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802 QoS Architectures

802 QoS Architectures

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802 QoS Architectures

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  1. 802 QoS Architectures Osama Aboul-Magd Nortel

  2. 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 802 QoS Architectures

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

  4. 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) 802 QoS Architectures

  5. Request Message Response Message 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 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 802 QoS Architectures

  7. Differentiating Model • 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 PHB1 PHB2 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 802 QoS Architectures

  9. 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 802 QoS Architectures

  10. Link Possible Implementation E-EF Class-based or Weighted Fair Queuing (WFQ) Scheduler Ethernet Frame E-AF2x E-AF1x PHB = PSC + Drop Precedence DF E-DiffServ Classes 802 QoS Architectures

  11. 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. 802 QoS Architectures

  12. 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 AIFS[AC], and congestion window, CWmin[AC] and CWmax[AC] • One-to-one mapping between UP and AC Mapping to AC AC UP Designation 001 AC_BK BK Background BK 010 AC_BK Background 000 BE AC_BE Best Effort Transmit Queues 011 BE AC_BE Best Effort 100 Video CL AC_VI 101 VI AC_VI Video Per Queue Channel Access Function AC_V0 110 VO Voice AC_VO NC 111 Voice 802 QoS Architectures

  13. IEEE 802.11 EDCA AIFS[j] • 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. AIFS[i] Busy Medium Contention Window DIFS DIFS/AIFS PIFS Next Frame SIFS 802 QoS Architectures

  14. 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 Peak Data Rate Maximum Burst Size 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 802 QoS Architectures

  15. IEEE 802.11 TSPEC Procedure (Admission Control) QAP QSTA • 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 ADDTS Request (TSPEC) ADDTS Response (TSPEC, Schedule) Maximum TXOP Duration Schedule Info Service Interval Service Start Time Specification Interval Elements ID Length 802 QoS Architectures

  16. IEEE 802.15 QoS 802 QoS Architectures

  17. 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 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. 802 QoS Architectures

  19. IEEE 802.16 Scheduled Class Summary 802 QoS Architectures

  20. 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. 802 QoS Architectures

  21. 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. 802 QoS Architectures

  22. IP Network Inter-working Scenraio IEEE 802.3 IEEE 802.11 • QoS inter-working is needed • IEEE 802.11 <--> 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. 802 QoS Architectures