IP Qo S Principles Theory and Practice Dimitrios

IP Qo. S Principles Theory and Practice Dimitrios Kalogeras

Agenda l l l 2 Introduction – History – Background Qo. S Metrics Qo. S Architecture Components Applications in Cisco Routers

A Bit of History l The Internet, originally designed for U. S. government use, offered only one service level: Best Effort. – – l No guarantees of transit time or delivery Rudimentary prioritization was available, but it was rarely used. Commercialization began in early 1990’s – – – Private (intranet) networks using Internet technology appeared. Commercial users began paying directly for Internet use. Commerce sites tried to attract customers by using graphics. Industry used the Internet and intranets for internal, shared communications that combined previously-separate, specialized networks -- each with its own specific technical requirements. New technologies (voice over the Internet, etc. ) appeared, designed to capitalize on inexpensive Internet technologies.

The Demands on Modern Networks l Network flexibility is becoming central to enterprise strategy – – l l l Rapidly-changing business functions no longer carried out in stable ways, in unchanging locations, or for long time-periods Network-enabled applications often crucial for meeting new market opportunities, but there’s no time to custom-build a network Traffic is bursty Interactive voice, video applications have stringent bandwidth and latency demands Multiple application networks are being combined into consolidated corporate utility networks – – Bandwidth contention as critical transaction traffic is squeezed by web browsing, file transfers, or other low-priority or bulk traffic Latency problems as interactive voice and video are squeezed by transaction, web browsing, file transfer, and bulk traffic

Qo. S Background Qo. S development inspired by new types of applications in IP environment: l l 5 Video Streaming Services Video Conferencing Vo. IP Legacy SNA / DLSw

Definitions l Quality of Service (Qo. S) classifies network traffic and then ensures that some of it receives special handling. – – l Differentiated Class of Service (Co. S) is a simpler alternative to Qo. S. – – l May track each individual dataflow (sender: receiver) separately. May include attempts to provide better error rates, lower network transit time (latency), and decreased latency variation (jitter). Doesn't try to distinguish among individual dataflows; instead, uses simpler methods to classify packets into one of a few categories. All packets within a particular category are then handled in the same way, with the same quality parameters. Policy-Based Networking provides end-to-end control. – The rules for access and for management of network resources are stored as policies and are managed by a policy server.

Statistical Behavior: Random Arrival l In random arrival, the time that each packet arrives is completely independent of the time that any other packet arrives. – – l If the true situation is that arrivals tend to be evenly spaced, then random arrival calculations will overestimate the queuing delay. If the true situation is that arrivals are bunched in groups (typical of data flows, such as packets and acknowledgements), then random arrival calculations will underestimate the queuing delay. Our intuition is usually misleading when we think of random processes. – – We tend to assume that queue size increases linearly as the number of customers increases. But, with random arrival, there is a drastic increase in queue size as the customer arrival rate approaches 80% of theoretical server capacity. There’s no way to store the capacity that is unused by late customers, but early customers increase the queue.

Random Arrival and Intuition l The surprising increase in queue length is best shown by a graph:

Random Arrival vs. Self-Similar l Although random arrival is very convenient mathematically (it’s relatively simple to do random arrival calculations), it has been shown that much data traffic is self-similar. – – l Self-similar traffic shows the same pattern regardless of changes in scale. – l Ethernet and Internet traffic flows, in particular, are self-similar. The rate of initial connections is still random, however. Fractal geometry (e. g. , a coastline) is an example. Self-similar traffic has a heavy tail. – – The probabilities of extremely large values (e. g. , file lengths of a gigabyte or more) don’t decrease as rapidly, as they would with random distributions of file lengths. This matches real data traffic behaviours. l l Long file downloads mixed with short acknowledgements Compressed video with action scenes mixed with static scenes

Implications of Self-Similar Behaviour l “If high levels of utilization are required, drastically larger buffers are needed for self-similar traffic than would be predicted based on classical queuing analysis [i. e. , assuming random behaviour]. ” [Stallings] – 10 Combining self-similar traffic streams doesn’t quickly result in smoother traffic patterns; it’s only at the highest levels of aggregation that random-arrival statistics can be used.

