Routing on Overlay Networks EECS 228 Abhay Parekh parekh@eecs.berkeley.edu October 28, 2002
What is an overlay network? � A network defined over another set of networks � The overlay addresses its own nodes A � Links on one layer are network segments of lower layers A’ A � Requires lower layer routing to be utilized � Overlaying mechanism is called tunneling � Example: Virtual Private Networks � Virtual topology defined via VPN nodes � Telecommuters appear as though they are on the corporate network � Sessions are more secure � Bits may traverse various kinds of underlying networks PSTN, Frame Relay etc. � October 28, 2002 Abhay K. Parekh: Topics in Routing 2
Routing On the overlay Underlying Network October 28, 2002 Abhay K. Parekh: Topics in Routing 3
Routing on the Overlay The underlying network induces a � complete graph of connectivity No routing required! � Underlying Network October 28, 2002 Abhay K. Parekh: Topics in Routing 4
Routing on the Overlay The underlying network induces a � complete graph of connectivity No routing required! 10 � But � 200 One virtual hop may be many 100 � underlying hops away. 90 Latency and cost vary significantly over 90 100 � the virtual links 100 10 20 State information may grow with E � (n^2) 10 October 28, 2002 Abhay K. Parekh: Topics in Routing 5
Routing Issues The underlying network induces a � complete graph of connectivity No routing required! � But � One virtual hop may be many � underlying hops away. Latency and cost vary significantly over � Underlying the virtual links Network State information may grow with E � (n^2) At any given time, the overlay network � picks a connected sub-graph based on nearest neighbors How often can vary � Also, structured (Chord) v/s � unstructured (Gnutella) October 28, 2002 Abhay K. Parekh: Topics in Routing 6
Routing Issues The underlying network induces a � complete graph of connectivity No routing required! � 1 2 But � One virtual hop may be many � underlying hops away. Latency and cost vary significantly over � 3 the virtual links State information may grow with E � (n^2) At any given time, the overlay network � 5 4 picks a connected sub-graph based on nearest neighbors How often can vary � Also, structured (Chord) v/s � unstructured (Gnutella) The overlay network must ROUTE! � October 28, 2002 Abhay K. Parekh: Topics in Routing 7
Routing Issues Overlay network users � may not be directly connected to the overlay nodes E.g. Akamai � 1 2 3 5 4 October 28, 2002 Abhay K. Parekh: Topics in Routing 8
Overlay Routing: Edge Mapping Overlay network users may � not be directly connected to the overlay nodes E.g. Akamai 1 2 � User must be redirected to a � “close by” overlay node Edge-Mapping, or redirection � function is hard since IP(5) 3 # potential users enormous � User clients not under direct ? � control When overlay clients are � 5 directly connected the edge 4 mapping function is obviated E.g. P2P: users/nodes � colocated October 28, 2002 Abhay K. Parekh: Topics in Routing 9
Overlay Routing: Edge Mapping Overlay nodes interconnect � clients Enhance nature of connection � 1 2 Multicast � Secure � Low Loss � Much easier to add � functionality than to integrate IP(5) 3 into a router ? 5 4 October 28, 2002 Abhay K. Parekh: Topics in Routing 10
Overlay Routing: Adding Function to the route Overlay nodes interconnect � clients Enhance nature of connection � 1 2 Multicast � Secure � Low Loss � Much easier to add � functionality than to integrate into a router 3 Overlay nodes can become � bottlenecks 5 4 October 28, 2002 Abhay K. Parekh: Topics in Routing 11
Overlay Routing: Resource Location Overlay network may contain � resources. Eg. Servers � 1 2 Files � Client makes request for B � resource D B E Overlay must “search” for � F “closest” node that has the 3 resource E.g. find the least loaded � B? server that has a piece of content and that is has low network latency to client 5 4 A A B D C October 28, 2002 Abhay K. Parekh: Topics in Routing 12
