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CP2073 Networking Lecture 5.

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Presentation on theme: "CP2073 Networking Lecture 5."— Presentation transcript:

1 CP2073 Networking Lecture 5

2 Introduction Physical and Logical Topologies Topologies Bus Ring Star
Extended Star Mesh Hybrid CP2073 Networking

3 Physical vs. Logical Topology
The actual layout of a network and its media is its Physical Topology The way in which the data access the medium and transmits packets is the Logical Topology A glance at a network is not always revealing. Cables emerging from a Hub does not make it necessarily a Star Topology – it may actually be a bus or a ring CP2073 Networking

4 Physical vs. Logical Topology (2)
Your choice of Logical Topology will affect the Physical Topology – and vice versa Design carefully – it may be difficult to change part way through the installation Your choice will determine cable installation, network devices, network connections, protocols (and where you will drill holes in the building !) CP2073 Networking

5 Factors Cost Scalability Bandwidth Capacity Ease of Installation
Ease of fault finding and maintenance CP2073 Networking

6 Bus Topology CP2073 Networking

7 Bus Topology (2) Network maintained by a single cable
Cable segment must end with a terminator Uses thin coaxial cable (backbones will be thick coaxial cable) Extra stations can be added in a daisy chain manner CP2073 Networking

8 Bus Topology (3) Standard is IEEE 802.3
Thin Ethernet (10Base2) has a maximum segment length of 200m Max no. of connections is 30 devices Four repeaters may be used to a total cable length of 1000m Max no. of nodes is 150 CP2073 Networking

9 Bus Topology (4) Thick Ethernet (10Base5) used for backbones
Limited to 500m Max of 100 nodes per segment Total of four repeaters , 2500m, with a total of 488 nodes CP2073 Networking

10 Bus Topology (5) Advantages Inexpensive to install
Easy to add stations Use less cable than other topologies Works well for small networks Disadvantages No longer recommended Backbone breaks, whole network down Limited no of devices can be attached Difficult to isolate problems Sharing same cable slows response rates CP2073 Networking

11 Ring Topology CP2073 Networking

12 Ring Topology (2) No beginning or end (a ring in fact !!)
All devices of equality of access to media Single ring – data travels in one direction only, guess what a double ring allows !? Each device has to wait its turn to transmit Most common type is Token Ring (IEEE 802.5) A token contains the data, reaches the destination, data extracted, acknowledgement of receipt sent back to transmitting device, removed, empty token passed on for another device to use CP2073 Networking

13 Ring Topology (3) Advantages Disadvantages
Data packets travel at great speed No collisions Easier to fault find No terminators required Disadvantages Requires more cable than a bus A break in the ring will bring it down Not as common as the bus – less devices available CP2073 Networking

14 Star Topology CP2073 Networking

15 Star Topology (2) Like the spokes of a wheel (without the symmetry)
Centre point is a Hub Segments meet at the Hub Each device needs its own cable to the Hub Predominant type of topology Easy to maintain and expand CP2073 Networking

16 Star Topology (3) Advantages Disadvantages
Easy to add devices as the network expands One cable failure does not bring down the entire network (resilience) Hub provides centralised management Easy to find device and cable problems Can be upgraded to faster speeds Lots of support as it is the most used Disadvantages A star network requires more cable than a ring or bus network Failure of the central hub can bring down the entire network Costs are higher (installation and equipment) than for most bus networks CP2073 Networking

17 Extended Star Topology
A Star Network which has been expanded to include an additional hub or hubs. CP2073 Networking

18 Mesh Topology (Web) CP2073 Networking

19 Mesh Topology (2) Not common on LANs
Most often used in WANs to interconnect LANS Each node is connected to every other node Allows communication to continue in the event of a break in any one connection It is “Fault Tolerant” CP2073 Networking

20 Mesh Topology (3) Disadvantages Advantages Expensive
Difficult to install Difficult to manage Difficult to troubleshoot Advantages Improves Fault Tolerance CP2073 Networking

21 Hybrid Topology CP2073 Networking

22 Hybrid Topology (2) Old networks are updated and replaced, leaving older segments (legacy) Hybrid Topology – combines two or more different physical topologies Commonly Star-Bus or Star-Ring Star-Ring uses a MAU (Multistation Access Unit (see later slide) CP2073 Networking

23 Types of Logical Topology
Previous slides showed Physical Topologies Only two Logical Topologies (Bus or Ring) Physical Bus or Ring easy to conceptualise Physical Star could be either a Bus or Ring in logical terms Confused ? See next slides CP2073 Networking

24 Logical Bus Modern Ethernet networks are Star Topologies (physically)
The Hub is at the centre, and defines a Star Topology The Hub itself uses a Logical Bus Topology internally, to transmit data to all segments CP2073 Networking

25 Logical Bus A single node failure does not bring the network down
Advantages A single node failure does not bring the network down Most widely implemented topology Network can be added to or changed without affecting other stations Disadvantages Collisions can occur easily Only one device can access the network media at a time CP2073 Networking

26 Logical Ring Data in a Star Topology can transmit data in a Ring
The MAU (Multistation Access Unit) looks like an ordinary Hub, but data is passed internally using a logical ring It is superior to a Logical Bus Hub – see later slide CP2073 Networking

27 Logical Ring (2) CP2073 Networking

28 Logical Ring (3) Advantages Disadvantages
The amount of data that can be carried in a single message is greater than on a logical bus There are no collisions Disadvantages A broken ring will stop all transmissions A device must wait for an empty token to be able to transmit CP2073 Networking

29 Summary Bus Topology Ring Topology Star Topology Other Topologies
Logical Topologies Questions and Answers CP2073 Networking

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