Appendix B: SIP Overview
507
SIP Header
Description
Via
Path taken by the request so far
Call ID
A unique number used to identify the call
CSeq
Used for keeping track of the conversation number
Contact
Used for identifying the user agent and the version of software
used by the user agent
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
s=call
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
a=rtpmap:3 gsm/8000
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
Session-level
information
Media-level
information
Summary of Contents for ONE IP
Page 4: ......
Page 19: ...Part I Getting Started...
Page 20: ...Part I Getting Started...
Page 47: ...Part II Administering the System...
Page 48: ...Part II Administering the System...
Page 195: ...Deploying the snom ONE IP Telephone System 526...
Page 223: ......