Protocols

What is a Protocol?

A protocol is an agreed way to communicate. It is a set of rules that two people (or computers) keep to when meeting and talking.

In the world of computer networking there are many protocols. Some are good for one job, others are better for other jobs.

Many protocols work at just one layer of the OSI 7 layer model.

Typically communication between two computers uses many protocols working together - for example the protocol stack of the OSI model.

To communicate both the sending computer and the receiving computer must be using the same protocols.

Routable -v- Nonroutable Protocols

Ten years ago most LANs we not connected to other LANs. Today many LANs are interconnected - for example all of the LANs across the Higher Colleges system are interconnected.

The protocols used in older LANs did not allow data to pass out of the LAN. These are called nonroutable protocols. Modern protocols which allow data to be transferred from one LAN to another are called routable protocols.

OSI -v- Other Protocol Stacks

When the OSI 7 layer model was developed in 1984 it was hoped that it would become the standard for computer networking. The most widely used systems today are similar to this model, but differ in detail.

TCP/IP - Transmission Control Protocol / Internet Protocol

This is a stack of protocols used for exchanging data between computers of different types. TCP/IP is a routable protocol and is often used to move data between networks.

TCP/IP has grown in importance over the last few years because it is the protocol of the Internet. It is likely to become more important over the next few years as Internet technology is increasingly used within companies in the form of intranets.

At the top of the stack - roughly equivalent to application and session layers are several protocols including:

FTP - File Transfer Protocol, used to download files from the Internet.

Telnet - used to login to remote computers across the Internet.

SMTP - Simple Mail Transfer Protocol - the protocol used for Internet e-mail.

In the middle of the stack are TCP (Transmission Control Protocol) and IP (Internet Protocol). These do roughly the same jobs as the session, transport and Network layers of the OSI model.

Novell Netware

Market leader Novell has developed its own protocol stack to support the Netware operating system. Netware can, however, work with other protocols as well. As I type these notes my PC is attached to a Netware server, but two protocol stacks are loaded - the Netware stack as shown above and a TCP/IP stack to let me connect to the Internet.

Windows NT

Windows NT is Microsoft’s network operating system. Built right in to NT is the ability to use several different protocols at the same time. The default protocol for NT is TCP/IP but NT may also use its own NWLink protocol.

The Physical and Data Link Layers

The stacks described above do not have their own physical and data link layer protocols - instead they use industry-standard protocols for the lowest levels. Two such standards were developed by the IEEE (Institute of Electrical and Electronics engineers) - they are:

                         802.3 - Ethernet

This is the system we use in our college. NICs check to see if the cable is free. If it is they send, if not they wait then retry. All other NICs check the destination address of the packet and either read it or ignore it as appropriate. Transmission speed is around 10 Mbps.

802.5 - Token Ring

This protocol makes a hub based network behave like a ring. A token is passed by the hub to each station in turn. There are two versions with transmission speeds of 4 Mbps and 16 Mbps

 

Binding

When we install a network operating system onto a PC we must choose which protocols to install. For example, on my home PC I have installed just TCP/IP, as the only network I use at home is the Internet.

The last stage of installing a protocol is called binding. This is the job of telling the NIC which protocol(s) it will use. Two protocols are bound to the NIC in my office PC - Novell’s SPX/IPX and TCP/IP. Some computers have several NICs with each one bound to a different protocol.

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