SIP SIP Dialogs and Transactions 2

Question 1

Which SIP response first creates a confirmed dialog between two user agents?

Accepted Answer

200 OK

Answer

A confirmed dialog is established when the UAC receives a 2xx final response, which includes the To tag that completes the dialog identifier tuple.

Question 2

Why do SIP proxies insert themselves into the Record-Route header?

Accepted Answer

To ensure subsequent in-dialog requests traverse the same proxy path

Answer

Proxies insert themselves into Record-Route so that UACs build a Route set ensuring future in-dialog requests follow the same path through those proxies.

Question 3

What occurs when a proxy forks an INVITE in SIP?

Accepted Answer

Multiple early dialogs may be created, one per responding branch

Answer

When a proxy forks an INVITE, each branch that returns a provisional response with a To tag creates a separate early dialog with the UAC.

Question 4

What is Timer F used for in non-INVITE SIP client transactions?

Accepted Answer

The non-INVITE client transaction timeout before giving up

Answer

Timer F is the non-INVITE client transaction timeout (64*T1 by default); if no final response arrives before it fires, the transaction is considered failed.

Question 5

How does a UAC properly terminate a confirmed SIP dialog (active call)?

Accepted Answer

By sending a BYE request within the existing dialog

Answer

A confirmed dialog is terminated by sending a BYE request within the dialog; CANCEL can only be used to terminate a pending INVITE transaction before confirmation.

(SIP) Session Initiation Protocol Practice Test

(SIP) Session Initiation Protocol Practice Test

SIP SIP Dialogs and Transactions 2