1. © 2001, Cisco Systems, Inc. Introduction

2. © 2001, Cisco Systems, Inc. QoS v1.0—1-2 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) List the IP QoS mechanisms available in Cisco IOS Describe what QoS features are supported by different IP QoS mechanisms

3. Introduction to IP Quality of Service QOS v1.0—1-3 © 2001, Cisco Systems, Inc.

4. QoS v1.0—1-4 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 Name some QoS mechanisms available in Cisco IOS Describe typical enterprise and service provider networks and their QoS-related requirements

5. © 2001, Cisco Systems, Inc. QoS v1.0—1-5 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.

6. © 2001, Cisco Systems, Inc. QoS v1.0—1-6 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)

7. © 2001, Cisco Systems, Inc. QoS v1.0—1-7 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.

8. © 2001, Cisco Systems, Inc. QoS v1.0—1-8 Available Bandwidth 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. IP 10 Mbps 256 kbps 512 kbps 100 Mbps BW max = min(10M, 256k, 512k, 100M)=256 kbps BW avail = BW max /Flows

9. © 2001, Cisco Systems, Inc. QoS v1.0—1-9 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 Propagation Delay (P1) Processing and Queuing Delay (Q1) IP Propagation Delay (P2) Processing and Queuing Delay (Q2) Propagation Delay (P3) Processing and Queuing Delay (Q3) Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms Propagation Delay (P4)

10. © 2001, Cisco Systems, Inc. QoS v1.0—1-10 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 Forwarding Processing Delay Queuing Delay Propagation Delay Bandwidth

11. © 2001, Cisco Systems, Inc. QoS v1.0—1-11 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 Forwarding IP Tail-drop

12. © 2001, Cisco Systems, Inc. QoS v1.0—1-12 How to Increase Available Bandwidth? Upgrade the link—the best solution but also the most expensive. FIFO queuing IPTCPData Fancy Queuing Take some bandwidth from less important applications. Compress the Headers cTCPData Compress the header of IP packets. Compress the Payload Compressed Packet Compress the payload of Layer 2 frames. Priority Queuing (PQ) Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queing (CBWFQ) Priority Queuing (PQ) Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queing (CBWFQ) Stacker Predictor Stacker Predictor TCP Header Compression RTP Header Compression TCP Header Compression RTP Header Compression

13. © 2001, Cisco Systems, Inc. QoS v1.0—1-13 How to Reduce Delay? Upgrade the link—the best solution but also the most expensive. FIFO queuing IPUDPData Fancy Queuing Forward the important packets first. Compress the Headers cRTPData Compress the header of IP packets. RTP Compress the Payload Compressed Packet Compress the payload of Layer-2 frames (it takes time). Priority Queuing (PQ) Custom Queuing (CQ) Strict Priority MDRR IP RTP Prioritization Class-Based Low-Latency Queuing (CBLLQ) Priority Queuing (PQ) Custom Queuing (CQ) Strict Priority MDRR IP RTP Prioritization Class-Based Low-Latency Queuing (CBLLQ) Stacker Predictor Stacker Predictor TCP Header Compression RTP Header Compression TCP Header Compression RTP Header Compression

14. © 2001, Cisco Systems, Inc. QoS v1.0—1-14 How to Prevent Packet Loss? Upgrade the link—the best solution but also the most expensive. FIFO queuing IP Data Fancy Queuing Guarantee enough bandwidth to sensitive packets. Dropper Prevent congestion by randomly dropping less important packets before congestion occurs. Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queuing (CBWFQ) Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-Based Weighted Fair Queuing (CBWFQ) Weighted Random Early Detection (WRED)

15. © 2001, Cisco Systems, Inc. QoS v1.0—1-15 Which Applications Have Which QoS Requirements? Enterprise networks are typically focused on providing QoS to applications. ThroughputDelayLossJitter Interactive (e.g., Telnet) Batch (e.g., FTP) Fragile (e.g,. SNA) Voice Low Not Important High Low Not Important None Not Important Low Low and Predictable Low VideoLow High Low and Predictable

16. © 2001, Cisco Systems, Inc. QoS v1.0—1-16 Which Services Can Be Implemented in a Network? Service provider networks typically offer services based on source and destination addresses. ThroughputDelayLossJitter Gold Silver Bronze Best Effort GuaranteedLow No Guarantee Low Guaranteed Low No Guarantee Guaranteed Limited No Guarantee

