Principles of Electronic Communication Systems

1. Principles of ElectronicCommunication Systems Third Edition Louis E. Frenzel, Jr.

2. Chapter 12 Introduction to Networking and Local-Area Networks

3. Topics Covered in Chapter 12 • 12-1: Network Fundamentals • 12-2: LAN Hardware • 12-3: Ethernet LANs • 12-4: Token-Ring LAN

4. 12-1: Network Fundamentals • Most computers today are networked, that is, connected to one another so that they can communicate with one another and share resources. • Virtually 100 percent of business and industrial computers are networked. • It is estimated that more than 70 percent of all home and personal computers are also networked.

5. 12-1: Network Fundamentals • A network is a communication system with two or more stations that can communicate with one another. • When it is desired to have each computer communicate with two or more additional computers, the interconnections can become complex. • The number of links L required between N PCs (nodes) is determined by using the formula L = N(N−1) / 2

6. 12-1: Network Fundamentals Figure 12-1: A network of four PCs.

7. 12-1: Network Fundamentals Types of Networks • Each computer or user in a network is referred to as a node. • The interconnection between the nodes is referred to as the communication link. • In most networks, each node is a personal computer, but in some cases a peripheral device such as a printer can be a node.

8. 12-1: Network Fundamentals Types of Networks • There are four basic types of networks: • Wide-area networks (WANs), • Metropolitan-area networks (MANs) • Local-area networks (LANs) • Personal-area networks (PANs)

9. 12-1: Network Fundamentals Types of Networks: Wide-Area Networks (WANs) • A WAN covers a significant geographical area. • Local telephone systems are WANs, as are the many long-distance telephone systems linked together across the country and to WANs in other countries. • Each telephone set is, in effect, a node in a network that links local offices and central offices.

10. 12-1: Network Fundamentals Types of Networks: Wide-Area Networks (WANs) • There are also WANs that are not part of the public telephone networks, e.g., corporate and military. • The nationwide and worldwide fiber-optic networks set up since the mid-1990s to carry Internet traffic are also WANs. • Known as the Internet coreor backbone, these high-speed interconnections are configured as either direct point-to-point links or large rings with multiple access points.

11. 12-1: Network Fundamentals Types of Networks: Metropolitan-Area Networks (MANs) • MANs are smaller than WANs and generally cover a city, town, or village. • Cable TV systems are MANs. • Other types of MANs, or metro networksas they are typically called, carry computer data.

12. 12-1: Network Fundamentals Types of Networks: Metropolitan-Area Networks (MANs) • MANs are usually fiber-optic rings encircling a city that provide local access to users. Businesses, governments, schools, hospitals, and others connect their internal LANs to them. • MANs also connect to local and long-distance telephone companies. The MANs provide fast and convenient connections to WANs for global Internet connectivity.

13. 12-1: Network Fundamentals Types of Networks: Local-Area Networks (LANs) • A LAN is the smallest type of network in general use. • A LAN consists primarily of personal computers interconnected within an office or building. • LANs can have as few as three to five users, although most systems connect to several thousand users. • Home networks of two or more PCs are also LANs and today most home LANs are fully wireless or incorporate wireless segments.

14. 12-1: Network Fundamentals Types of Networks: Personal-Area Networks (PANs). • A PAN is a short-range wireless network that is set up automatically between two or more devices such as laptop computers, personal digital assistants (PDAs), peripheral devices, or cell phones. • The distance between the devices is very short, no more than about 10 m and usually much less. • PANs are referred to as ad hoc networks that are set up for a specific single purpose, such as the transfer of data between the devices as required by some application. • Most PANs just involve two nodes, but some have been set up to handle up to eight nodes and sometimes more.

15. 12-1: Network Fundamentals Types of Networks: Storage-Area Networks (SANs) • SANs are an outgrowth of the massive data storage requirements developed over the years thanks to the Internet. • These networks usually attach to a LAN or Internet server and store and protect huge data files. • The SAN also provides network users access to massive data files stored in mass memory units, called redundant arrays of independent disks (RAIDs). • RAIDs use many hard drives interconnected to the network and may be located anywhere since access can be via the Internet or a fiber-optic WAN or MAN.

16. 12-1: Network Fundamentals Types of Networks: Network Hierarchy • LANs inside a building are usually connected to a MAN that may be, for example, a local telephone central office. • The MANs connect to the WANs, which may be a long-distance telephone network or one set up for data transmissions. • Some WANs are hierarchies of rings and direct connection points. • MANs and WANs are virtually all fiber-optic networks. • Interconnection points of the networks may be special computers called servers or routers.

17. 12-1: Network Fundamentals Network Topologies • The topology of a network describes the basic communication paths between, and methods used to connect, the nodes on a network. • The three most common topologies used in LANs are star, ring, and bus.

