Why Invest in QoS ?
Internet
FTP Server
SAP Server
Si
Si
W3 Server
To accelerate the deployment of network services,
by enabling predictable response for application
traffic and service requirements
Connecting people to information
QoS Signaling
In-Band
IPv4 Packet
Out-of-Band
ISL/802.1Q Frame
Data
Frame Relay LMI
(CIR Service)
ToS Field
3-Priority
3-Precedence
IPv6 Packet
RSVP
(Guaranteed Service
Controlled Load Service)
Tag/MPLS Header
Data
ATM UNI
(CBR, VBR, ABR,
UBR Services)
Priority Field
4-Priority
Connecting people to information
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 realtime 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
Connecting people to information
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
Connecting people to information
Cisco
Connecting people to information
®
IOS
QoS
®
IOS
Cisco
QoS
Diff Serv Components
Traffic
Conditioner
Drop
Scheduling
Marking
Mechanism
Network Effect
RED, WRED,
Flow RED
• Avoid Congestion by Notifying Source
• Prioritize which Traffic Is Told to Reduce
PQ, CQ, WFQ, CB
WFQ, WRR, MDRR
CAR, Policy Routing,
DSCP, NFCII
• Bandwidth Management: Traffic Priority
• Set Servicing Sequence
• Sets IP Precedence/DSCP
• By Application, Protocol, Address,etc
Metering
(Policing)
CAR
Shaping
GTS, FRTS
Compress
CRTP
Fragment
LFI, FRF.12
Connecting people to information
• Enforce a Maximum Transmission Rate
• Conform or Exceed Thresholds
• Conforms Traffic to Committed Bandwidth
• Interwork with Layer 2 Notification e.g., BECN
• Reduce the Volume of Traffic Sent
• Reduce Delay on Slower Speed Links
• Split, Recombine Larger Frames
IP QoS
11.1
11.2
• WFQ
• RED
• WRED
• RSVP
• NetFlow Switching
11.1CA
11.1CB (ISP8)
11.1CC (FIB)
11.1CD (ISP8+L3)
11.1CE (FIB+L3)
Connecting people to information
11.3
12.0
CYH2 ?8
11.1CC
11.1CC
• IP ATM CoS (Ph I)
• CEF
• CAR/DCAR
• DWFQ
• DWRED
• QoS Policy Propagation via BGP
• NetFlow Services
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
Connecting people to information
Sample Class Base
Service Deployment
Gold
Provisioned Service
E-Commerce,
ERP-Critical
Silver
Premium IP
E-mail, Web
Browsing
Bronze
Best Effort Delivery
Voice, SNA
Application Audit
Connecting people to information
Service Levels
Queuing’s Premise
• Getting better service is a matter
of managing 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
Connecting people to information
Queuing Algorithms
• Congestion management algorithms
–
–
–
–
First In First Out
Priority Queuing
Custom Queuing
Weighted Fair Queuing (WFQ)
Connecting people to information
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
Connecting people to information
FIFO
Transmit
Queue
Output Line
Connecting people to information
Pitfalls of FIFO
• 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
Connecting people to information
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
Connecting people to information
FIFO Example
caymans#sh int e0
Ethernet0 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
Connecting people to information
Simplest QoS Algorithm:
Priority Queuing
• Stated requirement:
– If <application> has traffic waiting,
send it next
• Commonly implemented
– Defined behavior of IP precedence
Connecting people to information
Priority Queuing
Forwarder
Priority Classification
(Access)
List
Low
Priority
Medium
Priority
Transmission
Queue
Connecting people to information
High
Priority
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
Connecting people to information
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
Connecting people to information
Priority Queuing (PQ)
High
Traffic
Destined
for Interface
Medium
Classify
Interface Hardware
• Ethernet
• Frame Relay
• ATM
• Serial Link
• Etc.
Transmit
Queue
Output
Line
Normal
Low
Q Length Defined
by Q Limit
Classification by:
• Protocol (IP, IPX, AppleTalk,
SNA, DecNet, Bridge, etc.)
• Incoming Interface
(EO, SO, S1, etc.)
