the new line - doesn't work).

Basically the line doesn't seem to like cisco routers, works fine with netgear and the crappy standard voyager modem. Doubt it's anything to do with line attenuation as all lines are 2mb when connected. Any suggestions as to what it could be? I know it's going to be a pain in the ass when i phone up BT tomorrow, they're just going to say that they dont support 3rd party hardware - as far as they're concerned as long as the line works with their equipment it's my problem. Has anyone experienced anything like this before?

 

[jneiberger]

Were these lines ordered at different times? Do you perhaps have two newer DMT lines and one older CAP line?

 

[g0at]

yes, the two older lines work fine; sorry; what's the difference between cap and dmt?

 

[g0at]

edit: DMT and CAP are line-coding methods for modulating the electrical signals sent over the copper wire in the local loop. Carrierless Amplitude and Phase (CAP) is a common line-coding method. CAP is a well-understood technology because of its similarity with QAM. Although CAP is well-understood and relatively inexpensive, some argue that it is difficult to scale because it is a single-carrier modulation technique and is susceptible to narrowband interference. DMT uses multiple carriers. At this point, DMT is capable of more speed than CAP. This is one reason that the ANSI committee T1E1.4 accorded it standards status in document T1.413.

This standard calls for 256 subbands of 4 KHz each, thereby occupying 1.024 GHz. Each subband can be modulated with QAM 64 for clean subbands, down to QPSK. If each of the subbands can support QAM-64 modulation, then the forward channel supports 6.1 Mbps. On the return path are 32 subbands, with a potential for 1.5 Mbps.

... oh

 

[jneiberger]

My thought was that perhaps the Netgear device was running CAP software and the 857s are only running DMT. If that were the case, that would explain why none of the 857s work on the other line.

It was just a thought. I would bet that all three lines are running DMT. I don't think anyone uses CAP anymore.

 

[g0at]

okay, tried the ansi-dmt command, seems to train now (i.e getting the cd light).. nothing happens after that - where do you go from here?

 

[jneiberger]

I don't know, to be honest with you. We use SOHO 97s here and the default config works great for DMT lines. I don't know why you'd have to tweak your config in an 857 to get it to work on that line. The line must be provisioned differently than the others but I have no way of knowing exactly what is different.

At least you're getting it to train!

 

[g0at]

well, seems to be working now, not 100% sure why though, maybe there were some things set up via sdm that were conflicting. Deleted the config and started again from scratch. Thanks for your replies though.