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QoS Algorithms

This project explores QoS frameworks and algorithms, comparing their strengths and weaknesses. It offers guidance on commercial chips and products and identifies the challenges of designing them.

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QoS Algorithms

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  1. QoS Algorithms by Joyce Yung David Chan Tony Leung Chris Kwan CSIT 560 Internet Infrastructure: Switches and Routers

  2. Project Description • to survey all the frameworks and algorithms proposed for QoS • compare their strengths and weaknesses • give guidance into the commercial chips and products • pinpoint the difficulties of designing them CSIT 560 Internet Infrastructure: Switches and Routers

  3. What is QoS? • to provide guarantees on the performance of a network to deliver predictable results • characterized by availability, delay, jitter, through-put, packet loss rate • Service Level Agreement (SLA) • Traffic Conditioning Specification (TCS) CSIT 560 Internet Infrastructure: Switches and Routers

  4. Why bother? • Higher link capacity means cheaper bandwidth, which in turns lowers the margin of traditional best-effort IP service • New source of potential revenue for ISP • Businesses started to use public IP network for critical application systems (VoIP, Video Conferencing, VPN, VLAN), but firstly… • Quality of Service must be guaranteed CSIT 560 Internet Infrastructure: Switches and Routers

  5. QoS Frameworks • 2 major frameworks proposed by IETF • Integrated Services (IntServ) • Differentiated Services (DiffServ) CSIT 560 Internet Infrastructure: Switches and Routers

  6. IntServ • Defined in RFC 1633 by IETF in 1994 • Reserve resources (bandwidth & buffer) on the network for each individual flow • Use RSVP for per-flow signaling CSIT 560 Internet Infrastructure: Switches and Routers

  7. resource ReSerVation Protocol CSIT 560 Internet Infrastructure: Switches and Routers

  8. IntServ – Classes of Service • Guaranteed: quantitative, provide an assured level of bandwidth with a firm end-to-end delay bound, no queuing loss; intended for real-time apps (voice & video) • Controlled Load: qualitative, “the appearance of lightly loaded network” CSIT 560 Internet Infrastructure: Switches and Routers

  9. IntServ – Pros & Cons • Pros: Guarantee quality – resources have already been reserved right from the beginning • Cons: Not scalable for large networks like Internet – routers along the path must keep states for each individual flow CSIT 560 Internet Infrastructure: Switches and Routers

  10. DiffServ • Defined in RFC 2475 by IETF in 1998 • divide traffic into different classes (behavior aggregates) and give them differentiated treatment • Per-hop behavior (PHB) – the means by which a node allocates resources to BAs CSIT 560 Internet Infrastructure: Switches and Routers

  11. DiffServ • PHB groups • Expedited Forwarding (EF) for very high priority traffic • Assured Forwarding (AF) • 4 independent classes with 3 levels of drop precedence, implemented using at least 2 different loss probability (RED recommended) CSIT 560 Internet Infrastructure: Switches and Routers

  12. DiffServ: Mark the packet • DiffServ renames the ToS field in IPv4 header as differentiated services field (DS field) and uses it to carry the service requirements for each packet CSIT 560 Internet Infrastructure: Switches and Routers

  13. DiffServ: High Level View CSIT 560 Internet Infrastructure: Switches and Routers

  14. DiffServ Edge Router • Classifiers • Behavior Aggregated (BA): check DS field • Multiple Fields (MF): check multiple fields • Meters • measure the incoming traffic, paying attention to parameters in TCS, depending on applicable actions, excess traffic or non-conforming traffic is passed to marker, shaper or dropper CSIT 560 Internet Infrastructure: Switches and Routers

  15. DiffServ Edge Router • Markers • remarks the traffic with a different DSCP, so it will get a different PHB in the network • Shapers • delay the traffic so that to make it conforms to TCS • Droppers • simply discard the packets CSIT 560 Internet Infrastructure: Switches and Routers

  16. DiffServ: Pros & Cons • Pros • Scalable, as multi-flow classification, policing, shaping and marking is done at the edge routers, core routers simply forward packets based on DSCP, maintaining no per-flow state • Cons • Still cannot archive end-to-end QoS all by itself (no absolute guarantee) CSIT 560 Internet Infrastructure: Switches and Routers

  17. QoS Algorithms • Scheduling Algorithms • Decide which packet to send next • Discard Algorithms • Decide which packet to drop • Applying different algorithms to different class of packets CSIT 560 Internet Infrastructure: Switches and Routers

