Protocol stacks

Computers on a network communicate in agreed-upon ways called ``protocols''. Protocols dictate which signals computers use across cables or radio waves, how they tell one another that they have received information, and how they exchange information.

Protocols are more accurately termed protocol ``stacks'' or protocol ``suites''. These terms reflect the fact that the communications functions are complex and are usually divided into independent layers or levels. A stack is a collection of protocol layers which implement network communication. The protocol associated with each layer communicates only with the layers immediately above and below it, and assumes the support of underlying layers. Lower layers are closer to the hardware; higher layers are closer to the user. The number of layers and tasks that each layer performs depends on which stack you are using.

Although there are many different types of networks, they fall into two general categories:

• A LAN (Local Area Network) connects computers that are in the same office or in adjacent buildings. All the computers on a LAN are connected to a single cable or hub, unless they use a gateway or bridge. A computer on a LAN can communicate directly with any other computer on that LAN.

• A WAN (Wide Area Network) connects computers over long distances using serial lines and sometimes satellite connections. Computers on a WAN can be several hundred feet apart or on the other side of the world from each other. Sometimes messages must go through additional computers (called ``gateways'', ``routers'', or ``bridges'') to reach their destination.

• SCO TCP/IP (provided with some SCO OpenServer products)

• Microsoft^® NetBEUI (provided with SCO Advanced File and Print Server)

• other SCO OpenServer-compatible transport stacks

• PPP (Point-to-Point Protocol)

• SLIP (Serial Line Internet Protocol)

For an overview of SCO OpenServer protocol stack support, see ``Networking protocol stacks''.