What is a T1 line?

[Ocean West]

Transmission Control Protocol/Internet Protocol (TCP/IP) 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 packets (see 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 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 a 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).