INVITE - VoLTE

INVITE is a session initiation (session creation) process in SIP based communication. There are some SIP communication that does not require a session establishement (e.g, SMS over IMS or some other form of Short Message), but most of the IMS/SIP based communication (e.g, VoLTE, Video, File Transfer etc) are going on in a session.  Whenever the session needs to be established, it is done by INVITE process. The critical part of this process is 'INVITE' at the beginning and 200 OK at the end. But in reality, many other steps are going on between the INVITE and 200OK and the detailed sequences of messages between INVITE and 200 OK differs depending on what kind of session is to be established. (If you are not familiar with what Session means, refer to Session page)

The example in this page is the simplest form of INVITE being used in VoLTE. The example in this page focus only the INVITE and its corresponding 200 OK. If you want to know the details of other messages and contents of those messages, refer to MO VoLTE with PreCondition.

(1) INVITE -----------------------------------

INVITE sip:user1@192.168.1.11:35057 SIP/2.0

Via: SIP/2.0/UDP 192.168.1.12:64701;branch=z9hG4bK635101086453090273;rport;transport=UDP

Max-Forwards: 69

Call-ID: 635101086453000268@192.168.1.2

CSeq: 7 INVITE

Via: SIP/2.0/UDP 192.168.1.2:64627;branch=z9hG4bK635101086453000268;transport=UDP

To: <sip:user1@anritsu-cscf.com>

From: <sip:0123456789@anritsu-cscf.com>;tag=1111111111

Contact: <sip:0123456789@anritsu-cscf.com:64627;transport=udp>

Allow: INVITE, UPDATE, ACK, CANCEL, BYE, PRACK, MESSAGE

Supported: 100rel

Supported: precondition

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.gsma-vs";require;explicit

Privacy: id

Content-Type: application/sdp

Content-Length: 565

Record-Route: <sip:192.168.1.2;lr>

(8) 200 OK -----------------------------------

SIP/2.0 200 OK

Via: SIP/2.0/UDP 192.168.1.12:64701;rport=64701;branch=z9hG4bK635101086453090273;transport=UDP

From: <sip:0123456789@anritsu-cscf.com>;tag=1111111111

To: <sip:user1@anritsu-cscf.com>;tag=1076437947

Contact: <sip:user1@192.168.1.11:35057;transport=udp>

Call-ID: 635101086453000268@192.168.1.2

CSeq: 7 INVITE

Content-Type: application/sdp

Content-Length: 527

Via: SIP/2.0/UDP 192.168.1.2:64627;branch=z9hG4bK635101086453000268;transport=UDP

Record-Route: <sip:192.168.1.2;lr>

Allow: ACK, BYE, CANCEL, INVITE, MESSAGE, NOTIFY, OPTIONS, PRACK, REFER, UPDATE

(9) ACK -----------------------------------

ACK sip:user1@192.168.1.11:35057 SIP/2.0

Via: SIP/2.0/UDP 192.168.1.12:64703;branch=z9hG4bK635101086492402521;rport;transport=UDP

Max-Forwards: 69

Call-ID: 635101086453000268@192.168.1.2

CSeq: 7 ACK

To: <sip:user1@anritsu-cscf.com>;tag=1076437947

From: <sip:0123456789@anritsu-cscf.com>;tag=1111111111

Via: SIP/2.0/UDP 192.168.1.2:64627;branch=z9hG4bK635101086453000268;transport=UDP

Content-Length: 0