Cisco 400-051 CCIE Collaboration Online Training

Question #41

Refer to the exhibit.

How many SIP signaling dialog(s) took place in this SIP message exchange between two SIP user agents?

A . 1
B . 2
C . 3
D . 4
E . 5
F . 6

Correct Answer: A
A

Explanation:

During the establishment, maintenance and termination of a SIP session, signaling messages are

exchanged between the two SIP endpoints. There are two different kinds of signaling “conversations” that those messages take part in: transactions and dialogs. A transaction is a SIP message exchange between two user-agents that starts with a request and ends with its final response (it can also contain zero or more provisional responses in between). For example, during the termination of a SIP session, one user releases the call by sending a BYE request and the other party replies back with a 200 OK response. This message exchange is called a transaction. But what happens in the case of the INVITE request? The establishment of a SIP session starts basically with an INVITE request and is considered as completed upon the receipt of the ACK. In this case, the transaction starts with the INVITE request and ends with the 200 OK, so the ACK is not part of the transaction. The ACK can be considered as a transaction on its own.

However, when the final response to an INVITE is not a 2xx response, then the ACK is considered as part of the transaction. A dialog is a complete exchange of SIP messages between two user-agents. That means that transactions are actually parts of a dialog. For example, in the case of a SIP session establishment, a dialog starts with the INVITE200 OK transaction, continues with the ACK and ends with the BYE-200 OK transaction. The picture below depicts the dialog and transactions that take place during the establishment of a SIP session:

Note: There can also be subsequent requests that belong to the same dialog, such as a BYE or a re-INVITE message. As out-of-dialog requests are considered messages such as an initial INVITE request for a new session or an OPTIONS message for checking capabilities. There are different SIP headers/parameters that identify the dialogs and transactions, and they will be analyzed in later posts.

References: https://telconotes.wordpress.com/2013/03/13/sip-transactions-vs-dialogs/

Question #42

Which two statements describe characteristics of Binary Floor Control Protocol? (Choose two.)

A . Its binary encoding is designed to work in high-bandwidth environments.
B . It is designed for audio or video conference sessions of three or more participants.
C . It enables management of shared content resources independent of video streams.
D . It supports TLS-based authentication.
E . It supports SIP as well as H.323.

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Question #43

What is the minimum number of TCP sessions needed to complete a H.323 call between two H.323 gateways using slow start?

A . 0
B . 1
C . 2
D . 3
E . 4

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Question #44

Which element was added to H.225 messages to enable Fast Connect in H.323 version 2?

A . fastStart
B . fastConnect
C . H.245 PDU
D . User-User Information
E . Connection Information

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Question #45

What is the name of the logical channel proposal that is transmitted from the called entity to the calling entity in H.323 Fast Connect?

A . Forward Logical Channel
B . Backward Logical Channel
C . Reverse Logical Channel
D . Originator Logical Channel
E . Destination Logical Channel

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Question #46

Which procedure uses H.225 messages to exchange H.245 Master-Salve Determination information?

A . H.323 Fast Connect
B . H.245 tunneling
C . H.225 tunneling
D . H.323 early media
E . H.245 terminal capability set

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Question #47

Which two VoIP protocols use SDP to describe streaming media sessions? (Choose two.)

A . SCCP
B . H.323
C . SIP
D . MGCP
E . RAS
F . cRTP

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Question #48

Which RAS message is used between two gatekeepers to resolve an alias address?

A . GRQ
B . ARQ
C . IRQ
D . LRQ
E . RRQ

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Question #49

When a Cisco IOS gatekeeper receives an ARQ from a registered endpoint, what is the first step it will take in an attempt to resolve the destination address?

A . Check to see if the destination address is locally registered.
B . Check to see if the destination address matches the technology prefix.
C . Check to see if the destination address matches the local zone prefix.
D . Check to see if the destination address matches the remote zone prefix.
E . Check to see if the destination address matches the default technology prefix.

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Question #50

When a Cisco IOS gatekeeper receives an LRQ, what is the first step it will take in an attempt to resolve the destination address?

A . Check to see if the LRQ reject-unknown-prefix flag is set.
B . Check to see if the destination address matches the technology prefix.
C . Check to see if the destination address matches the hop-off technology prefix.
D . Check to see if the destination address matches the remote zone prefix.
E . Check to see if the LRQ forward-queries flag is set.

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