Connecting people to information Internet W3 Server SAP Server FTP Server Why Invest in QoS ? To...

Connecting people to information

SiSi

SiSi

Internet

W3 Server

SAP Server

FTP ServerWhy Invest in QoS ?

To accelerate the deployment of network services, by enabling predictable response for application traffic and service requirements


QoS Signaling

IPv4 PacketData

3-Precedence

ToS Field

IPv6 PacketData

4-Priority

Priority Field

3-Priority

ISL/802.1Q Frame

Tag/MPLS Header

In-Band

RSVP(Guaranteed Service

Controlled Load Service)

Out-of-Band

ATM UNI(CBR, VBR, ABR,

UBR Services)

Frame Relay LMI(CIR Service)

3-Priority


Integrated Services

• IntServ (IETF Working group) calls for an explicit signaling protocol (RSVP)

• Resource Reservation Protocol (RSVP)

– Receiver initiated layer 3 signaling protocol

– Designed to reserve bandwidth for in-elastic real-time traffic

– Meant for audio/video streams and multi-cast sessions and not for apps with transient flows

– RSVP classifies traffic based on IP addresses/port numbers


Integrated Services - IntServ

• An application explicitly signals its QoS requirements to the network

• Network uses admission and policy control to decide if it can meet the application’s requirements.

• Signaling is done using RSVP and flows from receiver to sender (RESV message)

• At each hop, the network device enforces the contract via policing and prioritizes forwarding via multiple transmit queues


Cisco IOS® QoS


Cisco IOS® QoS Diff Serv Components

Network EffectMechanismTraffic

Conditioner

Drop RED, WRED, Flow RED

Scheduling

Marking

Metering (Policing)

Shaping

Compress

Fragment

PQ, CQ, WFQ, CB WFQ, WRR, MDRR

CAR, Policy Routing, DSCP, NFCII

CAR

GTS, FRTS

CRTP

LFI, FRF.12

• Sets IP Precedence/DSCP• By Application, Protocol, Address,etc

• Reduce the Volume of Traffic Sent

• Enforce a Maximum Transmission Rate• Conform or Exceed Thresholds

• Bandwidth Management: Traffic Priority• Set Servicing Sequence

• Avoid Congestion by Notifying Source• Prioritize which Traffic Is Told to Reduce

• Conforms Traffic to Committed Bandwidth• Interwork with Layer 2 Notification e.g., BECN

• Reduce Delay on Slower Speed Links• Split, Recombine Larger Frames


IP QoS11.1 11.2 11.3

11.1CA11.1CB (ISP8)11.1CC (FIB)11.1CD (ISP8+L3)11.1CE (FIB+L3)

11.1CC

12.0

• WFQ • RED• WRED• RSVP• NetFlow Switching

• CEF• CAR/DCAR• DWFQ• DWRED• QoS Policy Propagation via BGP• NetFlow Services

CYH2 ?8

11.1CC• IP ATM CoS (Ph I)

12.0T• IP ATM CoS (Ph II)


One Common Policy

Policy Required:Treat Gold traffic with the highest service level over Silver and Bronze

traffic


Sample Class Base Service Deployment

GoldGold

BronzeBronze

Silver

Provisioned Service

Best Effort Delivery

Premium IP

Voice, SNA

E-mail, WebBrowsing

E-Commerce,ERP-Critical

Application Audit Service Levels


Queuing’s Premise

• Getting better service is a matter of managing congested queuesmanaging congested queues

• Over-all latency and bandwidth are constant– Make some traffic absorb latency, and therefore give up

bandwidth– Shield other traffic from latency, and therefore gain bandwidth


Queuing Algorithms

• Congestion management algorithms– First In First Out– Priority Queuing– Custom Queuing– Weighted Fair Queuing (WFQ)


FIFO Queuing

• Premise– Packets leave in order of arrival

• Fixed queue lengths– Results in dropping from tail of

queue under load– Results in flow synchronization


FIFO

Transmit Queue

Output Line


• Order of Arrival completely determines the bandwidth, promptness and buffer allocation

• Does not provide protection against ill-behaved sources• Bursty sources may cause high delay in delivering some

time sensitive control/signaling messages• Queuing delay of packets is on average and uniform across

all sources

Pitfalls of FIFO


FIFO Default and Config

• FIFO is a default queuing algorithm on interfaces that don’t support fancy queuing– i.e. X.25, tunnel