Qo. S Metrics: What are we trying to control? l Four metrics are used to describe a packet’s transmission through a network – Bandwidth, Delay, Jitter, and Loss l Using a pipe analogy, then for each packet: is the perceived width of the pipe 2. Delay is the perceived length of the pipe 3. Jitter is the perceived variation in the length of the pipe 4. Loss is the perceived leakiness if the pipe Bandwidth 11 A The path as perceived by a packet! Delay B

Qo. S Metrics – Bandwidth The amount of bandwidth available to a packet is affected by: 1. The slowest link found in the transmission path 2. The amount of congestion experienced at each hop – TCP slow-start and windowing 3. The forwarding speed of the devices in the path 4. The queuing priority given to the packet flow 100 Mb/s 2 Mb/s Maximum Bandwidth 12 10 Mb/s

Qo. S Metrics – Delay The amount of delay experienced by a packet is the sum of the: 1. Fixed Propagation Delays 1. Bounded 2. Fixed by the speed of light and the path distance Serialization Delays 1. The time required to physically place a packet onto a transmission medium 3. Variable Switching Delays 1. The time required by each forwarding engine to resolve the next-hop address and egress interface for a packet 4. Variable 1. The Queuing Delays time required by each switching engine to queue a packet for transmission 13

Qo. S Metrics – Jitter The amount of Jitter experienced by a packet is affected by: ~214 ms Serialization Delay for a 1500 -byte packet at 56 Kb/s 1. Serialization delays on low-speed interfaces 2. Variations in queue-depth due to congestion 3. Variations in queue cycle-times induced by the service architectures – First-Come, First-Served, for example 60 B every 20 ms 60 B every 214 ms Voice 1500 Bytes of Data Voice 10 Mbps Ethernet 56 Kbps WAN 14

Qo. S Metrics – Loss The amount of loss experienced by a packet flow is affected by: § § Buffer exhaustion due to congestion caused by oversubscription or rate-decoupling Intentional packet drops due to congestion control mechanism such as Random Early Discard DS-3 GE GE Oversubscribed 15 GE Buffer Exhaustion

Qo. S Architecture Models l l l 16 Best Effort Service Integrated Service Differentiated Service

Qo. S Implementation Models No State Aggregated State Per-Flow State 1. Best Effort 2. Int. Serv/RSVP 3. Diff. Serv 4. RSVP+Diff. Serv+MPLS 17

Best Effort Service What exactly IP does: l l l 18 All packets treated equally Unpredictable bandwidth Unpredictable delay and jitter

Int. Serv (RFC 1633) 19

Integrated Services (Int. Serv) 1. 2. 3. 4. 5. The Integrated Services (Int. Serv) model builds upon Resource Reservation Protocol (RSVP) Reservations are made per simplex flow Applications request reservations for network resources which are granted or denied based on resource availability Senders specify the resource requirements via a PATH message that is routed to the receiver Receivers reserve the resources with a RESV message that follows the reverse path RESV Sender Receiver PATH 20

Int. Serv – Components The Integrated Services Model can be divided into two parts – the Control and Data Planes Control Plane Routing Selection Admission Control Reservation Setup Reservation Table Data Plane Flow Identification 21 Packet Scheduler

Int. Serv – Components Control Plane § § § Route Selection – Identifies the route to follow for the reservation (typically provided by the IGP processes) Reservation Setup – Installs the reservation state along the selected path Admission Control – Ensures that resources are available before allowing a reservation Data Plane 1. 2. 22 Flow Identification – Identifies the packets that belong to a given reservation (using the packet’s 5 -Tuple) Packet Scheduling – Enforces the reservations by queuing and scheduling packets for transmission

Int. Serv – Service Models Applications using Int. Serv can request two basic servicetypes: § Guaranteed Service §Provides guaranteed bandwidth and queuing delays end-to-end, similar to a virtual-circuit §Applications can expect hard-bounded bandwidth and delay § Controlled-Load Service §Provides a Better-than-Best-Effort service, similar to a lightly-loaded network of the required bandwidth §Applications can expect little to zero packet loss, and little to zero queuing delay These services are mapped into policies that are applied via CB-WFQ, LLQ, or MDRR 23

Int. Serv – Scaling Issues 1. 2. 3. 4. 24 Int. Serv routers need to examine every packet to identify and classify the microflows using the 5 tuple Int. Serv routers must maintain a token-bucket per microflow Guaranteed Service requires the creation of a queue for each microflow Data structures must be created and maintained for each reservation

Diff. Serv (RFC 2474/2475) 25

Differentiated Services (Diff. Serv) § § The Diff. Serv Model specifies an approach that offers a service better than Best-Effort and more scalable than Int. Serv Traffic is classified into one of five forwarding classes at the edge of a Diff. Serv network Forwarding classes are encoded in the Differentiated Services Codepoint (DSCP) field of each packet’s IP header Diff. Serv routers apply pre-provisioned Per-Hop Behaviors (PHBs) to packets according to the encoded forwarding class 5 26 4 3 2 1 5 4 3 2 1

Diff. Serv – Compared to Int. Serv § § § 27 Diff. Serv allocates resources to aggregated rather than to individual flows Diff. Serv moves the classification, policing, and marking functions to the boundary nodes – the core simply forwards based on aggregate class Diff. Serv defines Per-Hop forwarding behaviors, not end-toend services Diff. Serv guarantees are based on provisioning, not reservations The Diff. Serv focus is on individual domains, rather than endto-end deployments

