WiMAX QoS Classes-UGS, rtPS, ertPS, nrtPS, BE QoS types
WiMAX Standard 802.16 mentions following 5 QoS classes:
• Unsolicited Grant Service(UGS)
• Extended Real Time Polling Service(ertPS)
• Real Time Polling Service(rtPS)
• Non Real Time Polling Service(nrtPS)
• Best Effort Service(BE)
Each of these wimax QoS classes has their own parameters such as bandwidth request type, min. throughput requirement as well as delay or jitter constraints.
This Wimax QoS class provides fixed bandwidth allocation on periodic basis. Once the connectivity is established, no more requests are needed. For application of this type refer table-1. QoS parameters for this type are MST, tolerated jitter and max. latency. Refer-table 2 for comparison with other wimax QoS types.
This QoS type is developed to support VOIP along with silence suppression. There will be no traffic transmission during silence time. QoS parameters are same as UGS type. Check table-1 for application of this type. ertPS is similar to UGS in which base station assigns MST on active mode and no BW is allocated during silent time period. Here BS need to poll mobile subscriber to know whether silent period has been ended or it is continuing.
It is used for VBR real time traffic for example MPEG video. Unlike UGS where in fixed allocation is made by BS, here BS regularly polls MS to findout allocation need. Hence bandwidth is allocated on need basis and is adaptive in nature. For this wimax QoS type Min. reserved traffic rate and MST need to be mentioned separately. For UGS and ertPS Min. reserved traffic rate and MST are both same. QoS parameters are same as UGS.
This type is used for non real time Variable bit rate traffic with no delay guarantee. But min. rate is guaranteed. FTP falls under this QoS type.
In this class, BW is granted to mobile subscriber if and only there will be left over bandwidth from other QoS classes. This QoS class guarantess neither delay nor throughput. It allows min. reserved traffic rate and max. sustained traffic rate.
|WiMAX QoS type||Applications/Uses||Scheduling||Bandwidth requests/
BW REQ types
|UGS||CBR real time traffic(periodic), for example T1/E1 connection||Static allocation type, grant equal to MST(Maximum Sustained Traffic Rate)||Reserves bandwidth during setup time, poll-me bit for unicast polling,
no piggyback requests, no bandwidth strealing.
No other kinds of polling, GM can be used for BW REQ in case of rate mismatch compensation
|MST equal to Min. reserved traffic rate, max. latency, tolerated jitter, uplink grant scheduling type, unsolicited grant interval|
|ertPS||VOIP(silence suppression), video conference(real time variable size data,periodic)||Dynamic allocation||reserves bandwidth during setup, allows piggyback requests, allows bandwidth stealing. allows all kinds of poling||MST is equal to min. reserved traffic rate, max. latency and unsolicited grant interval|
|rtPS||Real time video(real time variable size data on periodic basis)||Dynamic allocation||allows piggyback,bandwidth stealing and unicast polling||Min.reserved traffic rate, max. sustained traffic rate, max. latency and uplink grant scheduling type|
|nrtPS||FTP, variable size data||Dynamic allocation||allows piggyback,bandwidth stealing and all kinds of polling||Min. reserved traffic rate, max. sustained traffic rate, traffic priority and uplink grant scheduling type|
|BE||Web Traffic||Dynamic Allocation||Allows piggyback, bandwidth stealing and all kinds of polling||Min. reserved traffic rate, Max. sustained traffic rate, traffic priority and uplink grant scheduling type|
Let us compare to check similarities and difference between various WIMAX QoS classes.
|UGS||No overhead, meet guaranteed latency of Mobile Subscriber requests for real time service||Bandwidth may not be utilized fully as they are granted irrespective of need|
|ertPS||Optimal latency and data overhead efficiency||Need to use polling and mechanism to inform BS when the traffic starts during silence.|
|rtPS||Optimal data transport efficiency||requires overhead of BW REQ and polling latency|
|nrtPS||provides efficient service for non real time traffic with min. reserved rate||Not Applicable|
|BE||Provides efficient service for BE(Best Effort) Traffic||No service guarantee, some connections may stay for long time period|
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