Connecting people to information
Interface Buffer
Resources
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
Connecting people to information
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}
Connecting people to information
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>
Connecting people to information
Priority Queuing Examples
Example 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
Connecting people to information
Priority Queuing Examples
Example 5:
caymans(config)#priority-list
200
caymans(config)#priority-list
caymans(config)#priority-list
caymans(config)#priority-list
4 protocol decnet medium lt
4 protocol ip medium tcp 23
4 protocol ip medium udp 53
4 protocol ip high
Example 6:
caymans(config)#priority-list
caymans(config)#priority-list
caymans(config)#priority-list
caymans(config)#priority-list
3
3
3
3
interface ethernet 0 high
interface ethernet 1 medium
interface serial 1 medium
default low
Example 7:
caymans(config)#interface serial 0
caymans(config-if)#priority-group 4
Connecting people to information
Priority Queuing Example
caymans# sh queueing priority
Current priority queue configuration:
List
1
1
1
1
1
2
2
2
3
3
3
3
4
4
4
4
Connecting people to information
Queue
high
high
medium
high
low
medium
high
medium
low
high
medium
medium
medium
medium
medium
high
Args
protocol decnet
protocol ip
protocol ip
limit 10
limit 90
protocol decnet
protocol bridge
protocol ip
default
interface Ethernet0
interface Ethernet1
interface Serial1
protocol decnet
protocol ip
protocol ip
protocol ip
list 10
gt 200
lt 200
tcp port telnet
udp port domain
Priority Queuing Example
caymans#sh int s0
Serial0 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
Connecting people to information
Class-Based Queuing
• Cisco feature: custom queuing
• Stated requirement:
– traffic with <characteristics>
needs a guaranteed rate or latency
•
Characteristics may be:
– Application
– Traffic source
Connecting people to information
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
Connecting people to information
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
Connecting people to information
Custom Queuing
Forwarder
Control Traffic
Priority
(Access)
List
Queue #0
Queue #1
Queue #9
Queue #10
Queue #2
Queue #3
Queue #11
Queue #12
Queue #4
Queue #5
Queue #13
Queue #6
Queue #14
Queue #15
Queue #7
Queue #8
Queue #16
Transmission Queue
Connecting people to information
Custom Queuing (CQ)
1/10
Traffic
Destined
for Interface
2/10
3/10
2/10
Classify
Interface Hardware
• Ethernet
• Frame Relay
• ATM
• Serial Link
• Etc.
Transmit
Queue
Output
Line
3/10
Up to 16
Q Length
Deferred by
Queue Limit
Classification by:
• Protocol (IP, IPX, AppleTalk,
SNA, DecNet, Bridge, etc.)
• Incoming interface
(EO, SO, S1, etc.)
Connecting people to information
Interface
Buffer
Resources
Link
Utilization Weighted Round
Robin Scheduling
Ratio
(byte count)
Allocate
Proportion of
Link Bandwidth)
Pitfalls of Custom Queuing
• FIFO by class:
– Within class, still unpredictable
Connecting people to information
Custom Queuing Commands
•
queue-list protocol
– Establishes queuing priority based on protocol type
[no] queue-list <list-number> protocol <protocolname> <queue-number> <queue-keyword> <keywordvalue>
•
queue-list interface
– Establishes queuing priority based on incoming interface
[no] queue-list <list-number> interface
<interface-name> <interface-number> <queue #>
Connecting people to information
Custom Queuing Commands
•
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 <queuenumber>
•
queue-list queue limit
– Designate queue length limit for a custom queue
[no] queue-list <list-number> queue <queuenumber> limit <limit-number>
Connecting people to information
Custom Queuing Commands
•
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 <queuenumber>
•
custom-queue-list
– Assigns a specified queue-list to an interface
[no] custom-queue-list <list>
Connecting people to information
Custom Queuing
Example
caymans(config)#queue-list
caymans(config)#queue-list
6
caymans(config)#queue-list
7
caymans(config)#queue-list
caymans(config)#queue-list
caymans(config)#queue-list
caymans(config)#queue-list
caymans(config)#queue-list
Connecting people to information
4 interface e0 5
4 interface ethernet 1
4 interface ethernet 2
4
4
4
4
4
interface serial 0 8
default 10
protocol arp 4
protocol bridge 3
protocol ipx 9
Custom Queuing Example
queue-list configuration:
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
Connecting people to information
Custom Queuing
Example
caymans#sh queueing custom
Current custom queue configuration:
List
Queue Args
1
5
lowest custom queue
1
3
protocol decnet
1
7
protocol ip
2
2
protocol decnet
gt 200
2
8
protocol ip
udp port domain
3
10
default
3
2
protocol decnet
lt 200
3
1
protocol ip
list 10
3
7
protocol ip
4
10
default
4
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
Connecting people to information
Custom Queuing
Example
caymans#sh int s0
Serial0 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: 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
Connecting people to information
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
Connecting people to information
Design Intent of Weighted
Fair Queuing
• Stated requirement:
–“Traffic latency must be predictable
“Reserved flows must achieve
a certain bandwidth and latency”
–“Configuration must be straightforward”
–“Should normally do the right thing without
manual intervention ”
Connecting people to information
Weighted Fair Queuing
(WFQ)
Two 100 Byte Packets
Transmitted for Every
One 200 Byte Packet
Configurable Queues
Therefore = “Fair”
Two 100 Byte
Voice Packets
1
1
2
1
2
Dequeue
1
One 200 Byte
Data
Packet
2
1
Classify
Interface Buffer
Resources
Flow Classification/Sorting
•Source and destination address
•Protocol
•Session identifier (Port/Socket)
Connecting people to information
Transmit
Scheduling
Weighted Fair Scheduling
•Requested Qos (IP Precedence, RSVP)
•Frame Relay FECN, BECN, DE
•Flow throughput (Weighted-Fair)
1
Feature Description
Dynamically identifies data streams using an
interface
Dynamically prioritizes those data streams
Connecting people to information
So What?
