TCP/IP REVIEW
What is tcp/ip ? TCP/IP (Transmission Control Protocol/Internet
Protocol) is the basic communication language or protocol of the Internet.
It can also be used as a communications protocol in a private network (either
an intranet or an extranet). When you are set up with direct
access to the Internet, your computer is provided with a copy of the TCP/IP
program just as every other computer that you may send messages to or get
information from also has a copy of TCP/IP.
TCP/IP is a
two-layer program. The higher layer, Transmission Control Protocol,
manages the assembling of a message or file into smaller packet that are
transmitted over the Internet and received by a TCP layer that reassembles the
packets into the original message. The lower layer, Internet Protocol,
handles the address part of each packet so that it gets to the right
destination. Each gateway computer on the network checks this address
to see where to forward the message. Even though some packets from the same
message are routed differently than others, they'll be reassembled at the
destination.
TCP/IP uses
the client/server model of communication in which a computer user (a
client) requests and is provided a service (such as sending a Web page) by
another computer (a server) in the network. TCP/IP communication is primarily
point-to-point, meaning each communication is from one point
(or host computer) in the network to another point or host computer.
TCP/IP and the higher-level applications that use it are collectively said to
be "stateless" because each client request is considered a new request
unrelated to any previous one (unlike ordinary phone conversations that require
a dedicated connection for the call duration). Being stateless frees network
paths so that everyone can use them continuously. (Note that the TCP layer
itself is not stateless as far as any one message is concerned. Its connection
remains in place until all packets in a message have been received.)
Many Internet
users are familiar with the even higher layer application protocols that use
TCP/IP to get to the Internet. These include the World Wide Web's Hypertext
Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet)
which lets you logon to remote computers, and the Simple Mail Transfer Protocol
(SMTP). These and other protocols are often packaged together with TCP/IP as a "suite." Personal computer users with an analog
phone modem connection to the Internet usually get to the Internet
through the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol
(PPP). These protocols encapsulate the IP packets so that they can be sent over
the dial-up phone connection to an access provider's modem.
Protocols related
to TCP/IP include the User Datagram Protocol (UDP), which is used instead
of TCP for special purposes. Other protocols are used by network host
computers for exchanging router information. These include the
Internet Control Message Protocol (ICMP), the Interior Gateway Protocol (IGP),
the Exterior Gateway Protocol (EGP), and the Border Gateway Protocol (BGP).
