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Peer-to-peer networks Ant Rowstron Microsoft Research 1.

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Presentation on theme: "Peer-to-peer networks Ant Rowstron Microsoft Research 1."— Presentation transcript:

1 Peer-to-peer networks Ant Rowstron Microsoft Research 1

2 Talk overview Overview of Overlays/DHTs Overview of Wireless Routing protocols Description of Virtual Ring Routing – A routing protocol inspired by DHTs 2

3 Underlays (Networks) 3 Provides point-to-point communication A B

4 Overlay 4 A B

5 Overlay and underlay 5

6 Unstructured overlays – No/weak constraint on neighbors (for correctness) – Algorithmically simple – poor performance Flood based techniques etc. 6 Example: Gnutella, BitTorrent

7 Unstructured overlays – No/weak constraint on neighbors (for correctness) – Algorithmically simple – poor performance Flood based techniques etc. 7 Example: Gnutella, BitTorrent

8 Structured overlays – Constraints on neighbors – Algorithmically more complex DHT API, KBR API 8 Example: Distributed Hash Table (DHTs) - CAN, Chord, Pastry, Tapestry (2001)

9 Distributed Hash Tables (Pastry) 9 root node for key id space nodeId key Large id space NodeIds picked randomly from space Keys picked randomly from space Key is managed by its root node: Live node with id closest to the key

10 Node routing state 10 0*1*2*3* 20*21*22*23* 200*201*202*203* 2030*2031*2032*2033* 203231 Topology aware routing table NodeIds and keys in some base 2 b (e.g., 4) Prefix constraints on nodeIds for each slot Pick closest node satisfying slot constraints leaf set nodeId

11 Routing Prefix matching: each hop resolves an extra key digit 11 323310 323211 322021 313221 203231 nodeId key route(m, 323310)

12 Using DHTs root node for key id space nodeId key Keys picked randomly from space E.g. SHA1(www.microsoft.com) Generic building block – Application-level multicast – File Systems – Web Caches – File Sharing – Etc Generic building block – Application-level multicast – File Systems – Web Caches – File Sharing – Etc 12

13 DHT experiences DHTs are: – Self-organizing – Decentralized – Fault-tolerant/churn tolerant – Scalable – Performance Question: – Can we apply lessons to underlay routing protocols? 13

14 Wireless routing protocols Large number of wireless routing protocols Numerous scenarios: – Mesh, Sensor, Mobile, VLAN, etc Protocols traditionally target a scenario Protocols use either: – Flooding – Coordinates 14

15 Proactive routing x Nodes have complete topology map Example: OLSR, DSDV 15

16 Reactive routing Example: DSR, AODV 16

17 Coordinate-based routing 17 (x,y) y x q at (2,2) p lookup service lookup(p) p at (4,1) at (4,1) fixed identifier address Example: GPSR, BVR

18 Previous work on wireless routing Flooding based algorithms scale poorly – Flood on topology changes or discover routes Geographical and landmark routing – Scale well but nodes have identifier and address Some apps (sensor networks) may require just address – DHT-like structure to translate between the two Route setup delays Additional maintenance overhead Another target for attacks 18

19 VRR: Virtual Ring Routing A fundamentally different approach 19 No flooding Single topology- independent address Virtual Ring Routing

20 8F6 90E 910 8F0 8E2 0 FFF Topology-independent node identifiers Nodes organized into virtual ring by increasing identifier value Each node maintains a virtual neighbor set (vset) VRR: The Virtual Ring 20

21 VRR: Routing paths physical network topology 8F6 Nodes only maintain routing paths to virtual neighbors: Paths maintained proactively Paths are bidirectional and typically multi-hop

22 VRR: Forwarding table Paths recorded in forwarding tables along path Forwarding table contains Paths between node and vset members Paths between other nodes that go through node Paths to physical neighbors endpointB pathId nextA nextB endpointA 10E 10 me F42 31 8F690E 910 forwarding table for node 8F6 8F6 me 14A 140F4210E 2 8F6 F42 me F42 FF 14A 140 F42 10E 8F6

23 Physical network topology VRR: Forwarding table state 23 Physical neighbors VSet paths Other VSet paths

24 VRR: Example routing physical network topology

25 VRR: Example routing physical network topology

26 VRR: Example routing physical network topology

27 VRR: Example routing physical network topology

28 VRR: Example routing physical network topology

29 VRR: Routing summary Paths to virtual neighbors ensure correctness Stretch empirically small Many alternate paths to route around failures

30 VRR: Node joining Network Topology 19A 164 8F6 16E broadcast hellos to find physical neighbors Send setup request to 16E

31 VRR: Node joining Network Topology 19A 164 8F6 16E 171 164 sends setup to 16E with its vset 16E sends setup requests to nodes in received vset 16E adds node to vset when it receives setup

32 VRR: Handling failures Routing state is hard – No end-to-end heartbeats – Failures detected on missing acks or hellos – Local repair attempted first; – Otherwise, teardowns sent along all affected paths Two techniques to ensure consistency – Symmetric failure detection and acks on teardowns If x marks y faulty, y is guaranteed to mark x faulty – Lightweight optimistic transactions If in doubt abort (teardown)

33 Evaluation Evaluated using: – Simulations (ns-2) Mobility – Testbeds UCB Sensor Testbed with 68 mica2dot motes MSRC 111 node 802.11a Wireless Testbed 33

34 Sensor Mesh: VRR vs BVR 34 Increasing packets BVR delivery ratio drops

35 Failures: VRR vs BVR 35 Fail 10% nodes BVR delivery ratio drops

36 Office Mesh: VRR vs LQSR 36

37 Mobility: Simulation Simulation in ns-2 – 802.11b MAC – Mobility: 0-20 m/s – CBR: 1 packet/sec 37

38 Implementing Networking Services Implement lookups using key-based routing? 38 Nodes organized into virtual ring. VRR ARP: Flood-based ARP: ARP: 192.169.0.45 Hash(192.169.0.45) 192.169.0.45

39 Conclusions Overlay routing at the network layer VRR implements wireless routing – Scalable: no flooding – Single location-independent identifier per node No translation from identifiers to addresses – No route discovery or translation delays VRR implements a DHT – Strong consistency – No additional overhead

40 Further information VRR Paper: – M. Caesar, M. Castro, E. Nightingale, G. O'Shea and A. Rowstron, "Virtual Ring Routing: Network routing inspired by DHTs", Sigcomm 2006 http://research.microsoft.com/~antr/ 40


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