Equal access for File Transfer traffic
Priority for Interactive Traffic
Future: Guarantees for Real Time Traffic
Hands Free! No Access Lists!
Connecting people to information
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
Connecting people to information
Configuration
fair-queue [congestive discard threshold]
[#hashed_queues] [reserved_queues]
congestive discard policy
hits conversations with more than one message
occurs when
total number of messages > threshold
Connecting people to information
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
Connecting people to information
Diagnostics/Troubleshooting
show interface [interface name]
show queue interface name
show queueing [fair | custom | priority]
Connecting people to information
Pitfalls of Weighted Fair
Queuing
• Requires more sorting
than other approaches
Connecting people to information
WFQ Monitoring
lazy-ccartee-dont-touch#sh int ser 3/3
Serial3/3 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
Connecting people to information
WFQ Monitoring
lazy-ccartee-dont-touch#show queueing
Current fair queue configuration:
Interface
Serial3/0
Serial3/1
Serial3/2
Serial3/3
Discard
threshold
64
64
64
64
Dynamic
queue count
256
256
16
256
Current priority queue configuration:
Current custom queue configuration:
Current RED queue configuration:
lazy-ccartee-dont-touch#
Connecting people to information
Reserved
queue count
0
0
0
0
WFQ Monitoring
Show queue serial:
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
Connecting people to information
Policing & Shaping
Connecting people to information
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
Connecting people to information
Policing
Traffic Rate
Traffic
Traffic
Traffic Policing vs. Shaping
Time
Shaping
Traffic Rate
Time
Connecting people to information
Traffic
Traffic
Time
Traffic Rate
Traffic Rate
Time
Policing vs. Shaping
• Rate limiting allows larger bursts
– More uneven utilization
• Shaping sends smaller bursts in equal
intervals
– smoother utilization
– easier for receiving end
Connecting people to information
Ways to Limit Throughput
• Policing
– Committed Access Rate (CAR)
• Traffic shaping
– Generic Traffic Shaping(GTS)
– Frame Relay Traffic Shaping (FRTS)
Connecting people to information
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
Connecting people to information
Token Bucket
Tokens
p
Overflow
Tokens
Burst Size
p
Token Arrival Rate
B
Packets
Arriving
Connecting people to information
B
Conform
Exceed
Basic Shaping Mechanism
Leaky Bucket
• Data is transmitted at a given rate
• Buffer (“bucket”) allows for bursts to
arrive
• If buffer is full packets are dropped
Connecting people to information
Leaky Bucket
Packets
Arriving
Overflow
Packets
BBurst size
pLeak rate
Packets Are Leaked
at a Rate Specified
by p
Connecting people to information
B
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
Connecting people to information
Committed Access Rate (CAR)
• Two functions
– Packet classification—IP precedence
and QoS group setting
– Access bandwidth management
through rate limiting (policing)
Connecting people to information
Marking: IP Precedence
IP Packet
• QoS marking
• Inband
• Differentiated
network services
across any media
or topology
Connecting people to information
Data
Type of Service (ToS)
IP Precedence
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)
Connecting people to information
Committed Access Rate (CAR)
• Two functions
– Packet Classification IP precedence
and QoS group setting
– Access Bandwidth Management
through rate limiting
Connecting people to information
CAR—Action Policies
• Configurable actions
– Transmit
– Drop
– Continue (go to the next rate-limit
in 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)
Connecting people to information
Committed Access Rate (CAR)
Bandwidth Management
Application Hosting
2) Apply Rate Limiting to
Matching Traffic Pattern e.g.
