How do networks work?

Each network has its own technology, topology and protocols. These three aspects of the network govern how it works. There are several popular network technologies including Token Ring and Ethernet. The two main protocols that are in use are TCP/IP and IPX - the former is the protocol used by the Internet and the latter is used internally by Novell NetWare.

The following sections go into some technical detail so a summary section has been provided afterwards.

Token Ring
Computers in a Token Ring network are connected together in a ring. A small packet called a token is circulated along the ring. When a particular computer receives the token it has the opportunity to send a data packet.

When each computer in the ring receives the data packet it compares its address with the data packet's destination address. If they match the data packet is copied before being sent to the next computer in the ring. The packet continues around the ring until it arrives back at the sending computer. It must then pass the token on and the process starts again.

Token Ring networks are more resilient than Ethernet networks, but are also more expensive

Ethernet and CSMA/CD

Ethernet can support a variety of different cabling standards, making it easy to design a network for price and performance. It uses a system called CSMA/CD which stands for carrier sense multiple access with collision detection.

Carrier sense means that each computer in the network is constantly "listening'' for network traffic and will examine each piece of data that is transmitted.

Multiple access means that any of the computers connected to the network can choose to send data at any time as long as the network appears to be idle.
Because it takes a finite amount of time for transmitted data to propagate through the physical network, it is possible for two computers to both think the network is not in use and begin transmitting.

Collision detection means that the computers are aware that such collisions can occur. If two computers do transmit at the same time, they will both detect the collision, cease transmitting and wait a short, random amount of time before attempting to transmit again.

Networks and Roads
This type of behavior compares well to the idea of a system of roads. the network can be thought of as a main road, with all of the client computers being side roads and the frames of data being cars traveling along the roads. When cars reach a give-way onto a main road they have to wait for a break in traffic before joining on. This is exactly what happens with transmitted data. In fact data on networks is often referred to as network traffic.

Frames and Packets

Ethernet sends data across a network in frames. There are several different standards for Ethernet frames which can all be used on the one physical network. However for two computers to communicate they must both be configured to use the same standard.
Each frame basically contains a small amount of data along with a destination address. When a frame is transmitted successfully, every other computer on the network will have listened and received it. Each individual computer can then look at the frame's address. The computer whose address matches the destination address on the frame accepts the data and the others ignore it.

(Note that every computer on the network receives every frame that is transmitted so theoretically a computer could examine the data in every piece of network traffic. However there is normally too much traffic on the network for this to be practical.)

Frames and Delivery Vans
A Frame can be thought of as a delivery van driving on the ``road'' of the network - many different types of packages can be carried by the one type of van. The network must be set up to deal with one type of frame, just like a company deciding to use a certain type of delivery van.

Inside each frame is a packet of data which will conform to a certain network protocol. A computer can send some data using a certain protocol, but the receiving computer must use the same protocol or else it will not be able to understand the data.

Protocols and Delivery Vans
Network protocols can be thought of as types of packaging being used by a company to deliver things - any shape, size or type of packaging can fit into the delivery van. The receiving computer must know about the protocol used by the sending computer because, after all, a customer would become very confused if he was expecting a bill and received it in a large, wooden box instead of an envelope.

Summary

Ethernet is a type of network technology. If a network is using Ethernet then it will be using a certain type of cabling and certain network interface cards.
Every computer on an Ethernet network is constantly listening for data to be transmitted. All of the computers on the network receive data from a sender at once, but only the receiving computer will accept the data - all of the other computers will ignore it.
A computer waits for a gap in the network traffic before it attempts to transmit data. Because it takes a finite time to start transmitting it is possible for two computers to transmit at once. If this happens they will both detect a collision - both computers will back off and wait for a random amount of time before attempting to send the data again.
Data is transmitted across Ethernet using frames. A frame is like a package with an address on the outside and some data on the inside. Only the physical network and the interface cards deal with frames.
There are different network protocols which use different types of data packets. Each packet is enclosed inside a frame so it can be sent across the network. However, both the sending computer and the receiving computer must use the same protocol or else they will not understand each other, even though they are on the same network.

Bright House Networks High Speed Online Authorized Resellers.

LAKELAND WEB
P.O. BOX 2004
LAKELAND, FLORIDA  33806
Voice: 863-644-4292
email:  info@lakelandweb.net