T1 diagnostics...

[jlazzaro]

I've been having some problems with a T1 circuit...ISP claimed it checked out good to the CSU but was seeing all 1's. They claimed all 1's point toward the CSU > Router cable, WIC, etc...basically the customer side equip.

Just curious, where are these all 1's coming from...CSU diagnostics? What exactly does it mean? How is it derived?

 

[ScottMac]

"All Ones" aka "Unframed Ones" aka "Blue Alarm" aka "AIS" (Alarm Indication Signal) aka "Keepalives" (and some other names / acronyms, depending on who you work for and how far back you go).

When an interface loses framing (for a designated time), it goes to a 'Red Alarm' - meaning Loss of Signal (LOF) ... which is also usually a Loss of Signal (LOS), but not necessarily.

The Red Alarmed interface sends a "Yellow Alarm" back (red alarm = receive LOF, Yellow send notification upstream)

The device that receives the Yellow, send a "Blue Alarm" upstream / downstream (depends on perspective). The Blue Alarm (aka "All Ones") is a legacy mechanism to keep the remaining stream of active infrastructure in-sync and active during the failure. In the "good ol' days" LOF/LOS would cause the neighbors to shut down, and they'd have to be manually brought back online one chunk at a time... the solution was to stream ones (All ones, unframed ones, ...) to prevent that shutdown, hence one of the other names, 'Keep Alive".

What it means is that something died up/down stream. Since the Telco/provider is saying it sees "all ones" from your equipment, it would actually be seen from your stuff *to* the smartjack/NIU ... so, your CSU/DSU could be bad .... more likely the cable from the SmartJack/NIU has one bad pair (transmit FROM the SmartJack/NIU .... your CSU is seeing LOF/LOS (from the SmartJack/NIU) and is sending Yellow TO the smartjack, which is passing the Blue Alarm (all ones, unframed ones, keepalive) back to the Telco / provider.

This is fairly common, it's nearly always the IW (Inside Wireing, usually an "Extended Demarc" ... a run of cabling from the SJ/NIU to the router / CSU/DSU0.

Good Luck

Scott

 

[SoulAssassin]

T1 was good, the 2nd one rocked as well. 3rd one was better than I thought it would be but nothing special, I can't believe they're making a....oh that T1. Sorry...err...whatever Scott Mac said.

 

[jlazzaro]

Good stuff Scott, thanks for going into such detail.

I'm thinking about picking up the T1 Survival Guide. Day to day its just not stuff I have to deal with. If anything, it will help me interface with Verizon and other big carriers better.

SoulAssasin, your input was invaluable

 

[SoulAssassin]

Originally posted by: jlazzaro
SoulAssasin, your input was invaluable

I'm sure it was worth every ounce of thought I put in it.

 

[jersiq]

Save the money on the book and purchase a test set instead.

If you're only doing T1, a test set will be relatively cheap. There is nothing greater than running head to head with a provider on a circuit. Sometimes they may test from a point in a circuit where the actual problem occurs, and hence, can't see the problem.

If you want to get more fancy, there are some test sets that allow remote access, so you can test from anywhere (of course this depends on your topology for Demarcs for your providers.