The document discusses guaranteed greedy routing in overlay networks. It proposes constructing an overlay network using a Nearest Neighbors Convex Set (NNCS) that guarantees nodes will always have a neighbor closer to the destination. This allows for greedy routing to make progress at each hop. The NNCS is constructed by dividing the virtual space around each node into half-spaces defined by its neighbors. Various applications like multicast trees, service discovery, and spatially-bound querying can take advantage of the NNCS approach. Evaluation shows the NNCS outperforms Pastry in terms of relative path stretch.
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Guaranteed Greedy Routing in Overlay Networks
1. Conference on Future Internet
Communications 2013
Guaranteed Greedy Routing in
Overlay Networks
Dragan Milic and Torsten Braun
Universität Bern, Switzerland
braun@iam.unibe.ch, cds.unibe.ch
2. Overview
> Introduction
— Motivation
— Greedy Routing in Virtual Spaces
— Greedy Routing Failure
> Overlay Network Construction for Greedy Routing
— Nearest Neighbours Convex Set (NNCS)
— Algorithm for NNCS Maintenance
— NNCS Robustness
— Routing Optimization
> NNCS Applications
— Building of Multicast Trees
— Service Discovery
— Spatially Bound Query Flooding
— Network Optimization / QoS
> Evaluation: Relative Path Stretch
> Conclusions
CFIC, Coimbra, May 16, 2013
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3. Motivation
> Overlay network construction does often not consider
underlying network topology.
> Overlay network routing protocols
— optimize number of hops along the path, but
— disregard paths’ RTT stretch
= actual RTT on the path through the overlay network
RTT along the optimal path in the underlying network
> Proposal: apply greedy routing in virtual spaces,
where distance between nodes is proportional to their RTT
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4. CFIC, Coimbra, May 16, 2013
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Positioning Hosts in a Virtual Space
Host 1
Host 2
Host 8
Host 3
Host 5
Host 7
Host 4
Host 6
Physical Network
Virtual Space
Host 1
Host 8
Host 2
Host 3
Host 7
Host 4
Host 5
Host 6
x
y
5. Greedy Routing in Virtual Spaces
> Next hop =
neighbour with minimal
distance to destination
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6. Greedy Routing Failure
> Problem
— There might not always be
a neighbour closer to the
destination.
> Solutions
— For geographical routing in
mobile ad-hoc networks:
backup routing modes,
e.g., using right-hand rule
in GPSR
— For overlay networks:
construct an overlay
network that ensures to
have always a neighbour
closer to the destination
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7. Overlay Network Construction
for Greedy Routing
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> Delaunay triangulation
— can ensure existence of
closer neighbours towards
destination,
— but distributed approach is
complex.
> Solution
— Nearest Neighbors
Convex Set (NNCS)
is based on dividing the
virtual space into half spaces.
Current Node
Neighbour Node
Half Space
8. Nearest Neighbours Convex Set (NNCS)
> Construct half spaces
for all neighbours of a node
> NNCS
— is a convex set
defined by intersection of
all half spaces.
— guarantees that
greedy routing makes
progress at each node.
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Current Node
Neighbour Node
Other Nodes
Half Space
9. Algorithm for NNCS Maintenance
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10. NNCS Robustness
> Problem
— In case of churns or
failures, NNCS may lead to
routing failures or isolated
nodes.
> Solution
— Add second NNCS layer by
constructing a NNCS without
considering the nodes in the
first layer of the NNCS
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11. Routing Optimization
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> Problem
— NNCS selects close
neighbours, which leads to many
hops.
— Fisheye overlay network with a
mix of close and distant
neighbours, but greedy routing
using a Fisheye overlay network
does not guarantee progress.
> Solution
— maintain NNCS and Fisheye
overlay network sets
— select next hop making most
progress from both node sets
D. Milic, T. Braun: “Fisheye: Topology aware
choice of peers for overlay networks”,
34th IEEE Local Computer Networks, 2009
12. Applications
> Building of Multicast Trees
> Service Discovery
> Spatially Bound Query Flooding
> Network Optimization / QoS
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13. Building of Multicast Trees
> Reverse path multicast routing
> Node R forwards a received
multicast message to all
nodes that would use R
for routing a unicast
message to the source
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14. Service Discovery
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> Problem
— Service discovery is
usually based on flooding.
— Efficient flooding
mechanisms
> Solution
— Forwarding of query
message along reverse path
Query Source
End Systems
with Query Source
in their NNCS
Other Nodes
Flooding Path
15. Spatially Bound Query Flooding
> Queries can easily bound
within a certain area, e.g.,
a hyper ball, to ensure RTT
between query source and
server.
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Query Source
End Systems
with Query Source
in their NNCS
Other Nodes
Flooding Path
16. Network Optimization / QoS
> Paths fulfilling RTT / QoS
requirements must be within
an ellipsoid around source
and destination.
> Ellipsoid as bounding area
for path to be selected.
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17. Relative Path Stretch
> NNCS evaluation using OMNET++
> Different data sets
— PlanetLab data for 217 overlay nodes
— KING data for 462 overlay nodes
> Comparison of NNCS using different
virtual space dimensions with Pastry
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18. Conclusions
> NNCS enables greedy routing in overlay networks using
virtual space embedding.
> Various applications can take advantage of NNCS.
> NNCS based approach outperforms Pastry.
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19. Thanks for your Attention !
> cds.unibe.ch
> slideshare.net/torstenbraun
> braun@iam.unibe.ch
Torsten Braun: Guaranteed Greedy Routing in Overlay Networks
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