wireless communications and mobile...

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Wireless Communications and

Mobile Computing

MAP-I

Manuel P. Ricardo

Faculdade de Engenharia da Universidade do Porto

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♦ In this lecture we will recall the QoS basics concepts and then focus in the QoS in wireless networks, namely 3GPP-QoS and IEEE-wireless-QoS

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Quality of Service

♦ From a user’s point of view » level of satisfaction experienced by the user of an application whose

traffic is delivered through a network. Depends on– User’s subjective evaluation and expectations– Terminal capabilities– Performance of networks

♦ From a network point of view» ability of providing differentiated treatment to

traffic flows or traffic classes » provide them with different levels of delivery guarantees

– bandwidth, delay, loss

» network behaviour characterizable by a set of performance parameters

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QoS principles

♦ The provisioning of QoS requires» cooperation of various communications layers » cooperation of network elements in the end-to-end chain

♦ QoS requirements of users/applications must be mapped into values of network service attributes

♦ Attributes of a network service » may be described by a set of performance (QoS) parameters» which must be observable, measurable and controllable

♦ Networks and users must negotiate contracts, which are described by means of offered traffic and QoS parameters

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QoS

QoS is an end-to-end problem, handled at several communication layers

Physical

Network

Transport

Data link

Application

Mob

ility

Secu

rity

Mul

ticas

t

Qua

lity o

f Ser

vice

IP layer

IP user plane IP control plane

Application app. control

Application node

IP layer

IP user plane IP control plane

Application app. control

IP IP

Control

IP IP

Control

Application control (e.g. SIP)

App. node-backbone control plane interface

App. node-backbone user plane (IP) interface

IP Backbone

Inter-domain interface

Application node

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QoS building blocks in a packet network• Data plane (traffic flows/packets)

– Shaping, Policing– Classification & Marking– Queuing and Scheduling

(service discipline)– Congestion control and Queue

management

• Control plane– QoS mapping– Admission control– QoS routing– Resource reservation/allocation

• Management plane– Resource provisioning– Policy management

network

packet switch(router, switch)

Traffic source/previous network element

feed-back based,end-to-end (TCO, RTP+RTCP)

inter-network element

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IP QoS Models

♦ 2 service models» IntServ - oriented towards the support of QoS per flow» DiffServ - oriented towards the provisioning of QoS to traffic classes

♦ Integrated Services (IntServ) model» Resource ReSerVation Protocol

(RSVP)» TSpec, FlowSpec» Controlled load» Guaranteed service (maximum delay)

♦ Differentiated Services (DiffServ) model» DS field» Per-Hop Behaviours (PHB)» Assured Forwarding (AF)» Expedited Forwarding (EF)» Bandwidth broker

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IntServ - RSVPResourceReSerVation Protocol (RSVP)

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IntServ – Tspec, FlowSpec

♦ The FlowSpec - information that characterizes » the traffic to submit to the network (TSpec) » the service requested from the network (RSpec)

♦ TSpec includes the following parameters» p – peak rate» r – token bucket rate» b – bucket size» M – maximum datagram size» m – minimum policed unit

♦ RSpec is specified only for the Guaranteed service and includes» R – service rate (must be > r)» S – delay slack (acceptable delay in addition to the delay obtained with R

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IntServ – QoS Services

♦ Guaranteed Service» hard guarantees provided to real-time applications

– Guaranteed bandwidth– Bound on end-to-end delay– No losses of conforming packets on the routers

» Resources reserved per flow, based on a Flowspec (TSpec and RSpec)

♦ Controlled-Load Service» emulates the service provided by a moderately loaded best-effort network» only qualitative guarantees

– Very high percentage of transmitted packets are successfully delivered – Delay of the majority of the packets

will not greatly exceed the minimum delay of a packet

» The sender does not specify RSpec

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0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | DSCP | CU | +---+---+---+---+---+---+---+---+ DSCP: differentiated services codepoint CU: currently unused

DiffServ – DSCP field

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Diff Serv – PHB, AF, EF

♦ Per-Hop Behaviours (PHB)» Packets marked with the same DSCP, receive similar treatment

♦ 3 PHBs defined» Best effort

» Assured Forwarding (AF)– Service provides qualitative guarantees, based on priorities– Service characterized by a high probability of packet delivery – may be used to implement the Olympic service (gold, silver and bronze classes)

» Expedited Forwarding (EF)– aimed at building services characterized by

low packet loss ratio, low latency and low jitter

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DiffServ - Bandwidth broker

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QoS in UMTS

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Quality of Service in UMTS

TE MT RAN CN EDGE NODE

CN Gateway

TE

UMTS

End-to-End Service

TE/MT Local Bearer Service

UMTS Bearer Service External Bearer Service

UMTS Bearer Service

Radio Access Bearer Service CN Bearer Service

Backbone Bearer Service

RAN Access Bearer Service

Radio Bearer Service

Physical Radio Bearer Service

Physical Bearer Service

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QoS management functions,UMTS bearer service, user plane

Resource Manager

Mapper

Class if.

