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1 Addressing and Routing in Multi-substrate Overlay Networks Jorg Liebeherr University of Toronto Joint work with: Majid Valipour and Boris Drazic.

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Presentation on theme: "1 Addressing and Routing in Multi-substrate Overlay Networks Jorg Liebeherr University of Toronto Joint work with: Majid Valipour and Boris Drazic."— Presentation transcript:

1 1 Addressing and Routing in Multi-substrate Overlay Networks Jorg Liebeherr University of Toronto Joint work with: Majid Valipour and Boris Drazic

2 2 Substrate (underlay) network Overlay network What is an overlay anyway? An overlay network is a virtual network of nodes and logical links built on top of an existing network A virtual link in the overlay corresponds to a path in the underlay

3 Multi-substrate Network Colors indicate type of substrate Overlapping circles and links indicate bidirectional connectivity

4 Resulting Topology 4

5 Approaches to Routing 1.Vanilla Ad-hoc routing –Extensively explored –Not cognizant of substrates –Scalability limits 2.Single structured overlay –Simple addressing and routing –Scales to large networks –Not always viable 3.Hierarchical –Within and between groups of same color –Needs address and routing solutions 5

6 6 Overlays over multiple substrates Goal: Improve ability to build an overlay over multiple substrates Problem: How to efficiently propagate information about address bindings? Solution: Protocol mechanisms for exchanging address bindings Cross Substrate Advertisement (CSA)

7 Address Bindings in Single-substrate Overlay Address binding: [A; SA(A)] 7 Overlay node identifier Substrate address

8 Address Bindings in Multi-substrate Overlay More complex address binding: [A; SA S1 (A), SA S3 (A)] 8 Overlay node identifier Substrate address

9 9 Cross Substrate Advertising (simplified) - Outgoing - ID = A Source: A SA S1 (A)SA S2 (A)SA S3 (A) SA S1 (A) SA S2 (A) SA S3 (A) List of substrate addresses Source: A SA S1 (A)SA S2 (A)SA S3 (A)

10 10 Cross Substrate Advertising (simplified) - Incoming - IDSubstrate addresses ASA S1 (A), SA S1 (A), SA S1 (A) Source: A SA S1 (A)

11 Implementation CSA Protocol realized as part of an open source overlay software system (www.hypercast.org)www.hypercast.org Implemented as a layer: –Mechanisms are independent of protocol that builds topology Considers preference for substrates CSA message types: –Request address list –Update 11

12 12 Evaluate Methods for Relayed Address Exchange Exchange address lists periodically Attach address lists to protocol messages Add address list to each message with info on node Request address list when info is needed Add preferred address to each message with info on node PushPullPush Single Gossip Protocol-driven dissemination

13 Experimental Evaluation Local Emulab Testbed 20 Linux nodes Software: Hypercast with CSA Delaunay Triangulation protocol Multiple UDP/IP substrates CPU2xQuad-Core Xeon 5400 (2 Ghz) RAM4G DDR2 Interface8x1Gbps (4 Intel card, 4 NetFPGA)

14 Mapping of Nodes to Substrates K x K substrates (K+1) x (K+1) regions Nodes distributed uniformly across regions K=2 S1S1 S2S2 S4S4 S3S3 R 11 R 22 R 12 R 13 R 23 R 31 R 21 R 33 R 23

15 Performance metrics Stability: Do nodes reach a stable state? –% of nodes satisfying stability criterion for local neighborhood Connectivity: Do nodes form a single overlay? –# of partitioned topologies 15 A single stable overlay topology has formed when (1) 100% of nodes are stable; and (2) there is one topology

16 Stability K=8 (64 substrates), 648 nodes Push/Pull None Push-single Gossip Push-single and gossip 250 ms 500 ms 1000 ms

17 Connectivity K=8 (64 substrates), 648 nodes Number of partitions

18 Protocol overhead Received Traffic (average per node): K=17 (289 substrates), 2592 nodes

19 Approaches to Routing 1.Vanilla Ad-hoc routing –Extensively explored –Not cognizant of substrates –Scalability issues 2.Single structured overlay –Simple addressing and routing –Scales to large networks –Not always viable 3.Hierarchical –Within and between groups of same color –Needs address and routing solutions 19

20 Reachability Domain 20 Substrate: Set of compatible attachment points Reachability Domain: Maximal set of nodes with path in same substrate Nodes in the same reachability domain must be able to agree on the scope and identifier of a reachability domain. Hierarchical routing: First find destination RD, then node within RD

21 Dynamic Reachability Domains 21 Number and location of reachability domains are dynamic New reachability domain Location of reachability domain changes Keeping consistent routing tables may not be feasible

22 Strawman: Landmark Domain Routing 22 Inspired by Landmark Routing and Compact Routing Key concepts: –Use least volatile reachability domains as landmark domains –Route to destination via landmark domain Nodes know how to route to landmark domain Locator is reverse path from landmark domain –Locator has one entry per traversed reachability domain

23 Reachability Domain 23 Route from A K Ks Locator: {RD 6 ; H, J} Step 1: Use next-hop information to reach node in landmark domain Step 2: Use locator for exit node in landmark domain Step 3: Follow reverse path to K

24 Preliminary Evaluation 24 Random static topology 100 nodes per substrate with up to 70 reachability domains Multiple landmark domains

25 Related Works Adhoc Routing –Hierarchies or clustering for scalability e.g., [Ramanathan & Steenstrup `98] [Pei et.al. `00] [Eriksson et.al.`04] –Structured overlays for ad-hoc routing e.g., [Viana et.al. 04] Scalable Routing –Landmark e.g., [Francis `88] –Compact Routing e.g., [Thorup & Zwick `01] –Metric Spaces e.g., [Krioukov `10] Overlay-based Routing –Identifier-based e.g, [VRR 06] [IHR 08] [ROFL 06] –Locator-based + directory e.g., [SEATTLE `08] [SpoVNeT 08] 25

26 Summary Self-organizing overlay protocols over multiple substrates Cross-Substrate Advertisement improves ability to form a structured overlay over multiple substrates Hierarchical routing between reachability domains Landmark domain routing awaits full exploration: –Provable bounds on path stretch –Scalability vs. dynamics


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