Wireless internet routing Philippe Jacquet

Internet and networking Internet –User plurality connected to –Sources plurality

Wireless architectures Three main architectures –Point to point –Base station –Mesh

Signal processing complexity in ground wireless networks Diagram Capacity-Range GSM UMTS Wavelan IEEE Hiperlan1&2 IEEE802.11a UMTS pico- cell UMTS micro-cell Capacity in bit/s distance in m bluetooth

Mobile ad hoc networks Mesh and mobile

6 DARPA’s proposal for LANdroids 2. Wireless network capabilities required

7 2. Which wireless networks? MANET VANET wireless sensors Wireless community network

Wireless networks Mobile ad hoc networks –Mobility makes link failure a necessity Refresh period 1 second Automatic self-healing –Local neighborhood is local space Unlimited neighborhood size –Stadium network: N=10,000, with average degree 1,000 BGP needs links exchange per refresh time BGP fails on Wifi networks with 20 users at walking speed. Heavy density kills link state management.

Wireless internet Mobile ad hoc routing Mobile Ad hoc NETworks –Two protocol classes: Proactive class Reactive class

Proactive class Link state protocols –Full internet legacy –Topology compression –Periodic control traffic –Permanent routing tables –OLSR

Reactive class Distance vector based –Partial internet legacy –Path limited topology –On demand route discovery –Temporary routing tables –AODV

Optimized Link State Routing protocol Topology compression –Run light and fast, only on best routes Carry a subset of the local table Stay on selected links

Topology compression graph(V,E) Optimized Link State Routing (OLSR) –A mobile network can be very dense (ex: |V|=10 4,|E|=10 7 ) –Instead advertizing all links, a node advertizes only its multipoint relays. –The multipoint relay set much smaller than neighbor set

Multipoint relay sets Multipoint relay set of a terminal : Neighbor subset that covers the two hop neighbors Goal: find the smallest posible multipoint relay set Multipoint relay links

Multipoint relay set Local computation –Need to know two-hop neighborhood –Optimal is NP hard –Greedy algorithm is optimal to factor Good enough for performance

Multipoint relay set Greedy selection algorithm On node A Intialize N 2  N 2 (A), E r (A) . While (N 2  ) do Find y in N(A) which maximizes |N 2  N(y)| Add Ay to E r (A) N 2  N 2 - N(y) Return E r (A)

Topology compression In Erdös-Rényi random graph models: In unit disk random graph model:

B A Topology compression The union of multipoint relay link sets is a remote-spanner –Nodes compute their routing tables with the remote-spanner and their local table. Topology compression is lossless. –Optimal routes in tables also optimal in genuine topology.

Route optimality proof By recursion: if D is at distance k from A in G(V,E) there exists a route of length k in G(V,E(A)+E r ) from A to D –true for k=1: (A,D)  E(A). –If true for k, then if D at distance k+1, let the chain F-H-D with d(A,F)=k-1 and d(A,H)=k. Node F is a two hop neighbor of node D. –Let M the multipoint relay of D which covers F. –M is at distance k from A, thus there exists a route L of length k in G(V,E(A)+E r ) from A to M. –(M,D)  E r, thus L+(M,D) is in G(V,E(A)+E r ) and is of length k+1. AD FH M

Control traffic reduction Topology reduction –Topology compression Dissemination reduction –Information about topology move only on multipoint relay links Further dissemination reduction –Wireless flooding Total reduction

Wireless flooding A single transmission per node –broadcast emission –Instead of a copy per link

Dissemination reduction link flooding (cost |E|) packet P node A P←reception(); If !(P==null) then if!(P  received) then insert P in received; B←last_emitter(P); for each C  N(A) do if(C≠B) then send(P,C); broadcast flooding (cost |V|) P←reception(); If !(P==null) then if!(P  received) then insert P in received; broadcast(P);

Multipoint relay flooding Only multipoint relays flood the information (reduction factor |E r |/|E|) P←reception(); If !(P==null) then if!(P  received) then insert P in received; B←last_emitter(P); if(BA  E r ) then broadcast(P);

Multipoint relay flooding Packet P dissemination from node S. Any arbitrary A –Closest emitter of P to A: distance k –Prove that k≤1

Multipoint relay flooding A F G H G’

OLSR neighbor sensing Partial Link control on network layer Periodic broadcast of hello message –Contain list of heared neighbors –Two way check

MPR selection Collect the 2-way neighbor lists of neighbor nodes Run the selection algorithm. Advertize MPR set in hello