I have some concern on the draft-ietf-sip-session-policy-framework-01. IMHO, in a wireless network, an expensive resource is the air-interface and an expensive QoS parameter is the end-to-end call set up delay. Current draft-ietf-sip-session-policy-framework-01 increases message flows between user agents (UAs) and network in both ends of a call. In this draft, a UA is directly communicating both with the Proxy and the Policy servers in both end of the network (in Figure 3 and 4). This will consume air-interface bandwidth and increase end to end delay of a call. Note that, in a large country, the distance between a cell phone user and a office supporting a proxy and policy server is in hundreds of miles. The UA's policy offer/exchange with the proxy and policy server would significantly impact the end-to-end call set up delay performance. A better approach would be direct rendezvous of the Proxy and the Policy servers through SIP. Generally, proxy and policy server are co-located. In emerging devices, proxies and policy servers are embedded inside a single hardware. Direct communication between Proxy and Policy server would reduce messages (2)/ack, (3), (4), (6), (7), (9), and (10) to two message exchange in Figure 3. Similar reduction is possible in Figure (4).
Thank you. Sincerely, Sohel Khan, Ph.D. Product Engineering Comcast Cable Communications
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