Chapter 8 LAN Technologies and Network Topology

1. Chapter 8 LAN Technologies and Network Topology • Direct Point-to-Point Communication • Local Area Networks (LANs) • LAN Topologies • Ethernet • Token Ring • FDDI • LocalTalk • Wireless LAN

2. Direct Point-to-Point Communication • used in early computer communications systems • Advantages - Each point-to-point connection can use different network hardware, frame format, and bandwidth (fig 8.1) - Each point-to-point connection has exclusive access - Easy to enforce security and privacy • Disadvantages - fully meshed network becomes exponentially expensive as number of nodes increases (fig 8.2) - number of direct connections required = (N2 - N) / 2

3. Local Area Networks (LANs) • based on sharing the same communications medium. • emerged in 1980’s in local communications as alternative to expensive, dedicated point-to-point connections • shared networks confined to local communication because • more time would be spent coordinating the of sharing of network and less time spent actually transmitting data if two nodes are separated farther apart • Cost of providing high bandwidth is more expensive over long distance than over short distance • Locality of reference: computers usually communicate to another nearby computer.

4. LAN Topologies • Star network • all computers attached to a central point such as a hub (fig 8.3) • Fault tolerant advantage • Ring network • computers are logically arranged in circular loop (fig 8.4) • Physical orientation may be different ( offices on various floors using token ring). • One bad cable may disable the entire ring. • Token ring may be logical ring but physical star. • Bus network • usually consist of a single shared long cable to which computers attach (fig 8.5) • One bad cable may cripple the entire bus. • Ethernet network can be logical bus but physical star.

5. Ethernet Network • Manchester Encoding (fig 8.6) • Originally a bus network (ANIM06_1.MOV) in which multiple computers share a single transmission medium. • While one computer transmits a frame, all other computers must wait (fig 8.7) • Uses CSMA (carrier sense multiple access with collision detect) (ANIM06_2.MOV) • Uses binary exponential backup in recovering from collision. Delay time is doubled after each successive collision.

6. Wireless LAN • Uses antennas to broadcast RF signals through air • Carrier Sense Multiple Access with Collision Avoidance CSMA/CA (fig 8.8) • IEEE 802.11b • Up to 11 Mbps • frequency hopping spread spectrum (FHSP) • direct sequence spread spectrum (DSSS) • radio frequencies in range of 2.4 GHz - 2.483 GHz • IEEE 802.11a • Up to 50 Mbps • radio frequencies in range of 5 GHz

7. LocalTalk Network • bus network designed by Apple. • Uses modified CSMA/CA (a short message is sent to reserve the medium before transmitting a large message) • Limited to 230 kbps • Easy to install: daisy-chain computers (fig 10.9)

8. Token Ring Network • token passing ring network (fig 8.9) • IBM’s token ring operate at 16Mbps • token is a special bit pattern or message different from normal data frames (bit stuffing of data may be used) • only one token circulates the ring at any time. To send data, computer waits for token to arrive, transmit one frame, and then pass token to next node (ANIM06_3.MOV) • guarantees fair access because nodes take turns.

9. FDDI Network • Fiber Distributed Data Interconnect (FDDI) • token ring technology operating at 100 Mbps using fiber. • Uses counter rotating ring for fault tolerance (fig 8.10) • Self healing • Ring is still up if there is one break in the ring