Information Technology Reference
In-Depth Information
The WAN designer must engineer the network with enough bandwidth to support the
needs of the users and applications that will use the network. How much bandwidth a net-
work needs depends on the services and applications that will require network bandwidth.
For example, VoIP requires more bandw idth than interactive S ec ure Shell (S SH) traffic. A
large number of graphics or CAD drawings require an extensive amount of bandwidth
compared to file or print sharing information being transferred on the network. A big
driver in increasing demands for more bandwidth is the expanded use of collaboration ap-
plications that use video interactively.
When designing bandwidth for the WAN, remember that implementation and recurring
costs are always important factors. It is best to begin planning for WAN capacity early.
When the link utilization reaches around 50 percent to 60 percent, you should consider in-
creases and closely monitor the capacity at that point. When the link utilization reaches
around 75 percent, immediate attention is required to avoid congestion problems and
packet loss that will occur when the utilization nears full capacity.
QoS techniques become increasingly important when delay-sensitive traffic such as VoIP
is using the limited bandwidth available on the WAN. LAN bandwidth, on the other hand,
is generally inexpensive and plentiful; in the age of robust real-time applications, however,
QoS can be necessary. To provide connectivity on the LAN, you typically need to be con-
cerned only with hardware and implementation costs.
WAN Link Cate gorie s
When you start to evaluate WAN link characteristics, they generally fall into three broad
categories: private, leased, and shared. There are many factors to consider, such as the how
the WAN is used, the cost, advantages, and what technologies are available in a given area.
Ta ble 6 - 5 identifies various WAN link characteristics.
Ta b l e 6 - 5
WA N L i n k C h a r a c t e r i s t i c s
Key
To p i c
Use
Cost
Advantages
Examples
Private
WA N t o c o n n e c t d i s -
tant LANs
Owner must buy
and configure
network.
Expensive to
maintain.
High security.
Tran s mis s ion qu alit y.
Metro Ethernet
using dark fiber
Leased
WA N t o c o n n e c t d i s -
tant LANs
High cost.
Equipment is
leased or private.
Provider is responsi-
ble for maintenance.
Dedicated band-
width.
TDM, SONET
Shared
Shared-circuit or
packet-switched
WA N
Cost is fair.
Bandwidth is
leased.
Equipment is
leased or private.
Provider is responsi-
ble for maintenance.
Shared network for
multiple sites.
MPLS or Frame
Relay