18. 12-1: Network Fundamentals Network Topologies: Star Topology • A basic star configuration consists of a central controller node and multiple individual stations connected to it. • The resulting system resembles a multipointed star. • The central or controlling PC, often referred to as the server, is typically larger and faster than the other PCs and contains a large hard drive where shared data and programs are stored.

19. 12-1: Network Fundamentals Network Topologies: Star Topology • A star-type LAN is extremely simple and straightforward. • New nodes can be quickly and easily added to the system, and the failure of one node does not disable the entire system. • If the server node goes down, the network is disabled but individual PCs will continue to operate independently.

20. 12-1: Network Fundamentals Figure 12-3: A star LAN configuration with a server as the controlling computer.

21. 12-1: Network Fundamentals Network Topologies: Ring Topology • In a ring configuration, the server or main control computer and all the computers are simply linked together in a single closed loop. • Usually, data is transferred around the ring in only one direction, passing through each node. • The ring topology is easily implemented and low in cost. • The downside of a ring network is that a failure in a single node generally causes the entire network to go down. • It is also difficult to diagnose problems on a ring.

22. 12-1: Network Fundamentals Figure 12-4: A ring LAN configuration.

23. 12-1: Network Fundamentals Network Topologies: Bus Topology • A bus is a common cable to which all of the nodes are attached. • The bus is bidirectional in that signals can be transmitted in either directions between any two nodes. • Only one node can transmit at a given time. • A signal to be transmitted can be destined for a single node, or transmitted or broadcast to all nodes simultaneously. • The bus is faster than other topologies, wiring is simple, and the bus can be easily expanded.

24. 12-1: Network Fundamentals Figure 12-5: A bus LAN configuration.

25. 12-1: Network Fundamentals Network Topologies: Mesh Topology • A mesh network is one in which each node is connected to all other nodes. • In a full mesh, every node can talk directly to any other node. • There are major costs and complications as the number of nodes increases, but the use of wireless interconnections between nodes helps to alleviate this problem.

26. 12-1: Network Fundamentals Network Topologies: Mesh Topology • A variation of the full mesh is the partial mesh, in which all nodes can communicate with two or more other nodes. • The primary value of the mesh network is that there are multiple paths for data to take from one node to another. • This offers redundancy that can provide a continuous connection when one or more of the links are broken, thus providing increased network reliability.

27. 12-1: Network Fundamentals Network Topologies: Other Topologies. • There are many variations and combinations of the basic topologies. • Two examples: • The daisy chain topologyis a ring that has been broken. • The tree topology isa bus design in which each node has multiple interconnections to other nodes through a star interconnection.

28. 12-1: Network Fundamentals LAN Applications • The common denominator of all LANs is the communication of information. • Networks are used for many applications other than centralizing and sharing expensive peripherals and for database applications: • E-mail • Internet access • Groupware (e.g., Lotus Notes)

29. 12-1: Network Fundamentals Client-Server and Peer-to-Peer LANs • Most LANs conform to one of two general configurations: client-server or peer-to-peer. • In the client-server type, one of the computers in the network, the server, essentially runs the LAN and determines how the system operates. • The server manages printing operations of a central printer and controls access to a very large hard drive or bank of hard drives containing databases, files, and other information that the clients—the other computers on the network—can access. • The server also provides Internet access.

30. 12-1: Network Fundamentals Client-Server and Peer-to-Peer LANs • In a peer-to-peer system, any PC can serve as either client or server; any PC can have access to any other PC’s files and connected peripherals. • Peer-to-peer LANs are smaller and less expensive than the client-server variety, and provide a simple way to provide network communication. • Disadvantages include: • Lower performance (lower-speed transmission capability). • Manageability and security problems (any user may access any other user’s files).

31. 12-2: LAN Hardware • All LANs are a combination of hardware and software. • The primary hardware devices are the computers, cables, and connectors. • Additional hardware includes: • Network interface cards (NICs) • Repeaters • Hubs and concentrators • Bridges • Routers • Gateways

32. 12-2: LAN Hardware Cables • Most LANs use some type of copper wire cable to carry data from one computer to another via baseband transmission. • The three basic cable types are: • Coaxial cable • Twisted pair • Fiber-optic cable

33. 12-2: LAN Hardware Cables: Coaxial Cable • Coaxial cable is far superior to twisted pair as a communication medium. • Its extremely wide bandwidth permits very high-speed bit rates. • Loss is generally high, but is usually offset by using repeaters that boost signal level. • The major benefit of coaxial cable is that it is completely shielded, so that external noise has little or no effect on it.

34. 12-2: LAN Hardware Figure 12-6: Coaxial cable.

