PROSE CS 218 Fall 2017

Another MANET Routing Approach Using prefix labels instead of more ordinary addresses And distributed hash tables to translate from the node’s permanent name to the prefix labels Prefix labels describe how to get to a node’s current location From a known root So knowing the label tells you how to route Prefix labels change as nodes move The DHT allows those who know the node’s name to find its prefix label

PROSE Prefix Labels Build a directed acyclic graph from the MANET nodes First elect a root node Then use a breadth first search to find nearby nodes to the root Label those nodes, then continue to search Each label specifies how to get from its owner to the root node

An Example Graph The root’s children The root Why isn’t E a child of the root? Because PROSE builds an acyclic graph

Distributed Hash Tables Store data associated with names at many different nodes Hash each name to find a matching key The key specifies which node stores the data associated with the name There are complexities . . .

How Does PROSE Use Its DHT? Nodes use it to find the prefix labels of other nodes Destinations they want to send messages to, typically Each destination hashes its unique node ID (e.g., its MAC) to a prefix label That prefix label (or nearest match) is the destination’s anchor node Destination node then sends its unique ID and its own prefix label to its anchor Any node sending to that destination hashes its ID Getting the same anchor identity Send request to anchor

What Does An Anchor Node Do? Either reply to request with the destination’s prefix label Or forwards request to destination Which replies to the source In either case, source learns the destination’s prefix label And can send directly to it without consulting the anchor again

An Example Node N wants to send to node K N hashes K’s identity to find its anchor, which is C C N K

Continuing the Example N asks C for the prefix label of K N already has C’s prefix label More precisely, can route toward it based on the hash C sends N K’s prefix label, which is 0000 C N 0000 K

Now N Can Send Directly To K Using the prefix label How to decide the route? Using simple rules based on how labeling is done C N K

That’s All Well and Good, But . . . What happens when someone moves? Different cases: The moving node is an ordinary node The moving node is an anchor The moving node is the root node Each case handled differently

Moving an Ordinary Node Perform a leave operation when move is started To free up the old label Which is geographically based Perform a join operation when move is completed To be spliced into the tree in a new location Simple for leaf nodes More complex for internal nodes If necessary, elect a new root Handles the case of the root moving

Moving an Anchor Anchor identity is based on candidate node prefix So if an anchor node moves, its prefix might change Which might cause it to stop being an anchor for other nodes In that case, they find a secondary anchor and get translation information to them It will be the node with the largest prefix matching the old anchor So on the path to the old anchor So in the physical vicinity of the old anchor

Performance Issues Moves cause fewer control messages than in AODV and OLSR Paths tend to be longer than shortest path Generally 2x or more Not likely to perform well in situations of high node mobility Especially if all moving If root and anchors tend not to move, fewer issues