Diff. Srv – The DS Field (RFC 2474) DS field § § § 28 CU The DS field is composed of the 6 high-order bits of the IP To. S field The DS field is functionally similar to the IPv 4 TOS and IPv 6 Traffic Class fields The DS field is divided into three pools: § § DSCP nnnnn 0 – Standards Use nnnn 11 – Experimental / Local Use nnnn 01 – Experimental / Local Use, possible Standards Use Class Selector Codepoints occupy the high-order bits (nnn 000) and map to the IPv 4 Precedence bits

Diff. Srv – Forwarding Classes DSCP § § 29 CS 1 001010 AF 11 001100 AF 12 001110 AF 13 010000 CS 2 010010 AF 21 010100 AF 22 010110 AF 23 011000 CS 3 011010 AF 31 011100 AF 32 011110 AF 33 100000 CS 4 100010 AF 41 100100 AF 42 100110 AF 43 CS 5 EF CS 6 111000 § An Expedited Forwarding (EF) Class Four Assured Forwarding Classes, each with three Drop Precedence (AFxy, where x=1 -4, and y=1 -3) Packets in a higher AF Classes have a higher transmit priority Packets with a higher Drop Precedence are more likely to be dropped 001000 110000 § Eight Class Selector Codepoints compatible with legacy systems (CS 0 -7) CS 0 (DE) 101110 § 000000 101000 The DS Field can encode: Codepoint CS 7

Diff. Serv – Per-Hop Behaviours § § § 30 A Per-Hop Behaviour (PHB) is an observable forwarding behaviour of a DS node applied to all packets with the same DSCP PHBs do NOT mandate any specific implementation mechanisms The EF PHB should provide a low-loss, low-delay, low-jitter, assured bandwidth service The AF PHBs should provide increasing levels or service (higher bandwidth) for increasing AF levels The Default PHB (CS 0) should be equivalent to Best-Effort Service Packets within a given PHB should not be re-ordered

Diff. Serv – Boundary Nodes Diff. Serv Boundary Nodes are responsible for classifying and conditioning packets as they enter a given Diff. Serv Domain Conditioning Remarker Classification Classifier Marker Meter Shaper Dropper § Classifier § Marker § Meter § Remarker § Shaper § Dropper 31 Examine each packet and assign a Forwarding Class Set the DS Field to match the Forwarding Class Measure the traffic flow and compare it to the traffic profile Remark (lower) the DS Field for out-of-profile traffic Shape the traffic to match the traffic profile Drop out of profile traffic

Diff. Serv – Summary Diff. Serv Domain Classification / Conditioning PHB LLQ/WRED Premium Gold 32 Silver Bronze

The Trouble with Diff. Serv § § Virtual wire using EF is OK, but how much can be deployed? § 33 As currently formulated, Diff. Serv is strong on simplicity and weak on guarantees Diff. Serv has no topology-aware admission control mechanism

RSVP-Diff. Serv Integration The best of both worlds – Aggregated RSVP integrated with Diff. Serv No State Aggregated State Per-Flow State RSVP + Diff. Serv Best Effort Diff. Serv Aggregated State Firm Guarantees Admission Control Int. Serv But – given the presence of a Diff. Serv domain in a network, how do we support RSVP End-to-End? 34

RSVP-Diff. Serv Integration – How? § Routers at edge of a DS cloud perform microflow classification, policing, and marking • Guaranteed Load set to the EF, Controlled load set to AFx, and Best Effort set to CS 0 • Service Model to Forwarding Class mapping is arbitrary § § The Diff. Serv core makes and manages aggregate reservations for the DS Forwarding Classes based on the RSVP microflow reservations § 35 RSVP signaling is used in both the Int. Serv and Diff. Serv regions for admission control The core then schedules and forwards packets based only on the DS Field

RSVP-Diff. Serv Integration Border Routers implement per-flow classification, policing, and marking Diff. Serv Region RSVP Signaling is propagated End-to End 36 The Int. Serv regions contain Guaranteed or Controlled Load Microflows The Diff. Serv region aggregates the flows into DS Forwarding Classes

RSVP-Diff. Serv Integration – Summary § § § 37 The forwarding plane is still Diff. Serv We now make a small number of aggregated reservations from ingress to egress Microflow RSVP messages are carried across the Diff. Serv cloud Aggregate reservations are dynamically adjusted to cover all microflows RSVP flow-classifiers and per-flow queues are eliminated in the core Scalability is improved – only the RSVP flow states are necessary – Tested to 10 K flows

Qo. S Architecture Components l l l l 38 Classification Coloring Admission Control Traffic Shaping/Policing Congestion Management Congestion Avoidance Signaling

Traffic Classification l l l 39 Most fundamental Qo. S building block The component of a Qo. S feature that recognizes and distinguishes between different traffic streams Without classification, all packets are treated the same

Traffic Classification/ Admission Control Issues l l 40 Always performed at the network perimeter Makes traffic conform to the internal network policy Marks packets with special flags (colors) Colors used afterwards inside the network for Qo. S management

Classification/ Admission Control Scheme Meter Admitted Classifier Packet Marker Shaper/ Policer Dropped 41

Classification Criteria l l 42 IP header fields TCP/UDP header fields Routing information Packet Content (NBAR) i. e. HTTP, HTTPS, FTP, Napster etc.

