Via: SIP/2.0/UDP 10.10.33.24:5070 branch=z9hG4bK9377fo00cg5ha7l0g3t0.1Īllow: ACK,BYE,CANCEL,INFO,INVITE,OPTIONS,PRACK,REFER,NOTIFYĪccept: multipart/mixed,application/media_control+xml,application/sdp NB that this inbound leg of this call will have a unique call ID that shows the origin of the call, highlighted below. An inbound call is received on the CUBE from the ITSP. This is because the To and From header fields in SIP are defi ned to indicate the direction of the request, not the direction of the message. Note that the To and From header fields are not reversed in the response message as one might expect them to be. Originator and destination of the SIP request. To: next header fields are the To and From header fields, which show the In SIP responses follow the via header except for future requests like ACK and BYE where responses are sent to the contact headerįrom: tag=25526~ffa80926-5fac-4dd6-b405-2dbbc56ae9a2-551664735 The image below shows the sent by field and this is where the required response will be sent to.
The Via header contains what is called the sent-by field. Via header fields contain protocol name, version number, and transport
This helps identify the origin of the call. Here we see that CUCM is the UA generating this invite and it stamps it IP on the call. Records its own address in a Via header field. The required Via header field is used to record the SIP route taken by a requestĪnd is used to route a response back to the originator. SIP port is 5060 and the Sip version is 2.0 The gateway responsible for routing to this number is 10.105.80.174 So here we see the called number is: 14107584528207 The device responsible for the called number or the device through which the called number will be routed This is the first part of the trace usually refrred to as the Request-URI This shows four key thingsĢ. Now let’s break it up or dissect this piece of information.Īs we can see there are lots of headers in this invite… Note this is very similar to what a debug ccsip messages will produce on a CUBE gateway.ĬUCM-sip trunk->CUBE-SIP Trunk->ITSP Let’s look at a sample SIP trace from CUCM.
#SIP MEANING FULL#
Headers are key parameters within the SIP invite and we shall look at them so as to gain full clarity of what’s going on. To identify the caller, the called number, the media information and resources advertised in the Invite, SIP invites use headers. If an INVITE does not contain media information, the ACK contains the media information of the UAC. The message body can also contain other session information, suchĪs a resource list in the case of an early offer. Telephony, it is similar to a Setup message in ISDNĪn INVITE usually has a message body containing the media information
The INVITE method is used to establish media sessions between user agents. The INVITE, REGISTER, BYE, ACK, CANCEL, and OPTIONS methods are the original six methods
There are Six SIP methods described in the SIP specification document RFC 3261. Ok enough of grammars, lets dive in! Ready?Īn Invite is a SIP requests called methods. They help us to understand the language been spoken so we are not lost like a non French speaking man in Paris! These messages are key in knowing what’s going on. We will look at these messages as we try to understand the debugs. To understand The output generated by this debug.We need to understand the Key/fundamental sip messages exchanged during a sip voice call. One popular debug used in troubleshooting a sip solution on a cisco IOS router is One key element of troubleshooting is this: To fix a problem, you need to understand the issue, how it works before you can restore it to order. In as much as I will try to define the under lying layer of the SIP messaging, this document will not go into in-depth analysis of the SIP protocol, so it is advisable to understand SIP protocol technology to be able to understand sip traces. We will look at various logs, the SIP messages, headers, SDP information and try to figure out what is going on in a sip voice call transaction. This document attempts to break down each component of the SIP interaction using a practical approach. Even though these traces are in clear text, these texts can be gibberish unless you understand fully what they mean. SIP traces provide key information in troubleshooting SIP Trunks, SIP endpoints and other SIP related issues.
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