Wireless Networks and Protocols MAP-Tele Manuel P. Ricardo - - PowerPoint PPT Presentation
WNP-MPR-qos 1 Wireless Networks and Protocols MAP-Tele Manuel P. Ricardo Faculdade de Engenharia da Universidade do Porto WNP-MPR-qos 2 Topics Scheduled for Today Quality of Service Characterization and models Case studies
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Faculdade de Engenharia da Universidade do Porto
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… Quality of Service
» Characterization and models » Case studies » Research issues
…
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Review of QoS basic concepts QoS in wireless networks
» 3GPP-QoS » IEEE-wireless-QoS
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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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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 is an end-to-end problem, handled at several communication layers
Physical Network Transport Data link Application Mobility Security Multicast Quality of Service
IP layer IP user plane IP control plane Application
Application node
IP layer IP user plane IP control plane Application
IP IP Control IP IP Control Application control (e.g. SIP)
control plane interface
user plane (IP) interface
IP Backbone
Inter-domain interface
Application node
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– Shaping, Policing – Classification & Marking – Queuing and Scheduling
(service discipline)
– Congestion control and Queue management
– QoS mapping – Admission control – QoS routing – Resource reservation/allocation
– 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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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) » 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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Resource
ReSerVation Protocol (RSVP)
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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 – mean 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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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
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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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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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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 net work 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 net work service RAN phys. BS
data f low with indication of direction
TE Ext. Netw.
Local BS External BS
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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
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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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 statistical delay distribution
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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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Traffic 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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Traffic class Conversational class Streaming 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/unknow n Speech/unknow n Signalling Indication Yes/No (9)
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GGSN
SGSN RAN MS
C1 C2
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MS SGSN GGSN
HLR
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IP Bearer Layer Access Bearer Layer (eg. UMTS Bearer) Local UE SGSN Scope of PDP Context IP Bearer Service Remote Access Point Gn/Gp GGSN Remote Host GGSN UE Remote AP Remote Host Backbone IP Network
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Uplink Data Downlink Data
QoS in UMTS controlled by PDP context. DS DS PDP Flow PDP Flow
GGSN UE Remote AP Remote Host
The UE controls the QoS mechanisms from the UE. The UE may control the QoS mechanisms from received information. QoS on remote access link controlled by DS. QoS on remote access link controlled by DS or other means. QoS in UMTS controlled by PDP context selected by TFT. QoS in backbone network controlled by DS. DS marking performed by GGSN. QoS in backbone network controlled by DS. DS marking performed by RUE, or remarking by RAP. Application Layer (eg. SIP/SDP) Application Layer (eg. SIP/SDP)
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Uplink Data Downlink Data
DS DS
GGSN Remote AP Remote Host
The UE controls the QoS mechanisms from the UE. The UE may control the QoS mechanisms from received information. The UE performs DS edge functions. QoS on remote access link controlled by DS. QoS on remote access link controlled by DS or other means. QoS in UMTS controlled by PDP context. UE DS marking carried transparently. QoS in UMTS controlled by PDP context selected by TFT. Remote DS marking/GGSN remarking carried transparently. QoS in backbone network controlled by DS. DS marking performed by UE (or remarking by GGSN). QoS in backbone network controlled by DS. DS marking performed by RUE, or remarking by RAP. PDP Flow PDP Flow Application Layer (eg. SIP/SDP) Application Layer (eg. SIP/SDP)
UE
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RSVP Signalling RSVP Signalling QoS in backbone network controlled by DS. DS marking performed by UE, or by GGSN based on PDP context signalling. RSVP signalling carried transparently. QoS in UMTS controlled by PDP context. UE DS marking and RSVP signalling carried transparently.
Uplink Data Downlink Data
DS DS
GGSN UE Remote AP Remote Host
The UE controls the QoS mechanisms from the UE. The UE may control the QoS mechanisms from received information. The UE performs DS edge functions and RSVP QoS in UMTS controlled by PDP context selected by TFT. Remote DS marking/GGSN remarking and RSVP signalling carried transparently. QoS in backbone network controlled by DS. DS marking performed by RUE (or remarking by RAP). RSVP signalling carried transparently. QoS on remote access link controlled by either DS or RSVP. QoS on remote access link controlled by either DS or RSVP. PDP Flow PDP Flow Application Layer (eg. SIP/SDP) Application Layer (eg. SIP/SDP)
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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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– 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),
need to be managed admission control
1 1 ) 1 ( N N C C I C
RN W N R W I C R W W I R C E
b
1 1
R W N 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 i i
R
1
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<
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Listen before-talk, CSMA/CA based Station transmist when medium is free for time greater than DIFS Random backoff used when medium is busy
AP
DIFS
S2 S1
SIFS DATA RTS DIFS S2-bo DATA
DATA
DIFS
CTS SIFS SIFS ACK
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Contention-free frame transfer Point Coordinator (PC / AP) pools stations PIFS time used to enter Contention Free Period Data+Poll
DATA+ACK Beacon 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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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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( Enhanced Station )
STA STA STA STA STA
STA STA STA STA STA
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During Contention Period
» Controlled Contention
– STA may send traffic with different priorities – STAs may also request resources
» HC can send polled TXOPs during CP
During Contention Free Period
» HC polls STAs and gives a station the permission to access channel » Specifies time and maximum duration of each TXOP
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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 Virtual Collision
AC1 AC2 AC3 AC4
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ACK
BackOff[AC0] + Frame BackOff[AC1] + Frame BackOff[AC2] + Frame
AIFS[AC0] AIFS[AC1] AIFS[AC2]
BackOff[AC3] + Frame
AIFS[AC3]
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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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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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In TXOP, frames exchange sequences are separated by SIFS
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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 are the time slots
» Used to transmit bits according to the modulations/codes used
WLAN enables to send differentiated traffic
» By giving priority to realtime 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