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IP Quality of Service

IP Quality of Service. Objectives. Upon completing this module, you will be able to: Describe the need for IP QoS Describe the Integrated Services model Describe the Differentiated Services model

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IP Quality of Service

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  1. IP Quality of Service

  2. Objectives • Upon completing this module, you will be able to: • Describe the need for IP QoS • Describe the Integrated Services model • Describe the Differentiated Services model • Describe the building blocks of IP QoS mechanisms (classification, marking, metering, policing, shaping, dropping, forwarding, queuing) Inner Mongolia University

  3. Introduction

  4. Objectives • Upon completing this lesson, you will be able to: • Describe different types of applications and services that have special resource requirements • List the network components that affect the throughput, delay, and jitter in IP networks • List the benefits of deploying QoS mechanisms in IP networks • Describe typical enterprise and service provider networks and their QoS-related requirements Inner Mongolia University

  5. Why IP QoS? • Application X is slow. • Video broadcast occasionally stalls. • Phone calls over IP are no better than over satellite. • Phone calls can have very bad voice quality. • ATMs (the money-dispensing type) are nonresponsive. Inner Mongolia University

  6. Because ... • Application X is slow! (not enough bandwidth) • Video broadcast occasionally stalls! (delay temporarily increases – jitter) • Phone calls over IP are no better than over satellite! (too much delay) • Phone calls can have very bad voice quality! (too many phone calls – admission control) • ATMs (the money-dispensing type) are nonresponsive! (too many drops) Inner Mongolia University

  7. What Causes ... • Lack of bandwidth?: Multiple flows are contesting for a limited amount of bandwidth. • Too much delay?: Packets have to traverse many network devices and links. • Variable delay?: Sometimes there is a lot of other traffic, which results in more delay. • Drops?: Packets have to be dropped when a link is congested. Inner Mongolia University

  8. Maximum available bandwidth equals the bandwidth of the weakest link. Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application. Available Bandwidth IP IP IP IP 512 kbps 256 kbps 10 Mbps 100 Mbps BWmax = min(10M, 256k, 512k, 100M)=256kbps BWavail = BWmax /Flows Inner Mongolia University

  9. End-to-End Delay • End-to-end delay equals a sum of all propagation, processing, and queuing delays in the path. • Propagation delay is fixed; processing and queuing delays are unpredictable in best-effort networks. IP IP IP IP Propagation Delay (P3) Propagation Delay (P1) Propagation Delay (P2) Propagation Delay (P4) Processing and Queuing Delay (Q1) Processing and Queuing Delay (Q2) Processing and Queuing Delay(Q3) Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms Inner Mongolia University

  10. Forwarding Queuing Delay Processing Delay Propagation Delay Processing, Queuing, and Propagation Delay • Processing delay is the time it takes for a router to take the packet from an input interface and put it into the output queue of the output interface. • Queuing delay is the time a packet resides in the output queue of a router. • Propagation or serialization delay is the time it takes to transmit a packet. IP IP IP IP Bandwidth Inner Mongolia University

  11. Forwarding Packet Loss • Tail-drops occur when the output queue is full. These are the most common drops which happen when a link is congested. • There are also many other types of drops (input queue drop, ignore, overrun, no buffer, etc), which are not as common and which may require a hardware upgrade. These drops are usually a result of router congestion. IP IP IP IP IP Tail-drop Inner Mongolia University

  12. Upgrade the link—the best solution but also the most expensive. TCP Header Compression RTP Header Compression cTCP Data Compress the Headers Fancy Queuing Compress the Payload Priority Queuing (PQ) Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queing (CBWFQ) Stacker Predictor Compressed Packet • Take some bandwidth from less important applications. • Compress the payload of Layer2 frames. • Compress the header of IP packets. How to Increase Available Bandwidth? FIFO queuing IP TCP Data Inner Mongolia University

