Intradomain Anycast for Content Centric Networks

Network Model Each node in the network has a unique NodeId A D C B E F G H

Network graph Nodes obtain a complete network graph – link state routing algorithm Nodes know the shortest path for every destination node A D C B E F G H B’s routing table* DestNext Hop AC DC EFF GFF *Metric is hop count

Routing Information objects have a unique ObjectId ObjectIds and NodeIds share the same id space NodeIs partition the ID space (DHT like) Network routes messages for ObjectIds to correspodent Nodes via the shortest path A D C B E F G H A requests H1 D requests H1

Duplicate Objects A copy of an object is located at a different node – E.g. Caching Requests should be routed to nearest location Cached object is announced to neighborhood A D C B E F G H CACHE H1

Shortcuts Upon receiving a CACHE ANNOUNCEMENT, a node compares if it’s worth creating a shortcut entry Compares distance between caching node and correspondent node Distance is subject to link state metric A D C B E F G H CACHE H1 If (distance(C) < distance(H) create shortcut entry for H1 If (distance(C) < distance(H) create shortcut entry for H1 ObjectNextHop H1C B’s shortcut table

Limiting the flood Nodes relay cache announcements if it’s really worth it Otherwise flooding is stopped A D C B E F G H CACHE H1 d(c) == d(h) Not worth it. Drop it A already forwards H1 to B. Not worth creating a shortcut entry. Relay cache announcement d(c) > d(h) Not worth it. Drop it

Anycast Upon receiving a message – Inspect shortcut table – If shortcut for this object is found, forward message to shortcut.nextHop – Else forward message to shortest path A D C B E F G H Request H1 ObjectNextHop H1C B’s shortcut table CACHE H1

Advantages Messages are routed through the shortest path, unless a detour is found along the way Link state routing ensures topological shortest paths – Not key based routing. – Logical distance d(ObjectId, NodeId) is not decreased on every hop. Cache announcements are flooded in a limited way – Nodes relay cache announcements as long as it’s worth willing

Disadvantages Link state does not scale to large topologies Suitable for intradomain routing

Can also be seen as Combination of structured and unstructured p2p systems DHT like key partitioning creates deterministic paths – If an object is not found at its correspondent node, then it’s not there at all Gossip style flooding is good for popular objects – In network caches

Can also be seen as (2) Link state routing for Node Ids Distance vector routing for Object Ids

Relation to Architectures Suitable for PSIRP – Rendezvous Network : publications and subscriptions are routed to correspondent node, unless a cache if found near by – Topology function in intradomain level – Nobody has actually presented a solution for intradomain yet Argument against CCN – CCN floods requests to network, we flood only caches (and that’s limited)

Usage Example: Probabilistic caching Assuming that object items can be distinguished based on popularity – Follow a Zipf distribution – Follow the rule A relatively small portion of the objects are responsible for the majority of traffic Let every node in the network cache an object with a probability p (e.g. 0.01%) Then, with high probability, popular items are cached in near by nodes Anycast scheme provides fast access to these objects