Data Communications and Networking

1. Data Communications and Networking 332 Hardware Components of Data Communications

2. Lecture Overview • Network Topology • Physical & Logical Topology • Bus Topology • Ring Topology • Star Topology • Tree Topology • Mesh Topology • Combined Topologies

3. Network Topology • Network topologies may be physical or logical with respect their functionality. • In general, physical topology relates to a core network whereas logical topology relates to basic network.

4. Physical Topology • Physical topology refers to the physical design of a network including the devices, location and cable installation. • The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to: • The layout of cabling • The locations of nodes • The interconnections between the nodes and the cabling • The physical topology of a network is determined by: • The capabilities of the network access devices and media • The level of control • Fault tolerance desired • The cost associated with cabling or telecommunications circuits

5. Logical Topology • Logical topology refers to how data is actually transferred in a network as opposed to its physical design. • The logical topology is define: • is the way that the signal act on the network media • The way that the data passed through the network from one device to the next without regard to the physical interconnection of the devices. • A network’s logical topology is not necessarily the same as its physical topology. For example: • The original UTP Ethernet using hubs/switches, but logically connected but topology layout. • Token ring is a logical ring topology, but is wired a physical star from the MSAU (Media Station Access Unit)

6. BUS Topology • A bus network topology is a network architecture in which a set of clients are connected via a shared communications line / medium, called a BUS topology. • The bus topology is often referred to as a linear bus because the computers are connected in a straight line. • This is the simplest and most common method of networking computers.

7. BUS Topology

8. BUS Topology • Advantages: • Easy to connect a computer or peripheral to a linear bus. • Easy to implement and extend • Well suited for temporary networks (quick setup) • Typically the cheapest topology to implement • Faster than a ring network • If any node on the bus network fails, the bus itself is not effected. • Requires less cable length than a star topology

9. BUS Topology • Disadvantages: • Difficult to administer/troubleshoot • Limited cable length and number of stations • A cable break can disable the entire network • Maintenance costs may be higher in the long run • Performance degrades as additional computers are added or on heavy traffic • Low security (all computers on the bus can see all data transmissions) • One virus in the network will affect all of them (but not as badly as a star or ring network) • Proper termination is required. (loop must be in closed path) • Significant. Capacitive load (each bus transaction must be able to stretch to most distant link).

10. STAR Topology • In Star topology, it uses a central component that allows other devices connected to it to communicate with each other, such devices are commonly called hubs or switches. • A hub does not perform any type of filtering or routing of the data. It is simply a junction that joins all the different nodes together. • If a device wants to communicate, it does so only through the central hub/switch. That switch then passes the data to its destination.

11. STAR Topology

12. STAR Topology • Advantages: • Good performance • Easy to set up and to expand; any non-centralised failure will have very little effect on the network • Disadvantages: • Expensive to install • Extra hardware required

13. RING Topology • In Ring topology, devices are connected circularly. • Each one can communicate directly with either or both of its neighbors but nobody else. • If it wants to communicate with a device farther away, it sends a message that passes through each device in between.

14. RING Topology • A ring network may be either unidirectional or bidirectional. • Unidirectional means that all transmissions travel in the same direction . Thus, each device can communicate directly with only one neighbor. • Bidirectional means that data transmissions travel in either direction, and a device can communicate directly with both neighbors.

15. RING Topology • An early ring topology was IBM’s Token Ring network, which connected PCs in a single office or department. • In a token ring network, communications are coordinated by passing a token (a predefined sequence of bits) among all the devices in the ring. • A device can send something only when it receives the token.

16. RING Topology • Advantages: • Data is quickly transferred without a ‘bottle neck’. (very fast, all data traffic is in the same direction) • The transmission of data is relatively simple as packets travel in one direction only. • Adding additional nodes has very little impact on bandwidth. • It prevents network collisions because of the media access method or architecture required.

17. RING Topology • Disadvantages: • Data packets must pass through every computer between the sender and receipient therefore this makes it slower. • If any of the nodes fail then the ring is broken and data cannot be transmitted successfully. • It is difficult to troubleshoot the ring. • Because all stations are wired together, to add a station you must shut down the network temporarily. • In order for all computer to communicate with each other, all computers must be turned on. • Total dependence upon the one cable.

18. RING Topology

19. TREE Topology • Tree topology integrates multiple star topologies together onto a bus. • In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices.

20. MESH Topology • Mesh topology involves the concept of routes. • Messages sent on a mesh network can take any of several possible paths from source to destination. • A mesh network in which every device connects to every other is called full mesh. • Partial mesh network also exist in which some devices connect only indirectly to others.

21. Fully Connected Topology • The fully connected topology has a direct connection between every pair of devices in the network. This is an extreme design. Communication becomes very simple because there is no competition for common lines. • If two devices want to communicate, they do so directly without involving other devices.

22. Combined Topologies • Many computer networks use combinations of the various topologies. • It has common bus, which connects many devices directly.

23. QUESTIONS?