QoS Provision for Mobile Access via GPRS - WINLAB VGs.pdfQoS Provision for Mobile Access via GPRS...

10/18/00 QoS Provision for Mobile Access 1

QoS Provision for Mobile Access via GPRS

Presented by:Shaily Verma


Overview

n Introduction to GPRSn QoS provision

n Purpose n Approach

n SSF simulation platformn Implementationn Simulation resultsn Next Steps


GPRS is GSM's extension for packet oriented data transmission.

Information Flow

Introduction to GPRS:


GPRS architecture


Purpose

n Multimedia applications need a wide range of QoS to be supported by the GPRS network.

n Adaptation and control strategies to ensure QoS have not been defined in GPRS.

n Aims to look at call admission and link adaptation schemes for both real time/non real time traffic in GPRS.

QoS Provisioning in GPRS


Where does QoS come into the picture?

MSBS

MS

SGSN

GGSN

PDN


QoS negotiations occur at the time of PDP (Packet Data Protocol) context activation/modification


QoS metric/ profile:

As per GSM 3.60, the QoS profile consists of the following parameters:

1. service precedence (priority)

2. reliability

3. delay

4. user data throughput

n peak

n mean


QoS profile

n Service precedence (priority)

n Indicates the relative priority of maintaining the service.

n High priority (class 1): Service commitments will be maintained ahead of all other precedence levels.

n Normal priority (class 2)

n Low priority (class 3)


Nrt

Nrt

Nrt

Rt

Rt

ReliabilityThe reliability class defines probability of data loss,

data delivered out of sequence, duplicate data

delivery and corrupted data.


Delay

n Defines the maximum values for the mean delayand 95- percentile delay.

n This includes the radio channel access delay, radio channel scheduling delay, the radio channel and GPRS network transit delay.

RTNRTNRTNRT


Throughput

n Indicates the user data throughput requested by the user.

n Defined by two negotiable parameters:

n Peak

n Mean

n Various classes defined according to peak and mean throughput requirements.


Approach

n Intends to see how QoS can be delivered for different traffic types through:

n call admission and control.

n radio resource management.

n link adaptation (changing code rate according to the current C/I).

• Provide QoS by abstracting the functionalities from LLC, RLC, MAC and BSSGP protocols.


UMTS traffic classes


Approach

n “All bits are not created equal!”n Have two main traffic classes in GPRS:

n GPRS Conversational class/real time (rt)n have absolute QoS requirements. n if the negotiated QoS cannot be met, the MS is

rejectedn GPRS non-conversational class/non real time(nrt)

n PDF (Packet data flows) adjust to the available bandwidth.

n the relative QoS between different PDFs is kept.


Approach

Call Admission and Control (CAC)n CAC criteria

n RT: check bandwidth requirement and also available bandwidth

n NRT: check nrt queue and buffers available.n Maintain separate queues for rt and nrt packets. n Schedule packets on the basis of priority and

delay class.n QoS profile in the BSS


Simulation: Top Level

packets MS BSS SGSNUpper layers

GMM SNDCP SMS

LLC LLC

BSSGP

Ntk. Svc

Ll

RLC

MAC

GSM RF

RLC BSSGP

MAC Ntk. Svc

GSM RF Ll

GMM SNDCP SMS

MS BSS SGSN

Transmission Plane Implementation


Simulation Platform:JSSF(JAVA SCALABLE SIMULATION FRAMEWORK)

n SSF provides a single, unified interface for discrete-event simulation.

n Makes it possible to build models that aren Efficientn Scalable n able to utilize parallel processor resources.n Object-oriented

n utilize and extend the frameworkn maximize the potential for direct reuse of

code


SSF Syntax

n The SSF syntax comprises five base class interfaces:n Entity : Object that can own processes and channel

endpoints, and can be aligned with other Entitiesn Event : sent on channels to processes in Entitiesn Process : sends events on outChannels.n inChannel : pipe leading to a process carrying events n outChannel : pipe going out from a process carrying

events


Scope of the simulator

Simulation scenario currently restricted to:n one GSM carriern one celln One BSS incorporating functionalities of BS and

SGSNn use of all coding schemesn mean C/I can be varied as also variancen concentrates on uplink performancen User can specify the number of MS


Scope of the simulator

n Traffic Models:n Mobitex (mean packet length 30 bytes)n Exponentially distributed packets (mean 200 bytes)

n Channel Modeln TU3

n RT and NRT packet separation n Delay class and priority based selection at the BSn RT packets are unacknowledged (no retransmissions)n NRT packets are acknowledged (selective ARQ)


Implementation:

n Physical Layer:n C/I value is generated from a lognormal distribution

with user specified parameters. n Emulated with a set of graphs of the BLER vs. C/I for

the 4 channel coding schemesn As per BLER, RLC block is dropped/transmitted.

n LLCn sole functionality is the segmentation and reassembly

of the LLC frames.


