Chapter 15


1:

What layers of the OSI model does Frame Relay cover?

A1:

Answer: Just Layer 2. Frame Relay uses the same Layer 1 specifications that point-to-point WAN links use.

2:

What is the name of the field in the Frame Relay header that identifies a PVC? Give the acronym and what the acronym stands for.

A2:

Answer: DLCIdata-link connection identifier

3:

Imagine that a company has a router, router A, at its headquarters. The router will use point-to-point WAN links to send and receive traffic to and from five remote sites. How many 4-wire cables need to be run from router A to the telco CO near router A?

A3:

Answer: You would need one 4-wire cable for each WAN link, or a total of five.

4:

Imagine that a company has a router, router A, at its headquarters. The router will use Frame Relay to send and receive traffic to and from five remote sites. How many 4-wire cables need to be run from router A to the telco CO?

A4:

Answer: Only one 4-wire cable would be needed.

5:

What term is used to describe the cable from a router to the CO when the router uses Frame Relay?

A5:

Answer: Access link

6:

Define the term "PVC."

A6:

Answer: PVC refers to the ability to transfer Frame Relay frames between two devices that are attached to the same Frame Relay network when the provider has preconfigured that ability. "PVC" stands for permanent virtual circuit.

7:

Does the access rate or the CIR define how many bits per second the telco commits to pass over a single PVC?

A7:

Answer: CIR

8:

Does the access rate or the CIR define the clock rate of the physical link between a router and the local CO?

A8:

Answer: Access rate

9:

What does the acronym CIR stand for?

A9:

Answer: Committed information rate

10:

Define the meaning of the term "DLCI."

A10:

Answer: The data-link connection identifier (DLCI) is a 10-bit number, usually written in decimal (range 01023), which identifies an individual Frame Relay PVC.

11:

Explain why the term "virtual circuit" is used to describe how Frame Relay sends data to and from a pair of routers.

A11:

Answer: One term for a WAN link between two routers is "leased circuit," or simply "circuit." Frame Relay allows a pair of routers to send and receive data. However, there is no real physical cable or line associated with each VC, so the term "virtual" refers to the fact that it's not physical, and the term "circuit" refers to the fact that it acts like a leased circuit in some ways.

12:

Explain the need for IP ARP on Frame Relay PVCs.

A12:

Answer: There is a need for something like ARP so that after a router knows the IP address to which it should forward the packet, it can then find the right data link address to put in the data link header of the frame. With Frame Relay, ARP is not used; instead, Inverse ARP is used.




Computer Networking first-step
Computer Networking First-Step
ISBN: 1587201011
EAN: 2147483647
Year: 2004
Pages: 173
Authors: Wendell Odom

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