802 QoS Architectures

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802 QoS Architectures

• Osama Aboul-Magd
• Nortel

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Outline

• QoS Components and Architectures
• Reservation model
• Differentiating model
• IEEE 802 QoS Models
• IEEE 802.1 QoS
• IEEE 802.11 QoS
• IEEE 802.15 QoS (no data is provided)
• IEEE 802.16 QoS
• IEEE 802.17 QoS
• Inter-working Model

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

• Reservation 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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Reservation Model

• 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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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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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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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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IEEE 802.1 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 802.1 QoS very close to IP differentiated
  services

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Possible Implementation
E-EF
Class-based or Weighted Fair Queuing (WFQ)
Scheduler
Ethernet Frame
E-AF2x
E-AF1x
PHB PSC Drop Precedence
DF
P-bits PHB PSC Drop Precedence
111 EF EF Low
110 AF41 AF4 Low
101 AF42 AF4 High
110 AF31 AF3 Low
011 AF32 AF3 High
010 AF21 AF2 Low
001 AF22 AF2 High
000 DF DF High
E-DiffServ Classes
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IEEE 802.11 (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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IEEE 802.11 Access Categories (AC)

• IEEE 802.11 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
  AIFSAC, and congestion window, CWminAC and
  CWmaxAC
• One-to-one mapping between UP and AC

Mapping to AC
AC
UP
Designation
001
BK
AC_BK
Background
BK
010
AC_BK
Background
000
BE
AC_BE
Best Effort
Transmit Queues
011
BE
AC_BE
Best Effort
100
CL
Video
AC_VI
101
VI
AC_VI
Video
Per Queue Channel Access Function
AC_V0
110
VO
Voice
AC_VO
NC
111
Voice
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IEEE 802.11 EDCA
AIFSj
AIFSi
Busy Medium
Contention Window
DIFS
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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IEEE 802.11 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

Service Start Time
Minimum Data Rate
Minimum Service Interval
Maximum Burst Size
Peak Data Rate
Mean Data Rate
Delay Bound
Nominal MSDU Size
Maximum MSDU Size
Maximum Service Interval
Suspension Interval
TS INFO
Element ID
Inactivity Interval
Length
Minimum Physical Rate
Surplus Bandwidth Allowance
Medium Time
TSInfo Ack Policy
Access Policy
User Priority
Traffic Type
Rsvd
Direction
Schedule
APSD
TSID
Aggregation
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IEEE 802.11 TSPEC Procedure (Admission Control)
QAP
QSTA
ADDTS Request (TSPEC)
ADDTS Response (TSPEC, Schedule)
Maximum TXOP Duration
Schedule Info
Service Interval
Service Start Time
Specification Interval
Elements ID
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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IEEE 802.15 QoS
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IEEE 802.16 QoS
DownLink
UpLink
Base Sstation (BS)
Subscriber Station (SS)

• IEEE 802.16 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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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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IEEE 802.16 Scheduled Class Summary
Class 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 dont think this is correct) Same as rtPS
nrtPS Data application with minimum rate requirements, e.g. FTP Variable-size packets, variable intervals Same as rtPS
BE Data applications with no minimum rate requirements Who cares Maximum sustained traffic rate
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IEEE 802.17 QoS

• IEEE 802.17 (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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Some Remarks

• IEEE 802 models are not homogeneous and follows
  different architectures
• IEEE 802.1 and IEEE 802.11 (EDCA) follows mainly
  a differentiating model
• IEEE 802.11 (HCCA), IEEE 802.16, and IEEE 802.17
  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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Inter-working Scenraio
IEEE 802.3
IEEE 802.11

• QoS inter-working is needed
• IEEE 802.11 lt--gt IEEE 802.1 (within 802 scope)
• IEEE 802.1 and IP (out of scope)
• Inter-working between IEEE 802.11 (EDCA) and IEEE
  802.1 is straightforward
• EDCA utilizes the same UP bits as in IEEE 802.1
• Other inter-working scenarios may be more
  interesting, e.g. IEEE 802.11 (HCCA) to IEEE
  802.11.