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.

UGS

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.

ertPS

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.

rtPS

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.

nrtPS

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.

BE

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

guarantees 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

Parameters/

specifications

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

Table-1

Let us compare to check similarities and difference between various WIMAX QoS classes.

WiMAX QoS PROS CONS

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

Table-2