How do you use SIP headers and parameters for transaction tracing?

1 What are SIP headers and parameters?

SIP headers and parameters are the key components of SIP messages, which are the requests and responses that SIP entities send and receive. SIP headers provide information about the message, such as the method, the sender, the recipient, the session, and the routing. SIP parameters are the modifiers that can be added to SIP headers to specify certain values or options. For example, the To header contains the URI of the intended recipient, and can have parameters such as tag, which is a unique identifier for the dialog.

2 How to read SIP headers and parameters?

To read SIP headers and parameters, you need to understand the syntax and structure of SIP messages. A SIP message consists of a start line, zero or more header fields, an empty line, and an optional message body. The start line indicates the type, method, and version of the message. The header fields are formatted as name:value pairs, and can be separated by commas or semicolons. The parameters are appended to the header values with semicolons, and can have a name and a value, or just a name. For example, the From header can have a display name, a URI, and parameters such as tag and user.

3 How to use SIP headers and parameters for transaction tracing?

To use SIP headers and parameters for transaction tracing, you need to look for information that can help you identify and analyze the SIP transactions and dialogs. A SIP transaction is a sequence of request and response messages that share the same method and branch parameter, while a SIP dialog is a logical association between two SIP entities that lasts for the duration of a session. The Via header shows the path of the message through the network and contains the branch parameter, which is a unique identifier for the transaction. The CSeq header contains the sequence number and method of the message within a dialog, helping you match requests and responses. The Call-ID header provides a unique identifier for the call, allowing you to correlate messages belonging to the same dialog. Additionally, the Contact header shows the URI where the sender can be reached, and helps you determine the location and availability of the SIP entities. Finally, the Record-Route header shows the list of proxies that need to be traversed by the message, helping you trace the routing of the session.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?