• FIFO can be explicitly configured by turning off WFQ on interface:

no fair-queue


caymans#sh int e0Ethernet0 is up, line protocol is up Hardware is Lance, address is 0000.0c14.5a18 (bia 0000.0c14.5a18) Internet address is 171.69.232.116/28 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output 00:00:02, output hang never Last clearing of "show interface" counters never

Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 78716 packets input, 25213248 bytes, 0 no buffer Received 78582 broadcasts, 0 runts, 0 giants, 0 throttles 3 input errors, 3 CRC, 3 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 71241 packets output, 6905654 bytes, 0 underruns 0 output errors, 1 collisions, 3 interface resets 0 babbles, 0 late collision, 39 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

FIFO Example


Simplest QoS Algorithm: Priority Queuing

• Stated requirement:– If <application> has traffic waiting,

send it nextsend it next

• Commonly implemented– Defined behavior of IP precedence


Priority Queuing

Priority (Access)

List

Forwarder

Low Priority

Medium Priority

High Priority

TransmissionQueue

Classification


Priority Queuing Implementation Approach

• Identify interesting traffic– Priority-list by protocol

– Priority-list by incoming interface

• Place traffic in various queues

• Dequeue in order of queue precedence


Priority Queuing cont.

• Four priority queues - – High, Medium, Normal, Low

• Packets not classified by priority-list mechanism fall into normal queue

• Priority queuing not supported over X.25 and Tunnel interfaces


Priority Queuing (PQ)

Traffic Destined

for Interface

Classification by:•Protocol (IP, IPX, AppleTalk, SN

A, DecNet, Bridge, etc.)•Incoming Interface

(EO, SO, S1, etc.)

Interface Buffer Resources

Transmit Queue

Output Line

Interface Hardware•Ethernet•Frame Relay•ATM•Serial Link•Etc.High

Medium

Normal

Low

Q Length Defined by Q

Limit

ClassifyClassify

Absolute Priority Scheduling


Pitfalls of Priority-Queuing

• Can cause traffic lockout if configured incorrectly

• FIFO within priority– Within priority, may still be unpredictable– Resource allocation– lower priority queues may starve


Priority Queuing Commands

• Priority-list protocol command

– Establishes queuing priority based upon protocol type:

[no] priority-list <list-number> protocol <protocol-name> {high | medium | normal | low} <queue-keyword> <keyword-value>

• Priority-list interface command

– Establishes queuing priority based on packets entering from interface:

[no] priority-list <list-number> interface <interface-type>

<interface-number> {high | medium | normal | low}


Priority Queuing Commands

• Priority-list default command

– To assign priority-queue for those packets that do not match any rule in priority-list. If not specified, normal queue is default

[no] priority-list <list> default <queuekeyword>

• Priority-list queue-limit

– Specify maximum number of packets that can be waiting in each priority queue[no] priority-list <list> queue-limit <high-lim> <medium-lim>

<normal-lim> <low-lim>

• Priority-group

– Assigns a specified priority-list to an interface– [no] priority-group <1-16>


Priority Queuing ExamplesExample 1:

caymans(config)#access-list 10 permit 239.1.1.0 0.0.0.255

caymans(config)#priority-list 1 protocol ip high list 10

Example 2:

caymans(config)#priority-list 1 protocol decnet high

caymans(config)#priority-list 1 protocol ip medium

Example 3:

caymans(config)#priority-list 1 queue-limit 10 40 60 90

Example 4:

caymans(config)#priority-list 2 protocol decnet medium gt 200

caymans(config)#priority-list 2 protocol bridge high

caymans(config)#priority-list 2 protocol ip medium


Priority Queuing Examples

Example 5:caymans(config)#priority-list 4 protocol decnet medium lt 200

caymans(config)#priority-list 4 protocol ip medium tcp 23

caymans(config)#priority-list 4 protocol ip medium udp 53

caymans(config)#priority-list 4 protocol ip high

Example 6:caymans(config)#priority-list 3 interface ethernet 0 high

caymans(config)#priority-list 3 interface ethernet 1 medium

caymans(config)#priority-list 3 interface serial 1 medium

caymans(config)#priority-list 3 default low

Example 7:caymans(config)#interface serial 0

caymans(config-if)#priority-group 4


caymans# sh queueing priorityCurrent priority queue configuration:

List Queue Args1 high protocol decnet 1 high protocol ip list 101 medium protocol ip 1 high limit 101 low limit 902 medium protocol decnet gt 2002 high protocol bridge 2 medium protocol ip 3 low default3 high interface Ethernet0 3 medium interface Ethernet1 3 medium interface Serial1 4 medium protocol decnet lt 2004 medium protocol ip tcp port telnet4 medium protocol ip udp port domain4 high protocol ip

