© 2001, Cisco Systems, Inc. IP QoS Andy Chien Cisco Systems

© 2001, Cisco Systems, Inc. IP QoS Introduction-2 Why IP QoS? Application X is slow! Video broadcast occasionally stalls! Phone calls over IP are no better than over satellite! Phone calls have really bad voice quality! ATM (the money-dispensing-type) are non- responsive!...

© 2001, Cisco Systems, Inc. IP QoS Introduction-3 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 have really bad voice quality! (too many phone calls – ADMISSION CONTROL) ATM (the money-dispensing-type) are non responsive! (too many DROPs)...

© 2001, Cisco Systems, Inc. IP QoS Introduction-4 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 that add up to the overall delay 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-5 Available Bandwidth Maximum available bandwidth equals the bandwidth of the weakest link Multiple flows are contesting 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)=256kbps BW avail = BW max /Flows

© 2001, Cisco Systems, Inc. IP QoS Introduction-6 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)

© 2001, Cisco Systems, Inc. IP QoS Introduction-7 Processing and Queuing 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 packets 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-8 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 that are not as common and may require a hardware upgrade (input drop, ignore, overrun, no buffer,...). These drops are usually a result of router congestion. IP Forwarding IP Tail-drop

© 2001, Cisco Systems, Inc. IP QoS Introduction-9 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 (CB-WFQ) Stacker Predictor TCP Header Compression RTP Header Compression

© 2001, Cisco Systems, Inc. IP QoS Introduction-10 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. Priority Queuing (PQ) Custom Queuing (CQ) Strict Priority MDRR IP RTP prioritization Class-based Low-latency Queuing (CB-LLQ) TCP Header Compression RTP Header Compression RTP Compress the Payload Compressed packet Compress the payload of layer-2 frames (it takes time). Stacker Predictor

© 2001, Cisco Systems, Inc. IP QoS Introduction-11 How to Prevent Packet Loss? Upgrade the link. The best solution but also the most expensive. FIFO queuing IPdata Fancy queuing Guarantee enough bandwidth to sensitive packets. Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) Class-based Weighted Fair Queuing (CB-WFQ) Dropper Prevent congestion by randomly dropping less important packets before congestion occurs Weighted Random Early Detection (WRED)

© 2001, Cisco Systems, Inc. IP QoS Introduction-12 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 Low Not Important High Low Low None LowLowLow Low and Predictable LowLow VideoLowLowHigh

© 2001, Cisco Systems, Inc. IP QoS Introduction-13 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 Guaranteed Limitted No Guarantee...

© 2001, Cisco Systems, Inc. IP QoS Introduction-14 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 requires special QoS

© 2001, Cisco Systems, Inc. IP QoS Introduction-15 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/or delay requirements The Integrated Services model (RFC1633) was introduced to guarantee a predictable behavior of the network for these applications

© 2001, Cisco Systems, Inc. IP QoS Introduction-16 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 Remote Admission Control Local Admission Control Policy Decision Point (PDP) request reply Policy Enforcement Point (PEP)

© 2001, Cisco Systems, Inc. IP QoS Introduction-17 Reservation and Admission Protocols The resource ReSerVation Protocol (RSVP) was developed to communicate resource needs between hosts and network devices (RFC ) Common Open Policy Service (COPS) was developed to offload admission control to a central policy server (RFC )

© 2001, Cisco Systems, Inc. IP QoS Introduction-18 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)

© 2001, Cisco Systems, Inc. IP QoS Introduction-19 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)

© 2001, Cisco Systems, Inc. IP QoS Introduction-20 Explicit RSVP Transport IntServ End-to-End All Routers WFQ applied per flow based on RSVP requests RSVP

© 2001, Cisco Systems, Inc. IP QoS Introduction-21 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-22 IntServ Support in IOS RSVP and Weighted Fair Queuing supported since ’95 RSVP signaling for VoIP calls supported on all VoIP platforms IOS supports hop-by-hop and pass-through RSVP RSVP-to-DSCP (DiffServ Code Point) mapping (RSVP proxy) in 12.1T

© 2001, Cisco Systems, Inc. IP QoS Introduction-23 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-24 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-25 Differentiated Services Model Differentiated Services model describes services associated with traffic classes Complex traffic classification and conditioning is performed at network edge resulting in a per-packet Differentiated Services Code Point (DSCP). No per-flow/per-application state in the core Core only performs simple ‘per-hop behavior's’ on traffic aggregates Goal is Scalability

© 2001, Cisco Systems, Inc. IP QoS Introduction-26 Additional 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-27 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 (DS code point) is used to mark packets to select a per-hop behavior Per-hop Behavior (PHB) is realized using a particular QoS mechanism Provisioning is used to allocate resources to traffic classes

© 2001, Cisco Systems, Inc. IP QoS Introduction-28 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-29 Downstream DS domain Traffic Stream = set of flows DS region Upstream DS domain Behaviour Aggregate (flows with the same DSCP) Topological Terminology DS Ingress Boundary node DS interior node DS Egress Boundary node Boundary link

© 2001, Cisco Systems, Inc. IP QoS Introduction-30 Traffic Terminology Flow: a single instance of an application-to- application flow of packets which 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 which traverse a path segment. A traffic stream may consist of a set of active flows which 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.