Cond.

Resource Manager

Resource Manager

Mapper

Resource Manager

Mapper

Resource Manager

Resource Manager

Cond.

Class if.

Cond.

MT Gateway CN EDGE RAN

BB netw ork service RAN Access network service RAN phys. BS

data f low with indication of direction

TE Ext. Netw.

Local BS External BS

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♦ Class » Classifies and marks packet» At the entry of network (downlink GGSN, uplink terminal)

♦ Cond – Traffic conditioner» Enforces compliance of flow with QoS attributes» At the entry of the network and radio segment

♦ Mapper» marks packet with QoS information related to bearer service below

♦ Resource manager» Decides when to send the packet so that QoS is satisfied» Manages the resources it sees

– Packet queues, ARQ mechanisms, modulations and codes, power, spreading codes

Resource Manager

Mapper

Class if.

Cond.

Resource Manager

Resource Manager

Mapper

Resource Manager

Mapper

Resource Manager

Resource Manager

Cond.

Class if.

Cond.

MT Gateway CN EDGE RAN

BB netw ork service RAN Access network service RAN phys. BS

data f low with indication of direction

TE Ext. Netw.

Local BS External BS

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UMTS QoS Classes

Traffic class Conversational class Streaming class Interactive class Background

Fundamental characteristics

Preserve time relation (variation) between information entities of the stream

Conversational pattern (stringent and low delay)

Preserve time relation (variation) between information entities of the stream

Request-response pattern

Preserve payload content

Destination is not expecting the data within a certain time

Preserve payload content

Example of the application

voice streaming video Web browsing Background download of emails

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UMTS Bearer Service Attributes – Examples♦ Traffic class ('conversational', 'streaming', 'interactive', 'background')♦ Maximum bitrate (kbit/s)

» compliance enforced by token-bucket (Maximum-bitrate , Maximum-SDU-size)

» used to reserve codes in WCDMA radio interface - downlink♦ Guaranteed bitrate (kbit/s)

» traffic compliance enforced by token-bucket (Guaranteed-bitrate , Maximum-SDU-size)

» Delay/ reliability attributes guaranteed only for traffic up to the Guaranteed bitrate» Used for admission control and resource allocation

♦ Maximum SDU size (octets)♦ SDU error ratio

» fraction of SDUs lost or detected as erroneous♦ Residual bit error ratio

» Undetected bit error ratio in the delivered SDUs♦ Transfer delay (ms)

» 95th percentile of the delay distribution

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Token Bucket

Token Bucket Counter (TBC) - number of remaining tokens at any time

b

TBC

Time

OK OK Non-compliant

L1<TBC L2<TBC L3>TBC

b-L1

b-L1+r*∆T

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QoS attributes versus traffic classesTraffic class

Conversational class

Streaming class Interactive class Background class

Maximum bit rate X X X X

Delivery order X X X X

Maximum SDU size X X X X

SDU format information

X X

SDU error ratio X X X X

Residual bit error ratio

X X X X

Delivery of erroneous SDUs

X X X X

Transfer delay X X

Guaranteed bit rate X X

Traffic handling priority

X

Allocation/ Retention priority

X X X X

Source statistics descriptor

X X

Signalling Indication X

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UMTS Bearer Service Attributes (Rel. 7!)Traffic class Conversational

classStreaming class Interactive class Background

class

Maximum bitrate (kbps) <= 256 000 (2) <= 256 000 (2) <= 256 000 (2) <= 256 000 (2)

Delivery order Yes/No Yes/No Yes/No Yes/No

Maximum SDU size (octets) <=1 500 or 1 502 (4)

<=1 500 or 1 502 (4)

<=1 500 or 1 502 (4)

<=1 500 or 1 502 (4)

SDU format information (5) (5)

Delivery of erroneous SDUs Yes/No/- (6) Yes/No/- (6) Yes/No/- (6) Yes/No/- (6)

Residual BER 5*10-2, 10-2, 5*10-

3, 10-3, 10-4, 10-5, 10-6

5*10-2, 10-2, 5*10-

3, 10-3, 10-4, 10-5, 10-6

4*10-3, 10-5, 6*10-

8 (7) 4*10-3, 10-5, 6*10-

8 (7)

