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AVCE Information & Communication Technology

AVCE-ICT Unit 2 Serving Organisations

This page was last edited on: Tuesday, 21 September 2004 at 03:31
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Network Topologies And Architectures

The backbone of any client/server system is the network on which it is installed.

It is the network that moves data from the server to the user.

The network might be a 10Mbps Ethernet or it might be the Internet itself.

Although network design is well beyond the scope of this book, the Visual Basic client/server developer should have a grasp of how his or her data is moved in order to properly model the application.

The expression network topology refers to how the network is physically laid out.

In contrast, the expression network architecture refers to how the network is implemented on that topology. In the following sections, I briefly discuss the more common topologies and architectures.

Star Networks

The star network topology implies a network where all computers are connected to a hub (a hub is a box similar to a telephone switchboard containing minimal intelligence).

Multiple hubs are connected to one another. Star networks are simple to maintain but offer minimal security constraints.

If a hub goes down, the entire network goes down.

Ring Networks

In a ring network, all computers are connected via a continuous cable.

A multiplexing unit monitors the network, allowing only one packet to circle the network at a time.

The packet is continually sent from computer to computer.

Each computer examines the packet to see if it is addressed to that workstation.

If a computer needs to send information, it waits for the packet and attaches a "request" to transmit.

The multiplexing unit gives permission to each workstation in turn in a procedure that is akin to a parliament (giving each "member" a turn to speak but also allowing for higher priority speeches such as error messages).

If the packet is accidentally destroyed, the multiplexer recreates it.

IBM’s Token Ring architecture runs on a ring technology.

It has the advantage of being very reliable, but because of the extra overhead of packet monitoring, it is somewhat expensive to maintain and does not scale to a large number of users.

Bus Networks

The bus topology connects computers in a single line of cable.

Although each computer is typically connected to a hub, the internal wiring of the hub still connects each computer serially.

When a workstation wants to send a packet of information, it "listens" for the line to be clear through a process known as electronic sensing.

Only one packet can travel on the network at a time, and if two computers happen to transmit at the same time, a packet collision occurs.

Each workstation listens for such collisions and, when they are detected, waits a random amount of time and then resends the packet.

The most common implementation of bus technology is Ethernet.

Although fairly simple and inexpensive to install and maintain, the network is vulnerable to any breaks in the cable.

Further, as more users are added to the network, performance can degrade drastically.

Still, Ethernet is by far the most common architecture.

To maintain satisfactory performance, network engineers break a large Ethernet network into smaller LANs connected via bridges.

 

 


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