Communication? Types of communication?Topology in computer network? Communication between two devices? Component of data communication? What is Protocol?

Communication: 

Communication is defined as transfer of information, such as thoughts and messages between two entities. The invention of telegraph, radio,telephone, and television made possible instantaneous communication over long distances.

Data communications means the transmission (sending and
receiving) of information between two locations by means of electrical
signals. The two types of electrical signals are analog and digital.

Analog & Digital Signals:  

Both Analog & Digital signals are used to transmit information through electric signal. In both the technologies information such as any audio or video transform into electric signal. 

In analog technology, information is transformed into electric pulses of varying amplitude. Ex: Speech

In Digital technique, information is transformed into binary form (such as 0 and 1) where each bit represents two distinct amplitude.  Ex: digital watch

Component of Data Communication System:

Data Communication system has 5 component: 

• Message

• Sender

• Receiver

• Transmission medium

• Protocol

Protocol:

Protocol is a set of rules that govern data communication. It represents an agreement between the communicating devices, without protocol two devices can be connected but not communicating.

Data Flow:

Communication between two devices can be SIMPLEX, HALF DUPLEX and FULL DUPLEX.

Simplex: In simplex communication, communication is possible only in one direction. There is one sender & one receiver. The sender and the receiver cannot change the role. 

Half-Duplex: In Half-Duplex, communication is possible in both the directions between two entities but one at a time. A walkie-talkie uses this approach.

Full Duplex: In a full-duplex communication system, the two parties the caller and the called can communicate simultaneously, as in a telephone system. Note that when two persons talk simultaneously, then there is no effectivecommunication!

Topology:  Topology defines how the devices (such as computer, printers etc) are connected and how the data flows from one device to another.

There are two conventions while representing the topologies:

Physical topology defines how the devices are physically wired.

Logical topology defines how the data flow from one device to another.

Topology Broadly categorized into:

• Bus
• Ring
• Star
• Mesh

1) Bus Topology: In Bus topology, each device is connected to other device through the transmission medium as backbone. There must be a terminator at each end to avoid signal reflection. Signal is sent in both the directions but some buses are unidirectional. 

• Bus topology was one of the first topologies used in early LAN.
• Re connection & fault identification is difficult.
• Easy for installation.

The  main problem with bus topology is failure of any medium will seriously affect the whole network. The whole network must be shut down & repaired. In such situation it is difficult to troubleshoot (find) & locate where the break in the cable is or which machine is causing the fault.

2) Ring Topology: In this, each device has point to point connection with two device on other side. A signal is passed along the ring in one direction until it reaches its destination.

• Less cabling
• Easy to install & reconfigure
• Fault identification is easy

3) Star Topology:  In a star topology each station is connected to a central node. The central node can be either a hub or a switch.

•  The star topology does not have the problem as seen in bus topology.
•  The failure of a media does not affect the entire network. Other stations can continue to operate until the damaged segment is repaired.
• The advantages are cabling is inexpensive, easy to wire, more reliable.

4) Mess Topology: A mesh physical topology is when every device on the network is connected to every device on the network; most commonly used in WAN configurations. Ex: Telephone regional office where each office is connected to every other office.

• Avoid traffic problem
• Fault identification is easy
• Amount of cabling is high
• Expensive

Hybrid Topology:  A hybrid topology is a combination of any two or more networktopologies in such a way that the resulting network does not have one ofthe standard forms. 

For example, a tree network connected to a treenetwork is still a tree network, but two star networks connected togetherexhibit hybrid network topologies.