Bandwidth Management and Scheduling in MPLS DiffServ Networks

1
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 Srinivasan Eion Ottawa, Canada
2
Outline

• Diverse QoS Requirements
• DiffServ Forwarding Classes
• Cisco Solutions
• Solutions based on fair queueing
• Our Solution
• Performance study

3
QoS requirements
4
QoS requirements for real time applications
Medium Application Degree of symmetry Typical Data rates/ Amount of Data Key performance parameters and target values Key performance parameters and target values Key performance parameters and target values
End-to-end One way Delay Delay Variation within a call Information Loss
Audio Conversational voice Two-way 4 - 64 kb/s lt150 msec Preferred lt400 msec limit lt 1 msec lt 3 Packet Loss Ratio
Video Videophone Two-way 16 -384 kb/s lt 150 msec preferred lt400 msec limit Lip-synch lt 100 msec lt 1 Packet Loss Ratio
Data Telemetry - two-way control Two-way lt28.8 kb/s lt 250 msec N.A Zero
Data Interactive games Two-way lt 1 KB lt 250 msec N.A Zero
Data Telnet Two-way (asymmetric) lt 1 KB lt 250 msec N.A Zero
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QoS requirements for interactive applications
Medium Application Degree of symmetry Typical data rate/ Amount of data Key performance parameters and target values Key performance parameters and target values Key performance parameters and target values
One-way Delay (response time) Delay Variation Information loss
Audio Voice Messaging Primarily one-way 4-32 kb/s lt 1 sec for playback lt 2 sec for record lt 1 msec lt 3 Packet Loss Ratio
Data Web-browsing - HTML Primarily one-way 10 kB lt 4 sec /page N.A Zero
Data Transaction services high priority e.g. e-commerce, ATM Two-way lt 10 kB lt 4 sec N.A Zero
Data E-mail (server access) Primarily One-way lt 10 kB lt 4 sec N.A Zero
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QoS requirements for streaming applications
Medium Application Degree of symmetry Data rate/ Amount of data Key performance parameters and target values Key performance parameters and target values Key performance parameters and target values
Start-up Delay Transport delay Variation Packet loss at session layer
Audio Speech, mixed speech and music, medium and high quality music Primarily one-way 5-128 kb/s lt 10 sec lt 1 msec lt 1 Packet loss ratio
Video Movie clips, surveillance, real- time video Primarily one-way 16 -384 kb/s lt 10 sec lt 1 msec lt 1 Packet loss ratio
Data Bulk data transfer/retrieval, layout and Synchronisation information Primarily one-way 10 kB 10 MB lt 10 sec N.A Zero
Data Still image Primarily one-way lt 100 kB lt 10 sec N.A Zero
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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.

• 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.

• Best Effort Service
• No service guarantee except for a minimum
  bandwidth to prevent service starvation.

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Cisco Solution

• LLQ or MDRR

VoIP, Interactive Game
High priority EF
EF
PQ
Video Conferencing
AF1x
Video on demand
AF2x
CBWFQ
Low priority AF and BE
E-commerce
AF3x

AF4x
BE
http,ftp, email
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.
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Cisco Solution
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.
BE 25
EFlt33
AF4
AF3
AF1
AF2
AFs and BE may not always get their bandwidth as
reserved !
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Cisco Solution

• AdvantageEF 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!

bytes
t
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)
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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!
If bandwidth other than the peak rate of EF
traffic is claimed allocatable, then AF QoS 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.
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Cisco Solution
Under LLQ, to minimize the service impact to AF
service Classes, EF bandwidth is Over-provisioned
.
EF average
BE25
EF wasted
AF4
AF3
AF1
AF2
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Other solutions

• Assign each class certain bandwidth

VoIP, Interactive Game
EF
Video Conferencing
AF1x
Video on demand
AF2x
WFQ/ DWRR
E-commerce
AF3x

AF4x
BE
http,ftp, email
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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.

?
If EF traffic is bursty, to have a small delay, a
large bandwidth reservation is needed, which
causes the same problem of wasted bandwidth.
s
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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?

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Our Solution

• Proposed scheduler architecture

VoIP, Interactive Game
EF
High priority
PQ
BE
Low priority
http,ftp, email
Video Conferencing
AF1x
CBWFQ
Video on demand
AF2x
E-commerce
AF3x

AF4x
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Our Solution

• EF and BE share the bandwidth

Link rate
Average rate
EF traffic rate
t
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Our Solution

• EF and BE share the bandwidth

Link rate
Peak rate
Reserved rate
Average rate
EF traffic rate
t
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Our Solution
rBE 25
-
AF4
AF3
AF1
AF2
The pie under WFQ or Cisco LLQ
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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.

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Simulation result
Src 0 EF traffic 7 on-off voice sources 369
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
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Simulation result

• EF delay under LLQ, DWRR and WPRR

LLQ provides the smallest Delay to EF
class. WPRR provides delay which is Comparable
tp LLQ DWRR provides a much longer Delay.
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Simulation result

• AF delay under LLQ, DWRR and WPRR

The same delay bound is Guaranteed under both
DWRR And WPRR. Under LLQ, the AF delay is
longer Due to the burstness of EF traffic. 6 of
the packets violate the delay Bound.
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Simulation result

• BE throughput

25
Simulation result

• BE throughput

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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.

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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 , Pages679 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,
  Pages344 - 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 , 
  Pages1846 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.
   

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• Thank You !