TCP/IP was found in the BSD implementation of UNIX from Berkeley, where it spread to all universities immediately. Today , TCP/IP networking tools are found in every major implementation of the UNIX systems as a built - in feature of its kernel

THE CONCEPT

TCP/IP expands to Transmission Control Protocol/ Internet Protocol, but the name is somewhat a misnomer because it is a collection of several protocols (of which TCP/IP are the most important one) and applications (commands). TCP/IP is an open standard in the sense that its specifications and some of the implementations are available to everyone. It is also characterized by the absence of any formal specification. All TCP/IP specification are available in the form of RFCs (Request for comments) -documents which are available widely on the Internet. 

Features of TCP/IP

A PROTOCOL IS A SET OF RULES THAT HAVE TO BE USED BY TWO OR MORE MACHINES TO TALK TO EACH OTHER.

The goals of TCP/IP were set by the Department of Defense and today, are its inherent features are:

• Independent of vendors, type of machine and networks. This was necessary to finally break the monopoly of vendors.
• Failure recovery- Being originally meant for the defence network, it shoutld be able to divert data immediately through other routes if one or more parts of the network went down.
• Facility to connect new subnetworks without significant disruption of services.
• High error rate handling- The transmission, irrespective of the distance travelrd, must be 100% reliable, with facilities for full error control
• Enable reliable transmission of files, remote login (the remote executions of commands).

TCP/IP originally began by the development of programs (the DRAPA set) that enable computers to talk among themselves. Later , Berkely developed an entire suit of  tools that are today known as the r - utilities because all their command names are prefixed with an " r " . Some of the most important a applications available in the TCP/IP family are :

• ftp and rcp for file transfer .
• telent are rlogin for logging in to remote machines
• rsh for executing a command in a remote machine without logging in
• The Network File System ( NFS) which lets one machine treat the file system of  remote machine as its own .
• The electronic mail service using the Simple Mail Transport Protocol (SMTP), Post Office Protocol (POP) and the mail , pine and elm mailers.
• Remote printing which allows people to access printers on remote computers as if they were connected locally.
• The Hyper Transport Protocol (HTTP) of the World Wide Web which browsers like  Netscape use to fetch HTML document .
• The Point - to - Point (PPP) which makes all these facilities available through a telephone line .

A TCP/IP NETWORK

In a network , a computer is known host , sometimes a node , an every such host has a host name . This name is unique throughout the network . Each machine is fitted with a network interface card that is connected by wire to the corresponding card in other machine. All communication between hosts normally takes place through these network interfaces only.

Every TCP/ IP network has an address that is used by external networks to direct their messages . Every host in the network has an address as well , and the combination of these two addresses forms the complete network address of the host . For instance , 192168 (or strictly speaking ,192 . 1680 . 0 ) could the address on a network , and a host within the network could have a host address of 45 .67 . In that case , 192 . 168 . 45 . 67 represents the complete network address of the host . This address has to be unique not only within the network , but also to all connected networks . And if the network is hooked up to the Internet , it has to be unique through the world .

When two or more networks are connected together , and uses the TCP / IP protocol for communication we have a  Internet , popularly known as Internet . Note that Internet is different form the Internet which (spelled with an uppercase) which is super - network of all networks . A local Internet or Internet easily be connected to the Internet , which also uses the same protocol .

There are various ways (topologies) of connecting machines in a network , and employ different technologies . The most common ones are Ethernet and the Token Ring . The significant feature of the Ethernet is that every host is logically connected to every host in the same network by a thick , thin or twisted pair cable . When a message is transmitted by one of the hosts , it reaches the other hosts in one hop . On the other hand , in a token ring network , a message from one host may require more than one hop to reach other host. It is easy for host to reach out to other host if both are in same network (i.e, either in Token ring or in Ethernet) . But if host belong to one network (say , to token ring) and to reach out to a other host who belongs to another network (say , in Ethernet) . It has to route its message through a host which servers as a gate way or router for both networks . This machine is actually part of both of them and has two addresses , one for each network . This machine is known as Router (or Gateway) because it diverts messages from one network to another . A router has more than one network care ; it receives data from one interface and sends it out through the other .

