Information Technology Reference
In-Depth Information
There are fixed and recurring costs in most WAN environments. Fixed costs include the
network equipment, circuit provisioning, and network management tools. The recurring
costs include the service provider monthly WAN service fees, maintenance costs of the
WA N , a n d t h e n e t w o r k o p e r a t i o n s p e r s o n n e l .
Optimizing Bandwidth Using QoS
QoS is an effective tool for managing a WAN's available bandwidth. Keep in mind that
QoS does not add bandwidth; it only helps you make better use of it. For chronic conges-
tion problems, QoS is not the answer; you need to add more bandwidth. However, by pri-
oritizing traffic, you can make sure that your most critical traffic gets the best treatment
and available bandwidth in times of congestion. One popular QoS technique is to classify
your traffic based on a protocol type or a matching access control list (ACL) and then give
policy treatment to the class. You can define many classes to match or identify your most
important traffic classes. The remaining unmatched traffic then uses a default class in
which the traffic can be treated as best effort.
Queuing, Traffic Shaping, and Policing
Cisco has developed many different QoS mechanisms, such as queuing, policing, and
traffic shaping, to enable network operators to manage and prioritize the traffic flow-
ing on the network. Applications that are delay sensitive, such as VoIP, require special
treatment to ensure proper application functionality. Queuing refers to the buffering
process used by routers and switching when they receive traffic faster than can be
transmitted. Different queuing mechanisms can be implemented to influence the order
in which the different queues are serviced (that is, how different types of traffic are
emptied from the queues).
Ta ble 6 - 6 identifies QoS considerations to optimize bandwidth.
Ta b l e 6 - 6
QoS Considerations
Key
To p i c
QoS Category
Description
Classification
Identifies and marks flow and provides priority to certain flows
Congestion management
Mechanism to handle traffic overflow using a queuing algo-
rithm
Link-efficiency
mechanisms
Reduce latency and jitter for network traffic on low-speed links
Traffic shaping and polic ing
Avoids congestion by polic ing ing res s and eg res s flows