25Kbps of Traffic to ‘Bronze’
San Jose
Backbone
Ottawa
1) Packet Classification
through IP Precedence
and QoS Group Settings
Connecting people to information
3) Invoke QoS Policy
Action Based on Edge
Classification, e.g. Drop
Low Priority via WRED if
Burst Limit Exceeded
CAR Traffic Measurement
• Uses the token bucket scheme
as a measuring mechanism
• Tokens are added to the bucket at
the committed rate and the number
of tokens in the bucket is limited
by the normal burst size
• Depth of the bucket determines
the burst size
Connecting people to information
CAR Traffic Measurement
• Packets arriving with sufficient tokens in
the bucket are said
to conform
• Packets arriving with insufficient tokens
in the bucket are said
to exceed
Connecting people to information
CAR Traffic Measurement
• 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)
Connecting people to information
CAR Traffic Measurement
• 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
Connecting people to information
Extended Burst
Exceed %
100
Bucket
Depth
Normal Extended
Burst
Burst
Connecting people to information
CAR Policy Examples
Recolor
Drop
Drop
Multimedia
Recolor
Mission-Critical
Per Application CAR
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
Connecting people to information
Marking IP Precedence: CAR
R1
S0
R2
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 1
ip address 200.200.14.250 255.255.255.252
!
access-list 101 permit tcp any any eq www
access-list 102 permit tcp any any eq ftp
!
Connecting people to information
Traffic Rate
Time
Connecting people to information
Traffic Shaping
Traffic
Traffic
Traffic Shaping
Traffic Rate
Time
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
Connecting people to information
Traffic Shaping Queue
Structure
Forwarder
• One queue per
–Sub-interface
–Access List
–DLCI
• Feeds into queues at
hardware layer
Within
Token
Bucket?
Sub-Interface
Fancy Queues
Yes
Interface
Congested?
No
Transmission
Queue
Connecting people to information
No
Yes
Hardware
Interface
Queues
Difference Between
CAR and FRTS
CAR
FRTS
Policer
Shaper
Policy Based on IP
Policy Based on DLCI
Input and Output Interfaces
Output Interfaces
Marking
No Marking
Runs in Distributed Mode
Does Not Run in
Distributed Mode
Does not Act on FECN/BECN
Understands
BECN/FECN
Connecting people to information
Traffic Shaping
Traffic
Destined
for Interface
Transmit Output
Queue
Line
Match
Classify
No Match
Configured
Queuing (e.g.
WFQ,
PQ, etc.)
“Leaky
Extended Access List Bucket”
Shaping
Functionality
Classification by:
Connecting people to information
Difference between FRTS and GTS
FRTS
GTS
Shaper FR Only
Shaper
Per DLCI
Interface Level or
Group-Based
Shaping Queue PQ,CQ
and WFQ(12.0(4)T)
Interface Queue 2
Level Priority
Shaping Queue WFQ
Can Be Anything
Supports FRF.12
No Support for FRF.12
Understands FECN/BECN
Understands BECN/FECN
Connecting people to information
Generic Traffic Shaping
Commands
• 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
Connecting people to information
Generic Traffic Shaping
Example
• 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
interval
Connecting people to information
Monitor Traffic Shaping
c7200_up(config-if)#traffic-shape rate 128000 16000 32000
c7200_up#show traffic-shaping
Access Target
Byte
I/F
List
Rate
Limit
Et5/0
128000
6000
c7200_up#
Sustain
bits/int
16000
Excess
bits/int
32000
Interval
(ms)
125
Increment Adap
(bytes) Act
2000
-
c7200_up(config-if)#traffic-shape rate 128000 8000 32000
c7200_up#show traffic-shaping
Access Target
Byte
I/F
List
Rate
Limit
Et5/0
128000
5000
Connecting people to information
Sustain
bits/int
8000
Excess
bits/int
32000
Interval
(ms)
62
Increment Adap
(bytes) Act
1000
-
Minimum Bandwidth Guarantee
Policy Required :
Gold Traffic will always receive a
minimum bandwidth of 512Kbps
available at all times
Connecting people to information
Class-Based WFQ
Gold
Silver
40%
Low Latency, High Servicing
25%
Premium IP
Best Effort
10%
Bronze
Step 1:
Define Scheduling
Step 2:
Define Bandwidth
• Class definition sets minimum bandwidth
• Queue servicing (metering) controls latency
• Unused capacity is shared amongst the
other classes
• Each class can be separately configured for QoS
Connecting people to information
Minimum Bandwidth Guarantee
Policy Required :
Reserve BW for my application which is
RSVP enabled and can signal to the
network for it’s requirements
Connecting people to information
RSVP Policy
• RSVP admission control
– Accept or deny RSVP requests
– Preempt existing reservations based
on policy
– Policy objects (future)
• Configure RSVP parameters such as
– Queuing parameters
– Traffic shaping parameters
Connecting people to information
Configuring RSVP
ip rsvp bandwidth [interface-kbps] [single-flow-kbps]
!
