Using Concurrent Multipath Transmission for Transport Virtualization: Analyzing Path Selection

Transcription

1 Institute of Computer Science Department of Distributed Systems Prof. Dr.-Ing. P. Tran-Gia Using Concurrent Multipath Transmission for Transport Virtualization: Analyzing Path Selection T. Zinner (Uni Würzburg), K. Tutschku (Uni Vienna), A. Nakao (NICT/UT), P. Tran-Gia (Uni Würzburg) ITG Fachgruppe Workshop: Technik und Grenzen der Virtualisierung

2 Motivation Resource Pooling: Multipath-Transmissions Resilience High capacity (e.g. videostreaming) Re-sequencing? different path delays out-of-order arrivals But: packets arrive out of order at the destination Re-sequencing necessary Buffer dimensioning? 2

3 Agenda Virtualization Transport virtualization Concurrent multipath transfer as implementation of transport virtualization System model Transmission model Simulation setup Delay model for a single path Results Conclusion 3

4 VIRTUALIZATION 4

5 Virtualization Virtualization is a technology that abstracts physical resources to generate logical resources Share type of Virtualization ti (one physical, multiple l logical) l) Aggregation type of Virtualization (multiple physical, one logical) 5

6 Transport Virtualization (TV) Transport Virtualization (Tutschku, Nakao, Zinner, Tran-Gia 2008): abstraction concept for data transport resources Physical location of transport resource doesn't matter Achieved by: abstract data transport resources combined from one or more physical/overlay transport resources, e.g. wave length or MPLS path, an overlay link, or an IP forwarding capability (even in different administrative domains) physical resources can be used preclusive or concurrently Advantages of TV: Increased reliability (don t rely on a single path) Higher capacity (parallel use of links) 6

7 Concurrent Multi-Path Transfer (CMT) Logical topology Routing overlays of provider II Aim: Very high and reliable transmission between two end hosts Aim: Very high and reliable throughput between two end hosts Solution: Transport Virtualization: Combine multiple paths (even from different overlays) pooled transport pipe Routing overlays of provider I POP Physical topology 7

8 Diversity in Multi-Provider Environment High diversity w.r.t. paths: Four North-american nation-wide ISPs Tier1: M. Liljenstam et al., 2003) Multiple routes for increased resilience are (theoretically) available Moreover: For 25% of the used paths shorter paths exist (TIV; Measurements in PlanetLab by S. Banerjee et al., 2004) Better paths exist; capacity is readily available 8

9 Alternative approaches Other Multipath transmission approaches: Multipath-TCP (UCL/Trilogy/IETF) Concurrent Multipath Transfer Using SCTP Multihoming (J.R. Iyengar et al.) Load balancing in MPLS (X. Hesselbach et al.) Resource pooling (COMCON, VNP, cf. Michael s Talk) Common problems: Out-of-order arrivals Possible solution: Re-sequencing buffer Buffer dimensioning Influence on the e2e delay Effective throughput of pooled resource Fast selection out of several single resources 9

10 Influence of Reordering on Voice - QoE 10

11 MODELING 11

12 Transmission Model Data stream divided at router into segments with k parts 1 2 overlay 1 Scheduling? p 1,1 p 1,n1 each provider will offer a set n i of parallel paths (i = 1 m) Assumption: use k parallel paths on m overlays src k paths dst k parts have arrived k 1 k 1 k p m,1 Resequencing buffer of size L k parts are send in parallel at time t mnkwith paths 1 overlay m p m,nm Reassemble data stream from obtained parts Buffer occupancy? 12

13 Our Methodology Related approach by Nebat and Sidi 2006: Parallel downloads for streaming applications: a resequencing analysis Analytical l approach Enables computation of re-sequencing buffer occupancy in case of round-robin scheduling Adapted methodology to transmission model, performed scenario studies Simulative approach Enables computation of re-sequencing buffer occupancy Different scheduling methods can be investigated Validation of the analytical approach possible 13

14 Experiments Input: Number of paths Scheduling delay Path delay distributions Path capacity Source Destination buffer delay Output: Re-sequencing buffer occupancy distribution Random delay generation w.r.t. the path delay distributions 14

15 Path Model 10 time series histogram de elay bability pro delay of i-th packet delay Constraint: t packets do not overtake each other on a single path, i.e. current delay previous delay interdeparture time 15

16 Markov Chain Model Markov-chain for modeling the delay d States are the delay d State-transition propability p i j between two departures 0 p 0 1 p 1 2 p 2 3 p i-2 i-1 p i-1 i p ii i-1 i p 1 0 p 2 1 p 3 2 p i-1 i-2 p ii-1 p i+1 i p 0 0 p 1 1 p 2 2 p i-1 i-1 p ii Solution of the matrix equation d P=d (fixpoint equation) Implementation with linear programming 16

17 Example Resequencing buffer occupancy (two paths): Overtaking packets on a single path No overtaking Computed buffer occupancy much higher in case of overtaking 17

18 RESULTS 18

19 Simulation vs. Analysis 19

20 Impact of Skewness Transmission over two concurrent paths Significant impact of different mean values Lower skewness leads to lower buffer distributions Path delay distributions with high asymetry should be avoided 20

21 Complexity of Path Selection Scenario: Multipath transmission over three paths (nbin or normal): First path: μ = 25 Second path: μ = 50 Third path: μ = Impact of third path on mean re-sequencing buffer occupancy Similar mean buffer occupancy for nbin and normal path delay distributions The higher the delay deviation, the higher the mean buffer occupancy Minimum mean buffer occupancy exists between μ = time units for third path 21

22 CONCLUSION & CURRENT WORK 22

23 Conclusion Transport Virtualization improves capacity and reliability Simulative approach for investigating g the resequencing buffer: Number of paths, different path delays, scheduling, capacity, Evaluation of path selection strategies possible Validation of analytical and simulative approach Case-Study of the re-sequencing buffer occupancy: Lower skewness leads to lower buffer distributions Path delay distributions with high asymetry should be avoided Further Work: Include packet loss, TCP, e2e delay, congestion, flash crowed. 23

24 Current Work EuroNF funded project MULTINEXT: Measurement of CMT in experimental facilities ETOMIC-Box / Dimes Traffic T generation TCPdump 1st path Wien ETOMIC-Box: Traffic consumption TCPdump Berlin 2nd path Tel-Aviv Würzburg Routing Overlay 3rd path PlanetLab? x i (t) SIG Multipath (GLAB) Multipath-TCP CMT for SCTP... 24

25 Q & A Thank you! zinner@informatik.uni-wuerzburg.de 25