Chapter 14: Local Area Network Technology

1. Chapter 14:Local Area Network Technology Business Data Communications, 4e

2. PC Networks • Client/Server Communication • Shared databases • Shared hardware resources • Shared Internet access • Peer-to-Peer Communication • Sharing work and information with colleagues • Low cost is high priority • Attachment costs in the hundreds of dollars

3. Backend & Storage Area Networks • “Computer room networks” • Interconnect large systems (mainframes, supercomputers, etc) • Key requirement is high-speed bulk transfer • Usually limited distance, few drops • Speed more important than cost • Attachment costs in the thousands of dollars

4. High-Speed Office Networks • Increased processing and transfer requirements in many graphics-intensive applications now require significantly higher transfer rates • Decreased cost of storage space leads to program and file bloat, increased need for transfer capacity • Typical office LAN runs at 1-20mbps, high-speed alternatives run at 100+

5. Backbone Local Networks • Used instead of single-LAN strategy • Better reliability • Higher capacity • Lower cost

6. Factory Networks • High capacity • Ability to handle a variety of data traffic • Large geographic extent • High reliability • Ability to specify and control transmission delays

7. Tiered LANs • Cost of attachment to a LAN tends to increase with data rate • Alternative to connecting all devices is to have multiple tiers • Multiple advantages • Higher reliability • Greater capacity (less saturation) • Better distribution of costs based on need

8. Tiered LAN Strategies • Bottom-up strategy: individual departments create LANs independently, eventually a backbone brings them together • Top-down strategy: management develops an organization-wide networking plan

9. Tiered LAN Diagram

10. LAN Topology • Arrangement of workstations in a shared medium environment • Logical arrangement (data flow) • Physical arrangement (cabling scheme)

11. LAN Topologies: Bus • Multipoint medium • Stations attach to linear medium (bus) using tap • Full-duplex between station and tap • Transmission from any stations travels entire medium (both directions) • Termination required at ends of bus

12. Bus LAN Diagram

13. LAN Topologies: Tree • Generalization of bus topology • Branching cable with no closed loops • Cable(s) begin at headend, travel to branches which may have branches of their own • Each transmission propagates through network, can be received by any station

14. Tree LAN Diagram

15. Bus/Tree Topology Problems • How do you identify who the transmission is intended for? • Data transmitted in frames • Each frame has header with addressing info • How do you regulate access? • Stations take turns sending, by monitoring control information in frames

16. LAN Topologies: Ring • Repeaters are joined by unidirectional point-to-point links in a ring • As a frame circulates past a receiver, the receiver checks its address, and copies those intended for it into a local buffer • Frame circulates until it returns to source, which removes it from network

17. Ring LAN Diagram

18. LAN Topologies: Star • Each station connected directly to central node, usually with two undirectional links • Central node can broadcast info, or can switch frames among stations

19. Star LAN Diagram

20. Choosing a Topology • Factors to consider include reliability, flexibility/expandability, and performance • Bus/tree is most flexible • Tree topology easy to lay out • Ring provides high througput, but reliability problems • Star can be high speed for short distances, but has limited expandability

21. Transmission Media Options • Twisted pair--digital signaling • Optical fiber--analog signaling • Baseband coax--digital signaling • Broadband coax--analog signaling • Uses FDM to carry multiple channels • Can be used over longer distances • Inherently unidirectional, due to amplifier limitations

22. Selecting Transmission Media • Capacity: Can it support expected network traffic? • Reliability: Can it meet requirements for availability? • Types of data supported: Is it well-suited to the applications involved? • Environmental scope: Can it provide service in the environments required?

23. Medium and Topology

24. Structured Cabling System • Standards for cabling within a building (EIA/TIA-568 and ISO 11801) • Includes cabling for all applications, including LANs, voice, video, etc • Vendor and equipment independent • Designed to encompass entire building, so that equipment can be easily relocated • Provides guidance for pre-installation in new buildings and renovations

25. Wiring Layouts • Wiring layout is different from logical topology • Linear layout minimizes amount of cable • Star layout uses individual cable from concentration point to subscribers • Can be used for bus and ring as well as star • Concentration point can be wiring closet or hub (an active node that accepts frames and regenerates signals for transmission)

26. LAN Standards (802.x) • Advantages of standards • Assure sufficient volume to keep costs down • Enable equipment from various sources to interconnect • IEEE 802 committee developed, revises, and extends standards • Use a three-layer protocol hierarchy: physical, medium access control (MAC), and logical link control (LLC)

27. Logical Link Control • Specifies method of addressing and controls exchange of data • Independent of topology, medium, and medium access control • Unacknowledged connectionless service (higher layers handle error/flow control, or simple apps) • Connection-mode service (devices without higher-level software) • Acknowledged connectionless service (no prior connection necessary)

28. Provides a means of controlling access to a shared medium Two techniques in wide use CSMA/CD Token passing LLC frames data, passes it to MAC which frames it again MAC control (e.g. priority level) Destination physical address Source physical address Medium Access Control

29. Bridges • Allow connections between LANs and to WANs • Operates at Layer 2 (Data Link Layer) of OSI • Used between networks using identical physical and link layer protocols • Provide a number of advantages • Reliability: Creates self-contained units • Performance: Less contention • Security: Not all data broadcast to all users • Geography: Allows long-distance links

30. Bridge Functions • Read all frames from each network • Accept frames from sender on one network that are addressed to a receiver on the other network • Retransmit frames from sender using MAC protocol for receiver • Must have some routing information stored in order to know which frames to pass

31. Bridge Operation

32. Hubs • The active central element of the star layout. • When a single station transmits, the hub repeats the signal on the outgoing line to each station. • Physically a star; logically a bus. • Hubs can be cascaded in a hierarchical configuration.

33. Two-Level Star Topology

34. Layer 2 Switches(Switching Hubs)

35. Ethernet Hubs and Switches • Shared medium hubs • Switched LAN hubs x

36. Advantages of Switched Hubs • No modifications needed to workstations when replacing shared-medium hub • Each device has a dedicated capacity equivalent to entire LAN • Easy to attach additional devices to the network

37. Types of Switched Hubs • Store and forward switch • Accepts a frame on input line • Buffers it briefly • Routes it to appropriate output line • Cut-through switch • Begins repeating the frame as soon as it recognizes the destination MAC address • Higher throughput, increased chance of error

38. Layer 3 Switches • Problems With Layer 2 Switches • Broadcast overload • Lack of multiple links • Can be solved with subnetworks connected by routers • Layer 3 switches implement the packet-forwarding logic of the router in hardware.