Traffic Coloring Options l l l 43 IP Precedence DSCP Qo. S Group 802. 1 p Co. S ATM CLP Frame Relay DE

Type-of-Service (RFC 791) Precedence Version Length 0 D T To. S Field R Unused Total Length 8 15 31 0 1 D Normal Delay Low Delay T Normal Throughput High Throughput R 44 … Normal Reliability High Reliability

IP Precedence Values 111 110 Internetwork Control 101 Critical 100 Flash Override 011 Flash 010 Immediate 001 Priority 000 45 Network Control Routine

DSCP Diffserv Code Point DSCP (6 bits) Unused Class 1 Class 2 Class 3 Class 4 001010 010010 011010 100010 Medium Drop Precedence 001100 010100 011100 100100 High Drop Precedence 001110 010110 011110 100110 Low Drop Precedence 46

Classification mechanisms l l 47 MQC ( Modular Qos Command Line Interface) CAR ( Commited Access Rate)

Modular Qo. S CLI (MQC) Command syntax introduced in 12. 0(5)T Reduces configuration steps and time Uniform CLI across all main Cisco IOS-based platforms Uniform CLI structure for all Qo. S features 48

Basic MQC Commands router(config)# class-map [match-any | match-all] class-name • 1. Create Class Map - a traffic class ( match access list, input interface, IP Prec, DSCP, protocol (NBAR) src/dst MAC address, mpls exp). router(config)# policy-map-name • 2. Create Policy Map (Service Policy) - Associate a class map with one or more Qo. S policies (bandwidth, police, queuelimit, random detect, shape, set prec, set DSCP, set mpls exp). router(config-if)# service-policy {input | output} policy-map-name • 3. Attach Service Policy - Associate the policy map with an input or output interface. 49

Basic MQC Commands l 1. Create Class Map – defines traffic selection criteria Router(config)# class-map class 1 Router(config-cmap)# match ip precedence 5 Router(config-cmap)# exit l 2. Create Policy Map- associates classes with actions Router(config)# policy-map policy 1 Router(config-pmap)# class 1 Router(config-pmap-c)# set mpls experimental 5 Router(config-pmap-c)# bandwidth 3000 Router(config-pmap-c)# queue-limit 30 Router(config-pmap)# exit l 3. Attach Service Policy – enforces policy to interfaces Router(config)# interface e 1/1 Router(config-if)# service-policy output policy 1 Router(config-if)# exit 50

Classification Configuring Sample MQC based IOS 12. 1(5)T class-map match-all premium match access-group name premium ! Traffic class definitions class-map match-any trash match protocol napster match protocol fasttrack ! policy-map classify class premium set ip precedence priority Qo. S policy definition class trash police 64000 conform-action set-prec-transmit 1 excess-action drop ! ip access-list extended premium ACL definition permit tcp host 10. 0. 0. 1 any eq telnet ! interface serial 2/1 Qo. S Policy attached ip unnumbered loopback 0 to interface service-policy input classify 51

Classification Configuring Sample CAR based ip cef ! interface serial 2/1 ip unnumbered loopback 0 rate-limit input access-group 100 64000 8000 conform-action set-prec-transmit 1 exceed-action set-prec-transmit 0 ! access-list 100 permit tcp host 10. 0. 0. 1 any eq http CAR definition ACL definition 52

Classification Configuring Sample Route-map based route-map classify permit 10 match ip address 100 set ip precedence flash ! Route-map definitions route-map classify permit 20 match ip next-hop 1 set ip precedence priority ! interface serial 2/1 ip unnumbered loopback 0 Route-map attached ip policy route-map classify to interface ! access-list 1 permit 192. 168. 0. 1 access-list 100 permit tcp host 10. 0. 0. 1 any eq http ACL definitions 53

Shaping/Policing l l 54 Used to assign more predictive behavior to traffic Uses Token Bucket model

Token Bucket Model Token Bucket characterizes traffic source Tokens v Token Bucket main parameters: l Token Arrival Rate - v l Bucket Depth - Bc l Time Interval – tc Overflow Tokens l Link Capacity - C Bc C tc = Bc/v 55 Incoming packets Conform Exceed

Token Bucket Model l l l 56 Bucket is being filled with tokens at a rate v token/sec. When bucket is full all the excess tokens are discarded. When packet of size L arrives, bucket is checked for availability of corresponding amount of tokens. If several packets arrive back-to-back and there are sufficient tokens to serve them all, they are accepted at peak rate (usually physical link speed). If enough tokens available, packet is optionally colored and accepted to the network and corresponding amount of tokens is subtracted from the bucket. If not enough tokens, special action on packet is performed.

