Subject: [Sipping] Question on ISUP to SIP mapping draft

From: Romel Khan <[email-masked]>
Date: Sun, 31 Mar 2002 15:05:10 -0500

1. Mapping ISDN cause to SIP status in section 6.2.4.1 states that cause 18
"no user responding" to SIP 408 Request Timeout. This is reasonable.
However, in section 7.2.6.1, for SIP to ISUP, it shows 408 to ISDN cause 102
Recovery on timer expiry. This is unreasonable. This interworking should be
bidirectional: 
SIP 408 <==> ISDN cause 18 "No User Responding"

An example of why it is unreasonable: With a SIP B2BUA where there is an
inbound leg and an outbound leg for a call going to a Softswitch which
terminates SS7. Callee starts ringing and does not pick up the phone within
a period which causes the ring timer in the Softswitch to expire. The
Softswitch then sends 408 to the B2BUA, which will send back the 408 on the
inbound leg. If the PSTN connectivity to the Inbound is SS7 or ISDN, don't
want the corresponding REL/DISC msg to interwork with cause 102 but rather
the cause should be 18 "No User Responding". Why should SIP 480 map to ISDN
cause 18 in this case? Why not please keep some of these interworking same
both ways (bidirectional) ==> simplifies many implementer's life, minimizes
departure from the spec.,enhances interoperability.

2. Need a SIP status code that interworks to ISDN cause 31 "Normal
Unspecified".

Thanks,
Romel 

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