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Chapter 7

Chapter 7. Local Area Networks: The Basics. Topics. Definition of LAN Primary function, advantage and disadvantage Difference between Client/Server network and peer-to-peer network Topologies of LANs MAC techniques Applications. Definition of LAN.

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Chapter 7

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  1. Chapter 7 Local Area Networks: The Basics

  2. Topics • Definition of LAN • Primary function, advantage and disadvantage • Difference between Client/Server network and peer-to-peer network • Topologies of LANs • MAC techniques • Applications

  3. Definition of LAN • A local area network is a communication network that interconnects a variety of data communicating devices within a small geographic area and broadcasts data at high data transfer rates with very low error rates.

  4. Primary Function • To provide access to hardware and software resources that will allow users to perform one or more of the following activities: • Manufacturing • Education (lab, office) • Interconnectivity with other networks

  5. Advantages • Ability to share hardware and software resources. • Individual workstation might survive network failure. • Component and system evolution are possible. • Support for heterogeneous forms of hardware and software. • Access to other LANs and WANs (Figure 7-1). • Private ownership. • Secure transfers at high speeds with low error rates.

  6. Disadvantages • Equipment and support can be costly. • Level of maintenance continues to grow. • Some types of hardware may not interoperate. • Just because a LAN can support two different kinds of packages does not mean their data can interchange easily. • A LAN is only as strong as it weakest link

  7. LAN Topologies • Four basic ones:

  8. Bus/Tree Topology • The original topology. • Workstation has a network interface card (NIC) that attaches to the bus (a coaxial cable) via a tap. • Data can be transferred using either baseband digital signals or broadband analog signals.

  9. Bus/Tree Topology • Baseband signals are bidirectional and more outward in both directions from the workstation transmitting. • Broadband signals are usually uni-directional and transmit in only one direction. Because of this, special wiring considerations are necessary. • Buses can be split and joined, creating trees.

  10. Star-wired Bus Topology • Logically operates as a bus, but physically looks like a star. • Star design is based on hub. All workstations attach to hub. • Unshielded twisted pair usually used to connect workstation to hub. • Hub takes incoming signal and immediately broadcasts it out all connected links. • Hubs can be interconnected to extend size of network.

  11. Single Hub Multiple-Hub

  12. Star-wired Bus Topology • Advantage: • Disadvantage

  13. Star-wired Ring Topology • Logically operates as a ring but physically appears as a star • Star-wired ring topology is based on MAU (multi-station access unit) which functions similarly to a hub • Where a hub immediately broadcasts all incoming signals onto all connected links, the MAU passes the signal around in a ring fashion • Like hubs, MAUs can be interconnected to increase network size

  14. Logical View Physical View

  15. Wireless LANs • Not really a specific topology since a workstation in a wireless LAN can be anywhere as long as it is within transmitting distance to an access point • Two basic components • Wireless NIC card • Access point (AP) • Acts as a bridge between the wired and wireless networks and can perform basic routing functions

  16. Wireless Standards • IEEE 802.11 (older 2 Mbps) • IEEE 802.11b (11 Mbps, 2.4 GHz, 200-300 feet) • Also named Wi-Fi (Wireless Fidelity) • IEEE 802.11g (54 Mbps, 2.4 GHz, in 2002) • IEEE 802.11a (54 Mbps, 5 GHz, in 2002, 90 feet) • HiperLAN/2 (European standard, 54 Mbps in 5 GHz band, 90 feet) Distance is inversely proportional to transmission speed - as speed goes up, distance goes down

  17. Peer-to-Peer Networks • Different from client-server architecture • May not possess servers • Focus on applications • Groupware/collaboration tools • Content-management • Distributed file-sharing • Distributed processing

  18. Medium Access Control Protocols • How does a workstation get its data onto the LAN medium? • A medium access control protocol is the software that allows workstations to “take turns” at transmitting data. • Three basic categories:

  19. Contention-Based Protocols • Essentially first come, first served • Carrier sense multiple access with collision detection (CSMA/CD) • If no one is transmitting, a workstation can transmit • If someone else is transmitting, the workstation “backs off” and waits • If two workstations transmit at the same time, a collision occurs • When the two workstations hear the collision, they stop transmitting immediately • Each workstation backs off a random amount of time and tries again • CSMA/CD is an example of a

  20. Round Robin Protocols • Each workstation takes a turn transmitting and the turn is passed around the network from workstation to workstation. • Most common example is token ring LAN in which a software token is passed from workstation to workstation. • Token ring is an example of a • Token ring more complex than CSMA/CD. What happens if token is lost? Duplicated? Hogged? • Token ring LANs are losing the battle with CSMA/CD LANs.

  21. Reservation Protocols • Workstation places a reservation with central server. • Workstation cannot transmit until reservation comes up. • Under light loads, this acts similar to CSMA/CD. • Under heavy loads, this acts similar to token ring. • Powerful access method but again losing out to CSMA/CD. • Most common example of reservation protocol is demand priority protocol.

  22. Local Area Network Systems • Ethernet • Most common form of LAN today • Star-wired bus or bus as the topology • CSMA/CD as the medium access protocol • Ethernet comes in many forms depending upon medium used and transmission speed and technology.

  23. Local Area Network Systems • IBM Token Ring • Deterministic LAN offered at speeds of 4, 16 and 100 Mbps. • Very good throughput under heavy loads. • More expensive components than CSMA/CD. • Losing ground quickly to CSMA/CD. May be extinct soon.

  24. Local Area Network Systems • FDDI(Fiber Data Distributed Interface) • Based on the token ring design using 100 Mbps fiber connections. • Allows for two concentric rings - inner ring can support data travel in opposite direction or work as backup. • Token is attached to the outgoing packet, rather than waiting for the outgoing packet to circle the entire ring. • Losing the battle to Ethernet?

  25. Local Area Network Systems • 100VG-AnyLAN • Deterministic LAN based on demand priority access method. • Similar to hub topology (star design). • Two levels of priority - normal and high. • Supports a wide-variety of media types. • Losing ground quickly to CSMA/CD. Will be extinct soon

  26. A Small Office Solution

  27. What about home networking?

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