Priority Queuing Example


caymans#sh int s0Serial0 is down, line protocol is down Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input never, output never, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0

Queueing strategy: priority-list 4 Output queue: high 0/20/0, medium 0/40/0, normal 0/60/0, low 0/80/0 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 16 packets output, 2841 bytes, 0 underruns 0 output errors, 0 collisions, 22339 interface resets 0 output buffer failures, 0 output buffers swapped out 108 carrier transitions DCD=down DSR=down DTR=up RTS=up CTS=down

Priority Queuing Example


Class-Based Queuing

• Cisco feature: custom queuing

• Stated requirement:– traffic with <characteristics>

needs a guaranteed rate or latencyguaranteed rate or latency

• Characteristics may be:– Application– Traffic source


Custom Queuing Implementation Approach

• Identify the traffic

• Distribute into FIFO queue by class

• Dequeue in some rotation– Remove some number of bytes at most– Move to next queue in round robin order


Custom Queuing

• Identify the traffic– queue-list by protocol– queue-list by incoming interface

• Distribute into FIFO queue by class– Total 17 queues– Queue number 1-16 is serviced sequentially– Queue number 0 is a system queue, ie. keepalives, therefore emptied first

• Round Robin Dequeue– Configurable byte count to transmit before servicing – the next queue


Custom Queuing

Queue #0Queue #0

Transmission QueueTransmission Queue

Queue #1Queue #1Queue #2Queue #2






Queue #15Queue #15Queue #7Queue #7Queue #16Queue #16Queue #8Queue #8

Control Traffic

PriorityPriority (Access) (Access)

List List

ForwarderForwarder


Custom Queuing (CQ)

Traffic Destined

for Interface

Interface Buffer

Resources

Q Length Deferred by Queue Limit

Up to 16

3/10

1/10

Weighted RoundRobin Scheduling(byte count)

Classification by:•Protocol (IP, IPX, AppleTalk,

SNA, DecNet, Bridge, etc.)•Incoming interface

(EO, SO, S1, etc.)

Allocate Proportion of

Link Bandwidth)

ClassifyClassify

Interface Hardware•Ethernet•Frame Relay•ATM•Serial Link•Etc.

2/10

3/10

2/10

Link Utilization Ratio

Transmit Queue

Output Line


Pitfalls of Custom Queuing

• FIFO by class: – Within class, still unpredictable


Custom Queuing Commands

• queue-list protocol

– Establishes queuing priority based on protocol type

[no] queue-list <list-number> protocol <protocol-name> <queue-number> <queue-keyword> <keyword-value>

• queue-list interface

– Establishes queuing priority based on incoming interface

[no] queue-list <list-number> interface <interface-name> <interface-number> <queue #>



• queue-list default

– Assigns priority-queue for those packets that do not match any rule in priority-list. If not specified, queue number 1 is default.

[no] queue-list <list-number> default <queue-number>

• queue-list queue limit

– Designate queue length limit for a custom queue [no] queue-list <list-number> queue <queue-number> limit

<limit-number>



• queue-list queue byte-count

– Designate byte-count allowed per queue

[no] queue-list <list-number> queue <queue-number> byte-count <byte-count-number>

• queue-list lowest-custom

– Sets lowest number of queue to be treated as custom

[no] queue-list <list-number> lowest-custom <queue-number>

• custom-queue-list

– Assigns a specified queue-list to an interface

[no] custom-queue-list <list>


Custom Queuing Example

caymans(config)#queue-list 4 interface e0 5

caymans(config)#queue-list 4 interface ethernet 1 6

caymans(config)#queue-list 4 interface ethernet 2 7

caymans(config)#queue-list 4 interface serial 0 8

caymans(config)#queue-list 4 default 10

caymans(config)#queue-list 4 protocol arp 4

caymans(config)#queue-list 4 protocol bridge 3

caymans(config)#queue-list 4 protocol ipx 9



caymans(config)#queue-list 1 protocol decnet 3

caymans(config)#queue-list 1 protocol ip 7

caymans(config)#queue-list 2 protocol decnet 2 gt 200

caymans(config)#queue-list 2 protocol ip 7 tcp 23

caymans(config)#queue-list 2 protocol ip 8 udp 53

caymans(config)#queue-list 2 protocol ip 9 tcp 23

caymans(config)#queue-list 3 protocol decnet 2 lt 200

caymans(config)#queue-list 3 protocol ip 1 list 10

caymans(config)#queue-list 3 protpcpl ip 7

caymans(config)#queue-list 3 protocol ip 7

caymans(config)#queue-list 3 default 10

caymans(config)#int s0

caymans(config-if)#custom-queue-list 1

caymans(config-if)#int s1

caymans(config-if)#custom-queue-list 4

queue-list configuration:



