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[sipcore] RFC4028 : Very basic question in 8.1

OKUMURA Shinji <ietf.shinji@gmail.com> Thu, 09 July 2020 13:09 UTC

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From: OKUMURA Shinji <ietf.shinji@gmail.com>
To: sipcore@ietf.org
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Date: Thu, 09 Jul 2020 22:09:40 +0900
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Subject: [sipcore] RFC4028 : Very basic question in 8.1
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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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