Content for  TS 23.333  Word version:  18.1.0

For message conferencing, the Message Session Relay Protocol (MSRP) (see RFC 4975) shall be used to transport messages. The message content may carry different media including text, image, video and audio. The Media types shall be MIME encoded. The TCP connection that the MSRP runs over shall be established when adding a new participant into the conference according to clause 6.2.20. In order to manage the message conferencing, the following features may be supported:

• Message statistics.
• Message filtering.

An MRFC and an MRFP that support a session based messaging, as defined in RFC 4975, shall support the following procedures. When receiving an SDP offer for a MSRP media, the MRFC:

• shall provide the value of the received "a=path" SDP attribute (defined in RFC 4975) to the MRFP in the "MSRP URI Path" information element, as part of a remote descriptor;
• shall indicate "TCP/MSRP" or "TCP/TLS/MSRP" (if e2e media security is applied) as transport protocol to the MRFP;
• if the "a=msrp-cema" SDP attribute, as defined in RFC 6714, is not contained in the SDP offer, should use the IP address and port within the first entry of the "a=path" SDP attribute from the received SDP offer to configure the remote IP address and port at the MRFP;
• shall request the MRFP to allocate the IP address, TCP port and MSRP session-id and provide this information in the "MSRP URI Path" information element;
• shall include the "a=path" SDP attribute received from the MRFP in an SDP answer it sends; and
• if the SDP offer included the "a=msrp-cema" SDP attribute, shall include the "a=msrp-cema" SDP attribute in the SDP answer.

When sending an SDP offer for MSRP media, the MRFC:

• shall request the MRFP to allocate an IP address, TCP port and MSRP session-id and provide this information in the "MSRP URI Path" information element;
• shall indicate "TCP/MSRP" or "TCP/TLS/MSRP" (if e2e media security is applied) as transport protocol to the MRFP;
• shall include the value of the "MSRP URI Path" information element received from the MRFP in the "a=path" SDP attribute of the SDP offer it sends; and
• should include the "a=msrp-cema" SDP attribute in the SDP offer.

When receiving a corresponding SDP answer for MSRP media, the MRFC:

• shall provide the value of the received "a=path" SDP attribute to the MRFP in the "MSRP URI Path" information element; and
• if the "a=msrp-cema" SDP attribute is not contained in the SDP answer, should use the IP address and TCP port within the first entry of the "a=path" SDP attribute from the received SDP answer to configure the remote IP address and port at the MRFP.

When the MRFP is configured to handle MSRP media and is requested to allocate an IP address, TCP port and MSRP session-id, it shall provide this information in the "a=path" SDP attribute and shall store this information. When the MRFP then receives MSRP packets, it shall compare the session-id part of the received MSRP packets with the stored session-id. The MRFP shall include MSRP URI(s) received in the "MSRP URI Path" information element from the MRFC in the "To-Path" header field of MSRP packets it sends.

The MRFP may report the statistics for the number of messages sent and/or received in two ways described as following. Figure 6.2.10.3.2.1 shows the message sequence chart example for reporting message statistics.

When the MRFC receives the trigger to config the filtering rules, the MRFC may initiate the "Configure Filtering Rules" procedure as specified in clause 8.52 to set filtering rules in the MRFP. The filtering rule is composed of two parts: the criteria and the treatment of the filtered message. The MRFP should handle messages according to the filtering rules. The MRFC may indicate to the MRFP the following criterias:

• Sender address
• Message size
• Message content type (e.g. video, audio)
• Message content format(e.g. mpeg, jpeg)
• Message subject

The MRFC may indicate to the MRFP the following message treatments:

• Block the delivery of the message content
• Store the message content
• Redirect the message to another address

The MRFC may indicate to the MRFP the "store url" when messages storage is needed, or the MRFC may indicate the MRFP to allocate the "store url" and return the generated "store url" to the MRFC. The MRFC may indicate to the MRFP the "redirect url" when messages redirection is needed. Figure 6.2.10.3.3.1 shows the message sequence chart example to config the filtering rules.