Token Bucket Model Actions performed on nonconforming packets: l Dropped (Policing) l Delayed in queue either FIFO or WFQ (Shaping) l Colored/Recolored 57

Token Bucket Model Bucket depth variation effect: l Bc = 0 Constant Bit Rate (CBR) l Bc No Regulation Bucket depth is characteristic of traffic burstiness Maximum number of bytes transmitted over period of time t: A( t)max = Bc+v· t 58

Excess Burst (Be) Cisco Implementation GTS ( Generic Traffic Shaping) If during previous tcn-1 interval bucket Bc was not depleted (there is no congestion), in the next interval tcn Bc+Be bytes are available for burst. In frame relay implementations packets admitted via Be tokens are marked with DE bit. 59

Excess Burst (Be) Cisco Implementation CBTS (Class Based Traffic Shaping) allows higher throughput in uncongested environment up to peak rate calculated as v. Peak = v. CIR(1+Be/Bc) Peak rate can be set up manually. 60

Excess Burst (Be) Cisco Implementation CAR allows RED like behavior: l traffic fitting into Bc always conforms traffic fitting into Be conforms with probability proportional to amount of tokens left in the bucket traffic not fitting into Be always exceeds l CAR uses the following parameters: t – time period since the last packet arrival l l 61 Current Debt (Dcur) – Amount of debt during current time interval Compound Debt (Dcomp) – Sum of all Dcur since the last drop Actual Debt (Dact) – Amount of tokens currently borrowed

Excess Burst (Be) Cisco Implementation Packet of length L arrived Bccur – L > 0 Y CAR Algorithm Conform Action Bccur = Bccur – L N Dcur = L - Bccur = 0 Dcomp = Dcomp + Dcur Dact = Dact + Dcur +v· t Dact > Be Exceed Action N Dcomp > Be N 62 Y Y Dcomp = 0

Shaping Configuration Sample GTS Based interface serial 2/1 ip unnumbered loopback 0 traffic-shape rate 64000 8000 1000 256 ! Shaper Definitions interface serial 2/2 ip unnumbered loopback 0 traffic-shape group 100 64000 8000 512 ! access-list 100 permit tcp host 10. 0. 0. 1 any eq http ACL definition Shaper can be only used to control egress traffic flow! 63

Policing Configuration Sample CAR Based IOS 12. 0(5)T ip cef interface serial 2/1 ip unnumbered loopback 0 rate-limit output access-group 100 64000 8000 16000 conform-action transmit excess-action drop CAR Definitions ! interface serial 2/2 ip unnumbered loopback 0 rate-limit input 128000 16000 32000 conform-action transmit excess-action drop ! access-list 100 permit tcp host 10. 0. 0. 1 any eq http ACL definition Policer can be used to control ingress traffic flow! 64

Shaping/Policing Configuration Sample MQI Based 65 IOS 12. 1(5)T class-map match-all policed match protocol http Class definitions class-map match-all shaped match access-group name ftp-downloads ! policy-map bad-boy class policed police 64000 8000 conform-action transmit exceed-action drop class shaped Qo. S policy definition shape average 128000 ! interface serial 2/1 Qo. S Policy attached ip unnumbered loopback 0 to interface service-policy output bad-boy ! ip access-list extended ftp-downloads ACL definition permit tcp any eq ftp-data any

CAR Policing Problem Why cannot my traffic reach CIR value? Cause: Improper setting of Bc and Be values CAR is aggressive, as drops excessive packets and the lost data needs to be retransmitted by upper layers (mainly TCP) after timeout. This also causes TCP to shrink its window reducing flow throughput. Cisco Systems recommends the following settings: Bc = 1. 5 x. CIR/8 Be = 2 x. Bc 66

Congestion Management 67

Queuing l l l 68 Traffic burst may temporarily exceed interface capacity Without queuing this excess traffic will be lost Queuing allows bursty traffic to be transmitted without drops Queuing strategy defines order in which packets are transmitted through egress interface Queuing introduced additional delay which signals to adaptive flows (like TCP) to back off their throughput

Queuing Algorithms l l 69 FIFO Priority (Absolute) Weighted Round Robin (WRR) Fair

FIFO l l l 70 Simplest queuing method with the least CPU overhead No congestion control Transmits packets in the order of arrival High volume traffic can suppress interactive flows Default queuing for interfaces > 2 Mbps (i. e. Ethernet)

FIFO average queue depth dependence on load 71

Absolute Priority Queuing l l 72 Generic Priority Queuing Custom Queuing RTP Priority Queuing Low Latency Queuing (LLQ)

