What do the acronyms UAC and UAS stand for? Define the difference between the two entities.

UAC stands for user agent client, and UAS stands for user agent server. The UAC originates the SIP session, and the UAS is the other endpoint of the session. It responds to INVITES and other messages sent from the UAC.

Name five types of SIP servers, and describe what they do.

The five types of SIP servers are proxy, registrar, location, redirect, and presence. Following is what each one does:

Proxy server Receives SIP requests from a UAC and forwards them to the next-hop device, such as a SIP server or the UAS.

Registrar server Registers UAs and provides location information upon request.

Location server Maintains the location database for registered UAs.

Redirect server Informs a UA about alternate locations for a called party that has moved.

Presence server Gathers presence information and subscriptions, and sends notifications of events.

Name the five types of SIP methods that Cisco routers can both generate and respond to. What is the purpose of each one?

The five types of SIP methods that Cisco routers can generate and respond to are REGISTER, INVITE, ACK, CANCEL, and BYE. Following is what each one does:

REGISTER Registers a UA address with a SIP server.

INVITE Requests that a UA participate in a session.

ACK Sent by the UAC when it has received the final response to an INVITE.

CANCEL Ends a pending session, not one that has already been accepted.

BYE Ends a call or session.

What command configures a dial peer to use SIP in its communication with its VoIP peer?

The session protocol sipv2 command under dial-peer configuration mode configures a dial peer to use SIP in its communication with its VoIP peer.

How does CallManager 4.x interact with a SIP gateway?

CallManager 4.x can register a SIP trunk to the gateway. The trunk is referred to as a signaling interface. It can also trunk to a SIP server, a CME gateway, or another CallManager cluster.

What additional SIP capabilities does CallManager 5.x add?

CallManager 5.x can register SIP phones and can function as a B2BUA.

Which Layer 4 protocol does SIP use by default, and what is the default port?

SIP uses UDP by default, but you can configure it to use TCP. The default port number is 5060.

What is the function of the SDP in SIP call setup?

SDP is used to exchange information about endpoint capabilities and negotiate call features, such as in an INVITE message. The SDP part of a SIP message contains information, such as the SDP version, the calling party organization, the IP address, expected media, and media attributes.