42.444 Telecommunications: A Management Perspective

1. 42.444 Telecommunications: A Management Perspective Local Area Network Technology Lecture 13 (Chapters 14) Dr Gerald Grant

2. Local Area Networks • Combination of hardware and software technologies that allow the interconnecting of computing and communications resources to support information and resource sharing. • LANs are usually confined to a single site or a small cluster of buildings. • LANs in one organization or site can be connected to LANs in other organizations using wide area network (WAN) services. Dr Gerald Grant

3. Reasons for the popularity of LANs • Hardware sharing • Software sharing • Service enhancement • Local control Dr Gerald Grant

4. Types of Local Area Networks • Personal Computer Local Networks • Backend Networks and storage area networks • High speed office networks • Backbone local networks • Factory LANs Dr Gerald Grant

5. Types of Local Area Networks Personal Computer Local Networks • Designed to support personal computers • Are usually implemented within individual department or business unit. • Connect user equipment to each other and to printers, local servers which handle such applications as file sharing , faxing, and printing. • Are relatively low cost and support departmental applications such as word processing, spreadsheets, project management tools and Internet access. Dr Gerald Grant

6. Types of Local Area Networks Backend Networks and Storage Area Networks (SAN) • Interconnecting of mainframes, supercomputers, and mass storage devices can be done in a LAN configuration. • Support high speed data transfer between devices in a small area. • Requires a very high level of reliability. • Generally support distributed access among a limited number of devices. • Are usually found in large computer centres typically associated with large companies or research centres. Dr Gerald Grant

7. Types of Local Area Networks Backend Networks and Storage Area Networks (SAN) • A SAN is a separate network to handle storage needs • The storage devices include hard disks, tape libraries, and CD arrays • The storage devices and servers are linked directly to the network • The SAN arrangement improves client-to-storage access efficiency, as well as direct storage-to-storage communications for backup and replication functions. Dr Gerald Grant

8. Types of Local Area Networks High speed office networks • New applications such as graphical and video image processing have increased the need for high speed networks within the office environment. • Typical LAN operating at speeds of 10 Mbps while more than adequate for data processing, it does not have sufficient capacity to handle the huge demands associated with image processing. • A combination of technological advances in storage devices and LAN technology has led to the development of high speed LANs within the office. Dr Gerald Grant

9. Types of Local Area Networks Backbone local networks • Used to connect local networks within single premises or cluster of buildings. • For example, while it is possible to connect all devices in a 6 floor building to a single LAN it might not be prudent to do so. • The proliferation of devices on the single network will reduce its capacity and reliability, and increase the cost of support. • A more flexible, reliable and cost effective approach is to set up smaller networks, say one for each floor, and then interconnect these with a backbone LAN. Dr Gerald Grant

10. Types of Local Area Networks Factory LANs • Used to tie automated equipments together to improve the manufacturing process and to provide detailed machine control • Key characteristics of a factory LAN include • high capacity • Ability to handle a variety of data traffic • Large geographic extent • High reliability • Ability to specify and control transmission delays Dr Gerald Grant

11. LAN configuration • Data processing equipment that is normally connected to LANs can be grouped into three categories. • Personal computers and workstations • Servers • Mainframes and supercomputers Dr Gerald Grant

12. LAN configuration Dr Gerald Grant

13. Topologies and Transmission Media • The cost, capacity, type of data transmitted, speed and efficiency of transmission, and the kinds of applications supported are all determined by the way various LAN technologies are combined. Dr Gerald Grant

14. Topologies and Transmission Media The key elements of LANs are: • Topology: bus and tree, ring, or star • Transmission medium: twisted pair, coaxial cable, or optical fibre • Layout: linear or star • Medium access control: CSMA/CD or token passing Dr Gerald Grant

15. LAN topology - Bus • Devices attach to the network in a linear fashion • They are connected in sequence directly to the transmission medium using the appropriate network interfacing device • Typically this is a network interface card with the appropriate connector. These are usually calledtaps • Data is transmitted simultaneously in both directions. • The data is sent the whole length of the medium and can be received by all the attached stations • A terminator is attached at each end of the bus to remove all the signals. Dr Gerald Grant

16. LAN topology - Ring • With ring topology the network represents a closed loop • Consists of a series of repeaters joined together by point-to-point links • Repeaters are simple devices that receive and pass on data from one link to another as fast as it is received • There is no buffering or reprocessing of the data at the repeaters • The links go in one direction only, thus allowing data to circulate around the ring (clockwise or counter-clockwise). Dr Gerald Grant

17. LAN topology - Ring • Each station or device attach to the network at the repeater • Data is transmitted frames as with bus or tree networks • As a frame passes the destination station a copy of it is absorb into the local buffer • The frame continues to circulate until it returns to the originating station • Since there are many stations on the ring, media access control is needed to determine at what time each station may insert a frame. Dr Gerald Grant

18. Bus topology - issues Two problems surface in bus arrangements. • How does the network determine which station the message is intended for. • How can the network regulate the flow of data along the transmission medium. • Problems are solved by transmitting data in frames. • Each frame contains a unique identifier and destination address included in the header • When the frame passes the intended address a copy is absorbed by the device. • To regulate the flow of data, each device takes turns in sending the frames. Dr Gerald Grant

19. LAN topology - Tree • A tree arrangement is similar to a bus arrangement except that the network in this configuration begin at a certain point called the headend and then branches in bus formation. • Transmission sent from one station can be received by all stations on the bus. • Networks arranged in tree formation can have many branches. Dr Gerald Grant

