In this Lesson, we’ll discuss the WAN. We’ll start
by defining what a WAN is, and then move on to talking about basic technology
such as WAN devices and circuit and packet switching. also cover transmission
options from POTS (plain old telephone service) to Frame Relay, to leased lines,
Finally, we’ll discuss wide area requirements including
a section on minimizing WAN charges with bandwidth optimization features.
Packet Switching and WAN Protocols
Line and Frame Relay
Requirements & Solutions
What Is a WAN?
So, what is a WAN? A WAN is a data communications network that
serves users across a broad geographic area and often uses transmission facilities
provided by common carriers such as telephone companies. These providers are companies
like MCI, AT&T, UuNet, and Sprint. There are also many small service providers
that provide connectivity to one of the larger carriers’ networks and may
even have email servers to store clients mail until it is retrieved.
- Telephone service is commonly referred to as plain old telephone
- WAN technologies function at the lower three layers of the OSI reference
model: the physical layer, the data link layer, and the network
Common WAN network components include WAN switches, access
servers, modems, CSU/DSUs, and ISDN Terminals.
A WAN switch is a multiport internetworking device used in
carrier networks. These devices typically switch traffic such as Frame Relay,
X.25, and SMDS and operate at the data link layer of the OSI reference model.
These WAN switches can share bandwidth among allocated service priorities, recover
from outages, and provide network design and management systems.
A modem is a device that interprets digital and analog signals, enabling data
to be transmitted over voice-grade telephone lines. At the source, digital signals
are converted to analog. At the destination, these analog signals are returned
to their digital form.
An access server is a concentration point for dial-in and dial-out connections.
A channel service unit/digital service unit (CSU/DSU) is a digital interface device
that adapts the physical interface on a data terminal equipment device (such as
a terminal) to the interface of a data circuit terminating (DCE) device (such
as a switch) in a switched-carrier network. The CSU/DSU also provides signal timing
for communication between these devices.
An ISDN terminal is a device used to connect ISDN Basic Rate Interface (BRI) connections
to other interfaces, such as EIA/TIA-232. A terminal adapter is essentially an
WAN Terminating Equipment
The WAN physical layer describes the interface between the
data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).
Typically, the DCE is the service provider, and the DTE is the attached device
(the customer’s device). In this model, the services offered to the DTE
are made available through a modem or channel service unit/data service unit (CSU/DSU).
CSU/DSU (Channel Service Unit / Data Service Unit) Device that connects the end-user
equipment to the local digital telephone loop or to the service providers data
transmission loop. The DSU adapts the physical interface on a DTE device to a
transmission facility such as T1 or E1. Also responsible for such functions as
signal timing for synchronous serial transmissions.
Unless a company owns (literally) the lines over which they transport data, they
must utilize the services of a Service Provider to access the wide area network.