Thursday, November 19, 2009

Quality of Service (QoS)

QoS is one or more measurements of desired performance and priorities of a communications system. The WiMAX system is designed with the ability to apply different QoS levels to downlink and uplink connections as well as provide multiple service types on a single connection to each user. QoS measures for WiMAX systems may include service availability, data throughput, delay, jitter, and error rate.

Service Availability

Service availability is the ratio of the amount of time an authorized user is able to access the services compared to the total time service is supposed to be available. Service availability can be affected by a variety of factors including admission control and oversubscription.

Admission control is the process of reviewing the service authorization level associated with users and determining the extent to which network resources will be allocated if they are available. Admission control is used to adjust, limit or assign the use of limited network resources to specific types or individual users. Admission control may allow for the assignment of higher access level priority for specific types of users such as public safety users.

Oversubscription is a situation that occurs when a service provider sells more capacity to end customers than a communications network can provide at a specific time period. This provides a benefit of reduced network equipment and operational cost.

Oversubscription is a common practice in communications networks as customers do not continuously use the maximum capacity assigned to them and they access the networks at different time periods. Unfortunately, over-subscription in telecommunications can cause problems when customers do attempt to access the network at the same time. For example, when customers open their presents at a holiday event (e.g. Christmas) and attempt to access the Internet at the same time.

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