Chapter 17

Question 1

Protocols in the network (data link) layer specify…

Answer 1

communication over a single LAN

Question 2

Two main disadvantages of a basic LAN setup:

Answer 2

1) LANs are designed for small areas (a typical Ethernet cable only allows 100 meters or 328 feet)

2) Possible congestion and poor performance due to large numbers of simultaneous transmissions

Question 3

LAN

Answer 3

Local Area Network (spans room or building)

Question 4

WAN

Answer 4

Wide Area Networks (Spans sites in multiple cities)

Question 5

Fiber Modem

Answer 5

• One of the simplest methods
• Communicates over an optical fiber
• Can span long distances
• Can be used to extend connection between computer and a distant network

Question 6

Repeater

Answer 6

• Operate on Layer 1
• Simply repeat and amplify signals
• Low Cost
• Disadvantage: amplifies and repeats noise

Question 7

Bridge

Answer 7

• Originally a stand-alone device to extend two LAN segments
• Now: stand-alone bridges are rarely used:
• Bridge technology is incorporated into other devices: DSL modems, Cable modems, Wi-Fi “repeaters”, Satellite systems

Question 8

Learning/Adaptive Bridges

Answer 8

• Can connect 2 or more LAN segments
• Makes connected segments appear to be a single, large LAN
• Operates on layer 2
• Promiscuous mode
• Doesn’t copy noise/collisions/frames
• Uses source MAC address in frames to automatically learn where each computer is located
• Advantage: A pair of computers on one segment can communicate at the same time as a pair of computers on another segment (forms separate collision domain)
• Disadvantage: Copies of a broadcast frame will be sent in the cycle forever

Question 9

Spanning Tree Protocol

Answer 9

• Executed at startup
• Each bridge runs distributed algorithm independently, until STP finishes
• Result is a tree

Question 10

Ethernet Switch

Answer 10

• Physically similar to a layer 2 hub
• Logically like a multiport network bridge

Question 11

VLAN (Virtual Local Area Network)

Answer 11

• Physically similar to a conventional Layer 2 Switch, has ports to which computers connect
• Logically: Can configure a single switch to appear as multiple independent switches that belong to different lans