[sipcore] Bypassing out-of-service intermediate Proxy

[<[e-mail]>]

Hi all,

I have a question regarding routeing of SIP requests and usage of ROUTE.

When a proxy or UA fails to send a SIP request to the next hop (because
this latter is not reachable) is it allowed to bypass this hop and send
the request to the hop whose URI is next in ROUTE header.

According to section 21.5.4 of RFC 3261, this proxy behaviour seems
allowed. See text in bold below:

Any opinions on this?

21.5.4 503 Service Unavailable


The server is temporarily unable to process the request due to a
temporary overloading or maintenance of the server.  The server MAY
indicate when the client should retry the request in a Retry-After
header field.  If no Retry-After is given, the client MUST act as if it
had received a 500 (Server Internal Error) response.

A client (proxy or UAC) receiving a 503 (Service Unavailable) SHOULD
attempt to forward the request to an alternate server.  It SHOULD NOT
forward any other requests to that server for the duration specified in
the Retry-After header field, if present.

Servers MAY refuse the connection or drop the request instead of
responding with 503 (Service Unavailable).


Youssef CHADLI
Orange Labs