20. LAN topology - Bus Dr Gerald Grant

21. LAN topology - Tree Dr Gerald Grant

22. LAN topology - Ring Dr Gerald Grant

23. LAN topology - Star • With star arrangement each station is connected directly to a common central node • Each station attaches to the central node, generally referred to as a star coupler, via two point-to-point links, one for transmission in each direction Dr Gerald Grant

24. LAN topology - Star • Data transmission in star networks can occur in two ways: broadcast or frame switching. • With broadcast data sent from one station is received by all • Only one station at a time can send frames • The star coupler can also act as a frame switching device • The incoming frame is retransmitted to the destination station Dr Gerald Grant

25. LAN topology - Star Dr Gerald Grant

26. Choosing a topology • Choice of LAN will depend on a myriad of factors associated with the type of application, the requirements for reliability, flexibility, expandability, and performance. • It also depends on • the physical set up • transmission medium • wiring layout, among other issues. Dr Gerald Grant

27. Choosing a topology • In general, bus and tree topologies • offer greater flexibility. • can handle a wide range of devices and is easy to layout • are best when data rates requirements are moderate and confined to smaller area. • Ring topology is good for high speed transmission over long distances. However, if one link or repeater fails the whole network goes down. • Star network is good for connecting devices at small areas. If a device goes down it is simply unplugged. Dr Gerald Grant

28. Transmission media • Most commonly used transmission media on LANS are • twisted pair • Baseband coaxial cable • Broadband coaxial cable • optical fiber. • Both shielded and unshielded twisted pair support digital signaling. • Fiber uses analog signaling. • Coaxial cable supports either digital and analog signaling. • The two forms of signaling are referred to as baseband and broadband. Dr Gerald Grant

29. Baseband bus • A baseband bus uses digital signaling to transmit binary data • The data is inserted directly into the medium as a series of voltage pulses using the appropriate coding technique. • Digital signals use the entire spectrum so there is no potential for having multiple channels • Data is propagated along the medium in both directions at the same time • Digital signaling therefore requires bus topology • The distance over which data can travel before suffering from attenuation is limited • Repeaters are used to increase the distance over which digital signals can be sent Dr Gerald Grant

30. Broadband Bus • Broadband, in the context of LANs, refers to analog signaling • Analog signaling allows for multiple channels to be created using techniques such as frequency division multiplexing. • Separate channels can support separate and independent data traffic. • With broadband transmission signals can be sent over much greater distances than with baseband. • Broadband signaling is unidirectional • Two separate data paths must be used for “inbound” and “outbound” transmission Dr Gerald Grant

31. Choice of transmission medium • The choice of medium depends on the topology chosen and other factors related to capacity, reliability, types of data supported, and environmental scope. • Generally, unshielded and shielded twisted pair are well understood and can be found pre-wired in most buildings. Dr Gerald Grant

32. Choice of transmission medium • Unshielded twisted pair is most cost effective for a single building, low-traffic LAN. • Shielded twisted pair and baseband coaxial cable are more expensive than UTP but have greater capacity. • Broadband coaxial cable is even more expensive but also provide greater capacity. • Fiber is the most expensive medium and it also provides the highest capacity. It’s use in LANs is still not widespread. Dr Gerald Grant

33. Choice of transmission medium Dr Gerald Grant

34. Structured cabling • To allow for the pre-planning of cable networks in commercial properties • Two structured cabling standards have been issued. • EIA/TIA-568 • ISO 11801 • These allow buildings to be generically wired in anticipation of future networking needs. Dr Gerald Grant

35. Structured cabling • The cabling strategy is based on a hierarchical, star-wired layout. It consists of • External cables from the local telephone company or WANs to the equipment room. • Backbone cable linking each telecommunications closets on each floor or section. • Horizontal cables form the telecommunications closet (wiring closets) to the wall outlets • Horizontal cables should not exceed 90 meters regardless of the media type. Dr Gerald Grant

36. Structured cabling Dr Gerald Grant

37. LAN Standards • LAN technology is very complex and difficult to implement. • The cost of connecting LANs must be much less expensive than the devices that are attached to them. • If this is not the case then most people would not invest in the LANs. • Standards help make investment in developing the technology worthwhile • Widely accepted LAN standards will ensure that a large enough market will develop. Dr Gerald Grant

38. LAN Standards • To develop standards for local area networks a committee was set up by the Institute of Electrical and Electronic Engineers (IEEE). • The IEEE 802 committee issued a set of standards that have been widely accepted and adopted by other standard making bodies such as ANSI and the International Organization on Standardization (ISO). Dr Gerald Grant

39. Structure of LAN standards • LAN standards developed based on two criteria. • the task of communication should be broken in several sub-tasks. • A variety of approaches was necessary because of the variety of topologies, media, and access methods. • The standards are organized into as a three-layer protocol • Logical link control (IEEE 802.2) • Media access control (IEEE 802.3, etc.) • Physical media Dr Gerald Grant

40. Structure of LAN standards Dr Gerald Grant

41. LAN Hardware • Servers • File, print, fax application, CD-ROM, DNS, etc. • Hubs • For connecting devices to the network • Act as repeaters or amplifiers • Switches • Type of hub which acts as a switch for incoming frames • Bridges • Connect two similar networks that use the same protocol. Dr Gerald Grant

42. LAN Hardware • Routers • Connects two similar networks having the same protocol • Chooses the best route between two networks when there are multiple paths between them • Brouters • Combines the function of a bridge and a router • Gateways • A device that connects two dissimilar networks • Allows different vendor networks to communicate by translating one vendors protocol into another. E.g. X.400 and TCP/IP Dr Gerald Grant

43. LAN Network Operating Systems (NOS) • NOS Server Software • Linux • Windows NT • UNIX • Novell • OS/2, etc. • NOS Client Software Dr Gerald Grant