Hi,

Afaik, this is a forwarding from ORIGiniating S-CSCF to TERMinating I/S-CSCF.

If the terminating user is registered at another S-CSCF or even at another domain than the originating user, then this procedure is obviously meaningful.

If we have only one network and one S-CSCF, then the procedure seems to be redundant, however for clarity of call flows, the procedure is not optimized but kept as it is.

If you have only one (logical) S-CSCF in your network, then you could try to omit the I-CSCF, just an idea.

Hope this helps.

Christoph

From: sr-users sr-users-bounces@lists.kamailio.org On Behalf Of Iman Mohammadi Sent: Thursday, May 23, 2019 12:26 PM To: Kamailio (SER) - Users Mailing List sr-users@lists.kamailio.org Subject: [SR-Users] Call Routing at IMS

Hi Everyone

When P-CSCF receives INVITE from client it sends INVITE to S-CSCF then S-CSCF without any look up(checking the user is registered or not)sends INVITE to I-CSCF then I-CSCF sends LIR and receives LIA and sends INVITE to same S-CSCF (in case of one S-CSCF exists).My Question is here why without any look up S-CSCF sends INVITE to I-CSCF??this procedure affects system performance and increases call set up time

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