[cisco-voip] help with modem calls going PRI -> 2811 -> PRI?

[John Callahan]

Help!  I have a single telco PRI terminated in a RAS (dial-up V.90 modems)
that is only serving a few users at this point, but they don't have any
other access options (other than satellite) so we continue to run it...

I would like to move the access numbers to our main PRI that terminates in
an MGCP gateway on a Cisco 2811 and then provide a "network side" PRI from
that same 2811 to the RAS box so I don't have to pay for a full PRI for just
a few concurrent users.

Everything seems to work except when I route the PRI through the 2811,
negotiated speeds drop way down and retrains go way up.  Often a modem will
retrain 10 times and just give up.

The incoming PRI (from telco) and the outgoing PRI (towards RAS) are both on
the same 2811, so I presume packet loss and jitter shouldn't be an issue --
I am wondering if it is somehow a clock issue?  Do I just give up because
this is unrealistic?

Here is the relevant IOS config - 0/0/0 is my normal voice PRI, 0/1/0 is the
PRI normally going directly to the RAS , 0/1/1 is the PRI provided to the
NAS (note the isdn protocol emulate network)

========================================================
network-clock-participate wic 0
network-clock-participate wic 1
network-clock-select 1 T1 0/0/0

controller T1 0/1/0
 framing esf
 linecode b8zs
 cablelength short 133
 pri-group timeslots 1-24 service mgcp
!
controller T1 0/1/1
 framing esf
 linecode b8zs
 cablelength short 133
 pri-group timeslots 1-24 service mgcp
!
interface Serial0/1/0:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn bind-l3 ccm-manager
 no cdp enable
!
interface Serial0/1/1:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn protocol-emulate network
 isdn incoming-voice voice
 isdn bind-l3 ccm-manager
 no cdp enable
!
mgcp modem passthrough voip mode nse
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