caymans#sh queueing customCurrent custom queue configuration:List Queue Args1 5 lowest custom queue1 3 protocol decnet 1 7 protocol ip 2 2 protocol decnet gt 2002 8 protocol ip udp port domain3 10 default3 2 protocol decnet lt 2003 1 protocol ip list 103 7 protocol ip 4 10 default4 5 interface Ethernet0 4 6 interface Ethernet1 4 7 interface Ethernet2 4 8 interface Serial0 4 3 protocol bridge 4 4 protocol arp 4 9 protocol ipx



caymans#sh int s0Serial0 is down, line protocol is down Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/25

5 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input never, output never, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: custom-list 1 Output queues: (queue #: size/max/drops) 0: 0/20/0 1: 0/20/0 2: 0/20/0 3: 0/20/0 4: 0/20/0 5: 0/20/0 6: 0/20/0 7: 0/20/0 8: 0/20/0 9: 0/20/0 10: 0/20/0 11: 0/20/0 12: 0/20/0 13: 0/20/0 14: 0/20/0 15: 0/20/0

16: 0/20/0 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 17 packets output, 3138 bytes, 0 underruns 0 output errors, 0 collisions, 22891 interface resets 0 output buffer failures, 0 output buffers swapped out 116 carrier transitions


Why Use WFQ?

• Provides relative bandwidth guarantees–Fair Queuing (FQ) allocates equal share of bandwidth to each active queue–Weighted Fair Queuing (WFQ) allows for unequal allocation of bandwidth


Design Intent of Weighted Fair Queuing

• Stated requirement:–“Traffic latency must be predictablepredictable “Reserved flows must achieve a certain bandwidthbandwidth and latencylatency”–“Configuration must be straightforward”–“Should normally do the right thing without manual intervention ”


Weighted Fair Queuing (WFQ)

One 200 Byte Data

Packet

Interface BufferResources

TransmitScheduling

Two 100 ByteVoice Packets

Classify

1

11

De-queue

12

Configurable Queues

2

11

Two 100 Byte Packets Transmitted for Every One 200 Byte Packet

Therefore = “Fair”

Flow Classification/Sorting•Source and destination address•Protocol•Session identifier (Port/Socket)

Weighted Fair Scheduling•Requested Qos (IP Precedence, RSVP)•Frame Relay FECN, BECN, DE•Flow throughput (Weighted-Fair)

1122


Feature Description

Dynamically identifies data streams using an interface

Dynamically prioritizes those data streams


So What?

Equal access for File Transfer traffic

Priority for Interactive Traffic

Future: Guarantees for Real Time Traffic

Hands Free! No Access Lists!


Fair Queuing “Conversations”

Ideally: data streams exchanged by applications

Practically: discernible data streams

Source and destination address

Protocol type

Session identifier (port or socket number)

QoS/TOS


Configuration

congestive discard policy

hits conversations with more than one message

occurs when

total number of messages > threshold

fair-queue [congestive discard threshold]

[#hashed_queues] [reserved_queues]

fair-queue [congestive discard threshold]

[#hashed_queues] [reserved_queues]


Configuration Default

inactive on LANs and high speed lines

inactive on serial lines with LAPB, X.25, PPP Compression, etc.

active on other serial lines at E-1 speed or below

eg: PPP, HDLC, Frame Relay, SMDS


Diagnostics/Troubleshooting

show interface [interface name]show interface [interface name]

show queue interface nameshow queue interface name

show queueing [fair | custom | priority]show queueing [fair | custom | priority]


Pitfalls of Weighted Fair Queuing

• Requires more sorting than other approaches


WFQ Monitoring

lazy-ccartee-dont-touch#sh int ser 3/3Serial3/3 is up, line protocol is up Hardware is cxBus Serial Internet address is 1.1.2.1/24 MTU 4470 bytes, BW 2000 Kbit, DLY 20000 usec, rely 255/255, load 138/255 Encapsulation HDLC, loopback not set, keepalive not set Last input 00:00:11, output 00:00:00, output hang never Last clearing of "show interface" counters 00:05:31 Input queue: 0/75/0 (size/max/drops); Total output drops: 12101 Queueing strategy: weighted fair Outputqueue: 69/64/12102 (size/threshold/drops) Conversations 69/71 (active/max active) Reserved Conversations 0/0 (allocated/max allocated) 30 second input rate 1080000 bits/sec, 584 packets/sec 30 second output rate 1087000 bits/sec, 588 packets/sec 26529 packets input, 6147500 bytes, 0 no buffer Received 6 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 26731 packets output, 6200224 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 output buffer failures, 38989 output buffers swapped out 0 carrier transitions RTS up, CTS up, DTR up, DCD up, DSR up


