0!1. Overlaying mechanism is called tunneling. Overlay Network Nodes. ATM links can be the physical layer for IP

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1 epartment of lectrical ngineering and omputer Sciences University of alifornia erkeley '!$$( network defined over another set of networks The overlay addresses its own nodes Links on one layer are network segments of lower layers Requires lower layer routing to be utilized Overlaying mechanism is called tunneling $)$*+ $)$*+ Overlay Network Nodes Overlay Networks are extremely popular MON, kamai, Virtual Private Networks, Napster, Gnutella Overlay Networks may even peer!, $)$*.$! c a d b TM links can be the physical layer for IP - /

2 ! "$*$! a c d Underlying Network b Virtual ircuit under atagram! "$*$! "$*$! Underlying Network 9 9 ut One virtual hop may be many underlying hops away. Latency and cost vary significantly over the virtual links State information may grow with (n^) "$* "$* Underlying Network ut One virtual hop may be many underlying hops away. Latency and cost vary significantly over the virtual links State information may grow with (n^) ut One virtual hop may be many underlying hops away. Latency and cost vary significantly over the virtual links State information may grow with (n^)

3 "$*!*! $#$*$ "$*!*! $#$*$ Message from Message from xtreme Inefficiencies Possible, "$* $# ut One virtual hop may be many underlying hops away. Latency and cost vary significantly over the virtual links State information may grow with (n^) t any given time, the overlay network picks a connected subgraph based on nearest neighbors How often can vary lso, structured (hord) v/s unstructured (Gnutella) a) Physical Topology b) Naive unicast transmission c) IP multicast d) pplication level multicast rom omputer Networks, by Peterson & avie - / $# Three kinds of Overlays. Only Hosts: Peer to Peer Networks (PP) xample: Gnutella, Napster. Only Gateway nodes: Infrastructure Overlays ontent istribution Networks (Ns) xample: kamai. Host and Gateway Nodes: Virtual Private Networks Overlay node structure Regular: hord, Pastry dhoc: Gnutella unctions Route nhancement: etter QoS, pplication Level Multicast Resource iscovery: PP m? m? m m m m m m m m m m m

4 )$ )$ istribute file location Idea: multicast the request Hot to find a file: Send request to all neighbors Neighbors recursively multicast the request ventually a machine that has the file receives the request, and it sends back the answer dvantages: Totally decentralized, highly robust isadvantages: Not scalable; the entire network can be swamped with request (to alleviate this problem, each request has a TTL) ssume: m s neighbors are m and m; m s neighbors are m and m; m m? m? m?? m m $ Infrastructure Overlays dding performance and route functionality Resource iscovery PP Overlays Resource iscovery in Gnutella xample of an Infrastructure Overlay pplication Level Multicast xample of a PP Overlay ontent ddressable Networks onclusions $ Overlay network users are not directly connected to the overlay nodes.g. kamai "$*#*$* "$*#*$*? IP() Overlay network users are not directly connected to the overlay nodes.g. kamai User must be redirected to a close by overlay node dge-mapping, or redirection function is hard since # potential users enormous User clients not under direct control When overlay clients are directly connected the edge mapping function is obviated.g. PP: users/nodes colocated? IP() Overlay nodes interconnect clients nhance nature of connection Multicast Secure Low Loss Much easier to add functionality than to integrate into a router,

5 "$*##$*%$$! Overlay nodes interconnect clients nhance nature of connection Multicast Secure Low Loss Much easier to add functionality than to integrate into a router Overlay nodes can become bottlenecks? s. g. iles lient makes request for.g. find the least loaded content and that has low - /? s. g. iles lient makes request for.g. find the least loaded content and that is has low single index is not scalable Overlay launches a query to locate? s. g. iles lient makes request for.g. find the least loaded content and that is has low single index is not scalable Overlay launches a query to locate Query is Routed through the overlay until object is located? s. g. iles lient makes request for.g. find the least loaded content and that is has low single index is not scalable Overlay launches a query to locate Query is Routed through the overlay until object is located? s. g. iles lient makes request for.g. find the least loaded content and that is has low single index is not scalable Overlay launches a query to locate Query is Routed through the overlay until object is located

