ahmed helmy, usc1 architectural framework for large- scale multicast in mobile ad hoc networks ahmed...
DESCRIPTION
Ahmed Helmy, USC3 Motivation Target Environment –Infrastructure-less mobile ad hoc networks (MANets) –MANets are self-organizing, cooperative networks –Expect common interests & sharing among nodes –Tens of thousands of mobile wireless nodes –Need scalable group-communication (multicast) Example applications: –Search and rescue (disaster relief) –Location-based service (tourist/visitor info, navigation) –Rapidly deployable remote reconnaissance and exploration missions (military, oceanography,…)TRANSCRIPT
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Ahmed Helmy, USC 1
Architectural Framework for Large-Scale Multicast in Mobile
Ad Hoc Networks
Ahmed HelmyElectrical Engineering Department
University of Southern California (USC)[email protected]
http://ceng.usc.edu/~helmy
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Ahmed Helmy, USC 2
Outline
• Motivation• Architectural Design Requirements• Architectural Components
– Multicast Service Bootstrap/Rendezvous Model– Contact-based Small World Hierarchy
Formation• Future Work
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Ahmed Helmy, USC 3
Motivation• Target Environment
– Infrastructure-less mobile ad hoc networks (MANets)– MANets are self-organizing, cooperative networks– Expect common interests & sharing among nodes– Tens of thousands of mobile wireless nodes– Need scalable group-communication (multicast)
• Example applications:– Search and rescue (disaster relief)– Location-based service (tourist/visitor info, navigation)– Rapidly deployable remote reconnaissance and
exploration missions (military, oceanography,…)
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Ahmed Helmy, USC 4
Architectural Design Requirements• Functional Requirements (Multicast Service)
– Dynamic creation of groups– Dynamic membership (nodes join/leave at will)
• participants unknown a priori
• Robustness– Adaptive to link/node failure, and to mobility
• Scalability & Energy Efficiency– Avoids global flooding– Provides simple hierarchy formation
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Ahmed Helmy, USC 5
Architectural Components• (1) Mechanisms for Bootstrapping of groups
and Rendezvous of participants • (2) Simple Hierarchy Formation Scheme
– zone-based architecture– small world contact extensions
• (3) Multicast Routing (on-going/future work)
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Ahmed Helmy, USC 6
First Architectural Component: (1) Bootstrap and Rendezvous Mechanisms
• Problem Statement:– 1. Provide a rendezvous mechanism for group
participants (senders and receivers) to meet– 2. Provide a bootstrap mechanism to initiate and
discover new groups• Approach:
– View the problem as that of resource discovery• Design a scalable efficient scheme to search for and
discover resources (information about groups and senders)
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Ahmed Helmy, USC 7
Alternative Multicast Rendezvous Designs
• Broadcast-and-prune (flooding of packets or sender advertisements)
• Expanding ring search (scoped flooding)• Center-based tree (rendezvous-point)• Hierarchical (e.g., domain-based, needs AS
hierarchy)
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Ahmed Helmy, USC 8
The Multicast Model• New Multicast Model: sender push, servers
cache, receivers pull• Where are the servers located? And how do
participants find these servers?– Do we have to resort to global flooding?– Can we maintain this info. in well-known
rendezvous node? (A node can move or fail, so bootstrapping will be hard)
– Use multiple nodes within a known Rendezvous Region (RR) (Still need bootstrap)
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Ahmed Helmy, USC 9
Search and Resource Discovery Scheme
• The geographic topology is divided into rendezvous regions (RRs)
• The multicast space is divided into group prefixes (Gprefix)
• Mapping between Gprefix RR is provided to all nodes (e.g., through a small table, or could also be algorithmic)
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Ahmed Helmy, USC 10
Assumptions
• Nodes know their (approximate location) [using GPS or GPS-less schemes]
• Nodes capable of geographic routing (as in location-aided routing (LAR) and geocast)
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Ahmed Helmy, USC 11
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
Get location ~(x,y)
RR1 Gprefix1
RR2 Gprefix2
… ...
RRn Gprefixn
(x,y)RRiGprefixi
SDS: sender discovery server
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Ahmed Helmy, USC 12
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
RRleave
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Ahmed Helmy, USC 13
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
Sender to group G
RR1 Gprefix1
RR2 Gprefix2
… ...
RRn Gprefixn
GGprefixi RRi
S
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Ahmed Helmy, USC 14
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
contact
geo-cast
S
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Ahmed Helmy, USC 15
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
contact
S
RReceiver for G
GGprefixi RRi
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Ahmed Helmy, USC 16
Bootstrap Mechanism• The goal:
– To create sessions/groups dynamically– To announce these groups– To enable interested potential participants to obtain
information about new groups• Approach:
– Designate a well-known group (WKG) address for the ‘session/group announcement group’ as a bootstrap group.
– As any other group, this group is also supported by RR
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Ahmed Helmy, USC 17
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
RR1 Gprefix1
RR2 Gprefix2
… ...
RRn Gprefixn
WKGGprefixj RRj
Group Initiator
WKG: Well-known Group (a bootstrap group for initiating further groups)
Bootstrap (initiating, and knowing about, groups)
GI
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Ahmed Helmy, USC 18
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
Bootstrap (initiating, and knowing about, groups)
GI
GI: Group Initiator
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Ahmed Helmy, USC 19
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
Bootstrap (initiating, and knowing about, groups)
GI
MMMulticast Member
RR1 Gprefix1
RR2 Gprefix2
… ...