WFQ Monitoring

lazy-ccartee-dont-touch#show queueingCurrent fair queue configuration:

Interface Discard Dynamic Reserved threshold queue count queue count Serial3/0 64 256 0 Serial3/1 64 256 0 Serial3/2 64 16 0 Serial3/3 64 256 0

Current priority queue configuration:Current custom queue configuration:Current RED queue configuration:lazy-ccartee-dont-touch#


lazy-ccartee-dont-touch#sh queue ser 3/3 Input queue: 0/75/0 (size/max/drops); Total output drops: 59423 Queueing strategy: weighted fair Output queue: 68/64/59423 (size/threshold/drops) Conversations 69/71 (active/max active) Reserved Conversations 0/0 (allocated/max allocated)

(depth/weight/discards) 1/4096/782 Conversation 0, linktype: ip, length: 232 source: 1.1.1.1, destination: 1.1.2.49, id: 0x0001, ttl: 236, TOS: 0 prot: 17, source port 11111, destination port 22222

(depth/weight/discards) 1/4096/782 Conversation 2, linktype: ip, length: 232 source: 1.1.1.1, destination: 1.1.2.51, id: 0x0001, ttl: 250, TOS: 0 prot: 17, source port 11111, destination port 22222

WFQ Monitoring

Show queue serial:


Policing & Shaping


Traffic Policing & Shaping

• Ensures that traffic does not exceed a (contracted) bandwidth limit

• Policing & Shaping both limit bandwidth but with different impact on traffic– Policing drops more often - more retransmits– Shaping adds variable delay


Shaping

Tra

ffic

Time

Traffic Rate

Tra

ffic

Time

Traffic Rate

Traffic Policing vs. Shaping

Policing

Tra

ffic

Time

Traffic Rate

Tra

ffic

Time

Traffic Rate


Policing vs. Shaping

• Rate limiting allows larger bursts– More uneven utilization

• Shaping sends smaller bursts in equal intervals– smoother utilization– easier for receiving end


Ways to Limit Throughput

• Policing– Committed Access Rate (CAR)

• Traffic shaping– Generic Traffic Shaping(GTS)– Frame Relay Traffic Shaping (FRTS)


Basic Policing Mechanism - Token Bucket

• Data needs credits (“tokens”) to be transmitted, otherwise it is dropped

• Tokens are issued at the policing rate• Tokens usually are accumulated in a “bucket”

to accommodate bursts• No limit how fast tokens can be taken out of

the bucket, allows bursts to use large chunks of bandwidth


Token Bucket

p

Tokens

BOverflowTokens

PacketsArriving Conform

Exceed

BBurst Size

pToken Arrival Rate


Basic Shaping MechanismLeaky Bucket

• Data is transmitted at a given rate

• Buffer (“bucket”) allows for bursts to arrive

• If buffer is full packets are dropped


Leaky Bucket

PacketsArriving

BOverflowPackets

pBBurst size

pLeak rate

Packets Are Leakedat a Rate Specified

by p


Token vs. Leaky Bucket

• Token bucket–Passes bursts

–No buffering

–Does not smoothes or shapes traffic

• Leaky bucket–Smoothes or shapes traffic, this is achieved by buffering the traffic

–Used in ATM networks for traffic shaping and policing

•Known also as Generic Cell Rate Algorithm (GCRA) in ATM


Committed Access Rate (CAR)

• Two functions– Packet classification—IP precedence

and QoS group setting– Access bandwidth management

through rate limiting (policing)


Marking: IP Precedence

• QoS marking

• Inband

• Differentiated network services across any media

or topology

IP PacketData

IP Precedence

Type of Service (ToS)

Diff Serv Code Point (DSCP)

Data, Voice, Video


CAR—Traffic Matching Specification

• Identify packets of interest for packet classification or rate limiting or both

• Matching specification

–1) All traffic

–2) IP precedence

–3) MAC address

–4) IP access list—standard and extended (slower)


Committed Access Rate (CAR)

