LIC topology

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The next few pages show a bunch of topology diagrams. It's important to get a vague grasp of what a topology diagram before continuing.

A topology diagram is a simple picture used to describe a data network. A network topology is a simplified view of a network. It gives an idea of how computers are connected but it leaves out pretty much everything.

A map of the landscape would contain physical features. These are described by topography diagrams. There are a few coming up later.

what it is

A topology is a simplified view. An architect's blueprints are a simplified view of a building. A network diagram is a simplified view of a data network. It may show some computers and miss out their interfaces and cables. It may show networks as simple clouds with no hint of how they work.

A topology diagram is an intuitive guide to help understanding, not a true map of the landscape. If it is physical features you want, use a topography diagram.

A lot of the things found in the LIC are found in a home network. Many millions of people around the world have home networks connected to the Internet. If you sketch a picture of how the parts of the home network are connected, but leave out details like the IBM PCs, router and which rooms they are in, you have a network topology diagram.

The pictures below show a fiew topology diagrams, with most details thrown out and a few details left in.

LIC topology: views
1. home network with DMZ 2. LIC DMZs 3. LIC cable colours
home network
perimeter network
wireless router
Figure 1 shows a home network. This view shows gives an idea that things are connected but does not show any details of the IBM PCs, router or which rooms they are in. Figure 2 shows the LIC network. It looks exactly the same! So much detail has been left out that you can see no difference between this and the home network topology in figure 1. A topology view can hide too much detail. Figure 3 shows the LIC again. It shows the network cable colours I can see hanging out of the LIC computers. Many network cables connect each PC to the ethernet switches. Different colours are used for different types of network traffic.

This topology view is handy for people in a hurry. If someone builds a home network, he probably does not have the time to care about how a wireless router works. He is happy to accept that it is a magic box he must plug into other computers. He wants just enough information to get the job done.

The advantage of a topology diagram is its lack of detail. You can replace the computers with bigger faster ones and the topology won't change. You can swap the wireless router (the bit in the middle) connecting everything together from a router to an old lady at a switchboard, and the topology won't change.

the LIC as a rug

Let's imagine I take up rug weaving as a hobby. I take the topology view above and turn it into a great big rug. I can show which IBM PCs go in each area by placing them on my rug. This is what it looks like.

LIC topology: isometric view

No-one would lay out a data center like this because it takes up too much room. The real-life LIC hardware layout is a stack of computers on shelves.

This rug view of the LIC misses out many things. The only network components shown here are IBM PC base units.

what it isn't

It is difficult to capture the right information on a topology diagram. This can hamper some activities, such as bug hunting. Debugging need a holistic view of a computer system: working from topologies which leave out many details on purpose can make debugging impossible.