1. or, Providing Scalable, Decentralized Location and Routing Network Services Tapestry: Fault-tolerant Wide-area Application Infrastructure Motivation and Summary Wide-area resources present opportunities for new global-scale network applications Applications: dist. computing (Parabon, Entropia), dist. storage (OceanStore, P2P), wide-area streaming media Increased scale leads to issues in fault-tolerance, scalability, manageability and security Tapestry provides an overlay network infrastructure that Maps unique object IDs to network locations and routes messages to destinations given node ID Properties: efficient, adaptable to changes in resources, resilient to multiple failures and certain attacks Ben Y. Zhao John Kubiatowicz Anthony D. Joseph U.C. Berkeley SIGCOMM 2001 Wide-area Location and Routing Incremental suffix-based routing similar to Plaxton et al (SPAA97) Nodes and objects have unique bit-sequence identifiers Mobility Support 1.Fast state updates for mobile data 2.Location independent packet delivery to mobile nodes Key Features Performance Bounds 1.N = | namespace |, n = # of physical nodes, b = digit base 2.State kept at each node = S, 3bLog b n  S  3bLog b N 3.# of Logical hops = L, (bLog b n + 2)  L  bLog b N 4.Overlay location/routing distance  network distance Dynamic Algorithms 1.Dynamic node insertion: Recursively construct optimized routing tables Scoped notification 2.Dynamically mapping object ID to physical “root nodes” Fault-tolerance and Self-management 1.Announce-listen approach to state management 2.Machine heartbeats & object republish messages assist fast failure detection 3.Redundancy 1.Location: object IDs hashed to generate multiple roots Queries issued in parallel 2.Routing: Each route hop has multiple alternate pointers Tapestry Applications Bayeux: fault-tolerant wide-area data dissemination Uses natural Tapestry hierarchy for efficient packet duplication Routing leverages alternate Tapestry paths for successful delivery Tapestry location used as anycast to self-organize member partitions Leveraging dedicated infrastructure nodes for low overhead in routing (RDP) and bandwidth (stress) Continuing Work: Exploration of fault-tolerant routing via redundant overlay paths for reliable point to point communication Experimentation into effect of decentralized network architectures against Distributed Denial of Service (DDoS) attacks Embedding multi-criteria queries into distributed query routes 0325 B4F8 9098 7598 4598 87CA D598 1598 3E98 3098 0098 2BB8 L1 L2 L3 L1 L4 A2D8 L2 2118 L3 L4 00B1 L1 Routing - Each node keeps routing map - At each suffix length, maintain pointers to nearest node(s) with next unique digit - Match an additional digit to destination node at each hop Location - Publishing = mapping object ID to deterministic “root node” - Backpointers inserted at every hop from server to root node - Searches route to root node, route to object when pointer found Comparison of Overlay Infrastructures Tapestry Chord CAN Pastry Log b N Log 2 N O(d*N 1/d ) O(d) Base b bLog b N O(1)  O(1) O(1) ? O(Log b 2 N) O(Log 2 2 N) O(d*N 1/d )O(Log b N) Read/Write Log b N Log 2 N None Dimen d Base b bLog b N+O(b) Heuristics Read/WriteImmutable Read/Write Explicit Designed as P2P Indices Key Parameter Logical Path Length Routing State Size Routing Overhead (RDP) Correlation to Network Distances Messages to Insert Writable Objects Explicit Key Measurements Effect of location pointers in the network on search locality Stability via redundancy Improved latency and stability via redundant requests. Convergence of backup routes to a primary route path vs. position of branch point Packet delivery using FRLS routing on Tapestry vs. IP: A: IP success, Tapestry success B: IP success, Tapestry fails C: IP fails, Tapestry success D: Both fail, route exists E: Destination not reachable