January 14, 2008

To be able to send information between two devices, both must speak the same language. This language is called the protocol.

The protocols that appear in the application layer of the TCP/IP model are:

  • File Transfer Protocol (FTP)
  • Hypertext Transfer Protocol (HTTP)
  • Simple Mail Transfer Protocol (SMTP)
  • Domain Name Service (DNS)
  • Trivial File Transfer Protocol (TFTP)

The protocols of the transport layer are:

  • Transport Control Protocol (TCP)
  • User Datagram Protocol (UDP)

The protocol of the internet layer is:

  • Internet Protocol (IP)

The protocol of the network access layer is:

  • Ethernet

Application layer protocols

FTP or file transfer protocol is used for the transmission of files between two devices. It uses TCP to create a virtual connection for the control of information, then creates another connection to be used for delivery of data. The most commonly used ports are 20 and 21.

HTTP or hypertext transfer protocol is used to translate information into web pages. This information is distributed in a manner similar to that used for electronic mail. The most commonly used port is 80.

SMTP or simple mail transfer protocol is a mail service that is based on the FTP model. It transfers electronic mail between two systems and provides notifications of incoming mail. The most commonly used port is 25.

DNS or domain name service provides a means to associate a domain name with an IP address. The most commonly used port is 53.

TFTP or trivial file transfer protocol has the same functions as FTP but use UDP instead of TCP. This gives it more speed, but less security and trustworthiness. The most commonly used port is 69.

Transport layer protocols

 There are two protocols which can be used by the transport layer to deliver information segments.

TCP or transmission control protocol establishes a logical connection between the final points of the network. It synchronizes and regulates the traffic with what is known as the “Three Way Handshake”. In the “Three Way Handshake”, the originating device sends an initial packet called a SYN to the recipient device. The recipient device sends an acknowledgment packet, called a SYN/ACK. The originating  device then sends a packet called an ACK, which is an acknowledgment of the acknowledgment. At this point, both the originating device and the recipient device have established that there is a connection between the two and both are ready to send and receive data to and from each other.

UDP or user datagram protocol is a transport protocol which is not based on a connection. In this case, the originating device sends packets without warning the recipient device to expect these packets. It is then up to recipient device to determine whether or not those packets will be accepted. As the result, UDP is faster than TCP, but it cannot guarantee that a packet will be accepted.

Internet layer protocols

IP or internet protocol serves as a universal protocol to allow any computers to communicate through any network at any time. Like UDP, it is connectionless, because it does not establish a connection with the remote computer. Instead, it is what is known as a best effort service, in that it will do whatever is possible to ensure that it works correctly, but its reliability is not guaranteed. The Internet protocol determines the format for the packet headers, including the IP addresses of both the originating and the recipient devices.


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