6 Overlay network users are not directly connected to the overlay nodes.g. Napster, Gnutella No edge mapping problem No gateways to maintain ut Nodes have limited s storage, connectivity computational power Two kinds of overlays functions Overlay provides access to distributed s Overlay facilitates communication among other client applications Two kinds of virtual topologies Structured: mesh, ring etc. Unstructured Two kinds of client connectivty irect: PP Not direct: kamai Overlay Network unctions Select Virtual dges (fast or slow timescales) Overlay Routing Protocol dge Mapping Resource Location $ 9!:#$$ ontent Producer ontent Producer Media istribution Network Media lients ontent Producer ontent Producer, :#! :#$*$ Management Platform content management injection & real-time control network management monitoring & provisioning server management redirection management load balancing system availability viewer management subscriptions, PPV, monitoring, Neilson ratings, targeted advertising pplication-level information for management and tracking Works across multiple networks ontent Producer event programming with ad-hoc query audience statistics - /

7 :#$* $*$ Node Information Stream Switchover $$##; < = N is one of several recent PP architectures that imposes a structure on the virtual topology uses a distributed hash-table data structure abstraction Note: item can be anything: a data object, document, file, pointer to a file routes queries through the structured overlay attempts to distribute (object, location) pairs uniformly throughout the network supports object lookup, insertion and deletion of objects efficiently. Others: hord, Pastry, Tapestry $$##; < = ssociate to each node and item a unique id in an d-dimensional space Properties Routing table size O(d) Guarantee that a file is found in at most d*n /d steps, where n is the total number of nodes, 9.$$ Space divided between nodes ll nodes cover the entire space ach node covers either a square or a rectangular area of ratios : or : xample: ssume space size ( x ) Node n:(, ) first node that joins cover the entire space n 9.$$ Node n:(, ) joins space is divided between n and n n n,,

8 9.$$ Node n:(, ) joins space is divided between n and n 9.$$ Nodes n:(, ) and n:(,) join n n n n n n n n,,, 9.$$ Nodes: n:(, ); n:(,); n:(, ); n:(,);n:(,) Items: f:(,); f:(,); f:(,); f:(,); n n n f 9.$$ ach item is stored by the node who owns its mapping in the space n n n f n f f n n f f n f f,-,/ > ##$*?.$*$# ach node knows its neighbors in the d-space orward query to the neighbor that is closest to the query id xample: assume n queries f n n n f f n n f f New node picks a point P at random ssuming it can find any overlay node, it sends a join message to the node which owns that point When the message has reached P, the node divides itself in half along one of the dimensions (first x then y etc) Pairs are transferred and neighbor sets updated Similar reasoning handles departures and failures,,

9 +$#$* xample: Three landmarks -ms: level -ms: level -ms: level Node j measures latencies of ms, ms, ms to the three landmarks. The bin of node j is (l,l,l : ) Neighbors should be close to each other in terms of latency on the underlying network Pick a set of well known landmark hosts ach node distributively computes its bin Nodes in the same bin are close to each other Orders the landmark set in increasing order of RTT from it. Latency is partitioned into levels Thus, associated with each landmark, at each node is a rank and a level. These values identify the bin $## $*%$$ ddressing: Uniquely identify the nodes host IP address, group address, attributes set is dynamic! Topology Update: haracterize and maintain connectivity iscover topology Measure distance metric(s) ynamically provision (on slower timescale) estination iscovery: ind node identifiers of the destination set Route omputation: Pick the tree (path) Kind of path: Multicast, Unicast Global or istributed lgorithm Policy Hierarchy Switching: orward the packets at each node, - $#9!$* $$ ddressing: Uniquely identify the nodes host IP address, group address, attributes set Structured is dynamic! Topology Topology Update: haracterize and maintain connectivity iscover topology Measure dd/insert distance Nodes, metric(s) inning ynamically provision (on slower timescale) estination iscovery: ind Resource node identifiers Location of the dge destination Mapping set Route omputation: Pick the tree (path) Kind of path: Multicast, Unicast pplication Level Routing...g streaming broadcast Global or istributed lgorithm Policy Structured Topology Hierarchy Switching: orward the packets at each node Overlays are an irreversible trend in network Overlays add new functions to the network infrastructure much faster than by trying to integrate them in the router relying on a infrastructure service provider on deploy the function isadvantages Overlay nodes can create performance bottlenecks New end-to-end protocols may not work since the overlay nodes don t understand them Generally better to improve performance by building an underlay and add functionality by building an overlay - - 9