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Bandwidth Management and Scheduling in MPLS DiffServ Networks. Anand Srinivasan Eion Ottawa, Canada. Ximing Zeng, Chung-Horng Lung, Changcheng Huang Department of Systems and Computer Engineering Carleton University Ottawa, Canada. Outline. Diverse QoS Requirements - PowerPoint PPT Presentation
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Bandwidth Management and Scheduling in MPLS DiffServ Networks
Ximing Zeng, Chung-Horng Lung, Changcheng Huang
Department of Systems and Computer Engineering
Carleton University
Ottawa, Canada
Anand SrinivasanEion
Ottawa, Canada
Outline
Diverse QoS Requirements DiffServ Forwarding Classes Cisco Solutions Solutions based on fair queueing Our Solution Performance study
QoS requirements
0%
Packet Loss
Command/ control
(eg Telnet,Interactive
games)
Conversationalvoice and video
Voice/videomessaging
Streamingaudio/video
Transactions(eg E-commerce,Web-browsing, E-
mail access)
Messaging,Downloads
(eg FTP,still image)
Fax
Background(eg Usenet)
5%
100 msec 1 sec 10 sec 100 sec
Zeroloss
Delay
QoS requirements for real time applications
Medium Application Degree of symmetry
Typical Data rates/Amount of Data
Key performance parameters and target values
End-to-end Oneway Delay
Delay Variationwithin a call
InformationLoss**
Audio Conversationalvoice
Two-way 4 - 64 kb/s <150 msecPreferred*
<400 msec limit*
< 1 msec < 3% Packet
Loss Ratio
Video Videophone Two-way 16 -384 kb/s < 150 msecpreferred
<400 msec limitLip-synch : < 100 msec
< 1%Packet
Loss Ratio
Data Telemetry- two-way control
Two-way <28.8 kb/s < 250 msec N.A Zero
Data Interactivegames
Two-way < 1 KB < 250 msec N.A Zero
Data Telnet Two-way(asymmetric)
< 1 KB < 250 msec N.A Zero
QoS requirements for interactive applications
Medium Application Degree of symmetry
Typical data rate/Amount of data
Key performance parameters and target values
One-wayDelay
(response time)
DelayVariation
Informationloss
Audio VoiceMessaging
Primarilyone-way
4-32 kb/s < 1 sec forplayback < 2 sec for
record
< 1 msec < 3%Packet
Loss Ratio
Data Web-browsing- HTML
Primarily one-way
~ 10 kB < 4 sec /page N.A Zero
Data Transactionservices – high
priority e.g. e-commerce,
ATM
Two-way < 10 kB < 4 sec N.A Zero
Data E-mail(server access)
PrimarilyOne-way
< 10 kB < 4 sec N.A Zero
QoS requirements for streaming applications
Medium Application Degree ofsymmetry
Data rate/Amount of data
Key performance parameters and target values
Start-upDelay
Transport delayVariation
Packet loss atsession layer
Audio Speech, mixedspeech and music,medium and high
quality music
Primarily one-way
5-128 kb/s < 10 sec < 1 msec < 1% Packet lossratio
Video Movie clips,surveillance, real-
time video
Primarily one-way
16 -384 kb/s < 10 sec < 1 msec < 1% Packet lossratio
Data Bulk datatransfer/retrieval,
layout andSynchronisation
information
Primarily one-way
10 kB – 10 MB < 10 sec N.A Zero
Data Still image Primarily one-way
< 100 kB < 10 sec N.A Zero
DiffServ Service Classes
Expedited Forwarding (EF) PHB (RFC-2598) Provides a low-loss, low-latency, low-jitter, and assured bandwidth
service. Real-time applications such as voice over IP (VoIP), video, and online trading programs require such a robust network-treatment.
Best Effort ServiceNo service guarantee except for a minimum bandwidth to prevent service starvation.
Assured Forwarding (AFxy) PHB (RFC-2597) Provides certain forwarding assurance by allocating certain bandwidth and buffer space. Applications with certain QoS requirements but not real-time can use AF service. For example: streaming video.
Cisco Solution
LLQ or MDRR
VoIP, Interactive Game…
Video Conferencing…
Video on demand …
E-commerce …
……
http,ftp, email…
High priority EF
Low priorityAF and BE CBWFQ
PQ
EF
AF1x
AF3x
AF4x
BE
AF2x
Total reservable bandwidth is about 75%. BE reservation fixed around 25%.EF traffic is constrained and should not exceed 33%; small queue and packet size.AFs reserve the rest bandwidth.
Cisco Solution
EF<33%BE = 25%
AF1AF2
AF3
AF4
EF is assigned a bandwidth less than 33% of the link speed and is constrained according to the assigned bandwidth.However burst of EF traffic still exists.
BE reserves a certain amount of bandwidth.
The rest of the bandwidth can be allocated to AF services.
AFs and BE may not always get their bandwidth as reserved !
Cisco Solution Advantage:EF packets are guaranteed smallest delay possible
by given them high priority. Tradeoff: AF packets may be delayed due to burst of EF
packets and cannot meet its desired delay bound!
delay
backlog
σ
ρ
r
t
bytes
delay
backlog
t
bytes
To minimize the impact EF brings to the AF classes:EF has small queue size (therefore, close to CBR)EF has small packet size (shorter waiting time for other packets)
Cisco Solution
What if the EF traffic is bursty?
If bandwidth other than the average rate of EF traffic is claimed allocatable, then when EF burst comes, the bandwidth to AF classes cannot be guaranteed. Bad QoS!
