1. Osama Aboul-Magd Nortel
802 QoS Architectures
Osama Aboul-Magd
Nortel

2. Outline QoS Components and Architectures IEEE 802 QoS Models
Reservation model
Differentiating model
IEEE 802 QoS Models
IEEE QoS
IEEE QoS
IEEE QoS (no data is provided)
IEEE QoS
IEEE QoS
Inter-working Model
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802 QoS Architectures

3. QoS Components Policy Server Control Plane classification signaling
Routing
Admission
Control
Traffic
Conditioning
Outpout
I/F
Data
Path
Shaping
Scheduling
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802 QoS Architectures

4. QoS Architectures Reservation Model Differentiating Model
Require signaling for resource reservation
Require per session state
Usually includes defined services
Possible to support applications with stringent requirements
Examples include ATM QoS, IP Integrated Services (Intserv)
Differentiating Model
Different treatment of frames based on information carried in the frame header
Engineering is the main tool for assuring application performance
Examples includes IP Differentiated Services (Diffserv)
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802 QoS Architectures

5. Reservation Model
Request
Message
Response
Request message includes elements related to session identification, service class, and performance objectives
Response message indicates acceptance or rejection of the request
The signaling protocol can be a “soft” or a “hard” state protocol
Soft state requires refreshing the state from time to time
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802 QoS Architectures

6. Reservation Model Examples
IETF Integrated Service (IntServ)
Uses RSVP (soft state) for signaling
Two services are defined
Guaranteed Service (GS): provides mathematical upper bound on packet delays
Controlled Load Service (CLS): the service offered is the same as that seen by best-effort service on a lightly loaded netwok
ATM Forum Traffic Management
Uses PNNI (hard state) for signaling and routing
A number of service categories are defined. Among them:
Constant Bit Rate (CBR)
Variable Bit Rate (VBR)  both real-time and non-real-time
Unspecified Bit Rate (UBR) similar to best effort service
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802 QoS Architectures

7. Differentiating Model
PHB1
PHB2
No end-to-end signaling is required
Only edge switches need to maintain per flow state ad possibly perform policing and/or shaping
Core switches need only to forward packets according to their per hop behavior (PHB) information in the frame header.
No per-flow state allows scalability to a large number of flows
End-to-end services are constructed by combing edge rules and nodal behavior
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802 QoS Architectures

8. Differentiating Model Examples
IP Differentiated Service (Diffserv)
PHB information is carried in the IP header (ToS byte in IPv4 or class field in IPv6)
A number of PHBs were specified and standardized by the IETF
Expedited Forward (EF): ensure a limit on the time a packet stays in the queue
Assured forwarding (AF):
Class Selector (CS): introduced to support legacy routers. Introduces 8 straight priority levels
Ethernet (802.1) User Priority bits
Introduces 8 straight priority levels
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802 QoS Architectures

9. IEEE QoS
Follows a differentiated model with no resource reservation
3 User priority bits were introduced in 1999(??) as part of 802.1Q Tag.
Provides up to 8 straight priority levels similar to the differentiated service class selector PHB.
Recently augmented (802.1ad) to support drop precedence in a number of possible ways
7x1, 6x2, and 5x3 (five transmission classes with 3 discard levels)
Brings QoS very close to IP differentiated services
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802 QoS Architectures

10. Possible Implementation
E-EF
Class-based or Weighted Fair Queuing (WFQ) Scheduler
Ethernet Frame
E-AF2x
E-AF1x
Link
PHB = PSC + Drop Precedence DF
P-bits
PHB
PSC
Drop Precedence
111 EF
Low
110
AF41
AF4
101
AF42
High
AF31
AF3
011
AF32
010
AF21
AF2
001
AF22
000 DF
E-DiffServ Classes
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802 QoS Architectures

11. IEEE (WLAN) QoS
Supports both differentiating and reservation models.
EDCA (Enhanced Distributed Channel Access) supports four levels (Access Categories) of differentiated access
HCCA (HCF Controlled Channel Access) is centrally controlled and allocates TXOP (Transmission Opportunities) using polling and based on some scheduler.
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802 QoS Architectures

12. IEEE 802.11 Access Categories (AC)
IEEE defines 4 Access Categories (AC) for use with EDCA.
The priority of an AC to access the WM is determined by the Arbitration Inter-frame Spacing AIFS[AC], and congestion window, CWmin[AC] and CWmax[AC]
One-to-one mapping between UP and AC
Mapping to AC UP
Designation AC
001 BK
AC_BK
Background
010 BK
AC_BK
Background
000 BE
AC_BE
Best Effort
Transmit
Queues
011 BE
AC_BE
Best Effort
100 CL
AC_VI
Video
101 VI
AC_VI
Video
Per Queue
Channel Access
Function
110 VO
AC_V0
Voice
111 NC
AC_VO
Voice
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802 QoS Architectures

