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The TCP/IP Reference Model


  • TCP/IP means Transmission Control Protocol and Internet Protocol. It is the network model used in the current Internet architecture as well. 
  • Protocols are set of rules which govern every possible communication over a network. 
  • These protocols describe the movement of data between the source and destination or the internet. These protocols offer simple naming and addressing schemes.

Overview of TCP/IP reference model

  • TCP/IP that is Transmission Control Protocol and Internet Protocol was developed by Department of Defence's Project Research Agency (ARPA, later DARPA) as a part of a research project of network interconnection to connect remote machines.
  • The features that stood out during the research, which led to making the TCP/IP reference model were:     
  • Support for a flexible architecture. Adding more machines to a network was easy.
  • The network was robust, and connections remained intact untill the source and destination machines were functioning.
  • The overall idea was to allow one application on one computer to talk to(send data packets) another application running on different computer.



Description of different TCP/IP protocols
Layer 1: Host-to-network Layer
  • Lowest layer of the all.
  • Protocol is used to connect to the host, so that the packets can be sent over it.
  • Varies from host to host and network to network.
Layer 2: Internet layer
  • Selection of a packet switching network which is based on a connection less internetwork layer is called a internet layer.
  • It is the layer which holds the whole architecture together.
  • It helps the packet to travel independently to the destination.
  • Order in which packets are received is different from the way they are sent.
  • IP (Internet Protocol) is used in this layer.
  • The various functions performed by the Internet Layer are:
  1. Delivering IP packets
  2. Performing routing
  3. Avoiding congestion
Layer 3: Transport Layer
  • It decides if data transmission should be on parallel path or single path.
  • Functions such as multiplexing, segmenting or splitting on the data is done by transport layer.
  • The applications can read and write to the transport layer.
  • Transport layer adds header information to the data.
  • Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.
  • Transport layer also arrange the packets to be sent, in sequence.
Layer 4: Application Layer
  • The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc.
  • TELNET is a two-way communication protocol which allows connecting to a remote machine and run applications on it.
  • FTP(File Transfer Protocol) is a protocol, that allows File transfer amongst computer users connected over a network. It is reliable, simple and efficient.
  • SMTP(Simple Mail Transport Protocol) is a protocol, which is used to transport electronic mail between a source and destination, directed via a route.
  • DNS(Domain Name Server) resolves an IP address into a textual address for Hosts connected over a network.
  • It allows peer entities to carry conversation.
  • It defines two end-to-end protocols: TCP and UDP
TCP(Transmission Control Protocol) 

  • It is a reliable connection-oriented protocol which handles byte-stream from source to destination without error and flow control.
UDP(User-Datagram Protocol)

  • It is an unreliable connection-less protocol that do not want TCPs, sequencing and flow control. Eg: One-shot request-reply kind of service.


Merits of TCP/IP model
  •     It operated independently.
  •     It is scalable.
  •     Client/server architecture.
  •     Supports a number of routing protocols.
  •     Can be used to establish a connection between two computers.


Demerits of TCP/IP
  •     In this, the transport layer does not guarantee delivery of packets.
  •     The model cannot be used in any other application.
  •     Replacing protocol is not easy.
  •     It has not clearly separated its services, interfaces and protocols.

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