Average rate
Peak rateReserved rate
tEF traffic rate
Link rate
If bandwidth other than the peak rate of EF traffic is claimed allocatable, then AFQoS is guaranteed. Low bandwidth utilization!
A trade off has to be made! The actual bandwidth reserved to EF class should close to the peak rate to minimize the service impact.
Cisco Solution
BE=25%
AF1AF2
AF3
AF4
EF average
EF wasted
Under LLQ, to minimize the service impact to AF service Classes, EF bandwidth isOver-provisioned.
Other solutions
Assign each class certain bandwidthVoIP, Interactive Game…
Video Conferencing…
Video on demand …
E-commerce …
……
http,ftp, email…
WFQ/DWRR
EF
AF1x
AF3x
AF4x
BE
AF2x
Other solutions (WFQ)
Use weighted fair queueing to assign bandwidth to EF, AF and BE classes.
Advantage: Service to AF packets will not be affected by EF traffic, they always get their reserved bandwidth
Disadvantage: Over-provisioning is still needed to guarantee small delay to EF classes.
σ
ρ
delay
rIf EF traffic is bursty, to have a small delay, a large bandwidth reservation is needed, which causes the same problem of wasted bandwidth.
delay
r
Other solutions (DWRR)
Dynamically adjust the bandwidth to EF class according to the backlog of EF traffic. The unused bandwidth can be used by BE traffic.
Advantage: the EF still gets a relatively low delay. Practical problems: 1)How often should we adjust the bandwidth allocation? 2)If it is WFQ, how can we adjust the virtual finish time for all the
backlogged packets on line? 3)The bandwidth unused by EF can be used by BE, but is there
any guaranteed minimum bandwidth? Or how can we assign the unused bandwidth?
Our Solution
Proposed scheduler architectureVoIP, Interactive Game…
Video Conferencing…
Video on demand …
E-commerce …
……
http,ftp, email…
CBWFQ
EF
AF1x
AF3x
AF4x
BE
AF2x
PQ
High priority
Low priority
Our Solution
EF and BE share the bandwidth:
EF traffic rate
Average rate
Peak rateReserved rate
t
),max( EFres
BEEFavg rrrr
EFavgr
EFresr
Link rate
BE traffic rate
Our Solution
EF and BE share the bandwidth:
),max( EFres
BEEFavg rrrr
EF traffic ratet
Link rate
BE traffic rate Reserved ratePeak rate
Average rate EFavgr
EFresr
Our Solution
rBE = 25%
AF4
AF3AF2
AF1
The pie under WFQor Cisco LLQ
EFavgr
EFavgrEF
resr -AF4
AF3AF2
AF1
EF + BE = rBE +
Now free!
The pie under our solution.You can have an extra slice!
EFavgr
Our Solution
Advantages: EF is given no less (if not more) bandwidth than in WFQ.
Performance is guaranteed. AFs are guaranteed the same bandwidth, the same
performance can be expected. Bandwidth can be allocated to EF and AF users more efficiently!
Tradeoff: BE traffic may experience a longer delay due to EF bursts.
However, they are not delay sensitive and their average minimum throughput is still guaranteed.
Simulation result
Src 0: EF traffic: 7 on-off voice sources369 packets/sec in average.
Src 1: BE traffic: 800 packets/sce, Exponential
Src 2/3: AF traffic: 400 packets/sce,Exponential
Link speed: 2000 packets/sce.
Average load: 98.45%
Simulation result
EF delay under LLQ, DWRR and WPRR
LLQ provides the smallestDelay to EF class.
WPRR provides delay which isComparable tp LLQ
DWRR provides a much longerDelay.
Simulation result
AF delay under LLQ, DWRR and WPRR
The same delay bound is Guaranteed under both DWRRAnd WPRR.
Under LLQ, the AF delay is longerDue to the burstness of EF traffic.6% of the packets violate the delayBound.
Simulation result
BE throughput
Simulation result
BE throughput
Conclusion
We developed a new scheduler for DiffServ routers with the following advantage:
High bandwidth utilization Guaranteed QoS Guarantee small delay and loss for EF. Provide QoS guarantee to AF by reserving the bandwidth. Guarantee the minimum throughput of BE.
References [1] S.Blake, D.Black, M.Carlson, E.Davies, Z.Zhang, W.Weiss, “An Architecture for Differentiated Services.”
IETF RFC 2475. Dec 1998.
[2] V. Jacobson, K. Nichols, K. Poduri, “An Expedited Forwarding PHB.” IETF RFC 2598. June 1999.
[3] J. Heinanen, F. Baker, W. Weiss, J.Wroclawski, “Assured Forwarding PHB Group.” IETF RFC 2597. June
1999.
[4] J. Mao, W.M. Moh. B Wei, “PQWRR scheduling algorithm in supporting of DiffServ” 2001. ICC 2001. IEEE
International Conference on Communications,Volume: 3 , Pages:679 – 684.11-14 June 2001.
[5] A.K.Parekh, R.G.Gallager, “A Generalized Processor Sharing Approach to Flow Control in Integrated
Service Networks: The single node case,” IEEE/ACM Transactions on Networking, Pages:344 - 357. June 1993.
[6] H.Wang, C.Shen, K.G.Shin, “Adaptive-weighted packet scheduling for premium service” Communications,
2001. ICC 2001. IEEE International Conference on , Volume: 6 , Pages:1846 – 1850. 11-14 June 2001.
[7] F. Le Faucheur, L. Wu, B. Davie, S. Davari, P. Vaananen, R.Krishnan, P. Cheval, J. Heinanen, “Multi-Protocol
Label Switching (MPLS) Support of Differentiated Services.” IETF RFC 3270 May 2002.
Thank You !