WiMAX QoS Quality of Service

- an overview of the essentials of WiMAX QoS, Quality of service and the various WiMAX QoS Service Classes.

WiMAX QoS or WiMAX Quality of Service is a key element in the delivery of service over the WimAX medium. WiMAX QoS.

With techniques such as Internet Protocol being used, delays or latency and jitter can be introduced into the data transmission arena. While IP techniques provide improved levels of efficiency, this comes at a cost.

To overcome the effects of latency and jitter, the concept of quality of service is used. For WiMAX QoS several techniques and definitions are at the core of the implementation.

WiMAX QoS basics

In an ideal world it would be possible to send data over a network and gain the same performance as that achieved by a circuit switched network. However the nature of packet data means that the same channels are sued for data travelling to and from a variety of different sources and end points.

Within a packet data network, there are three main parameters that are key to the performance of the network, and the WiMAX QoS. These three parameters are:

  • Latency:   Latency is a measure of time delay experienced in a system - in the case of a telecommunications system such as WiMAX it is the time that it takes from the initiation of sending data until it arrives at its destination. In a WiMAX system. The WiMAX system can be split into three major elements as far as latency is concerned:

    • From the user to the base station via the WiMAX radio interface
    • Over the IP network
    • From the base station to the end user over the WiMAX radio interface
    Typically it is found that the maximum latency occurs within the IP network - this may be around 100ms in many instances with the WiMAX radio access network / interface introducing around 5ms.
  • Jitter:   In the context of computer networks and int hei case the WiMAX system, jitter is a measure of the variability over time of the packet latency across a network. A network with constant latency has no variation and hence no jitter. However as the levels of data are constantly varying, it takes a variable amount of time for a packet to arrive at its destination. Packet jitter is expressed as an average of the deviation from the network mean latency. Although the term jitter is often used, it is actually imprecise and a standards-based term, packet delay variation, PDV, is more correctly used. PDV is an important quality of service factor in assessment of network performance.
  • Packet loss:   Packet loss is the term used to indicate the loss of data packets during transmission over a network. Packet loss may occur for a variety of reasons but normally occurs as a result of high network latency or overloading of switches or routers that are unable to process or route all the incoming data.

WiMAX QoS definitions

In order to categorise the different types of quality of service, there are five WiMAX QoS classes that have been defined.

These WiMAX QoS classes are defined in the table below:

WiMAX QoS Class WiMAX QoS Class Details
Unsolicited Grant Service The Unsolicited Grant Service, UGS is used for real-time services such as Voice over IP, VoIP of for applications where WiMAX is used to replace fixed lines such as E1 and T1.
Real-time Packet Services This WiMAX QoS class is used for real-time services including video streaming. It is also used for enterprise access services where guaranteed E1/T1 rates are needed but with the possibility of higher bursts if network capacity is available. This WiMAX QoS class offers a variable bit rate but with guaranteed minimums for data rate and delay.
Extended Real Time Packet Services This WiMAX QoS class is referred to as the Enhanced Real Time Variable Rate, or Extended Real Time Packet Services. This WiMAX QoS class is used for applications where variable packet sizes are used - often where silence suppression is implemented in VoIP. One typical system is Skype.
Non-real time Packet Services This WiMAX QoS class is used for services where a guaranteed bit rate is required but the latency is not critical. It might be used for various forms of file transfer.
Best Effort This WiMAX QoS is that used for Internet services such as email and browsing. Data packets are carried as space becomes available. Delays may be incurred and jitter is not a problem.

By Ian Poole

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