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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 – 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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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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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)
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 controlsthe QoS mechanismsfrom the UE.
The UE may controlthe QoS mechanismsfrom received information.
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
Application Layer (eg. SIP/SDP)
Application Layer (eg. SIP/SDP)
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 controlsthe QoS mechanismsfrom the UE.
The UE may controlthe QoS mechanismsfrom received information.
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
Application Layer (eg. SIP/SDP)
Application Layer (eg. SIP/SDP)
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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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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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