• Two functions– Packet Classification Packet Classification IP precedence

and QoS group setting– Access Bandwidth ManagementAccess Bandwidth Management

through rate limiting


CAR—Action Policies

• Configurable actions– Transmit

– Drop

– Continue (go to the next rate-limitin the list)

– Set precedence and transmit (rewrite the IP precedence bits and transmit)

– Set precedence and continue (rewrite the IP precedence bits and go to the next rate-limit in the list)


Committed Access Rate (CAR)Bandwidth Management

Application Hosting

BackboneBackbone

3) Invoke QoS Policy Action Based on EdgeClassification, e.g. DropLow Priority via WRED if Burst Limit Exceeded

1) Packet Classificationthrough IP Precedence and QoS Group Settings

2) Apply Rate Limiting to Matching Traffic Pattern e.g. 25Kbps of Traffic to ‘Bronze’

San Jose

Ottawa


CAR Traffic Measurement

• Uses the token bucket schemetoken bucket scheme as a measuring mechanism

• Tokens are added to the bucket at the committed ratecommitted rate and the number of tokens in the bucket is limited by the normal burst size

• Depth of the bucket determines the burst size



• Packets arriving with sufficient tokens in the bucket are said to conformconform

• Packets arriving with insufficient tokens in the bucket are said to exceedexceed



• Packets arriving exceeding the normal burst but fall within the extended burst limit is handled via a RED-like managed drop policy

• This is to reduce TCP Slow-Start oscillation– (When the exceed-action is to drop packets)



• Token bucket configurable parameters– Committed rate (bits/sec)

• Configurable in increments of 8Kbits– Normal burst size (bytes)

• To handle temporary burst over the committed rate limit without paying a penalty

– Extended burst size (bytes)• Burst in excess of the normal burst size


Extended Burst

Exceed %

100

BucketDepth

ExtendedBurst

NormalBurst

CAR Policy Examples

Drop

Drop

Per Application CAR

Multimedia

Mission--Critical

Recolor

Recolor

28


Marking at the Edge: IP Precedence

• CAR access-list– [no] access-list rate-limit <1–99> <ip_precedence>– [no] access-list rate-limit <100–199>

<mac_address>

• CAR show command– Show interface [interface] rate-limit


Marking IP Precedence: CAR

R1#write term….!interface S0 description 128Kbps to R2 rate-limit input access-group 101 128000 8000 16000 conform-action set-prec-transmit 5 exceed-action set-prec-transmit 3 rate-limit input access-group 102 64000 8000 16000 conform-action set-prec-transmit 3 exceed-action set-prec-transmit 1ip address 200.200.14.250 255.255.255.252!access-list 101 permit tcp any any eq wwwaccess-list 102 permit tcp any any eq ftp!

R1S0

R2


Traffic Shaping

Traffic Shaping

Tra

ffic

Time

Traffic Rate

Tra

ffic

Time

Traffic Rate


Bandwidth Management: Traffic Shaping

• Shaping highly beneficial if downstream device is policing

• Packet bursts are queued instead of being dropped

• Resulting packet stream is “smoothed” and net throughput for bursty traffic is higher


Traffic Shaping Queue Structure

• One queue per –Sub-interface

–Access List

–DLCI

• Feeds into queues at hardware layer

ForwarderForwarder

WithinWithinTokenToken

Bucket?Bucket?

InterfaceInterface Congested? Congested?

Sub-InterfaceSub-InterfaceFancy Queues Fancy Queues

HardwareHardwareInterfaceInterfaceQueuesQueues

TransmissionTransmissionQueue Queue

No

Yes

Yes

No


FRTS

Shaper

Policy Based on DLCI

Output Interfaces

No Marking

Does Not Run in Distributed Mode

Understands BECN/FECN

Policer

Policy Based on IP

Input and Output Interfaces

Runs in Distributed Mode

Marking

Does not Act on FECN/BECN

CAR

Difference Between CAR and FRTS


Traffic Shaping

Transmit Transmit QueueQueue

Output Line

Traffic Destined

for Interface

Classification by:

Extended Access List Functionality

“Leaky Bucket” Shaping

Configured Queuing (e.g.

WFQ, PQ, etc.)

