TcpIp Essay Research Paper November 13 2000TCPIPTCP

Tcp-Ip Essay, Research Paper

November 13, 2000

TCP-IP

TCP and IP were developed by a Department of Defense (DOD) research project to

connect a number different networks designed by different vendors into a network of networks

(the “Internet”). It was initially successful because it delivered a few basic services that everyone

needs (file transfer, electronic mail, remote logon) across a very large number of client and server

systems. Several computers in a small department can use TCP/IP (along with other protocols) on

a single LAN. The IP component provides routing from the department to the enterprise network,

then to regional networks, and finally to the global Internet. On the battlefield a communications

network will sustain damage, so the DOD designed TCP/IP to be robust and automatically

recover from any node or phone line failure. This design allows the construction of very large

networks with less central management. However, because of the automatic recovery, network

problems can go undiagnosed and uncorrected for long periods of time.

As with all other communications protocol, TCP/IP is composed of layers:

IP – is responsible for moving packet of data from node to node. IP forwards each packet

based on a four byte destination address (the IP number). The Internet authorities assign

ranges of numbers to different organizations. The organizations assign groups of their

numbers to departments. IP operates on gateway machines that move data from

department to organization to region and then around the world.

TCP – is responsible for verifying the correct delivery of data from client to server. Data

can be lost in the intermediate network. TCP adds support to detect errors or lost data and

to trigger retransmission until the data is correctly and completely received.

Sockets – is a name given to the package of subroutines that provide access to TCP/IP on

most systems.

Network of Lowest Bidders

The Army puts out a bid on a computer and DEC wins the bid. The Air Force puts out a bid and

IBM wins. The Navy bid is won by Unisys. Then the President decides to invade Grenada and

the armed forces discover that their computers cannot talk to each other. The DOD must build a

“network” out of systems each of which, by law, was delivered by the lowest bidder on a single

contract.

The Internet Protocol was developed to create a Network of Networks (the “Internet”).

Individual machines are first connected to a LAN (Ethernet or Token Ring). TCP/IP shares the

LAN with other uses (a Novell file server, Windows for Workgroups peer systems). One device

provides the TCP/IP connection between the LAN and the rest of the world.

To insure that all types of systems from all vendors can communicate, TCP/IP is absolutely

standardized on the LAN. However, larger networks based on long distances and phone lines are

more volatile. In the US, many large corporations would wish to reuse large internal networks

based on IBM’s SNA. In Europe, the national phone companies traditionally standardize on

X.25. However, the sudden explosion of high speed microprocessors, fiber optics, and digital

phone systems has created a burst of new options: ISDN, frame relay, FDDI, Asynchronous

Transfer Mode (ATM). New technologies arise and become obsolete within a few years. With

cable TV and phone companies competing to build the National Information Superhighway, no

single standard can govern citywide, nationwide, or worldwide communications.

The original design of TCP/IP as a Network of Networks fits nicely within the current

technological uncertainty. TCP/IP data can be sent across a LAN, or it can be carried within an

internal corporate SNA network, or it can piggyback on the cable TV service. Furthermore,

machines connected to any of these networks can communicate to any other network through

gateways supplied by the network vendor.

Addresses

Each technology has its own convention for transmitting messages between two machines within

the same network. On a LAN, messages are sent between machines by supplying the six byte

unique identifier (the “MAC” address). In an SNA network, every machine has Logical Units with

their own network address. DECNET, Appletalk, and Novell IPX all have a scheme for assigning

numbers to each local network and to each workstation attached to the network.

On top of these local or vendor specific network addresses, TCP/IP assigns a unique number to

every workstation in the world. This “IP number” is a four byte value that, by convention, is

expressed by converting each byte into a decimal number (0 to 255) and separating the bytes with

a period. For example, the PC Lube and Tune server is 130.132.59.234.

An organization begins by sending electronic mail to Hostmaster@INTERNIC.NET requesting

assignment of a network number. It is still possible for almost anyone to get assignment of a

number for a small “Cl

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