We are looking to build an enterprise wide QoS design for our upcoming VoIP project. We will be tagging the voice and data traffic on our switches, setting up the appropriate buffers to expedite the voice traffic through the switches on the LAN, and applying the appropriate service-policy on the Serial interface out to the WAN.
The question I have though, since really all of this traffic is basically applied to an interface in an output fashion (meaning towards the WAN), is there any reason to set up the Ethernet port buffers on the router for inbound traffic? If you look at a full T1 coming into the router, would there be any need to put something on the Ethernet port of the router to ensure voice packets did not get delayed in processing or hung up in a buffer going through it? Would/could that ever happen? (1.544Mbps going to 100Mbps) All of the examples I have looked at for QoS on a router do not signify a need to do that, but I haven't been able to find a reason why we wouldn't (unless the buffers are able to process packets faster than it can receive them).
The second part to this question would be if the router was acting like a "router on a stick" model. That is, it has multiple subinterfaces and is handling routing for the entire LAN. If someone on a segment made a VoIP call to so-so on a different LAN segment through the same router and another person fired off an FTP through the router, how would we ensure that voice traffic is not delayed or dropped on the inbound?