17. © 2001, Cisco Systems, Inc. QoS v1.0—1-17 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

18. © 2001, Cisco Systems, Inc. QoS v1.0—1-18 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 Name some QoS mechanisms available in Cisco IOS Describe typical enterprise and service provider networks and their QoS-related requirements

19. © 2001, Cisco Systems, Inc. QoS v1.0—1-19 Review Questions 1.What are the relevant parameters that define quality of service? 2.What can be done to give more bandwidth to an application? 3.What can be done to reduce delay? 4.What can be done to prevent packet loss? 5.Name the two QoS models.

20. Integrated Services Model QOS v1.0—1-20 © 2001, Cisco Systems, Inc.

21. QoS v1.0—1-21 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)

22. © 2001, Cisco Systems, Inc. QoS v1.0—1-22 Integrated Services The Internet was initially based on a best-effort packet 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.

23. © 2001, Cisco Systems, Inc. QoS v1.0—1-23 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. request reserve Local Admission Control Policy Decision Point (PDP) Policy Enforcement Point (PEP) request reply Remote Admission Control

24. © 2001, Cisco Systems, Inc. QoS v1.0—1-24 Reservation and Admission Protocols The Resource Reservation 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).

25. © 2001, Cisco Systems, Inc. QoS v1.0—1-25 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).

26. © 2001, Cisco Systems, Inc. QoS v1.0—1-26 IntServ Implementation Options 1)Explicit RSVP on each network node 2)RSVP ‘pass-through’ and CoS transport - map RSVP to CoS at network edge - pass-through RSVP request to egress RSVP Class of Service or Best Effort 3)RSVP at network edges and ‘pass-through’ with - best-effort forwarding in the core (if there is enough bandwidth in the core)

27. © 2001, Cisco Systems, Inc. QoS v1.0—1-27 Explicit RSVP Transport IntServ End-to-End All Routers WFQ applied per flow based on RSVP requests RSVP

28. © 2001, Cisco Systems, Inc. QoS v1.0—1-28 RSVP Pass-Through IntServ - DiffServ Integration Precedence Classifier Premium Standard Ingress Router RSVP protocol Mapped to classes Passed through to egress Backbone WRED applied based on class Egress Router RSVP protocol sent on to destination WFQ applied to manage egress flow RSVP WRED

29. © 2001, Cisco Systems, Inc. QoS v1.0—1-29 IntServ Support in IOS RSVP and Weighted Fair Queuing supported since ’95 RSVP signaling for VoIP calls supported on all VoIP platforms Cisco IOS supports hop-by-hop and pass- through RSVP RSVP-to-DSCP (DiffServ code point) mapping (RSVP proxy) in 12.1T

30. © 2001, Cisco Systems, Inc. QoS v1.0—1-30 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

31. © 2001, Cisco Systems, Inc. QoS v1.0—1-31 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

32. © 2001, Cisco Systems, Inc. QoS v1.0—1-32 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)

33. © 2001, Cisco Systems, Inc. QoS v1.0—1-33 Review Questions 1.What are the two building blocks of the Integrated Services model? 2.Which protocol is used to signal QoS requirements to the network? 3.Which protocol is used to offload admission control to a central policy server?

34. Differentiated Services Model QOS v1.0—1-34 © 2001, Cisco Systems, Inc.

35. QoS v1.0—1-35 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

36. © 2001, Cisco Systems, Inc. QoS v1.0—1-36 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.

37. © 2001, Cisco Systems, Inc. QoS v1.0—1-37 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

38. © 2001, Cisco Systems, Inc. QoS v1.0—1-38 DiffServ Elements The service defines QoS requirements and guarantees provided to a traffic aggregate. The conditioning functions and per-hop behaviors are 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. Provisioning is used to allocate resources to traffic classes.

39. © 2001, Cisco Systems, Inc. QoS v1.0—1-39 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.

40. © 2001, Cisco Systems, Inc. QoS v1.0—1-40 Downstream DS Domain Traffic Stream = set of flows DS Region Upstream DS Domain Behavior Aggregate (flows with the same DSCP) Topological Terminology DS Ingress Boundary Node DS Interior Node DS Egress Boundary Node Boundary Link

41. © 2001, Cisco Systems, Inc. QoS v1.0—1-41 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.

