As far as the carrier designs are concerned, I am assuming that you are will either be passing the voip traffic to the T1 ( CAS or PRI or E1R2 signaling) to the carriers or accepting the traditional telephony calls on these T1 interfaces and packetizing the calls to send over ip.
The first thing to note would be the equipment. Depending on the traffic your choices can vary from 36xx, 37xx series router for medium traffic to AS53xx routers for heavy traffic volumes.
As far as signaling protocols are concerned you would have choice of either PRI , CAS or E1 R2 and that would depend on what carrier you choose and their capability. Cisco routers can be configured to do all three.
For Call admission control you it would be a good idea to install a Gatekeeper. A cisco 36xx is a good platform for the GK functionality. Bear in mind that GK is an optional feature and not necessary to be installed.
Please review the following doc, it has some good guidlines.
Introduction: The "external-out enable" command is available for
configuration under the "router ospf process" in case of the IOS-XR
operating system. This command basically enables advertisement of
intra-area routes on the device as external routes in th...
IntroductionIn this article we'll discuss how to troubleshoot packet
loss in the asr9000 and specifically understanding the NP drop counters,
what they mean and what you can do to mitigate them. This document will
be an ongoing effort to improve troublesh...