[Sip-implementors] [RFC 3398] SIP->ISUP->SIP issue (480 -> 18 -> 408)

[Iñaki Baz Castillo]

Hi, RFC 3398 (mapping SIP/ISUP) states that SIP 480 is mapped to ISUP 18:

480 Temporarily unavailable --> 18 No user responding

but at the same time it states that ISUP 18 is mapped to SIP 408:

18 no user responding --> 408 Request Timeout


Why? Note that ISUP 19 is also mapped to SIP 480:

19 no answer from the user --> 480 Temporarily unavailable


Then, shouldn't 480 be mapped to 19? In this way it would be a 1:1 relationship.
Also, 480 doesn't mean the same as 408 (even if both are the worst SIP
status codes as they are vaguely defined and are ambiguous).

I'm experimenting interoperability problems due to this exact issue
(480 -> 18 -> 408).


Thanks for any comment.

[Iñaki Baz Castillo]

Post by Iñaki Baz Castillo
Then, shouldn't 480 be mapped to 19? In this way it would be a 1:1 relationship.
Also, 480 doesn't mean the same as 408 (even if both are the worst SIP
status codes as they are vaguely defined and are ambiguous).

Also note what the section 7.2.8 of RFC 3398 says:

--------------------------------------------------
7.2.8 Timer T9 Expires

The expiry of this timer (which is not used in all networks)
signifies that an ANM has not arrived a significant period of time
after alerting began (with the transmission of an ACM) for this call.
Usually, this means that the callee's terminal has been alerted for
many rings but has not been answered. It may also occur in
interworking cases when the network is playing a status announcement
(such as one indicating that a number is not in service) that has
cycled several times. Whatever the cause of the protracted
incomplete call, when this timer expires the call MUST be released.
All of the gateway resources related to the media path SHOULD be
released. A '480 Temporarily Unavailable' response code SHOULD be
sent to the SIP network, and an REL message with cause value 19 (no
answer from the user) SHOULD be sent to the ISUP network. The PSTN
can be expected to respond with an RLC and the SIP network to respond
with an ACK indicating that the release sequence has been completed.
--------------------------------------------------

[Alejandro Orellana]

IMHO, there is now way to guarantee 1:1 mapping due to internetworking ,
have you looked at Q.1912.5 spec ??, ITU defined and more detailed than
3398.
the problem to me is from ISUP to SIP always there is a clearer mapping,
but from SIP to ISUP is not the clear so you have to make educated decision
, and i think that what it has been done in 3398.

Things you could try to overcome this is if possible to include the
Reason: header then you could include the real isup cause that could help
the gateway to a do better mapping.
Also SIPT will definitely ensure that that nothing get lost in translation.


regards

Post by Iñaki Baz Castillo
480 Temporarily unavailable --> 18 No user responding
18 no user responding --> 408 Request Timeout
19 no answer from the user --> 480 Temporarily unavailable
Then, shouldn't 480 be mapped to 19? In this way it would be a 1:1 relationship.
Also, 480 doesn't mean the same as 408 (even if both are the worst SIP
status codes as they are vaguely defined and are ambiguous).
I'm experimenting interoperability problems due to this exact issue
(480 -> 18 -> 408).
Thanks for any comment.
--
I?aki Baz Castillo
<ibc at aliax.net>
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