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
!
Connecting people to information
Verifying Reservation Accepted
bottom#sho ip rsvp installed
BPS
To
From
24K
10.1.1.1
10.1.1.2
Connecting people to information
Protoc DPort Sport Weight Conversation
UDP 16384 16384 4
264
The Problem of Congestion
Controlled Congestion
Throughput
Uncontrolled Congestion
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
Connecting people to information
Drop Policy
Policy Required:
Bronze or Silver traffic will be dropped
when there is congestion. Gold traffic
will be forwarded unaffected
Connecting people to information
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
Connecting people to information
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
Connecting people to information
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
Connecting people to information
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
Connecting people to information
Multiple Drops in TCP
• In the event of multiple drops
within the same session:
–Current TCPs wait for time-out
tic
tic
tic
Connecting people to information
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
Connecting people to information
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
Connecting people to information
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.
Connecting people to information
Random Early Detection (RED)
• 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
Connecting people to information
Random Early Detect (RED)
Queue
Packets
Arriving
Queue
Pointer
• 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
Connecting people to information
Random Early Detection
(RED)
Backbone
• RED:
Anticipates congestion
Slows down traffic before
queue overflows
Avoids TCP oscillations
Maximizes throughput
• RED uses selective packet loss
to signal TCP to slow down
Connecting people to information
RED
Weighted Random Early Detection
Gold
Silver
Bronze
High Precedence
Medium Precedence
Low Precedence
(Guarantees MissionCritical Apps, i.e.,Great
Plains, Claris,Pivotal,
Peoplesoft, Unified m
Messaging)
E-Mail, Interactive
Video, Web
E-Fax, FTP
Connecting people to information
RED
Drop
Thresholds
RED
Packet
Drop
ThresholdsRED
Probability
of Packet
Discard
Drop threshold
Minimum
Threshold
High Performance
Distributed Implementation
Connecting people to information
FIFO,
Tail
Drop
Maximum
Threshold
Average
Queue
Depth
Without
RED
Packet Drop
Probability
Random Early Detection
With
RED
Packet Drop
Probability
Queue Length
Queue Max
“Slope” is adjustable
With
WRED
Packet Drop
Probability
Queue Length
Queue Max
Premium
Service
Standard Service
Queue Length
Connecting people to information
Std. Min.
Prem. Min. Queue Max
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
Connecting people to information
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
Connecting people to information
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
Connecting people to information
Weighted RED
(WRED)
• WRED combines RED with IP
Precedence to implement
multiple service classes
• Each service class has a defined min and
max thresholds, and drop rates
Connecting people to information
Weighted Random
Early Detection (WRED)
Pass
Transmit
Queue
Discard
Test
Output
Line
Fail
FIFO Scheduling
Discard Text Based On:
• Buffer queue depth
• IP Precedence
• RSVP session
Connecting people to information
Interface
Buffer
Resources
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
Connecting people to information
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
drop UDP will not
Connecting people to information
Weighted RED (WRED)
Backbone
• Combines IP precedence
with RED
• Separate thresholds and
drop rates per class
• Higher priority traffic gets
preferred treatment
Connecting people to information
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
Connecting people to information
WRED Service Profile
Example
Two Service
Levels are Shown;
Up to Six
Can Be Defined
1
Packet
Discard
Probability
Standard
Service
Profile
Adjustable
Standard
Min
Connecting people to information
Standard
Max
Premium
Min
Premium
Service
Profile
Average
Queue
Size
Premium
Max
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
!
Connecting people to information