Match

No MatchNo Match

ClassifyClassify


Difference between FRTS and GTSGTS

Shaper

Interface Level or Group-Based

Shaping Queue WFQ

Can Be Anything

No Support for FRF.12

Understands BECN/FECN

FRTS

Shaper FR Only

Per DLCI

Shaping Queue PQ,CQ and WFQ(12.0(4)T)

Interface Queue 2 Level Priority

Supports FRF.12

Understands FECN/BECN


Generic Traffic ShapingCommands

• Traffic-shape rate bit-rate [burst-size [excess-burst-size]]

• Traffic-shape group access-list bit-rate [burst-size [excess-burst-size]] – bit-rate : access bit rate– burst-size : number of bits per interval – excess-burst-size : number of bits that can exceed

burst-size in first interval of congestion– interval : burst-size/bit-rate


Generic Traffic ShapingExample

• Traffic-shape rate 128000 16000 32000– interval = 16000 bits/128000 bps = 0.125 s– transmit 16000 bits per 0.125 s interval– allow to exceed by 32000 bits in the first int

erval


Monitor Traffic Shaping

c7200_up(config-if)#traffic-shape rate 128000 16000 32000

c7200_up#show traffic-shaping Access Target Byte Sustain Excess Interval Increment AdapI/F List Rate Limit bits/int bits/int (ms) (bytes) ActEt5/0 128000 6000 16000 32000 125 2000 -c7200_up#

c7200_up(config-if)#traffic-shape rate 128000 8000 32000

c7200_up#show traffic-shaping Access Target Byte Sustain Excess Interval Increment AdapI/F List Rate Limit bits/int bits/int (ms) (bytes) ActEt5/0 128000 5000 8000 32000 62 1000 -


Minimum Bandwidth Guarantee

Policy Required :Gold Traffic will always receive a minimum bandwidth of 512Kbps

available at all times


• Class definition sets minimum bandwidth

• Queue servicing (metering) controls latency

• Unused capacity is shared amongst theother classes

• Each class can be separately configured for QoS

Class-Based WFQ

40%

25%

10%

Gold

Silver

Bronze

Step 1:Define Scheduling

Step 2:Define Bandwidth

Low Latency, High Servicing

Premium IPBest Effort


Policy Required :Reserve BW for my application which is

RSVP enabled and can signal to the network for it’s requirements

Minimum Bandwidth Guarantee


RSVP Policy

• RSVP admission control– Accept or deny RSVP requests

– Preempt existing reservations basedon policy

– Policy objects (future)

• Configure RSVP parameters such as – Queuing parameters

– Traffic shaping parameters


!interface Serial0/0 ip address 10.1.1.2 255.255.0.0 ip rsvp bandwidth 96 96 bandwidth 128 fair-queue 64 256 1000!

ip rsvp bandwidth [interface-kbps] [single-flow-kbps]

Configuring RSVP


Verifying Reservation Accepted

bottom#sho ip rsvp installedBPS To From Protoc DPort Sport Weight Conversation24K 10.1.1.1 10.1.1.2 UDP 16384 16384 4 264


The Problem of Congestion

• Uncontrolled, congestion will seriously degrade system performance

– The system buffers fill up

– Packets are dropped, resulting in retransmissions

– This causes more packet loss and increased latency

– The problem builds on itself until the system collapses

Throughput

Congestion

Controlled CongestionControlled Congestion

Uncontrolled CongestionUncontrolled Congestion


Drop Policy

Policy Required:Bronze or Silver traffic will be dropped when there is congestion. Gold traffic

will be forwarded unaffected


Where Does Internet Congestion Come From?

• 95% of traffic is TCP

• TCP slow start/fast retransmit – Assures maximal utilization of bottleneck– Therefore assures deep queues absent a

control mechanism


TCP flow control

• TCP relies on advertised windows

• Smaller TCP receive windows are better for slow links (Trade-off: throughput)

• Larger TCP receive windows => more packets in transit


Behavior of a TCP Receiver

• When in receipt of “next message,” schedules an ACK

• When in receipt of something else, acknowledges all it can immediately

Ack N+1

Ack N+1

Ack N+1

N+1

N

N+2N+3


Sender Response to ACK

• If ACK acknowledges something– Update credit and send

• If not, presume it indicates a lost packet– Send first unacknowledged

message right away

N+1

Ack N+1

Ack N+1

Ack N+1

N+1

N

N+2N+3


N+1

Ack N+1

Ack N+1

Ack N+1

N+1

N

N+2N+3

Multiple Drops in TCP

• In the event of multiple drops within the same session:

–Current TCPs wait for time-out

N+3

Ack N+3

tictictic


RED Pushes Back by Drops

• Minimizes work done by router

• Minimizes average queue depth

• Appropriate to interfaces that keep one or less packets in queue per flow


Queuing Pushes Back in Time

• Delays acknowledgments

• Stabilizes delay experienced by packets

• Appropriate to:– Interfaces that keep several messages

in queue from each flow– Transactions


Random Early Detection (RED)

• “TCP slow-start” is used in the event of congestion– Pros: Congestion resolution– Cons: Possibility of global synchronization

when multiple senders reduce transmission rates then ramp up all at once.


