SIP Session Management 1 — Questions and Answers

Question 1: Which SIP method is used to establish a call between two endpoints?

BYE
INVITE (Correct answer)
CANCEL
UPDATE

Correct answer: INVITE

The SIP INVITE method is the fundamental request used to initiate a call or establish a session between two endpoints. It proposes a communication session, typically carrying an SDP (Session Description Protocol) payload that describes the media capabilities and parameters for the session. Upon acceptance, the INVITE method leads to the establishment of a call or multimedia session.

Question 2: What SIP method is typically used to modify an existing session, such as changing media parameters?

BYE
RE-INVITE (Correct answer)
OPTIONS
ACK

Correct answer: RE-INVITE

The RE-INVITE method is a special form of the INVITE method used to modify an existing, established SIP session without tearing it down. It allows endpoints to change session parameters, such as adding or removing media streams, changing codecs, or updating IP addresses. This provides flexibility for dynamic session management, enabling adjustments to an ongoing call's characteristics.

Question 3: Which SIP method is used to end an established call?

INVITE
OPTIONS
BYE (Correct answer)
CANCEL

Correct answer: BYE

The SIP BYE method is specifically designed to terminate an established call or session between two endpoints. When one party wishes to end the communication, they send a BYE request, which signals the graceful termination of the SIP dialog. This ensures that both sides are aware the session is concluding, allowing for proper resource release.

Question 4: What protocol is commonly used in conjunction with SIP to describe multimedia session parameters?

HTTP
SDP (Session Description Protocol) (Correct answer)
RTP (Real-time Transport Protocol)
ICMP (Internet Control Message Protocol)

Correct answer: SDP (Session Description Protocol)

SDP (Session Description Protocol) is commonly used in conjunction with SIP to describe the multimedia session parameters. While SIP handles the signaling for setting up, modifying, and tearing down calls, SDP defines the details of the media streams, such as codecs, IP addresses, ports, and bandwidth. This separation of concerns allows SIP to focus on call control and SDP on media description.

Question 5: What is a SIP Dialog?

A SIP message exchanged between two endpoints
A call leg maintained between two endpoints, which provides state and context for the call (Correct answer)
A method used to authenticate SIP requests
A type of SIP header used to route calls

Correct answer: A call leg maintained between two endpoints, which provides state and context for the call

A SIP Dialog represents a logical, stateful relationship or 'call leg' between two SIP user agents that persists for the duration of a call. It provides the necessary context and state information, such as sequence numbers and routing details, for all subsequent messages exchanged within that specific call. This ensures that related messages are correctly processed and associated with the ongoing session, maintaining call continuity.

SIP Session Management 1

Which SIP method is used to establish a call between two endpoints?