[c-nsp] subrate DS3 - can the remaining T1s be reused?

[Justin M. Streiner]

On Wed, 1 Feb 2006, Pete Templin wrote:

> We've got a 2xT1 MLPPP and several voice T1s internally that we'd like
> to upgrade.  For cost reasons, we'd rather use unchannelized T3
> (PA-2T3+) cards instead of channelized (PA-MC-2T3+) cards.  Can we
> demux/mux both ends of the DS3 carrier circuit to use some of the T1s
> for voice/test purposes, while still using the PA-2T3+ cards in subrate
> mode?

You should be able to.  The mux will need to handle breaking out 
individual T1 transports if you want to use some of them for other 
purposes, such as voice.

The PA-2T3+ will handle subrate DS3s without troubles.  I've used them on 
subrate circuits many times in the past.

> PA-2T3+---M13---(perhaps 20 T1s direct-connected)---M13---[carrier ckt]
>
> [carrier ckt]---M13---(perhaps 20 T1s direct-connected)---M13---PA-2T3+

There may be a mux out there that can split out just the T1s you need and 
pass the remaining channels on as a DS3, rather than needing to break 
every channel out as a T1 only to re-mux it back into a subrate DS3 for 
delivery into your routers.  You could also get into bigger timing issues 
if you de-mux and re-mux everything.  I don't have specific knowledge of a 
mux that will do exactly this because I've never had build a setup like 
this.  Also make sure that mux has some type of remote management 
capabilities (decent UI, ability to send SNMP traps or syslog messages, 
etc).

> Obviously, I'd need to set "dsu bandwidth 30880" or so, but would this
> work?  Do I always use T1s 1-N in this scenario?

At this level, the PA-(2)T3+ doesn't see the circuit as individual T1 
transports, just as a subrate DS3 transport.  To make your life easier, 
you should use the last channels on the DS3 as your T1 breakouts.

> Links are fine.  I just can't find any "under the hood" details to the
> subrate T3 cards on CCO.

As long as the muxes feed a C-bit framed DS3 to the router, you should be 
OK on that end.  Clocking can an issue as well, but using one mux on each 
end instead of two can help keep things manageable.

jms