© 2001, Cisco Systems, Inc. IP QoS Introduction-31 Traffic Terminology Behavior Aggregate (BA) is a collection of packets with the same DS code point crossing a link in a particular direction. Per-Hop Behavior (queuing in a node) externally observable forwarding behavior applied at a DS-compliant node to a DS behavior aggregate. PHB Mechanism: 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.

© 2001, Cisco Systems, Inc. IP QoS Introduction-32 DSCP field: 6bitsUnused: 2bits Former ToS byte = new DS field Packet Header Terminology DS code point: a specific value of the DSCP portion of the DS field, 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 RFC2474. The bits of the DSCP field encode the DS code point, while the remaining bits are currently unused.

© 2001, Cisco Systems, Inc. IP QoS Introduction-33 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-34 DSCPCU DS field DSCP DROP Precedence Class#1Class #2Class #3Class #4 Low Drop Precedence AF11 (001010) 10 AF21 (010010) 18 AF ) 26 AF41 (100010) 34 Medium Drop Prec AF12 (001100) 12 AF22 (010100) 20 AF ) 28 AF42 (100100) 36 High Drop Precedence AF13 (001110) 14 AF23 (010110) 22 AF33 (011110) 30 AF43 (100110) 38 High Priority = EF = = 46 Best Effort = = 0

© 2001, Cisco Systems, Inc. IP QoS Introduction-35 DSCP Usage DS Code point selects per-hop behavior (PHB) throughout the network Default PHB Class Selector (IP precedence) PHB Expedited Forwarding (EF) PHB Assured Forwarding (AF) PHB

© 2001, Cisco Systems, Inc. IP QoS Introduction-36 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 PHB’s Legacy node: a non-DS compliant node that interprets IPv4 ToS such as defined by RFC791 and RFC1812. DSCP is backward compatible with IP Precedence (Class Selector Code point, RFC 1812) but not with the ToS byte definition from RFC 791 (“DTR” bits)

© 2001, Cisco Systems, Inc. IP QoS Introduction-37 Class Selector Code Point Compatibility with current IP precedence usage (RFC 1812) “xxx000” DS code points Differentiates probability of timely forwarding (PTF) – PTF (xyz000) >= PTF(abc000) if xyz > abc

© 2001, Cisco Systems, Inc. IP QoS Introduction-38 Expedited Forwarding Expedited Forwarding (EF) 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-39 EF PHB Implementations Priority Queuing IP RTP Prioritization Class-based Low-latency Queuing (CB-LLQ) Strict Priority queuing within Modified Deficit Round Robin (MDRR) on GSR

© 2001, Cisco Systems, Inc. IP QoS Introduction-40 Assured Forwarding Assured Forwarding (AF) 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 drop probability

© 2001, Cisco Systems, Inc. IP QoS Introduction-41 AF Encoding Each AF class uses three DSCP values Each AF 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-42 AF PHB Definition A DS node MUST allocate a configurable, minimum amount of forwarding resources (buffer space and bandwidth) per AF 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 AF class

© 2001, Cisco Systems, Inc. IP QoS Introduction-43 AF PHB Implementation CBWFQ (4 classes) with WRED within each class (M)DRR with WRED within each class Optionally Custom Queuing (does not support differentiated dropping)

© 2001, Cisco Systems, Inc. IP QoS Introduction-44 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 Forwarding Output Processing 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... Process switching Fast/optimum switching Netflow switching CEF switching Input I/O Output I/O

© 2001, Cisco Systems, Inc. IP QoS Introduction-45 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)

© 2001, Cisco Systems, Inc. IP QoS Introduction-46 IP QoS Actions Marking – Some mechanisms have the capability to mark packets based on classification and/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.)

© 2001, Cisco Systems, Inc. IP QoS Introduction-47 DiffServ Mechanisms Most traditional QoS mechanisms include extensive built-in classifiers –Committed Access Rate (CAR) –QoS Policy Propagation via BGP (QPPB) –Route-maps –Queuing mechanisms –... Modular QoS CLI (first implemented in 12.0(5)T) separates classifier from other actions –Includes all traditional classifiers + Network Based Application Recognition (NBAR) Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping

© 2001, Cisco Systems, Inc. IP QoS Introduction-48 DiffServ Mechanisms 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 (CB-WFQ) –Class-based Low Latency Queuing (CB-LLQ) –Class-based Policing –Class-based Shaping –IP RTP Prioritization Inbound traffic stream ClassifierMarkerConditioner Meter Queuing Scheduling Dropping Shaping Dropping

© 2001, Cisco Systems, Inc. IP QoS Introduction-49 DiffServ Mechanisms 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 through BGP (QPPB) –Policy-based Routing (PBR) –Class-based Marking

© 2001, Cisco Systems, Inc. IP QoS Introduction-50 Comparison of Markers MarkerPreservation IP precedence Throught a network 8 values, 2 reserved (0 to 7) Value range DSCP Throught a network 64 values, 32 are standard (0 to 63) QoS group Local 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 bit Throughout a Frame Relay network 2 values (0 or 1) ATM CLP bit Throughout an ATM network 2 values (0 or 1) IEEE 802.1Q or ISL CoS Throughout a LAN switched network 8 values (0 to 7)

© 2001, Cisco Systems, Inc. IP QoS Introduction-51 DiffServ Mechanisms 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-52 DiffServ Mechanisms 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-53 DiffServ Mechanisms 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-54 DiffServ Mechanisms 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-55 DiffServ Mechanisms Tail drop on 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-56