Simplest Qo. S Algorithm: Priority Queuing l Stated requirement: –“If has traffic waiting, send it next” next l Commonly –Defined 73 implemented behavior of IP precedence

Priority Queuing Implementation Approach l Identify interesting traffic –Access l Place lists traffic in various queues l Dequeue in order of queue precedence 74

Priority Queuing (PQ) High Traffic Destined for Interface Medium Classify Normal Low Interface Hardware • Ethernet • Frame Relay • ATM • Serial Link • Etc. Transmit Queue Output Line Q Length Defined by Q Limit Classification by: • Protocol (IP, IPX, Apple. Talk, SNA, Dec. Net, Bridge, etc. ) • Incoming Interface (EO, S 1, etc. ) 75 Interface Buffer Resources Absolute Priority Scheduling

Priority Queuing Scheme High Empty? N Send packet from High 76 Y Medium Empty? N Send Packet from Medium Y Normal Empty? N Send Packet from Normal Y Low Empty? N Send Packet from Low Y

Generic PQ Drawbacks l l l 77 Needs thorough admission control No upper limit for each priority level High risk of low priority queues` starvation effect

Generic PQ Configuration Sample priority-list 1 protocol ip high tcp telnet priority-list 1 protocol ip high list 100 PQ Definition priority-list 1 protocol ip medium lt 1000 priority-list 1 interface ethernet 0/0 medium priority-list 1 default low ! interface serial 2/1 ip unnumbered loopback 0 PQ Attached priority-group 1 to Interface ! access-list 100 permit tcp host 10. 0. 0. 1 any eq http ACL definition 78

Custom Queuing (CQ) (Weighted Round Robin) 1/10 Interface Hardware • Ethernet • Frame Relay • ATM • Serial Link • Etc. 2/10 Traffic Destined for Interface 3/10 Classify 2/10 Transmit Queue Output Line 3/10 Up to 16 Q Length Deferred by Queue Limit Classification by: 79 • Protocol (IP, IPX, Apple. Talk, SNA, Dec. Net, Bridge, etc. ) • Incoming interface (EO, S 1, etc. ) Interface Buffer Resources Link Utilization Weighted Round Robin Scheduling Ratio (byte count) Allocate Proportion of Link Bandwidth)

WRR Drawbacks l l l 80 Unpredictable jitter Fairness significantly depends on MTU and TCP window size Complex calculations to achieve desired traffic proportions

CQ Byte-count Calculus Distribute bandwidth to 3 queues with proportion x: y: z and packet sizes qx, qy, qz. 1. Calculate ax=x/qx, ay=y/qy, az=z/qz. 2. Normalize and round ax, ay, az. ax’= round(ax/min(ax, ay, az)); ay’= round(ay/min(ax, ay, az)); az’= round(az/min(ax, ay, az)). 3. Convert obtained packet proportion into byte count bcx = ax’·qx; bcy = ay’·qy; bcz = az’·qz. 4. Actual bandwidth share of i-th queue can be calculated with the following formula: 5. For better approximation obtained byte-counts can be multiplied by some positive whole number. Starting with IOS 12. 1 CQ employs Deficit Round Robin algorithm and there is no need in such byte-count tuning. 81

CQ Configuration Sample queue-list 1 protocol ip 1 tcp telnet queue-list 1 protocol ip 2 list 100 queue-list 1 protocol ip 3 udp 53 queue-list 1 interface ethernet 0/0 4 queue-list 1 queue 1 byte-count 3000 CQ List Definition queue-list 1 queue 2 byte-count 4500 queue-list 1 queue 3 byte-count 3000 queue-list 1 queue 4 byte-count 1500 queue-list 1 default 4 ! interface serial 2/1 CQ Attached ip unnumbered loopback 0 to Interface custom-queue-list 1 ! access-list 100 permit tcp host 10. 0. 0. 1 any eq http ACL Definition 82

“Bitwise Round Robin” Fair Queuing TDM Model Time Division Multiplexer l Keshav, Demers, Shenker, and Zhang l Simulates a TDM l One flow per channel 83

TDM Message Arrival Sequence 6 4 5 1 2 3 84 Time Division Multiplexer

TDM Message Delivery Sequence 5 Time Division Multiplexer 85 6 4 1 3 2

Fair Queuing Algorithm Employs virtual bit-by-bit round robin model (BRR) BRR dynamics are described by the equation: i-th packet from flow a arriving at time t 0 is services at time t : Servicing of i-th packet from flow a will start at Sia and finish at Fia : Additional parameter is added for priority assignment to inactive flows : Packets are ordered for transmission according to Bia values. 86

Fair Queuing Approach l Enqueue traffic in the sequence the TDM would deliver it l As a result, be as fair as the TDM 87

