Describing The Sip Session - Snom ONE IP Technical Manual

SIP Header
Via
Call ID
CSeq
Contact

Describing the SIP Session

Besides methods and responses, SIP messages can also carry session descriptions in the
form of Session Description Protocol (SDP). SDP is used for describing multimedia
sessions for the purposes of session announcement, session invitation, and other forms
of multimedia session initiation. It includes information such as IP addresses, port
numbers, and times and dates when the session is active. SDP session descriptions are
text-based and consist of lines of text that are categorized as shown below (refer to Table
B-6 for details on the syntax):
v=0
o=root 839347042 839347042 IN IP4 192.168.1.101
Session-level
s=call
information
c=IN IP4 192.168.1.101
t=0 0
m=audio 52460 RTP/AVP 0 8 9 99 3 18 4 101
a=crypto:1 AES_CM_128_HMAC_SHA1_32 inline:zw00j/jEiq68b1fY0mJ
a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000
a=rtpmap:9 g722/8000
Media-level
a=rtpmap:3 gsm/8000
information
a=rtpmap:18 g729/8000
a=fmtp:18 annexb=no
a=rtpmap:4 g723/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=rtcp-xr:voip-metrics stat-summary=loss,dup,jitt
a=sendrecv
Path taken by the request so far
A unique number used to identify the call
Used for keeping track of the conversation number
Used for identifying the user agent and the version of software
used by the user agent
Appendix B: SIP Overview
Description
507