[c-nsp] Looping up far end smartjack

[Anton Kapela]

On Jun 24, 2010, at 8:53 AM, Andy Koch wrote:

> On Wed, Jun 23, 2010 at 22:00, Richey <mylists at battleop.com> wrote:
>> I've been looking around and can't find a clear cut answer to this question.
>> Is it possible to loop up a far end T1 smart jack using a PA-MC-T3 in a
>> 7206?

yes, there is.

> I believe the remote T1 loopback features are only for CSU/DSU.  The

fortunately for Richey, this is incorrect.

> to drop it without access to the CSU/DSU that I looped and manually
> clearing it (or inserting a T-BIRD and sending the right loop-down
> code).
> 
> If anyone else has experience in getting this to work, I would be
> interested to hear.

I suppose this can become a NIU/smartjack specific question. As far as I am aware, Cisco will send the proper bits in the FDL towards the, sending first the loopback enable command (which are stuffed into the 4kbit/sec FDL portion of the ESF header -- the other 4kbit of course are ESF CRC bits), and then sending loopback disable when the command is removed. This has worked fine in practice over several lec and clec TDM networks.

The commands that work for pa-mc-t3 and ct3-ip (yes, vip+7500 rocking out in 2010 = awesome) are:

(config-if)#loopback remote line fdl ?
  ansi      Per ANSI T1.403 Spec. (remote CSU)
  bellcore  Per TR-TSY-000312 Spec. (remote SmartJack)

I have found the cisco mft-t1 VWIC's will respond to CSU loopback commands, and nearly every single ADC, adtran, etc NIU has worked fine given bellcore FDL loopback commands.

Of course, I have also noticed anywhere from a 15 to 20 minute 'forced loopback timeout' -- so doing extended tests can be confounded by 'blips' where the smartjack will auto-disable its loopback state.

-Tk