  13. TCP Header Compression RTP Header Compression cRTP Data Compress the Headers Fancy Queuing Compress the Payload Priority Queuing (PQ) Custom Queuing (CQ) Strict Priority MDRR IP RTP Prioritization Class-Based Low-Latency Queuing (CBLLQ) Stacker Predictor Compressed Packet • Forward the important packets first. • Compress the payload of Layer-2 frames (it takes time). • Compress the header of IP packets. How to Reduce Delay? • Upgrade the link—the best solution but also the most expensive. FIFO queuing IP UDP RTP Data Inner Mongolia University

  14. Weighted Random Early Detection (WRED) Dropper Fancy Queuing Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queuing (CBWFQ) • Guarantee enough bandwidth to sensitive packets. • Prevent congestion by randomly dropping less important packets before congestion occurs. How to Prevent Packet Loss? • Upgrade the link—the best solution but also the most expensive. FIFO queuing IP Data Inner Mongolia University

  15. Which Applications Have Which QoS Requirements? • Enterprise networks are typically focused on providing QoS to applications. Throughput Delay Loss Jitter Interactive (e.g., Telnet) Not Important Low Low Low Batch (e.g., FTP) Not Important Not Important High Low Fragile (e.g,. SNA) Not Important Low Low None Low and Predictable Voice Low Low Low Low and Predictable Video High Low Low Inner Mongolia University

  16. Which Services Can Be Implemented in a Network? • Service provider networks typically offer services based on source and destination addresses. Throughput Delay Loss Jitter Gold Guaranteed Low Low Low No Guarantee No Guarantee No Guarantee Silver Guaranteed GuaranteedLimited No Guarantee No Guarantee No Guarantee Bronze No Guarantee No Guarantee No Guarantee No Guarantee Best Effort Inner Mongolia University

  17. How Can QoS Be Applied? • Best effort—no QoS is applied to packets (default behavior) • Integrated Services model—applications signal to the network that they require special QoS • Differentiated Services model—the network recognizes classes that require special QoS Inner Mongolia University

  18. Summary • Upon completing this lesson, you should be able to: • Describe different types of applications and services that have special resource requirements • List the network components that affect the throughput, delay, and jitter in IP networks • List the benefits of deploying QoS mechanisms in IP networks • Describe typical enterprise and service provider networks and their QoS-related requirements Inner Mongolia University

  19. Review Questions • What are the relevant parameters that define quality of service? • What can be done to give more bandwidth to an application? • What can be done to reduce delay? • What can be done to prevent packet loss? • Name the two QoS models. Inner Mongolia University

  20. Integrated Services Model

  21. Objectives • Upon completing this lesson, you will be able to: • Describe the IntServ model • List the key benefits and drawbacks of the IntServ model • List some implementations that are based on the IntServ model • Describe the need for Common Open Policy Service (COPS) Inner Mongolia University

  22. Integrated Services • The Internet was initially basedon a best-effortpacket delivery service. • Today's Internet carries many more different applications than 20 years ago. • Some applications have special bandwidth and delay requirements. • The Integrated Services model (RFC1633) was introduced to guarantee predictable network behavior for these applications. Inner Mongolia University

  23. IntServ Building Blocks • Resource reservation is used to identify an application (flow) and signal if there are enough available resources for it. • Admission control is used to determine if the application (flow) can get the requested resources. Local Admission Control Remote Admission Control Local Admission Control Policy Enforcement Point (PEP) request request request request reserve reserve reserve reserve reply request Policy Decision Point (PDP) Inner Mongolia University

  24. Reservation and Admission Protocols • TheResourceReservation Protocol (RSVP) was developed to communicate resource needs between hosts and network devices (RFCs 2205 to 2215). • Common Open Policy Service (COPS) was developed to offload admission control to a central policy server (RFCs 2748 to 2753). Inner Mongolia University

