What you are proposing is essentially the "piggyback model". There has
been an extensive discussion of the pros and cons of piggyback vs.
separate channel in SIPPING. A brief summary of this discussion can be
found in Section 4.2 of draft-ietf-sip-session-policy-framework-01.
Thanks,
Volker
Khan, Sohel wrote:
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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