42. © 2001, Cisco Systems, Inc. QoS v1.0—1-42 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.

43. © 2001, Cisco Systems, Inc. QoS v1.0—1-43 DSCP Field: 6 bitsUnused: 2 bits Former ToS Byte = New DS Field 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 in RFC 2474. The bits of the DSCP field encode the DSCP, while the remaining bits are currently unused.

44. © 2001, Cisco Systems, Inc. QoS v1.0—1-44 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

45. © 2001, Cisco Systems, Inc. QoS v1.0—1-45 DSCP Usage DSCP selects per-hop behavior (PHB) throughout the network: Default PHB Class selector (IP Precedence) PHB Expedited forwarding PHB Assured forwarding PHB

46. © 2001, Cisco Systems, Inc. QoS v1.0—1-46 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-DS0-compliant node that interprets IPv4 ToS as defined by RFC 791 and RFC 1812 DSCP: backward compatible with IP Precedence (class selector code point, RFC 1812) but not with the ToS byte definition from RFC 791 (“DTR” bits)

47. © 2001, Cisco Systems, Inc. QoS v1.0—1-47 Class Selector Code Point Compatibility with current IP Precedence usage (RFC 1812) “xxx000” DSCPs Differentiates PTF – PTF(xyz000) >= PTF(abc000) ifxyz > abc

48. © 2001, Cisco Systems, Inc. QoS v1.0—1-48 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

49. © 2001, Cisco Systems, Inc. QoS v1.0—1-49 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

50. © 2001, Cisco Systems, Inc. QoS v1.0—1-50 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

51. © 2001, Cisco Systems, Inc. QoS v1.0—1-51 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 ClassValue AF1001dd0 AF2010dd0 AF3011dd0 AF4100dd0 Drop Probability (dd) Value Low01 Medium10 High11

52. © 2001, Cisco Systems, Inc. QoS v1.0—1-52 Assured Forwarding PHB Definition A DS node must allocate a configurable, minimum amount of forwarding resources (buffer space and bandwidth) per assured forwarding class. Excess resources may be allocated between non-idle classes. The manner must be specified. Reordering of IP packets of the same flow is not allowed if they belong to the same assured forwarding class.

53. © 2001, Cisco Systems, Inc. QoS v1.0—1-53 Assured Forwarding PHB Implementation CBWFQ (four classes) with WRED within each class (M)DRR with WRED within each class Optional custom queuing (does not support differentiated dropping)

54. © 2001, Cisco Systems, Inc. QoS v1.0—1-54 Summary Upon completing this lesson, you should 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

55. © 2001, Cisco Systems, Inc. QoS v1.0—1-55 Review Questions 1.What are the benefits of the DiffServ model compared to the IntServ model? 2.What is a DiffServ code point? 3.Name the standard PHBs. 4.How was backward compatibility with IP Precedence achieved? 5.Describe the PHB of assured forwarding. 6.Describe the PHB of expedited forwarding.

56. Building Blocks of IP QoS Mechanisms QOS v1.0—1-56 © 2001, Cisco Systems, Inc.

57. QoS v1.0—1-57 Objectives Upon completing this lesson, you will be able to: Describe different classification options in IP networks Describe different marking options in IP networks List the mechanisms that are capable of measuring the rate of traffic List the mechanisms that are used for traffic conditioning, shaping, and avoiding congestion List the forwarding mechanisms available in Cisco IOS List the queuing mechanisms available in Cisco IOS

58. © 2001, Cisco Systems, Inc. QoS v1.0—1-58 Router Functions Depending on the configuration, a router may perform a number of actions prior to forwarding a packet (input processing) Depending on the configuration, a router may perform a number of actions prior to enqueuing a packet in the hardware queue (output processing) Input Processing Input Processing Forwarding Output Processing Output Processing Input I/O Output I/O Defragmentation Decompression (payload, header) Source-based QoS-label/precedence setting Destination-based QoS-label/precedence setting Rate limiting Class-based marking Policy-based routing... Defragmentation Decompression (payload, header) Source-based QoS-label/precedence setting Destination-based QoS-label/precedence setting Rate limiting Class-based marking Policy-based routing... Rate limiting Random dropping Shaping Compression (payload, header) Fragmentation Queuing and scheduling... Rate limiting Random dropping Shaping Compression (payload, header) Fragmentation Queuing and scheduling... Process switching Fast/optimum switching Netflow switching CEF switching Process switching Fast/optimum switching Netflow switching CEF switching