Implementation:

n RLC:n Acknowledged/Unacknowledged data transfer mode n BEC with sliding window ARQ mechanismn All four coding schemes are supported

n MAC:n Uses slotted ALOHA modeln Includes capture modeln Channel assignment by the BSS n Logical channels are implemented


Uplink Model Description

PDP context negotiation done

Contend for channel using slotted ALOHA

Contention winner sent PUA (Packet Uplink Assignment)

USF (uplink state flag) /channel allocation sent

Data blocks sent to BS:

RT:if delay class 1

NRT: if delay class 2,3,4

MS BS

packet

LLC RLC

ACK sent to NRT with retransmission bitmap and channels


Algorithm for Resource allocation(PDP negotiation)

MS BSS +SGSNQoS ProfileQoS Profile

Rt/nrt?

Peak throughput = PThroughput realizable per time slot = S=5KbpsLq = Length of nrt queueAvailable slots = av_slSlots for nrt = SnrtMax. # of slots for nrt = Snrt_max

yes

yes

Reject request

av_sl<P/S Lq>7Real time(rt) Non real time(nrt)

Add to queue

Allocate#_sl[MS_id] = P/Sav_sl = av_sl - P/S

no

Initially say out of the 7TS, one is allocated for nrt(on which 7 users can be mux.) and 6 TS are allocated for rt users.

Snrt < Snrt_maxno

yes Snrt=Snrt+1

no


Algorithm for Resource allocation(Channel request)

MS BSS +SGSNChannel_request[MS_id]Channel_request[MS_id]

Rt/nrt?Real time(rt) Non real time(nrt)

Add to nrt QAdd to rt Q

. Sort nrt Q as perpriority and delayclass. Allocate USFs

Sort rt Q as perpriority and delayclass. Allocate USFs


GPRS CODING SCHEMES

9.051811/2CS 1

21.44281CS 4

15.63123/4CS 3

13.42682/3CS 2

Data rate(Kb/s)

Payload(bits/block)

Code Rate Scheme


Optimizing Channel Capacity

Link Adaptation:Use higher coding schemes (less coding, more payload) when the radio conditions are good:n RT packets : use CS3n NRT packets:

n use CS1 at C/I <10dBn use CS3 at 10<C/I <18dBn use CS4 at C/I >=18dB


BS

Get PacketFromPG

in_Contend

PacketSetDownLink_Listener

PacketGenerator

Timer

Contend_Send

TimeOutSet

Sequence of messages on the MS side

MS(1)Packet from higher layer out_Contend

(2) PacketEvent

(3)

(32)If ACK,remove head

(7)ACTIVATE_PDP_ACCEPT/REJECTfrom BS with negotiated QoS(10)USF free from BS

(8) Change PDPstatefrom inactive to active

(20)Status 1->2(21)Start T3164(25)Stop T3164.Start T3166(31)Stop T3166.

(3)Sends ACTIVATE_PDP_REQUEST(QoS)(11)Sends PACKET_CHANNEL_REQUEST(26)Send RLCBlockEvent(Data_Block) to BS(30)Receive ACK/NACK for data block

(6)Sends ACTIVATE_PDP_ACCEPT/REJECT(9) RLCBlock from BS containing USF free(19)Sends Packet_Uplink_Assignment(24) Send USF=MS_ID

(4)Sends ACTIVATE_PDP_REQUEST(QoS)

Denotes processDenotes entityDenotes eventDenotes channels

Zone


Sequence of messages on the BS side

ControlMessagesRT_UPLINKREQset

Zone

MS

Frame_GeneratorControlMessagesNRT_UPLINKREQset

Contend and CaptureListen_to_Uplink

Listen_to_PDPUplink PDP_negotiator

ConnectionRtSet

ConnectionNrtSet

ControlMessagesACK_NACKset

Sink

to_BEM

in_BEM

Block Error Mgr

Downlink Sender

BS

(5)Sends ACTIVATE_PDP_REQUEST(QoS requested)(6)Sends ACTIVATE_PDP_ACCEPT/REJECT (QoS negotiated)

(12)RLCBlock containing channel request(27)Receive Data_Blockfrom MS

(13)

(14) ConnectionEvent

(16)Sort the requests based on priority. (17)Send RLCBLOCK with USF=USF_FREE in TS0(18)Send the PUA in TS0. Set uplink_sent to 1.(22)In other TS check if uplink

sent =1 in ConnectionRtSet/ConnectionNrtSet

(23)Send USF=MS_ID

(29)Send ACK/NACK for data blockfrom ControlMessagesACK_NACKset.

(4)Sends ACTIVATE_PDP_REQUEST

Sink

(15)

(28)Check for error


Total load per TS vs. total throughput per TS10 MS (3 RT, 7 NRT), exp. distributed packet (mean 200 bytes)

Total Load per TS (Kbps/TS)

Tota

l Thr

ough

put

per

TS (

Kbps

/TS)


Throughput vs. load10 MS (3 RT, 7 NRT), exp. distributed packet (mean 200 bytes)

NRT

Thro

ughp

ut(K

bps)

Total NRT Load (Kbps)

Total RT Load (Kbps)

RT

Thro

ughp

ut(K

bps)


Blocking and dropping

n Packets can be lost in two ways:n Blockingn Dropping

< 1%<1%NRT

<1%

Blocking

0%RT

DroppingTraffic


Next Steps

n Get BLER vs. C/I curves for the 8 coding schemes of EDGE and study the link adaptation gains of EDGE vs. GPRS.

n Investigate throughput and delay gains for other traffic models like railway and web through link adaptation.

Date post:	20-May-2018
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