  25. RSVP-Enabled Applications • RSVP is typically used by applications carrying voice or video over IP networks (initiated by a host). • RSVP with extensions is also used by MPLS Traffic Engineering to establish MPLS/TE tunnels (initiated by a router). Inner Mongolia University

  26. IntServ Implementation Options RSVP 1)Explicit RSVP on each network node Class of Service or Best Effort 2)RSVP ‘pass-through’ and CoS transport - map RSVP to CoS at network edge - pass-through RSVP request to egress 3)RSVP at network edges and ‘pass-through’ with - best-effort forwarding in the core (if there is enough bandwidth in the core) Inner Mongolia University

  27. Explicit RSVP TransportIntServ End-to-End RSVP • All Routers • WFQ applied per flowbased on RSVP requests Inner Mongolia University

  28. RSVP RSVP RSVP Pass-ThroughIntServ - DiffServ Integration Precedence Classifier WRED • Egress Router • RSVP protocolsent on to destination • WFQ applied to manage egress flow Premium Standard • Ingress Router • RSVP protocol • Mapped to classes • Passed through to egress • Backbone • WRED applied based on class Inner Mongolia University

  29. Benefits and Drawbacks of the IntServ Model • RSVP benefits: • Explicit resource admission control (end-to-end) • Per-request policy admission control (authorization object, policy object) • Signaling of dynamic port numbers (for example, H.323) • RSVP drawbacks: • Continuous signaling due to stateless architecture • Not scalable Inner Mongolia University

  30. Common Open Policy Service • Common Open Policy Service (COPS) provides the following benefits when used with RSVP: • Centralized management of services • Centralized admission control and authorization of RSVP flows • RSVP-based QoS solutions become more scalable Inner Mongolia University

  31. Summary • Upon completing this lesson, you should be able to: • Describe the IntServ model • List the key benefits and drawbacks of the IntServ model • List some implementations that are based on the IntServ model • Describe the need for Common Open Policy Service (COPS) Inner Mongolia University

  32. Review Questions • What are the two building blocks of the Integrated Services model? • Which protocol is used to signal QoS requirements to the network? • Which protocol is used to offload admission control to a central policy server? Inner Mongolia University

  33. Differentiated Services Model

  34. Objectives • Upon completing this lesson, you will be able to: • Describe the DiffServ model • List the key benefits of the DiffServ model compared to the IntServ model • Describe the purpose of the DS field in IP headers • Describe the interoperability between DSCP-based and IP-Precedence-based devices in a network • Describe the expedited forwarding service • Describe the assured forwarding service Inner Mongolia University

  35. Differentiated Services Model • TheDifferentiated Services model describes services associated with traffic classes. • Complex traffic classification and conditioning are performed at network edge, resulting in a per-packet Differentiated Services Code Point (DSCP). • No per-flow/per-application state exists in the core. • The core performs only simple “per-hop behaviors” on traffic aggregates. • The goal is scalability. Inner Mongolia University

  36. Additional DiffServ Requirements • Wide variety of services and provisioning policies • Decouple service and application in use • No application modification • No hop-by-hop signaling • Interoperability with non-DS-compliant nodes • Incremental deployment Inner Mongolia University

  37. DiffServ Elements • The servicedefines QoS requirements and guarantees provided to a traffic aggregate. • The conditioning functions and per-hop behaviorsare used to realize services. • The DS field value (DSCP) is used to mark packets to select a per-hop behavior. • Per-hop Behavior (PHB)is implemented using a particular QoS mechanism. • Provisioningis used to allocate resources to traffic classes. Inner Mongolia University

  38. Why Is Provisioning Important? • QoS does not create bandwidth! • QoS manages bandwidth usage among multiple classes. • QoS gives better service to a well-provisioned class with respect to another class. Inner Mongolia University

  39. Topological Terminology DS Interior Node DS Egress Boundary Node DS Ingress Boundary Node Boundary Link UpstreamDS Domain DownstreamDS Domain DS Region Traffic Stream = set of flows Behavior Aggregate (flows with the same DSCP) Inner Mongolia University

