Visual Basic 6 Client/Server Programming Gold Book:Table of ...

In the remainder of this chapter, I review some of the key concepts of the
underlying network architecture. Although the client/server developer does not
need to be a network engineer, it is helpful to understand the basics of the
physical model upon which the application is based.
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.
Peer-To-Peer Networks
A peer-to-peer network is one in which the computers are connected to one
another directly in series. Each PC typically contains a LAN adapter or
Network Interface Card (NIC) with two jacks. Typically, these jacks accept
RJ-11 pins (similar to the connectors on your phone cord). A line is run from
one computer to the next serially. Although it is simple to set up, such a
network is typically slow because data passes through each computer. It is
vulnerable to any individual workstation being powered down or crashing, and
because the network has no server, there are minimal security constraints. A
Windows 95 or Windows 98 network is a peer-to-peer network.
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.