Local Area Networks

1
Local Area Networks

• Chapter 17,
• Exploring the Digital Domain

2
In this chapter . . .
You will learn about

• the characteristics and advantages of LANs
• how devices in LANs are connected and transmit
  data
• how communication is organized among competing
  nodes
• how software facilitates networks
• ways to extend LAN size and performance
• how wireless LANs are organized and communicate

3
Basic Characteristics of LANs

• connectivity supporting two-way communication
• resource sharing
• limited geographical area
• transparency of use
• support from hardware and software

4
Costs and Benefits
costs
benefits

• need for additional equipment
• maintenance
• support staff

• communications
• management control
• cost-effectiveness

5
Transmission Media
bounded media
unbounded media

• twisted-pair cable
• UTP CAT-n
• coaxial cable
• optical fiber cable

• infrared transmission
• radio frequency broadcasting
• cellular network transmissions

6
Topologies

• star
• bus
• ring

star topology has a single node that serves as
the hub and central switching node for the rest
of the network
7
Topologies

• bus

bus topology is a single medium on which all
of the nodes are connected
8
Topologies

• ring

a ring topology is a closed path that is
directional signals are passed from node to node
9
Media Access Control

• Ethernet (AKA Carrier Sense Multiple Access with
  Collision Detection)
• nodes listen for silence on the bus
• when carrier is silent, node transmits packet
• if no collisions, transmission continues
• but if collisions, backoff procedure invoked

10
Media Access Control

• Token Passing
• node can capture a free token
• packets are transmitted via token to successor
• token transmitted from node to node
• acknowledged token eventually returned to sender

11
Media Access Control
token passing
12
Networking Software

• physical layer supports basic carrier signals
• data link layer manages point-to-point
  connectivity
• network layer routes data from sender to
  destination
• transport layer provides messaging services
• applications layer provide user functions

13
Extending LANs

• REPEATERS boost signal strength over medium
• BRIDGES isolate LANs from unnecessary traffic,
  but connect LANs to neighboring networks
• SWITCHES provide dedicated and shared
  connections for large numbers of nodes
• ROUTERS connect same or different protocol nets

14
Extending LANs
15
Wireless LANs

• infrared broadcasting
• radio frequency broadcasting
• spread spectrum (cell telephony)
• direct sequence spread spectrum (DSSS)
• frequency hopping spread spectrum (FHSS)

16
WLAN Topology

• Basic Service Set (BSS)
• access points (AP)
• Stationary
• nodes
• mobile

17
WLAN Topology

• ad hoc network
• temporary
• nodes
• mobile
• transitory

18
WLAN Standards

• HomeRF
• 2.4 GHz, 2 - 10 Mbps, 100-150 ft.
• Wi-Fi (802.11b)
• 2.4 GHz, 2 - 11 Mbps, 200 - 400 ft.
• 802.11a
• 5 GHz, up to 54 Mbps
• 802.11g
• 2.4 GHz, up to 54 Mbps

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Personal Area Networks

• PAN -- a group of digital devices assembled in a
  small area to communicate and share information
• Bluetooth
• 2.4 GHz, 1 Mbps
• FHSS
• up to 7 simultaneous connections