[c-nsp] Comparison of T3 and T1 PAs?

[Pete Templin]

Justin Shore wrote:
> Does anyone know of a good article, table or chart that compares the
> various T3 and T1 PA options?  I've found a variety of docs but nothing 
> of them giving a clear and concise list of differences between the PAs 
> (features, chassis support, NPE support, etc).
> 
> PA-T3
> PA-T3+
> PA-8T

These PAs, without -MC in the model, deal with their ports as a single 
interface.  In other words, if you insert a PA-8T into a 7206 in slot 6, 
I'd anticipate Serial6/0 through Serial6/7 showing up in your config.

> PA-MC-8DSX1
> PA-MC-8T1
> PA-MCX-8TE1-M
> PA-MC-T3
> PA-MC-T3+
> PA-MC-T3-EC

These PAs, with -MC in the model, are channelized ("Multi Channel"), and 
can (must?) deal with their ports as multiple channel groupings, each of 
which presents itself as a Serial interface once configured.

> I've found all sorts of docs on the DS3s but again nothing terribly 
> concise or a clear-cut comparison between the different models.  For 
> example I know that the PA-MC-T3-EC can do MLPPP in hardware but not on 
> the PA-MC-T3+.

Correct.  The PA-MC-T3+ depends on the system CPU for MLPPP.  AFAIK, the 
system CPU still handles the basic PPP duties, thereby negating some of 
the redundancy features that you'd hope/expect in a 7500.

> We bought the EC model for our T1 delivery service on 7200s (G2) but is 
> it really needed?  A fully-loaded 7200 with PA-MC-2T3-EC modules only 
> puts 12 DS3s in a chassis.  At full line-rate that's just shy of the 
> throughput limit on a G1 and still half that of our G2.  Now I'm sure if 
> all our DS1s were in MLPPP bundles that this would certainly add load to 
> the CPU but we're 25/75 CC DS1s and MLPPP bundles at this point.  I 
> could probably buy used PA-MC-T3 cards and do what I need if only I knew 
> what the feature differences were.

We converted a POP from 7507/RSP4/VIP2-50s to 7206/NPE-225, with one 
PA-MC-2T3+.  One T3 had fractional T1s on it (about 3/4 full), the other 
T3 had full T1s on it (about 3/4 full), with three MLPPP groups totaling 
about 10 T1s.  We saw CPU around 20-35%, which had me a little worried. 
  It's held steady in proportion to MLPPP traffic, so I've been OK.  I 
had an internal policy to limit 7206/7507s to no more than two 
PA-MC-2T3, for stability and config size, which should have kept the 
7206 CPU down sufficiently for us.

> One thing I need to know is on which T1 PAs is MLPPP supported.  I need 
> to know if MPLS (core-facing) would be supported on a bundle of T1s.  I 
> need to know which DS3 modules support core-facing MPLS.

MLPPP should be supported with most IOS, as long as you keep the bundle 
on a single PA.

Core-facing MPLS on MLPPP is going to be a problem.  You may want to 
search the archives for a post from Rodney Dunn on this particular 
topic.  He mentioned that it definitely wasn't supported under 
12.0(27)S, and I knew we were running it on that 12.0(27)S5.  I checked 
my routers, and found that VIP CPU on the relevant boxes was pegged at 
99% since a recent topology change, and was impacting packet forwarding 
heavily over that path.  That link was going away anyway, so we 
torpedoed it that night.

pt