Page 89 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes 5.1.3 TCP/IP Model
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.

Figure 5.3: The TCP/IP Model

TCP/IP is a two-layer program. The higher layer, Transmission Control Protocol, manages the
assembling of a message or file into smaller packets 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.
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.

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