49
WNP-MPR-qos 1 Wireless Networks and Protocols MAP-Tele Manuel P. Ricardo Faculdade de Engenharia da Universidade do Porto
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
» Research issues
…
WNP-MPR-qos 3
Review of QoS basic concepts
QoS in wireless networks
» 3GPP-QoS
» IEEE-wireless-QoS
WNP-MPR-qos 4
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
WNP-MPR-qos 5
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
WNP-MPR-qos 6
QoS
QoS is an end-to-end problem, handled at several communication layers
Physical
Network
Transport
Data link
Application
Mo
bil
ity
Sec
uri
ty
Mu
ltic
ast
Qu
ali
ty o
f S
ervi
ce
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
WNP-MPR-qos 7
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
WNP-MPR-qos 8
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)
» 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
WNP-MPR-qos 9
IntServ - RSVP
Resource
ReSerVation Protocol (RSVP)
WNP-MPR-qos 10
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 – 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
WNP-MPR-qos 11
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
WNP-MPR-qos 12
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| DSCP | CU |
+---+---+---+---+---+---+---+---+
DSCP: differentiated services codepoint
CU: currently unused
DiffServ – DSCP field
WNP-MPR-qos 13
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
WNP-MPR-qos 14
DiffServ - Bandwidth broker
WNP-MPR-qos 15
QoS in UMTS
WNP-MPR-qos 16
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
WNP-MPR-qos 17
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
WNP-MPR-qos 18
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
WNP-MPR-qos 19
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
WNP-MPR-qos 20
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 statistical delay distribution
WNP-MPR-qos 21
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
WNP-MPR-qos 22
QoS attributes versus traffic classes
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
WNP-MPR-qos 23
UMTS Bearer Service Attributes (Rel. 7!)
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)
WNP-MPR-qos 24
PDP Context Activation Procedure for Iu mode
GGSN
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
WNP-MPR-qos 25
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
WNP-MPR-qos 26
Protocol architecture of NAS supporting PS
mode, Terminal Equipment side
WNP-MPR-qos 27
Primitives and Parameters at
SMREG-SAP - MS side
WNP-MPR-qos 28
UMTS QoS Conceptual Models
IP BearerLayer
Access
Bearer
Layer
(eg. UMTS
Bearer)
Local
UE
SGSN
Scope of PDP Context
IP Bearer Service
RemoteAccess
Point
Gn/Gp
GGSN
Remote
Host
GGSNUE Remote
AP
Remote
Host
Backbone IPNetwork
WNP-MPR-qos 29
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 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)
WNP-MPR-qos 30
Local UE supports DiffServ (DS)
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
WNP-MPR-qos 31
Local UE supports RSVP signalling and DiffServ
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
GGSNUE 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)
WNP-MPR-qos 32
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?
WNP-MPR-qos 33
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
1
1
)1(
NNC
C
I
C
RN
W
NR
W
I
C
R
W
WI
RC
E
Ib
1
1
0
IEb
R
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
i
iR1
WNP-MPR-qos 34
Load Factor, Uplink
(from Holma & Toskala, 3rd edition)
WNP-MPR-qos 35
Load Factor, Uplink
(from Holma & Toskala, 3rd edition)
WNP-MPR-qos 36
Admission Control Based on Throughput
<
WNP-MPR-qos 37
WLAN- QoS
WNP-MPR-qos 38
DCF - Distributed Coordination Function
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
DATARTS
DIFS S2-bo
DATA
- Packet arrivalDATA
- Transmission of DATA DIFS - Time interval DIFS
CTS
SIFS
SIFS
ACK
WNP-MPR-qos 39
PCF - Point Coordination Function
Contention-free frame transfer
Point Coordinator (PC / AP) pools stations
PIFS time used to enter Contention Free Period
Data+Poll
DATA+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
WNP-MPR-qos 40
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)
WNP-MPR-qos 41
PC
BSS (Basic Service Set) QBSS (Basic Service Set for QoS)
( Enhanced Station )
EDCA HCCADCF PCF
HCF- Hybrid Coordination Function
STASTA
STA
STA
STA
HC
STASTA
STA
STA
STA
WNP-MPR-qos 42
HCF - Hybrid Coordination Function
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
WNP-MPR-qos 43
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
Virtual Collision
AC1 AC2 AC3 AC4
WNP-MPR-qos 44
ACK BackOff[AC0] + Frame
BackOff[AC1] + FrameBackOff[AC2] + Frame
AIFS[AC0]
AIFS[AC1]
AIFS[AC2]
BackOff[AC3] + Frame
AIFS[AC3]
Access Category AIFS
WNP-MPR-qos 45
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.
WNP-MPR-qos 46
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
WNP-MPR-qos 47
Transmission Opportunity (TXOP) (cont.)
In TXOP, frames exchange sequences are separated by SIFS
WNP-MPR-qos 48
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
WNP-MPR-qos 49
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 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
