Create loopback interfaces on both routers and use the 'H323-gateway voip bind srcaddr' command as the source of all the VOIP traffic.
If using G729, assume 24 K per call and base your priority statements on the LLQ to suit. The D channel should have 64K available as some PBX's will send continual fill in packets (eg NEC No.7 signalling)
Next, use low latency queueing to match on an access list that specifies the source of the local loopback and destination loopback IP addresses. This will make the LLQ config quite simple.
access-list 100 permit ip host 10.1.1.1 host 10.1.2.1
class-map voip
match access-group 100
policy-map TCCS_VOIP
class voip
priority 650
!
class class-default
fair-queue
!
apply the policy to the interface -
interface serial 1/0
ip address 100.1.1.1 255.255.255.0
service-policy output TCCS_VOIP
Make the VOIP dial peers point to the remote
loopback interface as well.
Add the voice vad time 100000 (10,000 msec) command so that if there is no audio after 10 seconds, the VAD will cut in on idle channels, saving bandwidth.
We have set up many site like this and they are working fine.