SIP/SDP packets explained

SIP/SDP packets explained

When looking through wireshark traces and network logs from the video intercom it is crucial to understand SDP packets and the information that they convey. An SDP packet is used during call setup and is never transmitted on its own. It is only attached to certain SIP messages that are using during call setup such as : INVITE, OKAY, and ACK. There is a lot of information sent in SDP packets but there are a few lines that are extremely importatnt and we will be looking at them frequently while reading through network logs. Here is an example of a SIP/SDP packet:

************ This is the SIP portion of the packet *********************************************

SIP/2.0 200 OK
Via: SIP/2.0/UDP;branch=z9hG4bK2634090914c
From: <sip:1652@>;tag=28978~dcd22a0f-91e1-4b1f-94e5-20a6f9b36120-31138062
To: <sip:667@>;tag=2359914029
Call-ID: 67e72980-9de137e8-88-220b0b0a@
CSeq: 101 INVITE
Contact: <sip:667@>
Content-Type: application/sdp
User-Agent: CyberData Outdoor Video Keypad/v1.3.0
Content-Length: 319
[1B blob data]

************This is the SDP portion of the packet ********************************************
o=667 1390 3632 IN IP4                                     <-- This line contains information about the sender, such as extension number and IP address.
c=IN IP4                                                             <-- This line contains network information.
t=0 0
m=audio 10500 RTP/AVP 0 8 101                                             <-- This line begins the audio codec portion. 10500 is the port. "0 8 101" are the 'types' of codec being sent.
a=rtpmap:0 PCMU/8000                                                           <-- This line contains information about the PCMU audio codec. 
a=rtpmap:8 PCMA/8000                                                           <-- This line contains information about the PCMA audio codec.

a=rtpmap:101 telephone-event/8000                                        
a=fmtp:101 0-15
m=video 9078 RTP/AVP 102 97
a=rtpmap:102 H264/90000
a=fmtp:102 profile-level-id=428014
a=rtpmap:97 H264/90000

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