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AN INTRODUCTION TO TCP/IP
The protocols that make Internet and intranets work


) ABSTRACT :-
One of the most important achievement of last decade is popularity of internet. Today internet has become part of our day to day life.TCP/IP in a broad sense can be explained as the concept on which internet works.The paper attempts to familiarize with some of the basic concepts of TCP/IP.It starts with a brief introduction of TCP/IP and provides the basics of it.It also gives a brief origin of TCP/IP and the basic function of these protocols.It also gives the structure of TCP/IP and explains how transmission of data takes place in real world network.It also gives description of some of the protocols that constitute TCP/IP.The conclusion summarizes the key points of TCP/IP.

2) INTRODUCTION :- Most of us know of TCP/IP as the glue that binds the Internet. But not as many can offer a cogent description of what it is and how it works. So what is TCP/IP, really?
TCP/IP is a means for networked computers to communicate with each other. It doesn't matter whether they are part of the same network or are attached to separate networks. It doesn't matter if one computer is a Cray and the other a Macintosh. TCP/IP is a platform-independent standard that bridges the gap between dissimilar computers, operating systems, and networks. It's the protocol that drives the global Internet, and it is to the Internet that TCP/IP owes much of its popularity.
Understanding TCP/IP is largely a matter of understanding a collection of arcane protocols that TCP/IP hosts use to exchange information. Let's look at some of those protocols and see what makes TCP/IP tick

3) TCP/IP BASICS :- TCP/IP stands for Transmission Control Protocol/Internet Protocol. In networking terms, a protocol is an agreed-upon standard that permits two computers to exchange data. TCP/IP isn't just one protocol, but several. That's why you'll often hear it referred to as a protocol suite, of which TCP and IP are the two principal protocols.










The TCP/IP software that you install on a computer provides platform-specific
implementations of TCP, IP, and other members of the TCP/IP family. Typically, it also includes high-level application programs, such as FTP (File Transfer Protocol), which permits users to perform network file transfers from the command line.

3.) ORIGIN OF TCP/IP :- TCP/IP is an outgrowth of research funded by the U.S. government's Advanced Research Projects Agency (ARPA) in the 97s. It was developed so that research networks around the world could be joined to form a virtual network known as an internetwork. The original Internet was formed by converting an existing conglomeration of networks, known as ARPAnet, over to TCP/IP; that Internet would eventually become the backbone of today's Internet.

3.2) TCP/IP AND INTRANETS :- The reason TCP/IP is so important today is that it allows standalone networks to be connected to the Internet or linked together to create private intranets. The networks that comprise an intranet are physically connected by devices called routers or IP routers. A router is a computer that transfers packets of data from one network to another. On a TCP/IP intranet, information travels in discrete units called IP packets or IP datagrams. TCP/IP software makes each computer attached to the network a sibling to all the others; in essence, it hides the routers and underlying network architectures and makes everything seem like one big network. Just as connections to an Ethernet network are identified by 48-bit Ethernet IDs, connections to an intranet are
identified by 32-bit IP addresses, which we express as dotted decimal numbers (for example, 28..2.3). Given a remote computer's IP address, a computer on an intranet or the Internet can send data to the remote computer as if the two were part of the same physical network.

3.3) BASIC FUNCTION OF TCP AND IP :- TCP/IP provides a solution to the problem of how two computers attached to the same intranet but belonging to different physical networks can exchange data. The solution comes in several parts, with each member of the TCP/IP protocol suite filling in one piece of the puzzle. The most fundamental TCP/IP protocol, IP, transmits IP datagrams across an intranet and performs an important function called routing--choosing the path that datagrams will follow to get from A to B and using routers to "hop" networks.
TCP is a higher-level protocol that allows applications running on different hosts to exchange data streams. TCP divides data streams into chunks called TCP segments and transmits them using IP. In most cases, each TCP segment is sent in a single IP datagram. If necessary, however, TCP will split segments into multiple IP datagrams that are compatible with the physical data frames that carry bits and bytes between hosts on a network. Because IP doesn't guarantee that datagrams will be received in the same order in









which they were sent, TCP reassembles TCP segments at the other end to form an uninterrupted data
stream. FTP and telnet are two examples of popular TCP/IP applications that rely on TCP.

3.4 USER DATAGRAM PROTOCOL :- Another important member of the TCP/IP suite is the User Datagram Protocol (UDP), which is similar to but more primitive than TCP. TCP is a "reliable" protocol because it performs the error-checking and handshaking necessary to verify that data makes it to its destination intact. UDP is an "unreliable" protocol because it doesn't guarantee that datagrams will arrive in the order in which they were sent or even that they will arrive at all. If reliability is desired, it's up to the application to provide it. Still, UDP has its place in the TCP/IP universe, and a number of applications use it. The SNMP (Simple Network Management Protocol) application provided with most implementations of TCP/IP is one example of a UDP application.

3.5) OTHER IMPORTANT PROTOCOLS OF TCP/IP :- Other TCP/IP protocols play less visible but equally important roles in the operation of TCP/IP networks. For example, the Address Resolution Protocol (ARP) translates IP addresses into physical network addresses, such as Ethernet IDs. A related protocol, the Reverse Address Resolution Protocol (RARP), does the opposite, converting physical network addresses into IP addresses. The Internet Control Message Protocol (ICMP) is a support protocol that uses IP to communicate control and error information regarding IP packet transmissions. If a router is unable to
forward an IP datagram, for example, it uses ICMP to inform the sender that there's a problem. For a summary of some of the other protocols that fall under the TCP/IP umbrella, see the sidebar above.
4) TCP/IP ARCHITECTURE :- Network designers often use the seven-layer ISO/OSI (International Standards Organization/Open Systems Interconnect) model when discussing network architectures. Each layer in the model corresponds to one level of network functionality. At the bottom sits the physical layer, which represents the physical medium through which data travels--in other words, the network cabling. Above that is the data-link layer, whose services are provided by network interface cards. The uppermost layer is the application layer, where application programs that use network services run.


















