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Network topology defines the structure of the network.
•One part of the topology definition is the physical topology, which is the actual layout of the wire or media.
•The other part is the logical topology, which defines how the media is accessed by the hosts for sending data.
Physical Topologies
•Commonly used physical topologies
1- Bus Topology
A bus topology uses a single backbone segment (length of cable) that all the hosts connect to directly.
Original Ethernet used a bus topology.
By the way, Ethernet hubs work the same as a “bus”.
2- Star topology
•Hubs allow computers and other network devices to communicate with each other, and use a star topology.
•Like a repeater, a hub regenerates the signal.
•Hubs have the same disadvantage as a repeater, anything it receives on one port, it FLOODS out all other ports.
•Wherever possible, hubs should be replace by switches.
•More LATER!
Physical Typologies Extended Star
•An extended star topology links individual stars together by connecting the hubs and/or switches.
•This topology can extend the scope and coverage of the network.
Physical Typologies Hierarchical
•A hierarchical topology is similar to an extended star.
•However, instead of linking the hubs and/or switches together, the system is linked to a computer that controls the traffic on the topology.
Physical Typologies Mesh
•A mesh topology is implemented to provide as much protection as possible from interruption of service.
•Each host has its own connections to all other hosts.
Logical Typologies
•The logical topology of a network is how the hosts communicate across the medium.
•The two most common types of logical typologies are broadcast and token passing.
Logical Typologies Broadcast
•Broadcast topology simply means that each host sends its data to all other hosts on the network medium.
•There is no order that the stations must follow to use the network.
•It is first come, first serve.
•Ethernet works this way.
Logical Typologies Token Passing
•Token passing controls network access by passing an electronic token sequentially to each host.
•When a host receives the token, that host can send data on the network.
•If the host has no data to send, it passes the token to the next host and the process repeats itself.
•Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI).
Ring Topology
Access Method :
Token Passing= 60 or 40 bytes
Operation:
To send data from pc2 to pc 5
Pc2
1- load the data to free token
2- set the addresses for both the S &D
3- relies the token to pc3
--------------------
PC3 & PC4
1- match the address
2-repeat the token
3-relise the token to pc4
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PC5
1-Match the address
2-copy the token
3-repeat the token
4-mark chick bit
5-relise the token
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PC2
Look the chick bit if it marked
Clean the token
If not relies the token
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