Re: [sipcore] RFC4028 : Very basic question in 8.1

Shinji,

This is a negotiation where all parties (UAC, UAS and proxies on path) must
agree on the session timer value. Min-SE is the minimum allowed value. SE
is the maximum allowed value. If Proxy needs a higher SE interval, it needs
to renegotiate maximum allowed session timer value with all the parties
upstream. This is why it rejects the request with 422 and a higher Min-SE
value.

BTW, there is no guarantee that session timer negotiation will succeed. In
general case it is possible that session timer requirements for all the
proxies UAC and UAS cannot be satisfied at the same time.

Once again, may I ask, what is your motivation for proposing this change?
Are you seeing an issue with a deployment somewhere?
_____________
Roman Shpount

On Thu, Jul 9, 2020 at 9:10 AM OKUMURA Shinji <ietf.shinji@gmail.com> wrote:

> Hi,
>
> This is very basic question.
>
> Why must a proxy not increase SE-value?
>
> 1. UA sends INVITE(SE:100)
> 2. proxy rejects INVITE with 422(MSE:200)
> 3. UA sends INVITE again.(SE:200)
> 4. proxy forwards INVITE(SE:200)
>
> +-----+             +-------+            +-----+
> | UA1 |             | Proxy |            | UA2 |
> +-----+             +-------+            +-----+
>     |                    |                   |
>     | INVITE(SE:100)     |                   |
>     |------------------->|                   |
>     |                    |                   |
>     |       422(MSE:200) |                   |
>     |<-------------------|                   |
>     |                    |                   |
>     | INVITE(SE:200)     |                   |
>     |------------------->|                   |
>     |                    |                   |
>     |                    | INVITE(SE:200)    |
>     |                    |------------------>|
>
> If proxy may increase SE-value,
> 1. UA sends INVITE(SE:100)
> 2. proxy forwards INVITE(SE:200)
>
> +-----+             +-------+            +-----+
> | UA1 |             | Proxy |            | UA2 |
> +-----+             +-------+            +-----+
>     |                    |                   |
>     | INVITE(SE:100)     |                   |
>     |------------------->|                   |
>     |                    |                   |
>     |                    | INVITE(SE:200)    |
>     |                    |------------------>|
>     |                    |                   |
>
> Needless to say, this sequence is much simpler.
>
> Regards,
> Shinji
>
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