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Virtualosity: Webster's Dictionary defines virtual
as "being such practically or in effect, although not in actual fact
or name." So for something to be a virtual network, it should act like
a network, yet not be one. It's a wonder then that anyone could
classify only some networks as virtual since all networks are virtual
to some extent. Perhaps we can make the separation based on physical
wiring. If there are real wires among all of the nodes, then the
network is not virtual. Based on this determination, WANs have been
virtual since the telcos stopped provisioning T1 circuits on
conditioned copper and started using channelized T3 circuits instead.
Perhaps a better determinant is whether the
network connections are on-demand or dedicated. An on-demand network
is made of connections that can be controlled by network
administrators, instead of their telecom partners. A network made of
connections controlled by a third party like a telco, ISP or telecom
analyst is a dedicated network. At some point in this type of network,
administrators lose control of the physical network, sometimes right
past the building hubs. Thus, for all practical purposes, on-demand
networks are built above the network layer because this is the only
place accessible to network administrators for their entire network.
Pssst! Got a Secret? What is
private for one person is all too often very public for the next. Over
the years I've heard of numerous cases of tapped lease circuits, both
legally and illegally. We shouldn't use the word private when we mean
secure. After all, my front yard is private, yet open for viewing to
anyone who wants to see my weedy lawn. Private is defined by Webster's
as "of, belonging to, or concerning a particular person or group; not
common or general." So a private network is one where you acquire
exclusive use of the network links. This is contrasted with a public
network where the ownership or payment is dispersed across all of the
network residents.
A secure network is an altogether different type
of network. Secure networks might be private or public. Security is
rarely accomplished in the manner in which the network is provisioned,
unless you have armed guards patrolling the wires. In many cases, only
the WAN links are secured as a part of their provisioning. This type
of secured netwo rking is done with encrypting hardware that delivers
security just below the network layer. Secure networking can be more
consistently provisioned above the network layer, just like on-demand
networking.
This exercise provides us with a handful of
interesting network types. The most common special type of network
found is the DPN (dedicated private network). A DPN is what you get
almost every time you order a WAN from a third party (regardless of
the method--leased circuits, frame relay or ATM) or build your LAN
with ATM switches instead of wiring hubs. These technologies let the
telecom analyst specify which devices actually have data paths between
them, which may be different from the actual physical wiring. Thus a
private network, again, is where the data paths are defined by someone
for someone and these can consist of physical wiring or specific data
links over shared wiring. |
