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Dipl.-Math. Dipl.-Inform. Kalman Graffi

KOM - Multimedia Communications LabDept. of Electrical Engineering and Information Technology, Dept. of Computer ScienceTUD – Technische Universität Darmstadt Merckstr. 25, D-64283 Darmstadt, Germany, Kalman.Graffi@KOM.tu-darmstadt.de Tel.+49 6151 164959, Fax. +49 6151 166152

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Overlay Bandwidth Management: Scheduling and Active Queue Management of Overlay Flows

Kalman Graffi, Konstantin Pussep, Sebastian Kaune, Aleksandra Kovacevic, Nicolas Liebau, and Ralf Steinmetz

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Example: Bandwidth Usage in Unst. P2P Overlay

Queries

I cannot hear youHelp!

Emergency!

Unimportant

Bandwidth usage :

• Irrelevant search queries starve relevant queries• Overlay flow specific QoS demands unconsidered

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Outline

Motivation and Scope

Background: Scheduling and Active Queue Management

Contribution:• Characteristics of Overlay Flows• Requirements and Related Work• Overlay Bandwidth Management Layer• HiPNOS.KOM - Our Solution

Evaluation

Future Work and Conclusion

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Motivation for Bandwidth Management

Emerging commercial P2P applications require• Quality of Service• Crucial for long-term success of P2P paradigm

Most critical resource in P2P systems: bandwidth• In most cases the bottleneck in the system• Required for maintenance and service provisioning

P2P specific bandwidth management needed• Control the bandwidth, provide QoS• Overlay independent solution

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Which Flows are in Focus?

Types of flows in P2P systems

• Layer 4 traffic flows: • Underlay perspective• Out of scope

• Direct P2P communication: • File transfer, application traffic, …• Few, but large data streams (elephants)• (Often) with low priority for the system

• Overlay flows• Multi-hop: maintenance, user queries…• Many, small messages (mice)• Varying relevance for system

Provide QoS to overlay flow according to its relevance

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Learn from network layer

• Scheduling• Reorder tasks/messages in queue• Reference: First-in-First-Out

• Active Queue Management • Drop msg. upon congestion of queue• Reference: Drop Tail

Research challenge: how to apply on overlay layer?

Scheduling and Active Queue Management

Message

1. Message SchedulingBefore:

After:

2. Queue ManagementBefore:

After:Queue Limit

Sched.+AQM

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Overlay Bandwidth Management

Generally applicable overlay bandwidth management• New layer Network Wrapper: API between overlay and underlay

Research challenge: Which requirements are defined• by overlay flow characteristics• for the SCHED + AQM used

In-from overlay

Insert msg in buffer

Apply AQM mech.

Timeout

Pick next msg (SCHED)

Out to underlay

Bandwidth available?

Receive message

yesno

Buffer management

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Observation• Huge number of contacts with few messages each• Overlay “flows” and traditional flows differ significantly

Conclusion • Stateless scheduler needed• Quality of service information are stored in messages

Analyzing Overlay Flows in Kademlia

Simulation of KademliaSetup:

• PeerfactSim.KOM• 10,000 peers, all join,

random store/lookupMetrics:

• # of contacts per peer• # of msg per contact

Results:

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Requirements and Related Work

Requirements:• QoS attributes per message (defined by higher layer):

• Introduce delay priority (ϵ PD) and loss priority (ϵ PL)• Quality req.:

Related Work see paper/Technical Reports of author• SCHED and AQM proposed for routing layer (L3)

Expect long-term flows, not existing in overlays• Overlay bandwidth management in overlays

• Mobile P2P (on UMTS/GSM), P2P multimedia streams Focus on underlay/multimedia

characteristics• GIA [Chawathe, 2003], controls incoming traffic

Sched. and AQM mechanism for overlay flows needed

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HiPNOS.KOM: Highest Priority First, No Starvation• Introduce (independent) message priorities

• For loss – criticality (1 byte)• For delay – criticality (1 byte)

Active Queue Management solution:• If buffer size exceeded:

• Drop message with lowest loss-prio.

Scheduling solution• If bandwidth available:

• Pick message with highest latency-prio.

Avoid starvation• Periodically increase delay-prio. of queued messages

Our Solution: Sched. and AQM of Overlay Flows

In-from overlay

Insert msg in buffer

Apply AQM mech.

Timeout

Pick next msg (SCHED)

Out to underlay

Bandwidth available?

Receive message

yesno

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Evaluation Setup

Compare HiPNOS.KOM with reference solution• First In, First Out: reference scheduling solution• Drop Tail: reference active queue management mech.

Simulation Setup:• Simulated: Kademlia on PeerfactSim.KOM• Scenario:

• 10000 peers join, heterogeneous bandwidths• Peers perform random store/lookup operations• Msgs with random delay/loss priorities: -128 to 127

• Varying: HiPNOS.KOM and FIFO/Drop Tail• 20 simulation runs per setup• Metrics: Delay of msgs and number of dropped msgs

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Evaluation Results of HiPNOS.KOM

Results:

Quality of service increases with priority • Delay antiproportional to priority• Loss decreases with increasing priority

QoS requirements of overlay flows can be fulfilled

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Future Work

Observation:• QoS requirements fulfilled: higher prio., better QoS• Even minimal mechanisms are sufficient

Conclusion:• Shift of research focus:

• Not how to provide QoS for overlay flows (solved)• But how set QoS priorities of overlay messages

Next steps:• Emergency Call Handling (ECH) over P2P Overlays

• Globase.KOM used to find closest Emergency Station• ECH messages have highest priority in overlay• Fulfills legal and technical requirements for ECH

• Security issues• Evaluate with more overlay types (unstructured…)

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ConclusionProblem: QoS for overlays currently not supported

• Overlays cannot be used for critical applications• Heterogeneity of message relevance not supported

Contribution:• Overlay flow characteristics identified: only mice flows• Introduce message priorities for loss and delay• HiPNOS.KOM enables P2P overlays to support QoS

demands

Evaluation:• Good/expected results show effectiveness of solution

Impact:• Increase of stability, scalability, robustness …

• of overlay and application• for low (no?) costs

• Enables QoS-based applications

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Questions?

Kalman Graffi

Peer-to-Peer Research Group

Dept. of Electrical Engineering and Information TechnologyMultimedia Communications Lab · KOM

Merckstr. 25 · 64283 Darmstadt · GermanyPhone (+49) 6151 – 16 49 59Fax (+49) 6151 – 16 61 52Kalman.Graffi@KOM.tu-darmstadt.de

Further information: http://www.KOM.tu-darmstadt.de/

Publications: http://www.KOM.tu-darmstadt.de/Research/Publications/publications.html