Hybrid Topology

Hybrid topology is the combination of using diffrent topologies with one as a backbone.
For example, a tree topology used as a back bone and secondry ring topology is used. So here the tree topology is backbone of ring topology and controlling the traffic and communication between the devices of all ring topolgy and may also attached devices in the tree topology itself.

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Ring Topology

In a ring topology each device has a dedicated point to point line configuration only with the two devices on either side of it. A signal trevels in one direction fron device to device untill it reaches the destination. Each device have a repeater which is used to boost the signal.

Advantages:


1. Easy installation and reconfiguration.
2. Easy to remove a device by removing two cables.
3. Fault locatingand isolation is easy.

Disadvantages:


1. Unidirectional traffic can be a disadvantage.
2. The break in the ring dtops all the communication of network.

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Bus Topology

In bus topology multi point line configuration is used. One long cable acts as a backboneto link all the devices in the network.
Nodes are connected to the cable by drop lines and taps.
A drop line is a connection running between the device and main cable.
A tap is a connector that attached to the main cable to its mattalic core.
The limited number of taps can be used in bus topology because the signals become weak while treveling through wire and loose their energy in the form of heat.

Advantages:


1. Easy installation by laying the main cable along the effecient path.
2. Less cabling is required.
3. Drop line has to reach to nearest point on main cable.

Disadvantages:


1. Difficult reconfiguration and fault isolation.
2. Difficult to add more devices.
3. A fault or break in connection stops the entire transmission.

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Tree Topology

A tree topology is a variation of the star topolgy. As in star topology devices are linked to central hub that control the traffic. However in tree topology the secondry central hubs are again linked to a central hub. In tree topology this central hub is the active hub to control the secondry hubs and traffic.
An active hub contains a repeater (hardware device) that regenrates the bit patterns before sending. It strengthens the transmission and boosted signal travels long distance.
The secondry hubs can be active or passive. The passive hub only provide a simple connection to the central hub and attached devices.

Advantages:

1. This is less expensive.

2. One link and one input/output port  is required.

3. Easy installation and reconfiguration.

4. Less cabling is required.

5. If one link fails then other remain active to communicate.

6. Make fault identification and isolation easy.

7. More devices can be attached.

8. It allows the network to isolate and prior the specific computer of a secondary hub to another computer of another secondary hub.

Disadvantages:

1. The only major disadvantage is that if the central hub or controller fails then the entire network goes down.

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Star Topology

In a star topology every device in the network has a dedicated point to point link to a central hub. The device not connected to each other in this network. Therefore all traffic flows through the central hub. If one device want to send data to another one then it must be sent to the central controller, which further relays data to other device.

Advantages:

1. This is less expensive.
2. One link and one input/output port  is required.
3. Easy installation and reconfiguration.
4. Less cabling is required.
5. If one link fails then other remain active to communicate.
6. Make fault identification and isolation easy.

Disadvantages:


1. The only major disadvantage is that if the central hub or controller fails then the entire network goes down.

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Mesh Topology

In a mesh topology every device has a dedicated point to point link to every other device. The term dedicated means that the link carries traffic between the only two connected devices. Therefore in a mesh topology used network has n(n-1)/2 links to n devices. For these links each device must have n-1 input/ouput ports.


Advantages:

1. Traffice errors resolved as each link carries its own data.
2. The disconnection of one link do not disturb the other links and network.
3. The privacy and security remains as only receipent can see the data using a dedicated link.
4. Using the dedicated link to locate the fault and to isolate is much easy.

Disadvantages:


1. The much number of cables and ports in devices are required.
2. Also the installation and reconfiguration is difficult.
3. More space is required for the cabling.

Therefore the mesh topology is apllied to a limited networks or it is used as a backbone in hybrid networks.

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Topology

The term topology refer to the representation of a network laid out either physically or logically.
When two or more devices are connected to a link then two or more links form a topology. It show the links of the entire network with the devcies attached for communication.

There are five basic topologies used for the communicating devices.

1. Mesh Topology
2. Star Topology
3. Tree Topology
4. Bus Topology
5. Ring Topology

There are two possible relationships for connecting the devices.


Peer-to-Peer
In peer to peer devices share the same link equally.

Primary-Secondary
In primary secondry devices one device controls the traffic and the others communicate through it.

Mesh and Ring topologies mostly use the peer to peer transmission. While Tree and Star topologies convenient for primary secondry connections. But Bus topology is equally convenient to both peer to peer and primary secondary.

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Line Configuration

Line configuration defines the attachment of communication devices to a link.

Point-to-Point Line Configuration


A point to point line configuration provides a dedicated link between two communicating devices. This link is reserved only for the communication of these two particular devices.

Multi Point Line Configuration


A multipoint line configuration is one in which more than two devices share a single link. In this several devices can share the link simultaneously.

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Components of Data Communication

Data communication consists of five basic components.

1. Messsage

The message is the information or data to be communicated. i can be text, numbers, pictures, sound or video or combination of these.

2. Sender

The sender is the device that sends the message. It can be a computer, work station, camera etc..

3. Receiver

The receiver is the device that receives the message.It can be a computer, work station, television etc..

4. Medium

The transmission medium is the path by which message trevels from sender to receiver. It can be a wire, coaxial cale, fibre optics, laser or radio waves etc..

5. Protocol

A protocol is a set of rules that governs the data communication. It represents the agreement of communicating devices. Without a protocol devices can not communicate to each other.

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Data Communication

Data communication is the exchange of data (in the form of 0s and 1s) between two devices via some form of transmission medium(as wire cable).
Data communication is considered local if the communicating devices are in the same building or geographical area.
Data communication is considered remote if devices are farther apart.
For data communication to occur,the communicating devices must be the part of communication system. The effectiveness of data communication depends upon these three fundamental characteristics.

1.Delivery
The system must deliver the data to the correct destination. The data must be received by the device or user to whom it was sent.

2.Accuracy
The system must deliver data accurately. Data that have been altered in transmission and left uncorrected are unusable.

3.Timeliness
The system must deliver data in a timely manner. Data delivered late are useless. In real time tranmission data must be delivered without significant delay as in case of audio and video data.

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