[c-nsp] subrate DS3, pa-mc-2t3+

[Mark Kent]

Hello,

I have an situation where, for testing/demo purposes, we need to nail
down the bandwidth on both ends of a DS3.  For example, we'ld like to
make a 22Mbs circuit, as if someone had purchased an actual half DS3
from a telco vendor.  And then we want to change it to, say, 5Mbs, etc.

I've only dealt with wide-open DS3... but I see this:

   Configures the PA-MC-2T3+ to emulate a proprietary 
   DSU subrate scheme.

here

http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a0080086fc3.html


I know that in the T1 world I can dial in, say, 12 channels on both
csu/dsu and end up with 12*64kbps = 768kbps.  And that would be 
a hard limit, and would behave exactly like we purchased a fractional
T1 with 12 channels (64k channels, not 56k) from the telco.

This concept does not seem to be exactly applicable in the 
DS3 world.  The command looks like this:

(config-if)#dsu bandwidth ?
  <1-44210>  Bandwidth maximum for the interface in Kbps

and it takes _any_ number between 1 and 44210, for example:

 dsu bandwidth 12345

and it doesn't auto-magically change it to a closest bw imposed
by the underlying technology (like in the T1 world it would be
increments of 64kbps).

I'm sure that with specific far-end equipment 
(Larscom, Kentrox, etc.) there are only a small 
set of meaningful settings (anyone know what they are?).  
But for cisco-to-cisco, how is this managed?

Thanks,
-mark

P.S. ranges are given for these far-end csu/dsu, but
      specific values within the range:

# 0  Digital Link or Cisco  300-44210 Kbps
# 1  ADC Kentrox T3/E3 IDSU  1500-35000, 44210 Kbps
# 2  Larscom Access T45  3100-44210 Kbps
# 3  Adtran T3SU 300  75-44210 Kbps
# 4  Verilink HDM 2182  1500-44210 Kbps