  18. Scheduling Algorithms • FIFO: First In First Out • Strict Priority: Low priority starvation? • Fair Queuing/Round Robin • WFQ: Weighted Fair Queuing: Popular • CBQ: Class-based queuing • And many more… all are pretty standard and well-known! CSIT 560 Internet Infrastructure: Switches and Routers

  19. Discard Algorithms • Drop-tail: simple • RED: Random Early Detection, avoiding the problem of TCP Global Synchronization • WRED: Weighted RED CSIT 560 Internet Infrastructure: Switches and Routers

  20. Multi-Protocol Labeled Switching (MPLS) • Provides connection oriented switching • Provides Traffic Engineering (enables pre-determined paths to specific destinations, explicit routing possible) • Could be combined with DiffServ to provide end-to-end QoS (RFC 3270) CSIT 560 Internet Infrastructure: Switches and Routers

  21. MPLS • (Short, fixed-length) labels are associated to streams of data (in the ingress edge MPLS router) • Packet belonging to those streams are forwarded along the LSP based on their labels (exact match, simple, no IP header examination in LSRs) • Moved the heavy processing to the edge of the network, core routers just need to perform label lookup, swap the label and decrement the TTL (scalable) CSIT 560 Internet Infrastructure: Switches and Routers

  22. MPLS: Label format • Depending on the link layer… • For ATM – use VPI,VCI in ATM headers • Otherwise – 32-bit Shim header (RFC 3032, added after the link layer header) • Stackable (allow routing hierarchy in the network) CSIT 560 Internet Infrastructure: Switches and Routers

  23. MPLS: Label Distribution • Label Distribution Protocol (LDP) • Discovery: announce and maintain the presence of an LSR • Session: carry LDP session parameters during session negotiation • Advertisement: establish new labels • Notification: carry advisory information, notify error conditions CSIT 560 Internet Infrastructure: Switches and Routers

  24. MPLS: Routing Mechanism • Packets enters into the MPLS network via an edge router which stores a number of Forward Equivalence Classes (FECs) • FEC defines which packets have to be forwarded in the same way • A label is assigned to the packet once it is classified into a FEC • The label is just meaningful locally to the edge router and its peer LSR • Packet is forwarded to the next LSR • LSR looks up the packet’s label, swap it with the label associated to this FEC that is meaningful to the next peer LSR • Continues until the packet reaches the edge egress router/destination CSIT 560 Internet Infrastructure: Switches and Routers

  25. Combining DiffServ & MPLS • RFC 3270 – Released in May 2002 • DiffServ + MPLS satisfies 2 necessary conditions for QoS: • DiffServ provides differentiated queue servicing treatment • MPLS forces applications flows into the paths with guaranteed bandwidth CSIT 560 Internet Infrastructure: Switches and Routers

  26. Combining DiffServ & MPLS • When a DiffServ packet arrives into a MPLS network, the ingress LSR examines the ToS field of the IP datagram to check the DSCP • The incoming traffic is then mapped to the appropriate LSP CSIT 560 Internet Infrastructure: Switches and Routers

  27. DiffServ + MPLS Mapping • EXP-Inferred-PSC LSP (E-LSP) • Multiple BAs map to 1 LSP • MPLS Exp field (3 bits) is used to specify PHB • Label-Only-Inferred-PSC LSP (L-LSP) • 1 BA map to 1 LSP • MPLS Exp field (3 bits) encodes drop precedence CSIT 560 Internet Infrastructure: Switches and Routers

  28. MPLS without DiffServ CSIT 560 Internet Infrastructure: Switches and Routers

  29. MPLS with DiffServ CSIT 560 Internet Infrastructure: Switches and Routers

  30. QoS Products - Motorola • Q-5 Traffic Management CoProcessor CSIT 560 Internet Infrastructure: Switches and Routers

  31. QoS Products - Motorola • Features CSIT 560 Internet Infrastructure: Switches and Routers

  32. QoS Products – Vitesse Pacemaker 3 CSIT 560 Internet Infrastructure: Switches and Routers

  33. QoS Challenges • Lack of standards, esp. inter-domain QoS • Not easy to justify (bigger pipes or QoS?) • Billing, Accounting CSIT 560 Internet Infrastructure: Switches and Routers

  34. Q&A CSIT 560 Internet Infrastructure: Switches and Routers

  35. YThank You YThank You CSIT 560 Internet Infrastructure: Switches and Routers

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