59. © 2001, Cisco Systems, Inc. QoS v1.0—1-59 IP QoS Actions Classification—Each class-oriented QoS mechanism has to support some type of classification (access lists, route maps, class maps, etc.). Metering—Some mechanisms measure the rate of traffic to enforce a certain policy (e.g., rate limiting, shaping, scheduling, etc.). Dropping—Some mechanisms are used to drop packets (e.g., random early detection). Policing—Some mechanisms are used to enforce a rate limit based on the metering (excess traffic is dropped). Shaping—Some mechanisms are used to enforce a rate limit based on the metering (excess traffic is delayed).

60. © 2001, Cisco Systems, Inc. QoS v1.0—1-60 IP QoS Actions (cont.) Marking—Some mechanisms have the capability to mark packets based on classification or metering (e.g., CAR, class-based marking, etc.). Queuing—Each interface has to have a queuing mechanism. Forwarding—There are several supported forwarding mechanisms (process switching, fast switching, CEF switching, etc.).

61. © 2001, Cisco Systems, Inc. QoS v1.0—1-61 DiffServ Mechanisms in IOS Most traditional QoS mechanisms include extensive built-in classifiers –Committed access rate (CAR) –QoS Policy Propagation on BGP (QPPB) –Route maps –Queuing mechanisms Modular QoS CLI (first implemented in 12.0(5)T) separates classifiers from other actions –Includes all traditional classifiers and network-based application recognition (NBAR) Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping

62. © 2001, Cisco Systems, Inc. QoS v1.0—1-62 DiffServ Mechanisms in IOS (cont.) Token bucket model is used for metering: –Committed access rate (CAR) –Generic traffic shaping (GTS) –Frame Relay traffic shaping (FRTS) –Class-based weighted fair queuing (CBWFQ) –Class-based low latency queuing (CBLLQ) –Class-based policing –Class-based shaping –IP RTP Prioritization Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping

63. © 2001, Cisco Systems, Inc. QoS v1.0—1-63 DiffServ Mechanisms in IOS (cont.) Marker is used to set: –IP Precedence –DSCP –QoS group –MPLS experimental bits –Frame Relay DE bit –ATM CLP bit –IEEE 802.1Q or ISL CoS Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping Marking mechanisms: –Comitted access rate (CAR) –QoS Policy Propagation on BGP (QPPB) –Policy-based routing (PBR) –Class-based marking

64. © 2001, Cisco Systems, Inc. QoS v1.0—1-64 Comparison of Markers MarkerPreservation IP PrecedenceThroughout a network 8 values, 2 reserved (0 to 7) Value Range DSCPThroughout a network 64 values, 32 are standard (0 to 63) QoS groupLocal to a router 100 values (0 to 99) MPLS experimental bits Throughout an MPLS network (optionally throughout an entire IP network) 8 values Frame Relay DE bitThroughout a Frame Relay network 2 values (0 or 1) ATM CLP bitThroughout an ATM network 2 values (0 or 1) IEEE 802.1Q or ISL CoSThroughout a LAN switched network 8 values (0 to 7)

65. © 2001, Cisco Systems, Inc. QoS v1.0—1-65 DiffServ Mechanisms in IOS (cont.) Shaping mechanisms: –Generic traffic shaping (GTS) –Frame Relay traffic shaping (FRTS) –Class-based shaping –Hardware shaping on ATM VC Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping

66. © 2001, Cisco Systems, Inc. QoS v1.0—1-66 DiffServ Mechanisms in IOS (cont.) Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping Dropping mechanisms: –Committed access rate (CAR) and class-based policing can drop packets that exceed the contractual rate. –Weighted random early detection (WRED) can randomly drop packets when an interface is nearing congestion.

