6.2.20 TCP bearer connection control

23.3333GPPMultimedia Resource Function Controller (MRFC) - Multimedia Resource Function Processor (MRFP) Mp interface: Procedures descriptionsRelease 17TS

6.2.20.1 TCP connection establishment

Figure 6.2.20.1.1 shows an example call flow for a MSRP session set-up procedure, where the UE wants to join a messaging conference.

NOTE: In the shown example it is assumed that the UE-A and the MRFC/MRFP support IETF RFC 6714 [40].

Figure 6.2.20.1.1: UE connecting into a messaging conference

The IMS UE-A and the MRFC perform an IMS conference session set-up according to 3GPP TS 23.228 [1], 3GPP TS 24.247 [17] and 3GPP TS 24.147 [4]. The procedure in the figure 6.2.20.1.1 is described step-by-step with an emphasis on the additional aspects for the MRFC and the MRFP of the TCP connection establishment.

1. The IMS UE-A wants to join a messaging conference. For this purpose the IMS UE-A assigns a local TCP port number for the MSRP communication and builds an SDP offer containing the "a=setup:actpass" SDP attribute specified in IETF RFC 4145 [36].

The IMS UE-A sends the SIP INVITE request with the SDP offer.

2. – 4. Upon reception of the SIP INVITE request with the SDP offer containing a media stream that uses "TCP/MSRP" transport protocol, the MRFC uses the "Reserve And Configure IMS resources" procedure to request a termination for "TCP/MSRP" media. The MRFC provides an IP address and TCP port received from the IMS UE-A as part of a remote descriptor, requests the MRFP to allocate a local IP address and TCP port and includes a Notify TCP connection establishment Failure Event information element to request the MRFP to report an unsuccessful TCP connection set-up. In accordance to the information in the "a=setup" SDP attribute that will be sent in an SDP answer the MFRC requests the MRFP to start a TCP connection establishment.

5. The MRFP sends a TCP SYN message towards the IMS UE-A to establish a TCP connection. The IMS UE-A answers with a TCP SYN ACK message and the MRFP replies with a TCP ACK message, completing the TCP connection establishment.

6. The MRFC builds the SDP answer containing the "a=setup:active" SDP attribute and inserts the IP address and TCP port received from the MRFP.

7. The MRFC sends the 200 (OK) final response (or 18x provisional response) to the SIP INVITE request with the SDP answer for the MSRP session towards the IMS UE-A.

6.2.20.2 TCP connection establishment Failure Indication

The MRFP shall use a Notify TCP connection establishment Failure Indication procedure to report TCP connection establishment related failures.

The figure 6.2.20.2.1 shows the message sequence chart example when the MRFP reports an unsuccessful TCP connection set-up to the MRFC.

Figure 6.2.20.2.1: TCP connection establishment Failure Indication