  40. Traffic Terminology • Flow: a single instance of an application-to-application flow of packets. A flow is identified by source address, source port, destination address, destination port, and protocol ID. • Traffic stream: an administratively significant set of one or more flows that traverse a path segment. A traffic stream may consist of a set of active flows that are selected by a particular classifier. • Traffic profile: a description of the temporal properties of a traffic stream, such as average and peak rate and burst size. Inner Mongolia University

  41. Traffic Terminology (cont.) • A behavior aggregate (BA) is a collection of packets with the same DSCP crossing a link in a particular direction. • Per-hop behavior (queuing in a node) is externally observable forwarding behavior applied at a DiffServ-compliant node to a DiffServ behavior aggregate. • A PHB Mechanism is a specific algorithm or operation (e.g., queuing discipline) that is implemented in a node to realize a set of one or more per-hop behaviors. Inner Mongolia University

  42. Packet Header Terminology • DSCP: a specific value of the DSCP portion of the DS field. The DSCP is used to select a PHB (Per-Hop Behavior; forwarding and queuing method) • DS field: the IPv4 header ToS octet or the IPv6 traffic class octet when interpreted in conformance with the definition given inRFC2474. The bits of the DSCP field encode the DSCP, while the remaining bits are currently unused. DSCP Field: 6 bits Unused: 2 bits Former ToS Byte = NewDS Field Inner Mongolia University

  43. DSCP Encoding • Three pools: • “xxxxx0” Standard Action • “xxxx11” Experimental/Local Use • “xxxx01” EXP/LU (possible std action) • Default DSCP: “000000” • Default PHB: FIFO, tail-drop Inner Mongolia University

  44. DSCP Usage • DSCP selects per-hop behavior (PHB) throughout the network: • Default PHB • Class selector (IP Precedence) PHB • Expedited forwarding PHB • Assured forwarding PHB Inner Mongolia University

  45. Backward Compatibility Using the Class Selector • Non-DS-compliant node: node that does not interpret the DSCP correctly or that does not support all the standardized PHBs • Legacy node: a non-DS-compliant node that interprets IPv4 ToS as defined by RFC791 and RFC1812 • DSCP: backward compatible with IP Precedence (class selector code point, RFC 1812) but not with the ToS byte definition from RFC 791 (“DTR” bits) Inner Mongolia University

  46. Class Selector Code Point • Compatibility with current IP Precedence usage (RFC 1812) • “xxx000” DSCPs • Differentiates Probability of Timely Forwarding (PTF) • PTF(xyz000) >= PTF(abc000) ifxyz > abc Inner Mongolia University

  47. Expedited Forwarding • Expedited forwarding PHB: • Ensures a minimum departure rate • Guarantees bandwidth—the class is guaranteed an amount of bandwidth with prioritized forwarding • Polices bandwidth—the class is not allowed to exceed the guaranteed amount (excess traffic is dropped) • DSCP value: “101110”; looks like IP Precedence 5 to non-DS-compliant devices Inner Mongolia University

  48. IOS Expedited Forwarding PHB Implementations • Priority queuing • IP RTP Prioritization • Class-based low-latency queuing (CBLLQ) • Strict priority queuing within modified deficit round robin (MDRR) on GSRs Inner Mongolia University

  49. Assured Forwarding • Assured forwarding PHB: • Guarantees bandwidth • Allows access to extra bandwidth if available • Four standard classes (af1, af2, af3, and af4) • DSCP value range: “aaadd0” where “aaa” is a binary value of the class and “dd” is the drop probability Inner Mongolia University

  50. Assured Forwarding Encoding • Each Assured Forwarding class uses three DSCP values • Each Assured Forwarding class is independently forwarded with its guaranteed bandwidth • Differentiated RED is used within each class to prevent congestion within the class Inner Mongolia University

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