SSCA Call Flows 4

Question 1

In a SIP three-way conference call flow using a mixer, what is the role of the focus UA?

Accepted Answer

It manages conference membership, mixes audio, and handles INVITE/BYE for each participant

Answer

The focus UA (conference server) maintains a separate dialog with each participant, mixes their audio, and manages conference state via the conference event package.

Question 2

What SIP mechanism allows a UA to subscribe to call state events, such as dialog state, for a monitored extension?

Accepted Answer

SUBSCRIBE/NOTIFY with Event: dialog package

Answer

The SUBSCRIBE method with Event: dialog is used to subscribe to dialog state information, enabling features like BLF (Busy Lamp Field).

Question 3

In a SIP REFER-based call transfer, after the REFER is sent, what ongoing mechanism keeps the transferring UA informed of the transfer progress?

Accepted Answer

NOTIFY requests sent to the implicit subscription created by REFER

Answer

REFER creates an implicit subscription; the recipient sends NOTIFY requests carrying the SIP response status (e.g., 100, 200) of the transfer attempt.

Question 4

Which SIP call flow scenario uses the UPDATE method instead of re-INVITE?

Accepted Answer

Modifying session parameters before the dialog is confirmed (during early dialog)

Answer

UPDATE is used to modify session parameters during an early dialog (before the final 200 OK), since re-INVITE can only be used after the dialog is confirmed.

Question 5

In a SIP call flow with PRACK, what is PRACK used to acknowledge?

Accepted Answer

Reliable provisional responses (1xx) when the 100rel extension is used

Answer

PRACK (Provisional ACK) is sent to reliably acknowledge provisional responses such as 180 Ringing when the 100rel extension is negotiated.

(SSCA) Sip School Certified Associate Practice Test

(SSCA) Sip School Certified Associate Practice Test

SSCA Call Flows 4