This page describes how SIP requests are routed to and from the IPSMGW .
The ICSCFURI and SipTransport parameters in the Shared Configuration Profile determine how SIP requests are routed to and from the IPSMGW.
Outbound SIP requests
The ICSCFURI parameter specifies the URI of the I-CSCF in the operator’s network.
The IPSMGW inserts this URI in the Route header of outbound requests.
This determines the address, port and transport protocol that will be used when sending the request.
ICSCFURI is parsed as a SIP URI as per section 19.1 of RFC 3621.
It may use hostnames or IP addresses, and also the port and transport may be specified.
Some valid examples are shown below:
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sip:icscf.home1.net -
sip:10.45.200.1:5062;lr;transport=tcp -
sip:server5.ims.example.com:5060
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The "lr" parameter is automatically added to the I-CSCF’s URI when it is used in an outgoing request’s Route header.
It does not need to be specified in ICSCFURI.
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In an operator network it will usually be preferable to use a FQDN without port or transport parameters, such as sip:icscf.home1.net.
The IPSMGW will then use RFC 3263 DNS procedures to dynamically resolve the address, port and transport of the I-CSCF.
This means the operator can easily change the I-CSCF location in the DNS, without needing to update clients.
For testing purposes it may sometimes be useful to use explicit IP addresses, ports or transports.
Inbound SIP requests
The SipTransport parameter is used when IPSMGW needs to construct its P-Asserted-Identity address.
The routing of inbound requests, such as delivery reports, is determined by this address.
The P-Asserted-Identity address is constructed using the local IP address and port configured in the SIP-SIS resource adaptor, and the transport specified by SipTransport.
This may be "tcp" or "udp".
An SM-over-IP receiver that sends a delivery report to the IPSMGW obtains the address from the P-Asserted-Identity header in the MESSAGE it received from the IPSMGW (3GPP TS 24.341 §5.3.2.4).
For example, when IPSMGW delivers a short message, it puts its own address in the P-Asserted-Identity header.
MESSAGE tel:+4475500002222 SIP/2.0
From: <sip:ipsmgw-address:5060;transport=udp>;tag=096724a
To: <tel:+4475500002222>
P-Asserted-Identity: <sip:ipsmgw-address:5060;transport=udp>
Content-Type: application/vnd.3gpp.sms
...When the SM-over-IP receiver sends its delivery report request, it uses this address in the Request-URI:
MESSAGE sip:ipsmgw-address:5060;transport=udp SIP/2.0
From: <tel:+4475500002222>;tag=5623989
To: <sip:ipsmgw-address:5060;transport=udp>
P-Asserted-Identity: <tel:+4475500002222>
Content-Type: application/vnd.3gpp.sms
...In this way, delivery reports are routed to the IPSMGW using the configured SipTransport.