Effects of Fair Queuing l Low-bandwidth flows get –As much bandwidth as they can use –Timely service l High-bandwidth –Interleave flows traffic –Cooperatively share bandwidth –Absorb latency 88

What Weighting Does l In TDM –Channel l In speed determines message “duration” WFQ –Multiplier on message length changes simulated message “duration” l Result: –Flow’s 89 “fair” share predictably unfair

Weighted Fair Queuing (WFQ) Traffic Destined for Interface Transmit Queue Classify Configurable Number of Queues 90 Flow-Based Classification by: • Source and destination address • Protocol • Session identifier (port/socket) Output Line Weighted Fair Scheduling Interface Weight Determined by: Buffer • Requested Qo. S (IP Procedure, RSVP) Resources • Frame Relay FECN, BECN, DE (For FR Traffic) • Flow throughput (weighted-fair)

Weighted Fair Queuing (WFQ) l l l 91 Fair bandwidth per flow allocation Low delay for interactive applications Protection from ill-behaved sources

Weighted Fair Queuing (WFQ) Flow classified by the following fields: l l l Source address Source port Destination address Destination port To. S Weight of each flow (queue) depends on To. S: weight = 1/(precedence+1) Bandwidth distributed in 1/weight proportions 92

Weighted Fair Queuing (WFQ) l l 93 Packets are ordered according to the expected virtual departure time of their last bit. Low volume flows have preference over high volume transfers. Low volume flow is identified as using less than its share of bandwidth. The special queue length threshold value is established, after which only low volume flows can enqueue. All the packets, that belong to high volume flows are dropped.

Drawbacks of Weighted Fair Queuing l Requires more sorting than other approaches 94

Weighted Fair Queuing (WFQ) Delay FTP Telnet t 95

Weighted Fair Queuing (WFQ) FTP Delay Telnet t 96

WFQ Configuration Sample interface serial 2/1 ip unnumbered loopback 0 fair-queue 32 128 0 Queue Threshold (packets) Number of reservable queues Maximal number of queues 97

RTP Priority Queuing l l l 98 Classifies only by UDP port range Only even ports from the range are classified Establishes upper limit via integrated policer Excess traffic dropped during congestion periods RTP PQ has priority over LLQ

RTP PQ Configuration Sample interface serial 2/1 ip unnumbered loopback 0 ip rtp priority 16384 16383 256 Starting UDP port Bandwidth Limit (kbps) Range length 99

Low Latency Queuing (LLQ) l l 100 Implemented using MQI Very rich classification criteria (class-map) Establishes upper limit via integrated policer Excess traffic dropped during congestion periods

LLQ Configuration Sample IOS 12. 0(5)T class-map match-all voice match access-group name voip ! policy-map llq class voip priority 30 class-default fair-queue 64 ! interface serial 2/1 ip unnumbered loopback 0 service-policy output llq ! ip access-list extended voip permit ip host 10. 0. 0. 1 any 101 Class definitions LLQ policy definition LLQ Policy attached to interface ACL definition

Class Based WFQ (CBWFQ) l l 102 Based on the same algorithm as WFQ Weights can be manually configured Allows to easily specify guaranteed bandwidth for a class Configuration based on Cisco MQI

CBWFQ Configuration Sample IOS 12. 0(5)T 103 class-map match-all premium match access-group name premium- cust class-map match-all low-priority match protocol napster ! policy-map cbwfq-sample class premium bandwidth 512 class low-priority shape average 128 shape peak 512 class-default fair-queue 64 ! interface serial 2/1 ip unnumbered loopback 0 max-reserved-bandwidth 85 service-policy output cbwfq-sample ! ip access-list extended premium- cust permit ip host 10. 0. 0. 1 any Class definitions Qos policy definition Qo. S Policy attached to interface ACL definition

CBWFQ Configuration Sample Hierarchical Design class-map match-all premium match access-group name premium- cust class-map match-all voice match ip precedence flash ! policy-map total-shaper class-default shape average 1536 service-policy class-policy-map class-policy class premium bandwidth 512 class voice priority 64 class-default fair-queue 128 104 IOS 12. 1(5)T interface fastethernet 1/0 ip unnumbered loopback 0 max-reserved-bandwidth 85 service-policy output total-shaper ! ip access-list extended premium- cust permit ip host 10. 0. 0. 1 any

Hierarchical CBWFQ Limitations l l l 105 Only two levels of hierarchy are supported set command not supported in child policy Shaping allows only in parent policy LLQ can be configured only either in child or parent policies but not in both FQ allowed only in child policy

Congestion Avoidance 106

Load Global Synchronization Effect Link Capacity Avg. Throughput t 107

Tail Drop and TCP Flow Control l Packet drops from all TCP sessions simultaneously High probability of multiple drops from the same TCP session Uniformly distributed drops from high volume and interactive flows Result: Low average throughput! 108

