Attribute | Description |
a= | Attributes to extend SDP in the form a=<attribute> or a=<attribute>:<value>. |
b= | Contains information about the bandwidth required for the session or media in the form b=<bandwidth_type>:<bandwidth>. |
c= | Connection data about the session including the network type (usually IN for Internet), address type (IPv4 or IPv6), the connection source address, and other optional information. For example: c=IN IPv4 10.31.101.20 |
i= | A text string that contains information about the session. For example: i=A audio presentation about SIP |
k= | Can be used to convey encryption keys over a secure and trusted channel. For example: k=clear:444gdduudjffdee |
m= | Media information, consisting of one or more lines all starting with m= and containing details about the media including the media type, the destination port or ports used by the media, the protocol used by the media, and a media format description. m=audio 49170 RTP 0 3 m-video 3345/2 udp 34 m-video 2910/2 RTP/AVP 3 56 Multiple media lines are needed if SIP is managing multiple types of media in one session (for example, separate audio and video streams). Multiple ports for a media stream are indicated using a slash. 3345/2 udp means UDP ports 3345 and 3346. Usually RTP uses even-numbered ports for data with the corresponding one-higher odd ports used for the RTCP session belonging to the RTP session. So 2910/2 RTP/AVP means ports 2910 and 2912 are used for RTP and 2911 and 2913 are used for RTCP. Media types include udp for an unspecified protocol that uses UDP, RTP or RTP/AVP for standard RTP and RTP/SAVP for secure RTP. |
o= | The sender’s username, a session identifier, a session version number, the network type (usually IN for Internet), the address type (for example, IPv4 or IPv6), and the sending device’s IP address. The o= field becomes a universal identifier for this version of this session description. For example: o=PhoneA 5462346 332134 IN IP4 10.31.101.20 |
r= | Repeat times for a session. Used if a session will be repeated at one or more timed intervals. Not normally used for VoIP calls. The times can be in different formats. For example. r=7d 1h 0 25h r=604800 3600 0 90000 |
s= | Any text that describes the session or s= followed by a space. For example: s=Call from inviter |
t= | The start and stop time of the session. Sessions with no time restrictions (most VoIP calls) have a start and stop time of 0. t=0 0 |
v= | SDP protocol version. The current SDP version is 0 so the v= field is always: v=0 |
z= | Time zone adjustments. Used for scheduling repeated sessions that span the time between changing from standard to daylight savings time. z=2882844526 -1h 2898848070 0 |