67. © 2001, Cisco Systems, Inc. QoS v1.0—1-67 DiffServ Mechanisms in IOS (cont.) Cisco Express Forwarding (CEF) is recommended from IOS 12.0. Some QoS features work only in combination with CEF. Inbound traffic stream ClassifierMarkerConditioner Meter ForwardingQueuing Scheduling Dropping Shaping Dropping

68. © 2001, Cisco Systems, Inc. QoS v1.0—1-68 DiffServ Mechanisms in IOS (cont.) Traditional queuing mechanisms –FIFO, priority queuing (PQ), custom queuing (CQ) Weighted fair queuing (WFQ) family –WFQ, DWFQ, CoS-based DWFQ, QoS-group DWFQ Advanced queuing mechanisms –Class-based WFQ, Class-based LLQ Inbound traffic stream ClassifierMarkerConditioner Meter ForwardingQueuing Scheduling Dropping Shaping Dropping

69. © 2001, Cisco Systems, Inc. QoS v1.0—1-69 DiffServ Mechanisms in IOS (cont.) Tail drop is used for most queue congestion. WFQ has an improved tail-drop scheme. WRED randomly drops packets when nearing congestion. Inbound traffic stream ClassifierMarkerConditioner Meter ForwardingQueuing Scheduling Dropping Shaping Dropping

70. © 2001, Cisco Systems, Inc. QoS v1.0—1-70 Summary Upon completing this lesson, you should be able to: Describe different classification options in IP networks Describe different marking options in IP networks List the mechanisms that are capable of measuring the rate of traffic List the mechanisms that are used for traffic conditioning, shaping, and avoiding congestion List the forwarding mechanisms available in Cisco IOS List the queuing mechanisms available in Cisco IOS

71. © 2001, Cisco Systems, Inc. QoS v1.0—1-71 Review Questions 1.Name the QoS building blocks. 2.What is the purpose of classification? 3.What is the purpose of marking? 4. Which parameters can be used to mark packets? 5.Which mechanisms can classify and mark packets? 6.Which mechanisms have the ability to measure the rate of traffic? 7.Which forwarding mechanisms exist in Cisco IOS ? 8.Which queuing mechanisms exist in Cisco IOS ? 9.How, when, and where do routers drop packets?

72. Enterprise Network Case Study QOS v1.0—1-72 © 2001, Cisco Systems, Inc.

73. QoS v1.0—1-73 Objectives Upon completing this lesson, you will be able to: Describe the typical structure of an enterprise network Describe the need for QoS in enterprise networks List typical QoS requirements in enterprise networks List the QoS mechanisms that are typically used in enterprise networks

74. © 2001, Cisco Systems, Inc. QoS v1.0—1-74 X.25 (ancient), Frame Relay (old), ATM (newer) X.25 (ancient), Frame Relay (old), ATM (newer) X.25 (ancient), Frame Relay (old), ATM (newer) X.25 (ancient), Frame Relay (old), ATM (newer) Traditional Enterprise Networks Traditional enterprise networks use a hub-and-spoke topology. Redundant connections are used to improve resilience. A partial mesh can be used between the core sites and the distribution sites. Core (central sites and data centers) Distribution (regional centers) Access (branch offices)

75. © 2001, Cisco Systems, Inc. QoS v1.0—1-75 MPLS/VPN (new) Modern Enterprise Networks Modern enterprise networks use a full mesh topology provided by an MPLS/VPN backbone. Redundant connections to the backbone can be used to improve resilience The MPLS/VPN backbone uses redundant connections and a partial mesh to improve resilience. Core (central sites and data centers) Access (branch offices)

76. © 2001, Cisco Systems, Inc. QoS v1.0—1-76 QoS in Enterprise Networks Typical enterprise networks have a large number of different applications. Some applications are business-critical and require some guarantees (bandwidth, delay). The network should provide enough resources to these business-critical applications. Applications are usually identified based on TCP or UDP port numbers.