RRn Gprefixn
WKGGprefixi RRi
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Ahmed Helmy, USC 20
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
Bootstrap (initiating, and knowing about, groups)
GI
MM
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Ahmed Helmy, USC 21
Performance Discussion
• What is the extent of the search for servers?• We expect group initiators to choose groups that
map to nearby RRs• We expect popularity of groups in certain
locations (e.g., for location-based services)• These factors increase the chances of localizing
the search for servers• More evaluation needed (on-going work)
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Ahmed Helmy, USC 22
Architectural Components
• (1) Mechanisms for Bootstrapping of groups and Rendezvous of participants
• (2) Simple Hierarchy Formation Scheme– zone-based architecture– small world contact extensions
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Ahmed Helmy, USC 23
Second Architectural Component:(2) Simple Hierarchy formation
• Problem Statement:– To discover group/sender servers with reduced
overhead (than in flooding or pure geocast)• Approach:
– Design a simple hierarchical architecture• Complex mechanisms incur lots of overhead with
mobility and network dynamics
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Ahmed Helmy, USC 24
Alternative Hierarchical Designs• Cluster-based hierarchy using cluster heads
– Cluster heads are elected dynamically– Traffic funnels through cluster head
• Landmark Hierarchy– Landmarks advertised and used for mgmt/addressing– Re-configuration needed if landmarks move
• Needs adoption/promotion/demotion mechanisms
• Zone-based Routing– Each node has its own neighboring zone– Hybrid routing:
• pro-active within zone, re-active out of zone
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Ahmed Helmy, USC 25
Contact-based ‘small world’ Hierarchy• Neighboring zone knowledge
– A node knows routes to neighbors up to R hops away (R is the zone radius) pro-actively
– A node maintains contacts to increase its view of the network
• Simplicity & Efficiency– No elections of cluster head or landmarks– Mobility does not lead to major re-configuration– Uses the concept of Small World Graphs (six
degrees of separation)
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Ahmed Helmy, USC 26
How to Create a Small World[Watts 98]
Small-World
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Ahmed Helmy, USC 27
i
- Clustering Coefficient (C) captures how many of a node’s neighbors are also neighbors for each other
i
Clustering = 3 Clustering = n.(n-1)/2 = 6
Clustering Coefficient for node i (Ci) = 3/6 = 0.5
(a) Given network (b) Fully connected network
Node i has n neighbors
Clustering
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Ahmed Helmy, USC 28
Small World Characteristics
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1
probability of re-wiring (p)
Clustering
Path Length
Desirable Region [Watts 98]
(C)
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Ahmed Helmy, USC 29
Taking Advantage of Mobility• Small world graphs
– Adding a small number of random short-cuts drastically reduces the average path length of graph
– For our case: choosing random nodes leads to unpredictable overhead.
• Choosing contacts:• Choose nodes whose characteristics you know (your
neighbors). • When they move, they will have a network view with less
overlap. • The resulting graph may tend to a small world graph.
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Ahmed Helmy, USC 30
Center NodeInternal NodeR
C
1 3
4
56
7
2
Border Node
Zone RadiusMobility
• Example of zoning: – Zone for center node C is shown (with radius R). Border nodes are
numbered (1-7). Nodes 1,3 and 6 are moving/drifting out of zone.
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Ahmed Helmy, USC 31
R
R
R
R
C
5
1
4
3
6
7
2
contact
contact
contact
Route
• C stays in contact with the drifting nodes using low overhead, which enables it to obtain better network coverage.
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Ahmed Helmy, USC 32
Choosing Contacts• A node chooses its contacts with probability p
proportional to – Energy estimates Eest of the node and the contact,
– Their relative stability Sest, and
– Activity level of the node Aest measured as rate of discovery requests.
• Also, p is inversely proportional to the number of zone contacts Zest.
• p EestSest Aest / Zest
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Ahmed Helmy, USC 33
Choosing Contacts (contd.)• Eest: Energy estimate for the lifetime of the node
itself and the contact node– Eleft: Energy left E: Energy drainage rate– Eest (Eleft / E)node(Eleft / E)contact
• Sest: Relative stability (possible presentation)
– (,t) model: estimates probability that nodes within range at t0 will be in range at t
– Received Power model: • RxdPwr/TxdPwr = 1/dn; where n=2 or 4• RxdPwrnew/RxdPwrold << 1 then nodes moving away
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Ahmed Helmy, USC 34
Conclusion• Designed architectural framework to support
multicast service in large-scale Ad Hoc networks
• Introduced the concept of rendezvous regions (RRs) as a base for bootstrapping and rendezvous mechanisms
• Introduced a new contact-based zone hierarchy based on small world concepts
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Ahmed Helmy, USC 35
On-going and Future Work• Detail and evaluate contact selection and
maintenance mechanisms• Investigate contact-based hierarchy
parameters– zone radius (R), number of contacts, max contact
distance, depth of contact query– performance evaluation in terms of degrees of
separation, selection/maintenance overhead, query response delay
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Ahmed Helmy, USC 36
Future Work (contd.)• Study characteristics of the graphs resulting
from the contact-based hierarchy• Evaluate the efficiency of the search for
group/sender servers under various scenarios• Design the multicast routing component
– Mesh-based with on-demand activation of alternative paths
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Ahmed Helmy, USC 37
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
S
R1
R2
R3 R4
Popularity overhead
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Ahmed Helmy, USC 38
RR1 RR2 RR3
RR4 RR5 RR6
RR7 RR8 RR9
S
R1
R2
R3 R4
elected local SDS
Popularity-based optimization: Local SDS election based on group popularity