Internet Protocols

Networks (hardware) provide computers the basic ability of transferring bits from one computer to another. In order to use networks we need a set of rules which all of the network's member agree on, that is a protocol.

Communication Protocol is a standard designed to specify how computers interact and exchange messages.
Protocol usually specifies:

• The format of the messages.
• How to handle errors.

In order to simplify the design and implementation of protocols, designers have decided to design a set of protocols, each has different responsibilities instead of one protocol responsible for all forms of communication. The set of protocols is called a Protocol Suite, and it cover all forms of communication as needed.

The OSI seven layers model

A layering model is the most common way to divide a protocol suite to subparts and describe them individually. Layering help us to have better understanding of a protocol suite. The seven layers model, introduced by the International Organization for Standardization more than 20 years ago, is shown below:

Layer	Responsibilities
1. Physical	Basic hardware components for networks. i.e. RS-232
2. Data Link	Frame format, Transmitting frames over the net. i.e. bit/byte stuffing, checksum
3. Network	Address assignment, Packet's forwarding methods
4. Transport	Transfer correctness
5. Session	Establishing a communication session, Security, Authentication i.e. passwords
6. Presentation	Computers represent data in different ways (char, integer) thus the protocol need to translate the data to and from the local node.
7. Application	Specifications for applications using the network, how to send a request, how to specify a filename over the net, how to respond to a request, etc.

Internet protocol suite

PPP or Point-to-Point Protocol - A protocol for creating a TCP/IP connection over both synchronous and asynchronous systems. PPP provides connections for host to network or between two routers, It also has a security mechanism. PPP is well known as a protocol for connections over regular telephone lines using modems on both ends. This protocol is widthly used for connecting personal computers to the internet.

SLIP or Serial Line Internet Protocol - A point-to-point protocol to use over a serial connection, a predecessor of PPP. There is also an advanced version of this protocol known as CSLIP (compressed serial line internet protocol) which reduce overhead on a SLIP connection by sending just a header information when possible, thus increasing packet throughput.

FTP or File Transfer Protocol - FTP enables transferring of text and binary files over TCP connection. FTP allows to transfer files according to a strict mechanism of ownership and access restrictions. It is one of the most commonly used protocols over the internet now days.

Telnet - Telnet is a terminal emulation protocol, defined in RFC854, for use over a TCP connection. It enables users to login to remote hosts and use their resources from the local host.

SMTP Simple Mail Transfer Protocol - This protocol is dedicated for sending EMail messages originated on a local host, over a TCP connection, to a remote server. SMTP defines a set of rules which allows two programs to send and receive mail over the network. The protocol defines the data structure that would be delivered with information regarding the sender, the recipient (or several recipients) and, of course, the mail's body.

HTTP Hyper Text Transport Protocol - A protocol used to transfer hypertext pages across the world wide web.

SNMP Simple Network Management Protocol - A simple protocol that defines messages related to network management. Through the use of SNMP network devices such as routers can be configured by any host on the LAN.

UDP User Datagram Protocol - A simple protocol that transfers datagram (packets of data) to a remote computer. UDP doesn't guarantee that packets will be received in the same order they were sent. In fact it doesn't guarantee delivery at all.

TCP Transmission Control Protocol - Like UDP, a protocol that enables a computer to send data to a remote computer. Unlike UDP, TCP is reliable i.e. packets are guaranteed to wind up at their target, at the correct order.

IP Internet Protocol - IP is the underline protocol for all the other protocols in the TCP/IP protocol suite. IP defines the means to identify and reach a target computer on the network. Computer in the IP world are identify by unique numbers which are known as IP address.

ARP Address Resolution Protocol - In order to map an IP address into a hardware address the computer uses the ARP protocol which broadcast a request message that contains an IP address, to which the target computer replies with both the original IP address and the hardware address.

NNTP Network News Transport Protocol - A protocol used to carry USENET posting between News clients and USENET servers.