Question : When to implement QoS inside the LAN network

We are a partnering with a carrier to ready networks for implementing VoIP. I understand the carrier implements QoS on their Router at the demarcation point at client site. That is where they stop and we begin. We are planning on implementing a VLAN for phone traffic. My question is this: At what point is it necessary to implement QoS INSIDE the network architechture (other than the router going out to the world)? We are working with small to medium businesses, 30-175 users.

It was recommended that this would be of little benefit to the customer considering the time and cost to implement QoS. I just want to confirm this from a professional.

Answer : When to implement QoS inside the LAN network

Bear in mind that if this solution is to be their telephony system, internal call traffic will be on the local network between end points.

According to http://www.3com.com/other/pdfs/legacy/en_US/3Com_503139.pdf, audio quality is one of the five critical considerations when implementing IP telephony. I think the carrier recommendation shows a total lack of consideration, especially since it will be you who will be responsible after their demarcation point. So the cost benefit perspective is your call, since it will need to be based on not only QoS, but network design, equipment comparison costs and the results obtained after testing a network's readiness.