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Re: [Sip] moving UDP support out of the core SIP document
Rohan Mahy wrote:
Hello Everyone,
I wanted to share some thoughts that I had about removing UDP from the
core SIP document when we go to draft standard.
[...]
Obviously UDP is still very attractive in wireless networks (due to RTT
issues) and in other typically private networks with well-understood
delay and loss characteristics. To make most implementations simpler
however, I am proposing that we make unreliable transports (UDP and
DCCP) of SIP optional in User Agents, and that we put the UDP-specific
mechanism (ex: much of the complication of the transaction layer for
handling retransmissions) in a separate Draft Standard document.
Making UDP optional is fine, but I think it should stay in the core
SIP specification. Over the years, the SIP state machines for
INVITE and non-INVITE transactions have evolved keeping multiple
transports in mind. The sourrounding text and the FSM figures
(Figure 5, 6, 7, and 8 in rfc3261) at this point in time are well
specified and, I beleive, well understood by the SIP community in
general.
Divorcing UDP transport from the core spec to another RFC raises other
questions:
1/ Since proxies are optional in SIP and a UA can initiate
a session directly with its peer, will a UDP-only UA
insert a "Require: udp" in the request?
2/ Issues such as reassembly, UDP response growing
larger than the request, etc. still remain.
If it is a choice between deprecating UDP entirely or moving it to
another RFC, I would choose the latter. But so long as we tacitly
support UDP, it would be nice to have it in the base document (maybe
degrade it to a MAY instead of a SHOULD).
Regards,
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566 Voice: +1 630 224 0216
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