Transcript 09/29/04

COMS 161
Introduction to Computing
Title: Local Area Networks
Date: September 27, 2004
Lecture Number: 14
1
Announcements
• This material is from chapter 17 in the
book
• Paper 1 due on Friday
• Homework 5
– Due next Wednesday 10/06/04
2
Review
• Connecting to the Digital Domain
3
Outline
• LANs
– Transmission media
• Bounded
• Unbounded
4
Differentiating LANs
• Transmission media
– What are the actual hardware connections
between nodes (computers) made from?
• Topologies
– In what way are the various nodes arranged and
interconnected?
5
Transmission Media
NETWORKS ARE BUILT ON PHYSICAL MEDIA
Type
Uses
Maximum Operating Principal
Distance (without amplification)
Cost
Twisted pair
Small LANs
300 feet
Low
Coaxial cable
Large LANs
600–2,500 feet
Medium
Fiber optic
Network backbones; WANs
1–25 miles
High
Wireless/infrared
LANs
3–1,000 feet (line of sight)
Medium
Wireless/radio
Connecting things that move
Varies considerably
High
6
LAN Topologies
• Topology
– The logical layout or geometric organization of a
network
– Topology indicates potential paths for
communications between nodes
– Many topologies possible, with pros and cons
•
•
•
•
Point-to-point
Star
Bus
Ring
7
Point-to-Point Topology
• Point-to-point is the simplest topology
– Each node connected to some of its neighbors
– Needs a control mechanism
• The Internet uses TCP/IP
• P2P file-sharing programs
(Napster, Kazaa, etc.) use
centralized directory servers
– While this works for the
Internet, it requires too much
overhead for a successful
LAN implementation
8
Star Topology
• All nodes are connected to a single hub
HUB
9
Star Topology
• Advantages
–
–
–
–
Simple to implement
Centralized management
Easy to add new nodes
Network can expand by
‘daisy-chaining’ hubs
– Not subject to failure due
to a single node or cable
failure
• Disadvantages
– Number of nodes limited
to size of hub
– Cabling must all feed
back to the hub
– Hub failure is catastrophic
– Hub can be a bottleneck
for data throughput
10
Bus Topology
• Single transmission medium (‘bus’ or
‘backbone’)
• Nodes connected to the bus by ‘taps’
11
Bus Topology
• Advantages
–
–
–
–
Simple to implement
Shorter cabling
Easy to add new nodes
Not subject to failure due
to a single node failure
• Disadvantages
– Length of backbone
limited
– Failure of the backbone
cable is catastrophic
– Centralized management
difficult
– Cannot expand network
through daisy-chaining
12
Ring Topology
• All nodes connected in a ring (‘token ring’)
• Once heavily promoted by IBM, now not used much
• Nodes have a specified order on the ring
1
6
2
5
3
4
13
Ring Topology
• Advantages
– Originally higher speed
than possible with other
types (first to 10 Mbps
– Exactly predictable delay
rate
• Disadvantages
– Size of ring limited
– Adding or removing
nodes is difficult
– Cannot expand network
through daisy-chaining
– Failure of the backbone
cable is catastrophic
– Failure of any single node
is also catastrophic
– No centralized
management
14