Topology

The term topology refers to the way a network is laid out, either physically or logically.
Five basic technologies are :

MESH

Every device has dedicated point-to-point link to every other device.
(n(n - 1))/2 physical channels are required to link n devices.

Advantages

1. No Traffic 
The use of dedicated links guarantees that each connection can carry its data load, thus eliminate traffic problems.

2. Robust
If one link becomes unusable, it does not affect the entire problem. .

3. Privacy or Security
Every message travels along a dedicated link, hence only the intended recipient sees it.

4. Fault identification' and fault isolation is easy.

Disadvantages

1. Installation and reconfiguration is difficult.
2. The sheer bulk of wiring can be greater than the available space can accommodate.
3. The hardware required to. connect each link (I/O port and cable) are expensive.

STAR 

Each device has a dedicated point-to-point link only to a central controller, usually called a hub.

Advantages 

1. Less expensive than mesh topology. 

2. Easy to install and configure 

3. Less cabling required compared to mesh 

4. Robust

One link is damaged then the complete system is not affected. This also leads to easy fault identification and isolation.

Disadvantages

1. More cabling compared to bus or ring topology. 

2. Central controller is required. 

TREE: (Variation of STAR)

In TREE majority devices are connected to a secondary hub that in turn is connected to the 

central hub.

Advantages

1. Less expensive than mesh topology.
2. Easy to install and configure
3. Less cabling required as compared to mesh
4. Robust
5. More devices can be attached to a single hub.
6. Allows network to isolate and prioritize communication from different Computers.

Disadvantage

1. More cabling compared to bus or ring topology.
2. Central controller is required.

BUS

It uses multi point configuration.
One long cable acts as a backbone to link all devices in the network.

Advantages

1. Ease of installation
2. Backbone cable can be laid along the most efficient path.
3. Less cabling required.

Disadvantages

1. Difficult reconfiguration and fault isolation.
2. Signal reflection at the taps can cause degradation in quality,
3. A fault or break in the bus cable stops transmission.

RING

Each device has a dedicated point-to-point line configuration only with the two devices on other side of it.

Advantages

1. Relatively easy to install and configure.

Disadvantages

1. Unidirectional traffic can be a disadvantage.
2. A break in the ring can disable the entire network.

Transmission Mode

Transmission mode term is used to define the direction of signal flow between two linked devices.
There are three types of transmission modes:

1. Simplex: 

In simplex mode, the communication is unidirectional. Only one of the two stations on a link can transmit, the other can only receive.

e.g. keyboard, T.V., pager.

2. Half duplex: 

In half duplex mode, each station can both transmit and receive, but not at the same time. e.g. Walky talky.

3. Full duplex: 

In full duplex mode, both stations can transmit and receive simultaneously. e.g. Telephone.