Tuesday, August 27, 2013

Network Connections and Layers

A computer network is a telecommunication network that allows any set of computers or devices connected to each other with the ability to exchange data. The connections between the devices are established using either cable or wireless media.  Internet is a part of computer network where each and every computing device connected with each other. In a nutshell, Internet is a network of networks. Internet is a system architecture that has revolutionized communications by allowing various computer networks around the world to interconnect. Some of the internet standards are IETF (Internet Engineering Task Force) and RFC (Request for comments).

Internet Layers

Application Layer: It is mainly responsible for supporting network applications. It Includes different protocols such as HTTP, FTP, SMTP
Transport Layer: It is mainly responsible for transporting application – layer messages between the client and server sides of an application. It includes two protocols such as  TCP, UDP
Network Layer: It is responsible for routing diagrams from one host to another. This layer has two principle components such as IP protocol and Internet Transport protocol
Link layer: The network layer routes a packet through a series of packet switches between the source and destination. To move a packet from one node to other node, network layer must rely on the link layer
PhysicaNetwork l Layer: It moves the individual bits within the frame from one to the next.


HTTP - HTTP abbreviated as Hypertext transfer protocol, web’s application-layer protocol and it is a heart of web. When the client and server interact with each other, HTTP defines the structure of the message, when the user request particular address with the help of URL (Uniform Resource Locator), it reaches the destination and fetches the records.

FTP – It involve in application layer and it is abbreviated as File Transfer protocol is a protocol for transferring a file from one host to another host. Both HTTP and FTP are file transfer protocols and have many common characteristics for illustration both run on top of TCP, Internet’s connection-oriented etc and at the same time both have differences.

SMTP - Simple mail Transfer protocol is a protocol for internet electronic mail. It uses the reliable data transfer service of TCP

Connectionless and connection oriented service
In order to establish connection and access application includes email, file transfer etc between internet and communicating devices can be done in two ways. They are 

Connection-Oriented Service

When an application uses the connection-oriented service, the client and the server (residing in different end systems) send control packets to each other before sending packets with real data (such as e-mail messages). This is called handshaking between the two points,  connection- oriented service is provided by TCP (Transmission control Protocol). Flow control, congestion control can be done in Connection-oriented service

Connectionless Service

There is no handshaking with the connectionless service. When one side of an application wants to send packets to another side of an application, the sending application simply sends the packets. Moreover, the service makes no provision for flow control or congestion control. The connectionless service is provided by UDP (User Datagram Protocol)

Four Principles of Quality of Service (QoS) for Network Applications

•    Packet Classification
•    Isolation: Scheduling and policing
•    High resonance utilization
•    Call admission

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