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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
GSMUMTS
WavelanIEEE 802.11
Hiperlan1&2IEEE802.11a
UMTS pico-cell UMTS
micro-cell
Capacityin bit/s
distance in m
bluetooth
Mobile ad hoc networks
• Mesh and mobile
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• DARPA’s proposal for LANdroids
2. Wireless network capabilities required
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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 1014 links exchange per refresh time• BGP fails on Wifi networks with 20 users at
walking speed.• Heavy density kills link state management.
Wireless internetMobile 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|=104,|E|=107)– Instead advertizing all links, a node advertizes only its
multipoint relays.– The multipoint relay set much smaller than neighbor
set |)(| EoEE r =→
)|(||| 2VOE =
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
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logV
Multipoint relay set
• Greedy selection algorithm
• On node AIntialize N2 N2(A), Er(A) .
While (N2) do
Find y in N(A) which maximizes |N2N(y)|
Add Ay to Er(A)
N2 N2- N(y)
Return Er(A)
Topology compression
• In Erdös-Rényi random graph models:
• In unit disk random graph model:
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τ r =E rE
=Ologn
n
⎛
⎝ ⎜
⎞
⎠ ⎟
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τ r =O n−
2
3 ⎛
⎝ ⎜
⎞
⎠ ⎟
BA
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)+Er) 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)+Er) from A to M.– (M,D) Er, thus L+(M,D) is in G(V,E(A)+Er) and is of length
k+1.A DF H
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
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τ r
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τ r
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V
E
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τ r2 V
E
Wireless flooding
• A single transmission per node– broadcast emission – Instead of a copy per link
Dissemination reduction
• link flooding (cost |E|) packet P node AP←reception();If !(P==null) then
if!(P received) theninsert 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) theninsert P in received;broadcast(P);
Multipoint relay flooding
• Only multipoint relays flood the information (reduction factor |Er|/|E|) P←reception();If !(P==null) thenif!(P received) then
insert P in received;B←last_emitter(P);
if(BA Er) 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
FG
H
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k
G’
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k −1
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k − 2
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
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