13. IEEE EDCA
AIFS[j]
AIFS[i]
Busy
Medium
DIFS
Contention Window
DIFS/AIFS
PIFS
Next Frame
SIFS
Each QoS station has a separate channel access function per AC.
Access rules are similar to those of DCF (CSMA/CA)
The TXOP duration is advertised by the AP in the EDCA Parameter Set IE.
The QoS station ensures that its transmission does not exceed the TXOP limit
Fragmentation may be employed
A “continuation” TXOP is granted if there is a frame available for transmission that fits in the remaining TXOP duration
A “continuation” TXOP is granted to the same AC that initially won the TXOP.
Internal collisions are handled as if they were external collision.
The higher priority AC gains access to the WM.
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802 QoS Architectures

14. IEEE HCCA
HCCA is a polling scheme that is centrally controlled by Hybrid Coordinator (HC)
HC resides in the AP.
TXOP are assigned by the HC to a QSTA at a regular interval and for a specified duration
TXOP duration and frequency are determined based on Traffic Specifications (TSPEC IE)
Traffic Streams (TS) are locally identified using TSID (part of TID)
HC may generate CFP. However it is mandatory for HC to use CFP for QoS data transfers
Controlled access phase (CAP) cab be initiated at anytime by the HC
Element ID
Length TS
INFO
Nominal
MSDU
Size
Maximum
MSDU
Size
Minimum
Service
Interval
Maximum
Service
Interval
Service
Start
Time
Minimum
Data
Rate
Peak
Data
Rate
Maximum
Burst
Size
Inactivity
Interval
Suspension
Interval
Mean
Data
Rate
Delay
Bound
Minimum
Physical
Rate
Surplus
Bandwidth
Allowance
Medium
Time
Traffic
Type
Access
Policy
TSInfo
Ack Policy
TSID
Direction
User
Priority
Aggregation
APSD
Schedule
Rsvd
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802 QoS Architectures

15. IEEE 802.11 TSPEC Procedure (Admission Control)
QSTA
QAP
ADDTS Request (TSPEC)
ADDTS Response (TSPEC, Schedule)
Schedule
Info
Service
Interval
Maximum
TXOP
Duration
Elements ID
Service
Start Time
Specification
Interval
Length
The AP uses the traffic parameters to perform admission control on the incoming request
Service Interval is the time between two successive service periods (SP)
Directly related to bandwidth reserved
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802 QoS Architectures

16. IEEE QoS
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17. IEEE QoS
DownLink
UpLink
Base Sstation
(BS)
Subscriber Station
(SS)
IEEE MAC is connection oriented. Each connection, upon establishment, subscribes to one of the scheduled services
Resource allocation, admission, and scheduling is controlled by the base station (BS)- centralized control architecture
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802 QoS Architectures

18. IEEE 802.16 QoS Scheduled services includes:
Unsolicited Grant Services (UGS): supports services that generates fixed units of data periodically (CBR service).
Real-time Polling Service (rtPS): supports real-time data streams with variable size data such as VoIP and video
Extended rtPS: supports real-time applications such as voice with silence suppresion.
Non-real-time Polling Service (nrtPS): supports delay tolerant data streams
Best Effort: supports data stream with no requirements on minimum service levels.
Traffic parameters include: maximum sustained traffic rate, minimum reserved traffic rate, maximum latency, and tolerated jitter.
Scheduled services and traffic parameters are similar to those defined for ATM.
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802 QoS Architectures

19. IEEE 802.16 Scheduled Class Summary
Possible Applications
Expected Application Traffic
Traffic Paramters
UGS
CBR Voice (no silence submission), circuit emulation
Fixed-size packets at fixed intervals
Sustained maximum traffic rate
rtPS
MPEG Video
Variable-size packets at fixed intervals
Maximum sustained traffic rate, minimum reserved traffic rate
Extended rtPS
Voice with silence suppression
Variable-size packets at fixed interval (I don’t think this is correct)
Same as rtPS
nrtPS
Data application with minimum rate requirements, e.g. FTP
Variable-size packets, variable intervals BE
Data applications with no minimum rate requirements
Who cares
Maximum sustained traffic rate
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802 QoS Architectures

20. IEEE QoS
IEEE (RPR) defines three traffic classes, class A, class B, and class C.
Class A is divided into classes A0 and A1
Class B is divided into B-CIR and B-EIR.
Class C is best effort service
Bandwidth allocated for A0 traffic is called reserved and can only be used by the station holding the reservation
Bandwidth allocated for A1 and B-CIR traffic is called reclaimable and may be used for other transmissions
Bandwidth reservation requests are broadcast on the ring using topology messages
Each station calculates how much bandwidth it can reserve.
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802 QoS Architectures

21. Some Remarks
IEEE 802 models are not homogeneous and follows different architectures
IEEE and IEEE (EDCA) follows mainly a differentiating model
IEEE (HCCA), IEEE , and IEEE follows reservation model with defined service classes for .16 and .17
QoS inter-working between different IEEE 802 technologies could follow rules established for other inter-working, e.g. between ATM service categories and IP differentiated services.
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802 QoS Architectures

22. Inter-working Scenraio
IEEE 802.3
IP Network
IEEE
QoS inter-working is needed
IEEE <--> IEEE (within 802 scope)
IEEE and IP (out of scope)
Inter-working between IEEE (EDCA) and IEEE is straightforward
EDCA utilizes the same UP bits as in IEEE 802.1
Other inter-working scenarios may be more interesting, e.g. IEEE (HCCA) to IEEE
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802 QoS Architectures