35. 12-2: LAN Hardware Cables: Twisted Pair • Twisted pair cable is two insulated copper wires twisted together loosely to form a cable. • Telephone companies use twisted pair to connect individual telephones to the central office. • The wire is solid copper, 22, 24, or 26 gauge. • The insulation is usually PVC. • Twisted pair has a characteristic impedance of about 100 Ω.

36. 12-2: LAN Hardware Figure 12-7 Types of twisted-pair cable. (a) Twisted-pair unshielded (UTP) cable. (b) Multiple shielded twisted-pair (STP) cable.

37. 12-2: LAN Hardware Cables: Twisted-Pair Cable • There are two basic types of twisted-pair cables in use in LANs: • Unshielded (UTP): UTP cables are susceptible to noise, particularly over long cable runs. • Shielded (STP): STP cables aremore expensive than UTP cables. • They have a metal foil or braid shield around them, forming a third conductor. • The shield is usually connected to ground and, therefore, provides protection from external noise and crosstalk.

38. 12-2: LAN Hardware Cables: Twisted-Pair Cable • The most widely used UTP is category 5 (CAT5). It can carry baseband data at rates up to 100 Mbps at a range up to 100 m. • Twisted-pair cable specifications also include attenuation and near-end cross talk figures. • Attenuation means the amount by which the cable attenuates the signal. The longer the cable, the greater the amount of loss in the cable and the smaller the output.

39. 12-2: LAN Hardware Cables: Twisted-Pair Cable • Near-end cross talk (NEXT): Cross talkrefers to the signal transferred from one twisted pair in a cable to another by way of capacitive and inductive coupling. Near-end cross talk is the signal appearing at the input to the receiving end of the cable. • Many newer office buildings are constructed with special vertical channels or chambers, called plenums,through which cables are run between floors or across ceilings. • Cable used this way, called plenum cable,must be made of fireproof material that will not emit toxic fumes if it catches fire.

40. 12-2: LAN Hardware Cables: Fiber-Optic Cable • Fiber-optic cableis a nonconducting cable consisting of a glass or plastic center cable surrounded by a plastic cladding encased in a plastic outer sheath. • Most fiber-optic cables are extremely thin glass, and many are usually bundled together. • Special fiber-optic connectors are required to attach them to the network equipment. • Speeds of up to 1 Tbps (terabits per second) are achievable by using fiber optics.

41. 12-2: LAN Hardware Figure 12-9: Fiber-optic cable.

42. 12-2: LAN Hardware Connectors: Coaxial Cable Connectors • All cables used in networks have special terminating connectors that provide a fast and easy way to connect and disconnect the equipment from the cabling and maintain the characteristics of the cable. • Coaxial cables in networks use two types of connectors: • N connectors are widely used in RF applications • BNC connectors are commonly used for attaching test leads to measuring instruments such as oscilloscopes.

43. 12-2: LAN Hardware Connectors: Coaxial Cable Connectors • BNC T connectors are used to interconnect two cables to the network hardware. • The barrel connector provides a convenient way to connect two coaxial cables. • A terminator is a special connector containing a resistor whose value is equal to the characteristic impedance of the coaxial cable (typically 50Ω).

44. 12-2: LAN Hardware Figure 12-10: Common coaxial connectors.

45. 12-2: LAN Hardware Figure 12-11: BNC connector accessories and adapters. (a) T connector. (b) Barrel connector.

46. 12-2: LAN Hardware Connectors: Twisted-Pair and Fiber-Optic Connectors • Most telephones attach to an outlet by way of an RJ-11 connector or modular plug. • RJ-11 connectors are used to connect PC modems to the phone line but are not used in LAN connections. • A larger modular connector known as the RJ-45 is widely used in terminating twisted pairs. • A wide range of connectors are available to terminate fiber-optic cables.

47. 12-2: LAN Hardware Figure 12-12 Modular (telephone) connectors used with twisted-pair cable. (a) RJ-11. (b) RJ-45.

48. 12-2: LAN Hardware Network Interface Cards and Chips • A network interface card (NIC) provides the I/O interface between each node on a network and the network wiring. • NICs usually plug into the PC bus or are built into the PC motherboard and provide connectors at the rear of the computer for attaching the cable connectors. • The NIC is the key hardware component in any LAN. • The NIC completely defines the protocols and performance characteristics of the LAN. • NICs are low in price and available from many manufacturers.

49. 12-2: LAN Hardware Figure 12-13: A network interface card.

50. 12-2: LAN Hardware Repeater • A repeater is an electronic circuit that takes a partially degraded signal, boosts its level, shapes it up, and sends it on its way. • Repeaters are small, inexpensive devices that can be inserted into a line with appropriate connectors or built into other LAN equipment. • Most repeaters are really transceivers, bidirectional circuits that can both send and receive data.