Databases Reference
In-Depth Information
before passing the data to the computer. Currently, the most commonly used
path for remote connectivity is the Internet. Many companies support connec-
tions over the Internet through a
virtual private network (VPN).
A VPN
provides a secure, reliable communication path. VPNs can be used over the
Internet, or over a private LAN or WAN. In either implementation, the VPN
acts as a network inside a network, with a protected communication path
deployed through a public pathway. Other than the details of how it is imple-
mented, a VPN is operationally like any other network. Technically, a VPN is a
network built out of “soft” components. It uses special software at each of the
nodes (connection points) and special protocols known as tunneling protocols.
The name of the protocols comes from the fact that the VPN “tunnels” through
the public media pathway, effectively isolating VPN traffic from the rest of the
network traffic.
Investigating the “Soft” Components
Connectivity requires more than just the physical path. Each end of the con-
nection needs communication software that manages the process. Today's oper-
ating systems come with multiple types of communication software embedded,
each for a specific use. The computers also need a protocol in common, which
is effectively the language that the computers use to communicate. A
protocol
defines the rules the computers use for data format and transmission. It deter-
mines, among other things, how the data is packaged for transmission and the
maximum size of data packets.
There are still more requirements. Look at the instant message (IM) com-
munication session shown in Figure 11-5. You need to have a way of identify-
ing the person (and/or computer) at the other end. There also has to be a way
of making sure that the message gets routed to the appropriate person, or more
accurately the appropriate computer, and their response gets routed back to
you.
The requirements are similar for database connectivity. There's a lot going on
in the background that you probably aren't aware of when you connect to a data-
base server. Your computer and the database server need:
▲
A way to identify each other.
▲
A common language.
▲
A way of ensuring that the information gets to the correct destination.
Think about that last point. It's more complicated than you might think.
A database might have hundreds, even thousands, of concurrent connections
it must manage and maintain. It has to keep track of each of these, including
the client computer, user, and any data associated with the connection. Even
at the client end there's a lot happening. Not only does the data have to arrive