SDU error ratio 10-2, 7*10-3, 10-3, 10-4, 10-5

10-1, 10-2, 7*10-3, 10-3, 10-4, 10-5

10-3, 10-4, 10-6 10-3, 10-4, 10-6

Transfer delay (ms) 100 – maximum value

300 (8) –maximum value

Guaranteed bit rate (kbps) <= 256 000 (2) <= 256 000 (2)

Traffic handling priority 1,2,3 (9)

Allocation/Retention priority 1,2,3 1,2,3 1,2,3 1,2,3

Source statistic descriptor Speech/unknown

Speech/unknown

Signalling Indication Yes/No (9)

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PDP Context Activation Procedure for Iu modeGGSN

9. Activate PDP Context Accept

4. Create PDP Context Response

4. Create PDP Context Request

1. Activate PDP Context Request

SGSNRANMS

5. Radio Access Bearer Setup

C1

C2

6. Invoke Trace

8. Update PDP Context Response

8. Update PDP Context Request

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Network-Requested PDP Context Activation Procedure

MS SGSN GGSN

3. PDU Notification Request

HLR

1. PDP PDU

2. Send Routeing Info for GPRS

2. Send Routeing Info for GPRS Ack

4. Request PDP Context Activation

5. PDP Context Activation procedure

3. PDU Notification Response

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Protocol architecture of NAS supporting PS mode, Terminal Equipment side

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Primitives and Parameters at SMREG-SAP - MS side

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UMTS QoS Conceptual Models

IP BearerLayer

AccessBearerLayer(eg. UMTSBearer)

LocalUE

SGSN

Scope of PDP Context

IP Bearer Service

RemoteAccessPoint

Gn/Gp

GGSN

RemoteHost

GGSNUE RemoteAP

RemoteHost

Backbone IPNetwork

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Local UE does not support IP QoS

Uplink Data

Downlink Data

QoS in UMTS controlled by PDP context.

DS

DS

PDP Flow

PDP Flow

GGSNUE RemoteAP

RemoteHost

The UE controlsthe QoS mechanismsfrom the UE.

The UE may controlthe QoS mechanismsfrom received information.

QoS on remote accesslink controlled byDS.

QoS on remote accesslink controlled byDS or other means.

QoS in UMTS controlled by PDP context selected by TFT.

QoS in backbone network controlled by DS. DS marking performed byGGSN.

QoS in backbone network controlled by DS. DS marking performed byRUE, or remarking by RAP.

Application Layer (eg. SIP/SDP)


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Local UE supports DiffServ (DS)

Uplink Data

Downlink Data

DS

DS

GGSN RemoteAP

RemoteHost



The UE performsDS edge functions.

QoS on remote accesslink controlled byDS.

QoS on remote accesslink controlled byDS or other means.

QoS in UMTS controlled by PDP context.UE DS marking carried transparently.

QoS in UMTS controlled by PDP context selected byTFT.Remote DS marking/GGSNremarking carried transparently.

QoS in backbone network controlled by DS. DS marking performed byUE (or remarking by GGSN).

QoS in backbone network controlled by DS. DS marking performed byRUE, or remarking by RAP.

PDP Flow

PDP Flow



UE

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Local UE supports RSVP signalling and DiffServ

RSVP Signalling

RSVP Signalling

QoS in backbone network controlled by DS. DS marking performed byUE, or by GGSN based on PDPcontext signalling.RSVP signalling carried transparently.

QoS in UMTS controlled by PDP context.UE DS marking and RSVPsignalling carried transparently.

Uplink Data

Downlink Data

DS

DS

GGSNUE RemoteAP

RemoteHost



The UE performsDS edge functions and RSVP

QoS in UMTS controlled by PDP context selected byTFT.Remote DS marking/GGSNremarking and RSVPsignalling carried transparently.

QoS in backbone network controlled by DS. DS marking performed byRUE (or remarking by RAP).RSVP signalling carried transparently.

QoS on remote accesslink controlled byeither DS or RSVP.

QoS on remote accesslink controlled byeither DS or RSVP.

PDP Flow

PDP Flow



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UMTS – Radio Resource Management

♦ UMTS – WCDMA♦ What are the causes of high packet delays?

» Low transmission information rate R high packet service time (transmission time) long queues high waiting time delay

» Packet retransmissions caused by packet loss

♦ What are the causes of packet loss?» High BER

♦ What are the causes high BER?

