1 COMS 161 Introduction to Computing Title: Local Area Networks Date: September 27, 2004 Lecture Number: 14

2 Announcements This material is from chapter 17 in the book Paper 1 due on Friday Homework 5 –Due next Wednesday 10/06/04

3 Review Connecting to the Digital Domain

4 Outline LANs –Transmission media Bounded Unbounded

5 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?

6 Transmission Media NETWORKS ARE BUILT ON PHYSICAL MEDIA TypeUses Maximum Operating Principal Distance (without amplification) Cost Twisted pairSmall LANs300 feetLow Coaxial cableLarge LANs600–2,500 feetMedium Fiber opticNetwork backbones; WANs1–25 milesHigh Wireless/infraredLANs3–1,000 feet (line of sight)Medium Wireless/radioConnecting things that moveVaries considerablyHigh

7 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

8 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

9 Star Topology All nodes are connected to a single hub HUB

10 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

11 Bus Topology Single transmission medium (‘bus’ or ‘backbone’) Nodes connected to the bus by ‘taps’

12 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

13 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

14 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