• Tool to avoid congestion collapse– All flows experience congestion => packet loss

=> slow start oscillation => collapse !

• Designed in 1993 by Van Jacobsen and Sally Floyd

• Underlying premise: Packet drops will throttle sender’s rate of sending



• Without Red, when the queue fills up, all packets that arrive are dropped—tail drop

• With Red, as opposed to doing a tail drop, the router monitors the average queue size and uses randomization to choose connections to notify that a congestion is impending

Random Early Detect (RED)Queue

QueuePointer

PacketsArriving



BackboneBackbone• RED:

Anticipates congestionSlows down traffic before queue overflowsAvoids TCP oscillationsMaximizes throughput

• RED uses selective packet loss to signal TCP to slow down

RED


Weighted Random Early Detection

GoldHigh Precedence

(Guarantees Mission-Critical Apps, i.e.,Great Plains, Claris,Pivotal, Peoplesoft, Unified m

Messaging)

SilverMedium Precedence

E-Mail, InteractiveVideo, Web

BronzeLow Precedence

E-Fax, FTP


RED Packet Drop Thresholds

RED Drop Thresholds

Drop threshold

Probability of Packet Discard

AverageQueue Depth

MaximumThreshold

MinimumThreshold

REDFIFO,TailDrop

High Performance Distributed Implementation


Random Early Detection

Pa

ck

et

Dro

p

Pro

ba

bil

ity

Queue Length

“Slope” is adjustable

Queue Max

Pa

ck

et

Dro

p

Pro

ba

bil

ity

Queue Length Queue Max

Pa

ck

et

Dro

p

Pro

ba

bil

ity

Queue Length

Standard Service

Queue Max

WithoutRED

WithRED

WithWRED

Premium Service

Std. Min. Prem. Min.


RED - How does it work ?

• Monitors queue depths, randomly selects flows from which to drop packets

• It is a preventive mechanism which aims to prevent router queues from overflowing


RED—Packet-Drop Probability

• Packets are dropped sufficiently frequently to control the average queue size

• The probability that a packet is dropped from a connection is proportional to the amount of packets sent by the connection


RED - When not to use it

• For protocols like voice over RTP over UDP over IP.

• For non-conforming traffic like Novell Netware of Appletalk


Weighted RED (WRED)

• WRED combines REDRED with IP IP PrecedencePrecedence to implement multiple service classes

• Each service class has a defined min and max thresholds, and drop rates


Weighted Random Early Detection (WRED)

Interface Buffer

Resources

Discard Text Based On:• Buffer queue depth• IP Precedence• RSVP session

FIFO Scheduling

Pass

Fail

Discard Test

Transmit Queue

Output Line


Weighted RED (WRED)

• Reduces the chances of tail-drop since it drops packets when the output interfaces begin to show signs of congestion

• WRED can be configured to ignore IP Precedence and make non-weighted drops


When Should I Use WRED?

• Congested long-haul links (e.g., trans-oceanic links)

• Not recommended for campus networks

• When the bulk of your traffic is TCP as oppose to UDP– Remember only TCP will react to a packet dRemember only TCP will react to a packet d

rop UDP will notrop UDP will not


Weighted RED (WRED)

BackboneBackbone• Combines IP precedence

with RED

• Separate thresholds and drop rates per class

• Higher priority traffic gets preferred treatment

WRED


WRED - Where is it configured?

• WRED operates in the output direction of an interface on core routers where congestion is expected

• Edge routers use tools like CAR to set IP precedence, WRED then acts on this IP precedence information


WRED Service Profile Example

Packet DiscardProbability

1

AverageQueue Size

Two Service Levels are Shown;

Up to SixCan Be Defined

StandardMin

StandardMax

PremiumMin

PremiumMax

StandardServiceProfile

PremiumServiceProfile

Adjustable


WRED Configuration Example

R3#write terminal!interface Hssi0/0/0 description 45Mbps to R1 ip address 200.200.14.250 255.255.255.252 random-detect exponential-weighting-constant 9 random-detect precedence 0 540 1080 10 random-detect precedence 1 607 1080 10 random-detect precedence 2 674 1080 10 random-detect precedence 3 741 1080 10 random-detect precedence 4 808 1080 10 random-detect precedence 5 875 1080 10 random-detect precedence 6 942 1080 10 random-detect precedence 7 1009 1080 10 random-detect!

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