Cisco CVOICE 642-437

Question 1

What fields are in the RTP header?

Answer 1

Timestamp, and sequence number.

Question 2

Which two signaling protocols are peer-to-peer?

Answer 2

H.323 and SIP

Question 3

What signaling protocol uses client-server architecture?

Answer 3

MGCP

Question 4

How many bytes are in the header of a RTP packet versus cRTP?

Answer 4

40 bytes versus 2-4 bytes.

Question 5

What are the benefits of SRTP versus VPN?

Answer 5

More efficient (less bandwidth) and more flexible since a VPN isn’t required.

Question 6

Regarding H.323 signaling, what features does H.225.0 RAS (Registration, Admission, and Status) support?

Answer 6

Gatekeeper (dial plan), and bandwidth control.

Question 7

What H.323 protocol is responsible for call setup and teardown?

Answer 7

H.225

Question 8

What H.323 protocol is responsible for negotiating codec and features?

Answer 8

H.245

Question 9

What messages are exchanged between H.323 gateways and gatekeepers using RAS?

Answer 9

ARQ (admission request), ACF (admission confirm), ARJ (admission reject), DRQ (disconnect request), DCF (disconnect confirm).

Question 10

What are the main benefits of SIP over H.323?

Answer 10

Text (ASCII) based messages, 3x less overhead, no bottleneck for state information.

Question 11

What is the difference between early offer and delayed offer in SIP call setup?

Answer 11

Early offer sends the SDP that negotiates settings such as codec in either the INVITE or RINGING messages, and delayed offer sends the SDP packets in OK and ACK messages toward the end of call setup.

Question 12

What UDP ports are used by MGCP?

Answer 12

2427 (receive) and 2727 (send)

Question 13

What signaling protocols work with CUBE?

Answer 13

SIP and H.323

Question 14

Where is the CoS value stored in a layer 2 header?

Answer 14

CoS is marked by 3 bits in the VLAN tag. It is not possible to mark CoS on a layer 2 frame unless it has a VLAN tag.

Question 15

What are the layer 2 and 3 QoS marking tools respectively?

Answer 15

CoS and ToS (DSCP)

Question 16

What QoS tool is used at the trust boundary?

Answer 16

Marking

Question 17

Where is the ideal trust boundary for a PC plugged into a phone that is attached to an access layer switch?

Answer 17

The boundary is between the PC and phone. The phone marks the packets, which saves processing overhead on the switch.

Question 18

Queuing is a member of which QoS tool?

Answer 18

Congestion management

Question 19

What happens to excess traffic in the priority queue when using LLQ?

Answer 19

The PQ is strict and policed, so excess traffic is dropped.

Question 20

How is traffic serviced in the LLQ priority queue?

Answer 20

FIFO (first in first out), which is why you only want one type of traffic in this queue.