MAC AND IP ADDRESSES

At the outset, one must bear in mind that every host in a network has two addresses- a logical software address and a machine address, the hardwired address of the network interface care. TCP/IP uses both these address, and one must know when and how one address gets converted to th other. The following discussions based on the Ethernet technology but applies to other technologies as well.

Every Ethernet network has a 48-bit physical address hard coded into the board by the hardware manufacturer. This address is unique throughout the world, and is known as the MAC address (Media Access Control) or Ethernet address. One can know th MAC address of any network card with teh administrator's ifconfig command. A typical line from the command output like this:

Echo Link encap: 10 Mbps Ethernet Hwaddr 00:00:E8:2E:47:0C

The MAC address (00:00:E8:2E:47:0C) consists of of a set of six colon delimited hexadecimal numbers. The IEEE and other standard organization have ensured the uniqueness of this address throughout the world. This machine address is used by one of the layer of the TCP/IP protocol stack.

TCP/IP: also understand an address (the logical software address) or Internet address because the numbering scheme it represents is also followed on teh Internet. This address is a sequence of four numbers separated by dots. A typical address look like this:192.168.33.45

All TCP/IP applications like telnet and ftp use this address to connect to a remote host. Since the network interface card does not understand this, TCP/IP provides a mapping facility, which converts one to the other. There are also a number of rules governing th allotment of these addresses.

THE FOUR LAYERS

TCP / IP has four layers , and is simple to work with . These four layers are   : 

• Application layer , representing the application 
• Transport layer , which controls the reliability to transmission 
• Internet layer , which  takes care of addressing of the data packets .
• Network access layer , which makes sure that IP address , are finally converted to MAC address .

Data originates from the application layer and traverses to other three layers . At the transport layer , the data is broken into chunks , which may be split at the Internet layer . These chunks have different names at the different layers , but are also universally known as datagrams (a data is actually the chunk of the Internet layer , but we'll be liberal in our definition) . Each layer also adds its own header information to the data received from the upper layer by a process known as encapsulation . The datagrams travel through the wire and moves up to a similar set of four layers ( but in the reverse direction) at ttthe receiving end . In a similar manner, they relieved to their headers before they are reassembled.

THE APPLICATION LAYER:

This layer contains the application like ftp, rlogin , telnet and so forth. Data originates from the application and is fed to the transpport layer in the form of a stream . The application layer don't add any headers to this stream . This is the only layer where new services are constantly been added . DNS,NFS and HTTP are some of the later addition to this laye

 THE TRANSPORT LAYER:

The transport layer features two protocols -TCP and UDP (user Datagram Protocol). TCP is a reliable and connection oriented mechanism for transporting data. It provides robust error detection and recovery facilities, and is used by most applications, which are not designed to handle such functions. UDP is unreliable and connection- less. It does not care whether data has reached the destination or not. Some applications (like NFS) use UDP instead of TCP.

THE INTERNET LAYER       

The Internet layer, takes care of all addressing requirements. It also has a limited role to play in the determinating the route of packet should take to reach its destination. IP is a dominant protocol in this layer and it often uses the services of ICMP (internet control message protocol) for the work.

THE NETWORK ACCESS LAYER

The network access layer also called the link layer, is the last in the TCP/IP protocol stack. It is the only layer with the knowledge of underlying hardware built into it. The layer comprises the network interface layer, the protocols and the details of the physical media. It accepts the datagrams from the Internet layer, and encapsulates them after converting all IP addresses to MAC addresses. It finally sends out a frame to the wire ARP (address resolution protocol) is the main protocol used by protocol used by this layer.

Compiled and written by:

Akhouri Monalisa Sinha

A part of our editorial team

Article Dated : 26-12-2001

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