Back

An introduction to packets, IP addresses and routers

Introduction
There are a number of common terms used when discussing networks. These include packets, IP addresses and routers.

Packets
When you send or receive information across a computer network, for example, when your computer downloads a web page from the Internet or you when you send an email to someone in another country, that information is broken up into fixed-sized 'packets' of information before being sent. Each packet contains a little bit of the actual information you want to send or receive and some extra 'helping' information. This includes:

    • The address of the sender of the packet.
    • The destination of the packet.
    • Email reassembling information.
    • A check sum for error detection.

How do packets help communication across networks
After a message has been broken up into packets, they are sent across the Internet using the cables in the standard telephone network. If you were sending an email from the UK to someone who lives in Australia, the email would be broken up into packets. Each of the packets would then be sent by different routes to get to Australia. It is only when all of the packets have been received that the message can be reassembled and read. If there are lots of different routes you can use to send a packet then it doesn't matter if one route is not working (perhaps because a cable is broken or a computer or server is not working) or is very busy. The packet can automatically be redirected via another route. Of course, there might still be a delay in a computer receiving all of the packets for one message. Because of the potential delay, communication is not always instant.

packet switching

IP addresses
As we have already said, when you, e.g. request a web page on the Internet, the web server who hosts the web page splits it up into packets. Each packet is then given some extra information, such as how to reassemble all the packets that make up a message, the sender's address and the destination address, known as IP or Internet Protocol addresses. A typical address looks like this: 123.101.10.114. The packets are then sent on the Internet, each one going by the best route available at the time, being constantly re-routed towards the destination by the routers on the networks that make up the Internet. In fact, each packet in a message might arrive at the destination by completely different routes. This is why the Internet is known as a 'packet-switched network'. But how does each packet 'know' which route to take? This is where the routers on the network come in.

Routers on the Internet
Each LAN connected to the Internet has a router. Consider your school's network. When you send a message or request a web page, you are sending/receiving packets of data. The router on the school network exchanges information with other routers on other networks on the Internet. They tell each other how busy a communication connection is between the routers, how quickly packets are being moved along a section of the line and whether there are any problems on it, for example. The router can then look at and evaluate the information it has received from the other routers and make decisions about which way to send a packet! Routers are key to the workings of the Internet. Without routers, the Internet could not work! You can see for yourself the route that a packet takes using the 'tracert' DOS command! Go to the DOS prompt on your computer and at the C:\ WINDOWS prompt type in: tracert www.theteacher.info and press Enter. You will then see a list of:

    • all the routers used in transferring a packet between the site and yourself
    • the times a packet takes to travel between your computer and the router
    • the name of the network router
    • the IP address of the network router.

 Back