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

[OKUMURA Shinji <[e-mail]>]

Roman,

I haven't proposed a fix for this YET. This is a pure question at this point in time.

> SE is the maximum allowed value.

UAC can send again with a greater Session-Expires and Min-SE. The proxy CAN NOT reject the INVITE just because "Session Interval Too Large". Therefore SE isn't 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.

If Proxy needs a higher SE interval, the proxy need only increase SE-value. This procedure definitely works. Because this is the very procedure for when the UAC does not support timer.
Again, proxies can't reject the INVITE just because the timer is too large.

> Once again, may I ask, what is your motivation for proposing this change?

My motivation is that bis become to be more clear and error-free.

> Are you seeing an issue with a deployment somewhere?

No, You seem to attach great importance to that point, but I don't understand the importance of that.
Do you argue that it is enough for each developer to address any issues on their own?

Regards,
Shinji

On 2020/07/09 22:17, Roman Shpount wrote:
> 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 <[e-mail]> 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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>