QoS requirements in DSL networks

We consider the evolution of the DSL access network within the economic constraints imposed by current deployments. We describe requirements and implementation constraints in delivering QoS in DSL access networks. In particular, the need for hierarchical traffic shaping mechanisms in the BRAS (broadband remote access server) to support both upstream and downstream QoS is identified. The need for session dynamic MTU (maximum transmit unit) renegotiation over the DSL line as QoS sessions are created or destroyed also seems appropriate for latency sensitive QoS sessions on low speed DSL upstream links.