77. © 2001, Cisco Systems, Inc. QoS v1.0—1-77 Case Study Typical line speeds: –Core to Distribution< 2 Mbps –Distribution to Branch64 kbps - 256 kbps Typical protocols: –SNA, NetBIOS, desktop protocols (IPX), some TCP/IP, voice, multimedia Typical QoS requirements: –SNA and voice are high priority –Guaranteed bandwidth for some applications –Rest of the traffic is best-effort

78. © 2001, Cisco Systems, Inc. QoS v1.0—1-78 Case Study Implementation #1 Core to Distribution: –Custom queuing Distribution to Branch: –Priority queuing or –Custom queuing with a priority queue Options: –Traffic shaping –Adaptation to Frame Relay congestion notification

79. © 2001, Cisco Systems, Inc. QoS v1.0—1-79 Case Study Implementation #2 Core to Distribution: –Class-based weighted fair queuing (CBWFQ) –Class-based low-latency queuing (CBLLQ) Distribution to Branch: –Class-based weighted fair queuing (CBWFQ) –Class-based low-latency queuing (CBLLQ) Options: –Class-based shaping –Adaptation to Frame Relay congestion notification –Class-based policing –Weighted random early detection (WRED)

80. © 2001, Cisco Systems, Inc. QoS v1.0—1-80 Summary Upon completing this lesson, you should be able to: Describe the typical structure of an enterprise network Describe the need for QoS in enterprise networks List typical QoS requirements in enterprise networks List the QoS mechanisms that are typically used in enterprise networks

81. © 2001, Cisco Systems, Inc. QoS v1.0—1-81 Review Questions 1.What is the typical enterprise network topology? 2.How is resilience achieved? 3.Based on what information do typical enterprise networks apply QoS?

82. Service Provider Case Study QOS v1.0—1-82 © 2001, Cisco Systems, Inc.

83. QoS v1.0—1-83 Objectives Upon completing this lesson, you will be able to: Describe the typical structure of a service provider network Describe the need for QoS in service provider networks List typical QoS requirements in service provider networks List the QoS mechanisms that can be used in service provider networks

84. © 2001, Cisco Systems, Inc. QoS v1.0—1-84 ATM, SONET/SDH, DPT, GE,... Frame Relay, ATM, leased line (analog, TDM), dial-up (PSTN, ISDN, GSM), xDSL, (fast) Ethernet,... Frame Relay, ATM, leased line (analog, TDM), dial-up (PSTN, ISDN, GSM), xDSL, (fast) Ethernet,... ATM, SONET/SDH, DPT, GE,... Typical Service Provider Networks Typical service provider networks use a high-speed partially meshed core (backbone). Regional POPs use two or more connections to the core. There may be another layer of smaller POPs connected to distribution-layer POPs. Customers are usually connected to the service provider via a single point-to-point link (a secondary link or a dial line can be used to improve resilience). Core Distribution (regional POPs) Access (customers) Redundant connections Rings Partial mesh Rings Single connections Optional redundant connections Dial backup

85. © 2001, Cisco Systems, Inc. QoS v1.0—1-85 QoS in Service Provider Networks Service providers extend their service offerings by introducing quality. Customers can get bandwidth guarantees (like CIR in Frame Relay). Customers can get delay guarantees (like CBR in ATM). Customers can get preferential treatment in case of congestion (Olympic service). QoS mechanisms have to be deployed where congestion is likely (usually at the network edge). The customer traffic is identified based on source or destination IP addresses.

86. © 2001, Cisco Systems, Inc. QoS v1.0—1-86 Case Study A service provider wants to offer bronze, silver, gold and premium services: Bronze gets 10% of available bandwidth Silver gets 20% of available bandwidth Gold gets 30% of available bandwidth Premium gets 40% of available bandwidth with a low-delay guarantee

87. © 2001, Cisco Systems, Inc. QoS v1.0—1-87 Case Study Implementation Class-based weighted fair queuing (CBWFQ) on slow to moderate-speed links Class-based low latency queuing (CBLLQ) on slow to moderate-speed links Weighted random early detection (WRED) on fast links

88. © 2001, Cisco Systems, Inc. QoS v1.0—1-88 Summary Upon completing this lesson, you should be able to: Describe the typical structure of a service provider network Describe the need for QoS in service provider networks List typical QoS requirements in service provider networks List the QoS mechanisms that can be used in service provider networks

89. © 2001, Cisco Systems, Inc. QoS v1.0—1-89 Review Questions 1.What is the typical topology of service provider networks? 2.How is resilience achieved? 3.Based on what information do typical service provider networks apply QoS?

90. © 2001, Cisco Systems, Inc. QoS v1.0—1-90 Module Summary Upon completing this module, you should 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) List the IP QoS mechanisms available in Cisco IOS Describe what QoS features are supported by different IP QoS mechanisms

91. © 2001, Cisco Systems, Inc. IP QoS Introduction-91