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Peer-to-peer and mobile networks gained significant attention of both research community and industry. Applying the peer-to-peer paradigm in mobile networks lead to several problems regarding the bandwidth demand of peer-to-peer networks. Time-critical messages are delayed and delivered unacceptably slow. In addition to this, scarce bandwidth is wasted on messages of less priority. Therefore, the focus of this paper is on bandwidth management issues at the overlay layer and how they can be solved. We present HiPNOS.KOM, a priority based scheduling and active queue management system. It guarantees better QoS for higher prioritized messages in upper network layers of peer-to-peer systems. Evaluation using the peer-to-peer simulator PeerfactSim.KOM shows that HiPNOS.KOM brings significant improvement in Kademlia in comparison to FIFO and Drop-Tail, strategies that are used nowadays on each peer. User initiated lookups have in Kademlia 24% smaller operation duration when using HiPNOS.KOM.
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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, [email protected] 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 [email protected]
Further information: http://www.KOM.tu-darmstadt.de/
Publications: http://www.KOM.tu-darmstadt.de/Research/Publications/publications.html
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