Hi,
And there still two questions left.
1. Is the 199 should be reliable or unreliable?
I think that 199 should be reliable if possible.
First, If a client receives an unreliable 199 response on a dialog
which has
not previously been created (this can happen if a 199 response
reaches the client before a 18x response) the client SHALL discard
the 199 responses.
The figure below shows an example.The 180 is sent first but arrives
later than 199.
If the 199 is reliable, the proxy should retransmit 199 (step 4),and then
the retransmitted
199 will be accepted by UAC,and the early dialog will be teminated.
UAC P
1. INVITE
--------------->
2. 180
<----- \/-------
/\ 3. 199
<-----/ \------
4. 199(retransmitted)
<---------------
second, According to practical use, 199 can be intended to teminate one
early dialog and release
resources associated with the specific early dialog, so the cost spent on
reliable 199 is worthy.
If the 199 cannot be sent reliable,then we should send it unreliable.
2. In your last letter, you said "the second 199 could include information
which is to be forwarded to the
UAC", then do you mean, the early dialog is still alive after the first
199 is accepted?
Also, In my last letter, I miss a "NOT" by mistake.
It should be
[Eric]: Surely the UAS is NOT allowed to send another reliable response
until the first one is acknowledged...
Regards,
Eric wang
"Christer Holmberg" <[email protected]>
2009-02-27 03:04
收件人
"Eric wang" <[email protected]>
抄送
<[email protected]>, <[email protected]>
主题
RE: Questions about "draft-ietf-sip-199-05"
Hi,
>I still have some difficult in using IETF and cannot find the whole
sorted comments about this draft, so i have some doubt about this draft.
>
> 1. "If a forking proxy receives a reliably sent 199 response for a
dialog, for which the proxy has previously generated and sent a 199
response, the proxy MUST forward the 199 response."
>
> Does it describe the case below? Although P1 have sent a 199
response, P1 havs to forword the send reliably 199 too.Or is the
first 199 mistaked for 18x?
>
> UAC P1 UAS_2
> --- INVITE ------>
> --- INVITE (leg 2) ->
> <-- 199(leg 2) --
> <-- 199 (leg 2) -----
> <-- 199(leg 2) --
>I think it shall be 199, as currently written.
>
>[Eric]: If this is 199, then Is there a special purpose to send two
199 in the same dialog?
>I think that one 199 is enough.
>And the first 199 may be reliable too, that will make it a little
difficult to send the second 199.
The second 199 could include information which is to be forwarded to the
UAC.
>2. "10. Usage with 100rel
>
> When a 199 Early Dialog Terminated provisional response is sent by a
UAS, since the provisional response is only used for information
purpose, the UAS SHOULD send it unreliably even if the 100rel
> option tag [RFC3262] is present in the Require header of the
associated request."
>
>
>I have seen a comment on this question,but still not understood about
>it. If the INVITE has a Require tag "Require: 100rel",does the UAS
still
>use unreliable 199 response?
>
>That is the recommendation, yes. The reasons is that we want to keep
199
>as "lightweight" as possible, without requireing re-transmissions and
>PRACKs.
>
>[Eric]: But reliable 199 have more advantage, and It is worth to use
the reliable 199,I think.
I don't know what that advantage would be, compared to having to send
PRACKs etc. This has been discussed quite much, so I would really need
some good justification to change it now.
Also, the draft doesn't forbid you to send the 199 reliably. It's only a
SHOULD.
>If 199 is reliable, there is one more advantage. If the 199 arrives
>before the first 18x response, UAC can discard the first 199 and
process
>it until UAC receives the first 18x response that has the same
>to-tag as 199, as the reliable 199 should be re-transmited until
>received PRACK.
>
>If the INVITE contains "Require: 100rel", the first 18x must also be
>sent reliably. And, I don't think the UAS is allowed to send another
>reliable response until the first one is acknowledged, so I don't think
>a reliable 199 would reach the UAC before the first reliable 18x.
>
>[Eric]: Surely the UAS is allowed to send another reliable response
until the first one is acknowledged,
If I remember correctly, the FIRST reliable response must be acknowleded
before the next reliable response is sent. But, we can double check in
the PRACK spec.
>but reliable 199 will be useful if the first 18x is unreliable, or the
first 18x has been acknwledged. It's another case different from the
above one whose INVITE contains "require: 100rel".
If 100rel is required the 18x cannot be unreliable.
Regards,
Christer
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