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Uplink Capacity –Maximum Number ( N ) of users

– Ideal power control (every sinal received same power)– N users transmitting at same data bitrate R bit/s

– Eb/Io decreases BER increases, or– Alternatively, for a given Eb/Io , BER,

• N, R need to be managed admission control

11

)1( −=

−=

NNCC

IC

11

0 −===

NRW

IC

RW

WI

RC

EI

b

IEbR

WN

0

1≅

N – number of users

C – power received form each user (W)

I – interference from other users (W)

Eb – energy received per information bit (J/bit)

I0 – Interference spectral density (J/Hz)

W –chip rate (chip/s)

R – information bitrate (bit/s)

∑=

N

iiR

1

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Load Factor, Uplink(from Holma & Toskala, 3rd edition)

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Load Factor, Uplink(from Holma & Toskala, 3rd edition)

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Admission Control Based on Throughput

<

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WLAN- QoS

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DCF - Distributed Coordination Function

♦ Listen before-talk, CSMA/CA based♦ Station transmists when medium is free for time greater than DIFS♦ Random backoff used when medium is busy

AP

DIFS

S2

S1

SIFS

DATARTS

DIFS S2-bo

DATA

- Packet arrival DATA - Transmission of DATA DIFS - Time interval DIFS

CTS

SIFS

SIFS

ACK

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PCF - Point Coordination Function

♦ Contention-free frame transfer♦ Point Coordinator (PC/AP) pools stations♦ PIFS time used to enter Contention Free Period

Data+PollDATA+ACKBeacon

Data+Poll

ACK

CF-End

PIFS SIFS SIFS SIFS SIFS

SIFS(no response)

PIFS

Contention Period

PC

Contention Free Period CP

Data+Poll

SIFS

Time

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802.11e – QoS Support for WLAN

♦ Basic elements for QoS» Traffic Differentiation

– 4 Access Categories, 8 Traffic Classes

» Concept of Transmission Opportunity (TXOP)– Transmission of multiple frames

♦ New Contention-based channel access» Enhanced Distributed Channel Access (EDCA)

♦ New Contention-free channel access» HCF Controlled Channel Access (HCCA)

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PC

BSS (Basic Service Set) QBSS (Basic Service Set for QoS)

( Enhanced Station )

EDCA HCCADCF PCF

HCF- Hybrid Coordination Function

STASTA

STA

STA

STAHC

STASTA

STA

STA

STA

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HCF - Hybrid Coordination Function

♦ During Contention Free Period» Polls STAs and gives a station the permission to access channel» Specifies time and maximum duration of each TXOP

♦ During Contention Period» Controlled Contention

– STA may send traffic with different priorities– STAs may also request resources

» HC can send polled TXOPs during CP

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EDCA♦ 4 Access Categories (AC)

» AC_VO (Voice)» AC_VI (Video)» AC_BE (best-effort)» AC_BK (background)

♦ Contention between ACs (and STAs)♦ An Inter-frame Space (IFS) for each AC

Arbitration Inter frame Space (AIFS)♦ Contention-Window (CW) depends on AC

♦ Mapping Priorities into AC» IEEE 802.1D and IEEE 802.1Q» See NSA slides

Virtual Collision

AC1 AC2 AC3 AC4

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ACK BackOff[AC0] + FrameBackOff[AC1] + Frame

BackOff[AC2] + Frame

AIFS[AC0]

AIFS[AC1]

AIFS[AC2]

BackOff[AC3] + Frame

AIFS[AC3]

Access Category AIFS

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MAC Parameters

• Prioritized Channel Access implemented using MAC parameters per AC

AC_VOice [0] AC_VIdeo [1] AC_BE [2] AC_BK [3]

AIFSN 2 2 3 7

CWmin 3 7 15 15

CWmax 7 15 1023 1023

AIFS [AC] = AIFSN [AC] * aSlotTime + SIFS

If CW[AC] is less than CWmax[AC], CW[AC] shall be set to the value (CW[AC] + 1)*2 – 1.

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Transmission Opportunity (TXOP)

♦ TXOP: duration a STA has to transmit frame(s)♦ When will a STA get a TXOP ?

» Winning a contention in EDCA during Contention Period» Receiving a “polled TXOP” from HC

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Transmission Opportunity (TXOP) (cont.)

♦ In TXOP, frames exchange sequences are separated by SIFS

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HCF Controlled Channel Access (HCCA)

♦ Procedure similar to PCF♦ Hybrid Coordinator (HC)

» Controls the iteration of CFP and CP– By using beacon, CF-End frame and NAV Mechanism (similar to PCF)

» Use polling scheme to assign TXOP to STA– Issue CF-poll frame to poll STA– Polling can be issued in both CFP & CP

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Resources Managed in WLAN

♦ Resources are the time slots» Used to transmit bits according to the modulations/codes used

♦ WLAN enables to send differentiated traffic» By giving priority to real type traffic

♦ WLAN enables a flow to get a bit rate /delay» By using polling

♦ What needs to be managed by the HC?» The time slots available» Who uses them and when

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