Overlay Routing: Resource Location Overlay network may contain � resources. Eg. Servers D B � 1 2 Files � Client makes request for B � resource D B E Overlay must “search” for F F � C “closest” node that has the 3 resource E.g. find the least loaded � B? A server that has a piece of C D content and that is has low E 5 network latency to client 4 A A single “index” is not A � B scalable D C Overlay launches a query to � locate resource October 28, 2002 Abhay K. Parekh: Topics in Routing 13
Overlay Routing: Resource Location Overlay network may contain � resources. Eg. Servers D B � 1 2 Files � Client makes request for B � resource D B E Overlay must “search” for F F � C “closest” node that has the 3 resource E.g. find the least loaded � B? A server that has a piece of C D content and that is has low E 5 network latency to client 4 A A single “index” is not A � B scalable D C Overlay launches a query to � locate resource Query is “Routed” through the � overlay until object is located October 28, 2002 Abhay K. Parekh: Topics in Routing 14
Overlay Routing: Resource Location Overlay network may contain � resources. Eg. Servers D B � 1 2 Files � Client makes request for B � resource D B 4 E Overlay must “search” for F F � C “closest” node that has the 3 resource 4 E.g. find the least loaded � A B? server that has a piece of C D content and that is has low E 4 5 network latency to client 4 A A single “index” is not A � B scalable D C Overlay launches a query to � locate resource Query is “Routed” through the � overlay until object is located October 28, 2002 Abhay K. Parekh: Topics in Routing 15
Overlay Routing: Resource Location Overlay network may contain � resources. Eg. Servers D B � 1 2 Files � Client makes request for B � resource D B 4 E Overlay must “search” for F F � C “closest” node that has the 3 resource 4 E.g. find the least loaded � A B? server that has a piece of C D content and that is has low E 4 5 network latency to client 4 A A single “index” is not A � B scalable D C Overlay launches a query to � locate resource Query is “Routed” through the � overlay until object is located October 28, 2002 Abhay K. Parekh: Topics in Routing 16
Summary Two kinds of overlays functions � Overlay contains resources � Overlay facilitates communication among other client applications � Two kinds of virtual topologies � Structured � Unstructured � Two kinds of client connectivty � Direct: P2P � Not direct: Akamai � Overlay Network Functions � Select Virtual Edges (fast or slow timescales) � Overlay Routing Protocol � Edge Mapping � Resource Location � Edge Mapping and Resource Location can be combined � October 28, 2002 Abhay K. Parekh: Topics in Routing 17
Example: Application Level Multicast Content Producer Media Distribution Media Distribution Network Network Content Producer Media Clients October 28, 2002 Abhay K. Parekh: Topics in Routing 18
The Broadcast Internet Content Producer Content Producer October 28, 2002 Abhay K. Parekh: Topics in Routing 19
Broadcast Overlay Architecture content management injection & real-time control Management Platform network management monitoring & provisioning Media Delivery System server management redirection management load balancing system availability Redirection viewer management subscriptions, PPV, monitoring, Neilson ratings, targeted advertising October 28, 2002 Abhay K. Parekh: Topics in Routing 20
Broadcast Management Scales to millions � Application-level � information for management and tracking Works across multiple � networks Content Producer � event programming with ad-hoc query audience statistics October 28, 2002 Abhay K. Parekh: Topics in Routing 21
Broadcast Manager Node Information Stream Switchover October 28, 2002 Abhay K. Parekh: Topics in Routing 22
Policy Management October 28, 2002 Abhay K. Parekh: Topics in Routing 23
Example: Content Addressable P2P Networks (CAN) � Ratnaswamy et. al � First generation P2P (Napster, Gnutella not scalable) � CAN is one of several recent P2P architectures that � impose a structure on the virtual topology � locate objects via distributed hash tables DHT Routes queries through the structured overlay � � attempt to distribute (object, location) pairs uniformly throughout the network � support object lookup, insertion and deletion of objects efficiently. � Others: Chord, Pastry, Tapestry October 28, 2002 Abhay K. Parekh: Topics in Routing 24
Recommend
More recommend
