Hardware Reference
In-Depth Information
Network Maps and Addresses
In the previous chapter, it was easy to keep track of where messages went because
there were only two points in the network you built: the sender and the receiver. In any
network with more than two objects—from three to three billion—you need a map
to keep track of which objects are connected to which. You also need an addressing
scheme to know how a message gets to its destination.
Network Maps: How
Things Are Connected
The arrangement of a network's physical connections
depends on how you want to route its messages. The
simplest way is to make a physical connection from each
object in the network to every other object. That way,
messages can get sent directly from one point to another.
The problem with this approach, as you can see from
the directly connected network in Figure 3-2, is that the
number of connections gets large very fast, and the con-
nections get tangled. A simpler alternative to this is to put
a central controller in the middle and pass all messages
through this hub, as seen in the star network shown
in Figure 3-2. This way works great as long as the hub
continues to function, but the more objects you add, the
faster the hub must be to process all the messages. A third
alternative is to daisy-chain the objects, connecting them
together in a ring. This design makes for a small number
of connections, and it means that any message has two
possible paths, but it can take a long time for messages to
get halfway around the ring to the most distant object.
In practice (such as on the Internet), a multitiered star
model, like the one shown in Figure 3-3, works best. Each
connector (symbolized by a light-colored circle) has a few
objects connected to it, and each connector is linked to
a more central connector. At the more central tier (the
dark-colored circles in Figure 3-3), each connector may be
linked to more than one other connector, so that enabling
messages to pass from one endpoint to another via
several different paths. This system takes advantage of the
redundancy of multiple links between central connectors,
but avoids the tangle caused by connecting every object
to every other object.
If one of the central connectors isn't working, messages
are routed around it. The connectors at the edges are the
weakest points. If they aren't working, the objects that
depend on them have no connection to the network. As
Figure 3-2
Three types of network: direct connections between all elements,
a star network, and a ring network.
Directly connected network
Star network
Ring network
Search WWH ::




Custom Search