Random Early Detection (RED) Developed by Van Jacobson in 1993 l l l 109 Starts randomly dropping packets before actual congestion occurs Keeps average queue depth low Increases average throughput

Load Global Synchronization Removed Link Capacity Avg. Throughput t 110

Random Early Detection (RED) p p Tail Drop RED 1 1 Adjustable 0 111 0 qmax qavg min max qavg

Random Early Detection (RED) RED Parameters: l l 112 min – Minimal threshold after which RED starts packet drops. Minimal recommended value is 5 packets. max – Maximal threshold after which all packets are dropped. Recommended value is 2 -3 times min. - Mark probability denominator denotes packet drop probability at max average queue depth. Optimal value – 0. 1. - Exponential weighting factor determines the level of backward value-dependence in average queue depth calculation: qavg = (qold · (1 - 2 - )) + (qcur · 2 - ) General recommendation = 9.

TCP Rate Control - 1 l l In TCP, the spacing of ACKs and the window size in the ACKs controls the transmitter’s rate. Rate Control manipulates the ACKs as they pass through the rate control device by: – – – l l Adjusting the size of TCP ACK window Inserting new ACKs Re-spacing existing ACKs Rate Control works only with TCP; other methods, such as Token Bucket, must be used with UDP. Rate Control violates the protocol layering design, as it allows network devices to manipulate a higher-layer protocol’s operation. Nevertheless, it usually functions well and provides fine-grained control.

TCP Rate Control - 2 l Example:

Weighted Random Early Detection (WRED) l l 115 Modified version of RED Weights determine the set of parameters: min , max and . Weight depends on To. S field value Interactive flows are preserved

WRED Configuration Sample Interface based interface serial ip unnumbered random-detect random-detect … 116 2/1 loopback 0 0 1 2 3 32 32 64 64 20 20 min max

WRED Configuration Sample MQI based policy-map red class-default random-detect 0 32 64 random-detect 1 32 64 random-detect 2 32 64 random-detect 3 32 64 … interface Serial 2/1 ip unnumbered loopback 0 service-policy output red min 20 20 max WRED is incompatible with LLQ feature! 117

Link Optimization 118

Link Fragmentation and Interleaving (LFI) For links < 128 kbps Jumbogram Voice Packet 64 kbps 1500 bytes 190 ms 119

Link Fragmentation and Interleaving (LFI) 64 kbps Supported interfaces: l Multilink PPP l Frame Relay DLCI l ATM VC 120

LFI Configuration Sample MLP version interface virtual-template 1 ip unnumbered loopback 0 ppp multilink interleave ppp multilink fragment-delay 30 ip rtp interleave 16384 1024 512 … 121

Signaling 122

Resource Reservation Protocol (RSVP) l l l 123 End-to-end Qo. S signaling protocol Used to establish dynamic reservations over the network Always establishes simplex reservation Supports unicast and multicast traffic Actually uses WFQ and WRED mechanisms

Resource Reservation Protocol (RSVP) 124

Resource Reservation Protocol (RSVP) 125

Resource Reservation Protocol (RSVP) Reservation Types: l Guaranteed Rate (uses WFQ and LLQ) l Controlled Load (uses WRED) Distinct Explicit Fixed Filter (FF) Shared Explicit (SE) Wildcard 126 Shared X Wildcard Filter (WF)

Resource Reservation Protocol (RSVP) 127

Qo. S Policy Propagation over BGP l l l 128 Qo. S policy can be shared inside single AS or among different ASs. Community attribute is usually used for color assignments Prevents manual policy changes in network devices

Qo. S Policy Propagation over BGP 129

QPPB Configuration Sample Router A ip bgp-community new-format ! router bgp 10 neighbor 10. 0. 0. 1 remote-as 20 neighbor 10. 0. 0. 1 send-community neighbor 10. 0. 0. 1 route-map cout ! route-map cout permit 10 match ip address 20 set community 60: 9 ! access-list 20 permit 192. 168. 0. 0. 0. 255 130 Router B ip bgp-community new-format ! router bgp 20 neighbor 10. 0. 0. 2 remote-as 10 table-map mark-pol ! route-map mark-pol permit 10 match community 1 set ip precedence flash ! ip community-list 1 permit 60: 9 ! interface Serial 0/1 ip unnumbered loopback 0 bgp-policy source ip-prec-map

Topics not Covered l l l 131 Multiprotocol Label Switching (MPLS) Frame Relay Qo. S ATM Qo. S Distributed Queuing Algorithms Multicast

Conclusion l l l 132 Qo. S is not an exotic feature any more Qo. S allows specific applications (Vo. IP, VC) to share network infrastructure with best-effort traffic Qo. S in IP networks simplifies their functionality avoiding Frame Relay and ATM usage

? Questions? ? ? 133