SIP SIP Dialogs and Transactions

Question 1

What is the primary purpose of a SIP transaction?

Accepted Answer

To represent a single request and all responses to that request

Answer

To establish a persistent connection between two endpoints

Answer

To maintain session state for the duration of a call

Answer

To route SIP messages across multiple proxies

Question 2

Which combination of headers uniquely identifies a SIP dialog?

Accepted Answer

Call-ID, From tag, and To tag

Answer

Call-ID and CSeq number

Answer

Via branch parameter and Call-ID

Answer

From URI and To URI only

Question 3

What is the role of the CSeq header in SIP?

Accepted Answer

To sequence transactions within a dialog and identify the method

Answer

To identify the dialog uniquely across the network

Answer

To route the message to the correct proxy server

Answer

To specify the content type of the SIP message body

Question 4

What is Timer B in SIP INVITE client transactions?

Accepted Answer

The maximum time a UAC waits for a final response to an INVITE before timing out

Answer

The retransmission interval for INVITE requests over UDP

Answer

The time a server waits before sending a 100 Trying response

Answer

The interval between sending ACK and cleaning up the transaction

Question 5

In SIP, what is an 'early dialog'?

Accepted Answer

A provisional dialog created when a UAC receives a 1xx response containing a To tag

Answer

A dialog established before session media parameters are available

Answer

A dialog created during the REGISTER process before authentication

Answer

A dialog that exists before the UAC sends the initial INVITE

Question 6

Which SIP entity initiates a client transaction by sending a request?

Accepted Answer

User Agent Client (UAC)

Answer

Proxy server acting as transaction agent

Answer

User Agent Server (UAS)

Answer

Registrar on behalf of the endpoint

Question 7

What fundamentally distinguishes a SIP dialog from a SIP transaction?

Accepted Answer

A transaction is a single request-response exchange; a dialog persists across multiple transactions

Answer

A dialog is limited to one message exchange; a transaction spans the entire call

Answer

A dialog only applies to REGISTER requests; a transaction applies to all SIP methods

Answer

A transaction includes media negotiation; a dialog handles only signaling