10.2.1 General

24.3793GPPMission Critical Push To Talk (MCPTT) call controlProtocol specificationRelease 18TS

10.2.1.1 Common Procedures

10.2.1.1.1 MONP message transport

In order to participate in a call of an MCPTT group, the MCPTT client:

1) shall send the MONP message as a UDP message to the multicast IP address of the MCPTT group, to UDP port 8809, with an IP time-to-live set to 255; and

2) shall treat UDP messages received on the multicast IP address of the MCPTT group and on port 8809 as received MONP messages.

The MONP message is the entire payload of the UDP message.

10.2.1.1.2 Session description

For an off-network MCPTT session, only MCPTT speech is used.

One off-network MCPTT session includes one media-floor control entity.

The MCPTT client shall generate an SDP body for a group call in accordance with rules and procedures of RFC4566 [12].

The MCPTT client:

1) shall include in the session-level section:

a) the "o=" field with the <username> portion set to a dash;

b) the "s=" field with the <session name> portion set to a dash; and

c) the "c=" field with the <nettype> portion set to "IN", the <addrtype> portion set to the IP version of a multicast IP address of the MCPTT group and the <connection-address> portions set to the multicast IP address of the MCPTT group;

2) shall include the media-level section for MCPTT speech consisting of:

a) the "m=" field with the <media> portion set to "audio", the <port> portion set to a port number for MCPTT speech of the MCPTT group, the <proto> field set to "RTP/AVP" and <fmt> portion set indicating RTP payload type numbers;

b) the "i=" field with the <session description> portion set to "speech";

c) the "a=fmtp:" attribute(s), the "a=rtpmap:" attribute(s) or both, indicating the codec(s) and media parameters of the MCPTT speech with the following clarification:

i) if the "/<x>/<x>/Common/PreferredVoiceCodec" leaf node is present in the group document configured on the group management client as specified in 3GPP TS 24.483 [45] containing an RTP payload format name as specified in IETF RFC 4566 [12], indicating a preferred voice codec for an MCPTT group; and

ii) if the MCPTT client supports the encoding name indicated in the value of the "name" attribute;

then the MCPTT client:

i) shall insert the value of the "/<x>/<x>/Common/PreferredVoiceCodec" leaf node in the <encoding name> field of the "a=rtpmap" attribute as defined in IETF RFC 4566 [12]; and

d) the "a=rtcp:" attribute indicating port number to be used for RTCP at the MCPTT client selected according to the rules and procedures of IETF RFC 3605 [13], if the media steam uses other than the default IP address; and

3) shall include the media-level section for media-floor control entity consisting of:

a) an "m=" line, with the <media> portion set to "application", the <port> portion set to a port number for media-floor control entity of the MCPTT group, the <proto> field set to "udp" and <fmt> portion set to "MCPTT"; and

b) the "a=fmtp:MCPTT" attribute indicating the parameters of the media-floor control entity as specified 3GPP TS 24.380 [5].