Figure : The OSI Protocol Reference Model
Figure shows how TCP/IP squares with the ISO/OSI model. It also illustrates TCP/IP's layered design and shows the relationships among the core protocols









4.) FLOWING OF DATA THROUGH EACH LAYER :- As a unit of data flows downward from a network application to the network interface card, it travels through a succession of TCP/IP modules. At each step along the way, it is packaged with information required by the equivalent TCP/IP module on the other end. By the time the data makes it to the network card, it's a standard Ethernet frame, assuming the network is an Ethernet network. The TCP/IP software on the receiving end recreates the original data for the receiving application by grabbing the Ethernet frame and passing it upward through the TCP/IP stack. (One of the best ways to understand the guts of TCP/IP is to use a "sniffer" program to look inside frames flying around the network for the information added by the various TCP/IP modules.)

4.2) TRANSMISSION OF DATA IN REAL WORLD NETWORK :- To picture
what role TCP/IP plays in real-world networks, consider what happens when a Web browser uses HTTP (HyperText Transfer Protocol) to retrieve a page of HTML data from a Web server attached to the Internet. The browser uses a high-level software abstraction called a socket to form a virtual connection to a server. To retrieve a Web page, it sends an HTTP GET command to the server by writing the command to the socket. The socket software in turn uses TCP to send the bits and bytes comprising the GET command to the Web server. TCP segments the data and passes the individual segments to the IP module, which transmits the segments in datagrams to the Web server.
If the browser and the server are running on computers connected to different physical networks (as is usually the case), the datagrams go from network to network until they reach the one to which the server is physically connected. Ultimately, the datagrams are delivered to their destination and reassembled so that the Web server, which reads chunks of data by performing reads on its socket, sees a continuous stream of data. To the browser and the server, data written to the socket at one end shows up at the other end, as if by magic. But underneath, all sorts of complex interactions have taken place to create an illusion of seamless data transfer across networks.
And that's what TCP/IP is all about: turning lots of small networks into one big one and providing the services that applications need to communicate with each other over the resulting Internet.


















5) GUIDE TO TCP/IP PROTOCOLS AND ACRONYMS :-

5.) ARP (Address Resolution Protocol): Converts 32-bit IP addresses into physical network addresses--for example, 48-bit Ethernet addresses.
5.2) FTP (File Transfer Protocol): Permits files to be transferred from one computer to another using a TCP connection. A related but less common file-transfer protocol, Trivial File Transfer Protocol (TFTP), uses UDP rather than TCP to transfer file data.

5.3) ICMP (Internet Control Message Protocol): Allows IP routers to send error and control messages to other IP routers and hosts. ICMP messages travel in the data fields of IP datagrams and are a required part of all IP implementations.

5.4) IGMP (Internet Group Management Protocol): Permits IP datagrams to be broadcast, or multicast, to computers that belong to multicast groups.

5.5) IP (Internet Protocol): A low-level protocol that routes packets of data across separate networks tied together by routers to form the Internet or an intranet. Data travels in packets called IP datagrams.

5.6) RARP (Reverse Address Resolution Protocol): Converts physical network addresses into IP addresses.

5.7) SMTP (Simple Mail Transfer Protocol): Specifies the format of messages that an SMTP client on one computer can use to send electronic mail to an SMTP server on another computer.

5.8) TCP (Transmission Control Protocol): A connection-oriented protocol that transmits data in byte streams. Data is transmitted in packets called TCP segments, which contain TCP headers and data. TCP is a "reliable" protocol because it uses checksums to verify data integrity and handshaking to make sure transmitted data is received intact.

5.9) UDP (User Datagram Protocol): A connectionless protocol that transmits data in packets called UDP datagrams. UDP is an "unreliable" protocol because the sender receives no information indicating whether a datagram was actually received.
6) CONCLUSION :- There's much more that could be said about TCP/IP, but here are three key points:
¢ TCP/IP is a set of protocols that permit physical networks to be joined
together to form an internet. TCP/IP combines the individual networks to form a virtual network in which individual hosts are identified not by physical network addresses but by IP addresses.














l TCP/IP uses a multilayered architecture that clearly defines each protocol's responsibilities. TCP and UDP provide high-level data transmission services to network application programs, and both rely on IP to transmit packets of data. IP is responsible for routing the packets to their destination.
l Data moving between two applications running on Internet hosts travels up and down the hosts' TCP/IP stacks. Information added by the TCP/IP modules on the sending end is stripped off by the corresponding TCP/IP modules on the receiving end and used to re-create the original data.

7) REFERENCES :-

) Daniel C. Lynch and Marshall T. Rose, Internet System Handbook, Addison
Wesley, pp. 4-4.
2) Daniel C. Lynch and Marshall T. Rose, Internet System Handbook, Addison
Wesley, pp. 8-8.
3) W. Richard Stevens, TCP/IP Illustrated, Volume I: The Protocols, Addison
Wesley, pp. 224.
4) W. Richard Stevens, TCP/IP Illustrated, Volume I: The Protocols, Addison
Wesley, pp. 37-4.