1. Network types Point-to-Point (Direct) Connection Dedicated circuit boards connected by cable; To transfer data from A to B: – A writes on its circuit board; – A’s board transfers data to B’s board; – B reads data from its board. AB

2. Point-to-Point Connection (cont.) Pros: – High transfer speed; – Secure connection; Cons: – Difficult to add a new computer to a set of communicating computers. – Difficult if communication is between heterogeneous computers; – Expensive: circuit boards needed for every pair of communicating computers; How many boards would you need to connect 5 computers via this method?

3. Local Area Network (LAN) A single shared medium, usually a cable, to which computers can attach. PC 1 Printer PC 2 File Server PC n

4. Local Area Networks (cont.) Designed and developed for communications and resource sharing in a local work environment (room, campus, building). Because sharing occurs: – Cost decreases – Computers have to coordinate the use of the network; Overall, LANs connect more computers than any type of network.

5. Connecting a Computer to a LAN Requires a network interface; A network interface consists of: – a circuit board that plugs into the computer – A cable that connects the circuit board to the LAN; The network interface isolates a computer from the LAN  heterogeneous computers can communicate across the LAN.

6. Network Topologies The configurations of network components Widely used network topologies – Bus – Star – Extended star – Ring – Mesh – Partial Mesh 6

7. Bus Network Topology Most simple network topology All devices connected to a common central cable (wire or other media ) Inexpensive Easily expanded If cable fails, the entire network will shut down Earlier Ethernet commonly implement a bus topology 7

8. Bus Network Topology (Continued) 8

9. Star Network Topology Star topology is centered around central routing device called a switch or a hub by point-to- point links. All network nodes connect to the hub Easy to install and update If hub fails, network fails Disadvantage that it require more cabling therefore, higher cost than the bus. Extended star 9

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11. Ring Network Topology Each node connected to two other nodes in a ring Similar to the buss, but with the ends of the buss connected together by unidirectional transmission link to form a single closed loop. Each station on the network connects to the network at a repeater. Expensive and difficult to install One example of a ring topology is Token Ring networks 11

12. Ring Network Topology (Continued) 12

13. Ring Topology (cont.) Sending a message: – There is a special message, called token; – Exactly one token exists on the ring at any time which is passed along the ring; – To send data, a computer waits for the token to arrive, and then transmits one message; – The message is transmitted to the next computer, and then to the next, until it arrives back to the sender. – After the message is transmitted, the computer holding the token, passes the token to the next computer in the ring. Dual-Ring – Tow rings allow data to be sent in both directions – Creates redundancy.

14. Mesh Network Topology Every node connected to every other node Fast Reliable – No hub or bus to fail – If one device goes down, it is the only node affected Expensive – Every node must be wired to every other node Difficult to add nodes – If there are 32 nodes in a mesh network and you wish to add a new node, how many new cables must you add? 14

15. Partial Mesh – At least one derive is connected to all other devices without being fully meshed. 15

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