Data Transmission In WAN

NETWORK:
A network is a combination of hardware and software that sends data from one location to another. The hardware consists of the physical equipment that carries signals from one point of the network to another. The software consists of instruction sets that make possible the services that we expect from a network.

DATA TRANSFER:
Data is transmitted from one machine(sender) to another(receiver).
In which data goes through many layers and then it will be received by receiver at the next end. Data transfer is the process of using computing techniques and technologies to transmit or transfer electronic or analogy data from one computer node to another.

Layered Model:

The OSI model is a layered framework for the design of network systems that allows communication between all types of computer systems. It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network . An understanding of the fundamentals of the OSI model provides a solid basis for exploring data communications.

We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail.
Each layer at the sending site uses the services of the layer immediately below it. The sender at the higher layer uses the services of the middle layer. The middle layer uses the services of the lower layer. The lower layer uses the services of the carrier.

Sender side

1…Application layer of Host A:
The host A will write email using a browser It is the application layer where the human or software can access the internet using the interface. When Host A write an email it is translated compressed an encrypted using application layer. This layer also ensures that the session stays open long enough to transfer all the data being exchanged. The data is divided into small chunks and then the data is passed to the transport layer

2….Transport Layer Host A:
The transport layer ensures that the whole message arrives intact and in order overseeing both error control and flow control at source to destination level. The network layer gets each packet to the correct computer the transport layer gets the entire message to the correct process on the computer. The message is divided into transmittable segments where each segment contains a sequence number which enable the transport layer to reassemble the message in proper order when arriving at a destination and replace the packets that were packets that were lost in the data transmission.

3….Network Layer Host A:
The network layer is responsible to ensure that the packet gets from its point of origin to its Final Destination Destination using IP address and routing tables. It attaches the IP header to the fragment and now it is called as. IP datagram. It consists of source IP and destination IP Source and destination IPs are attached in this step.

4….Datalink and Physical Layer:
IP datagrams are passes to the datalink layer. This layer formats the datagram into the frame by attaching a header to it MAC addresses which helps to identify the hosts that are in the same network. The physical layer coordinates the function required to carry out bit stream over a physical medium. It also defines procedure and functions that physical devices have to perform for transmission to occur.

The Packet:

Now the data packet is ready and contains the information like what kind of data it contains how it fits together with other data where the data come from and it’s final destination. Different packet of same set don’t have to follow the same path. That’s why the Internet is fast and robust.

Packet flow over the internet:
The packet is send to the switch. It switches the packet to the next device which is router. Once the router has received the signals, the packet will continue through cables, from this router and out to the world wide web.
Internet is made of many routers connected together. The packets may take different paths to arrive at the destination. Once the packet is arrived to the destination router it is passed to the appropriate switch and ultimately the packet will be passed to the device.

Receiver side

1….Physical and Data link layer of Host B:
The physical medium friendly signals are converted and interpreted using physical layer.The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. It makes the physical layer appear error-free to the upper layer (network layer).

2….Network Layer Of Host B:
The network layer is responsible for the source-to-destination delivery of a packet,possibly across multiple networks (links). Whereas the data link layer oversees the delivery of the packet between two systems on the same network (links).The network layer ensures that each packet gets from its point of origin to its final destination.

3….Transport Layer Of Host B:
Transport layer is responsible to arrange the packets in order.Transport layer gets the entire message to the correct process on the computer.The transport layer,on the other hand, ensures that the whole message arrives intact and in order.

4….Application Layer of Host B:
At this stage the data is converted to user required data. decryption extraction and delivery of Data takes place.Where now host B will be able to read the email send by host B.

In brief, when data gets transferred through layers, each layer adds its own header, can remove or add some elements in the existing data, each layer may fragment data units to match the size of the downstream layer to reduce fragmentation. This process is called network data encapsulation.
TCP segment encapsulates application data, IP datagram encapsulates TCP segment, data link layer like ethernet encapsulates IP datagram into frames, physical layer converts those frames into physical medium friendly signal.