1. Ad Hoc Routing and Mobility in the Internet
Emmanuel Baccelli
April 6th 2006

2. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
MANET scaling to large topologies

3. Internet & Wireless
Since the 1990’s, two telecom. revolutions in “parallel” :
Internet
Mobile wireless communication
(hundreds of millions of users worldwide)
Internet
access
point
Recently: desire to merge the advantages of the two
scalable, “cheap”, multimedia network
wireless mobility, ubiquitous access
1rst step: wireless Internet edge access
wLAN (popular, cheap)
3G cell services (deploying, expensive)
2nd step: desire to use wireless connectivity beyond edge access with mobile ad hoc networking

4. Traditional Networking
vs Ad Hoc Networking
non-directional
radio connectivity
user devices
(hosts)
A both user
and router E A C B
shared access
medium D
Mobile ad hoc networks: → different characteristics
One device type
Medium (radio) not fully shared
Interferences, less bandwidth
Nodes = potential router + host
Nodes are mobile
routing
protocol
(ex: OSPF)
routers
Traditional routing protocols fail
New levels of performance needed
→ new routing mechanisms must be used

5. The Main MANET Routing Solution Families
Proactive routing
Nodes maintain routes to all destinations
Most protocols: link-state
→ Adaptation of traditional Internet routing, predictable performance
Reactive routing
Nodes discover routes only on-demand
Based on route request flooding and route reply messaging
→ Departure from traditional Internet routing, unpredictable performance
ROUTE
REQUEST
(global scope)
link state flooding
(global scope) S
HELLO
(local scope)
ROUTE
REPLY D
distribute neighborhood
description to all the nodes
discover neighborhood

6. MANET Routing in the Internet
Focus on proactive link-state MANET routing
easier integration in the Internet
Every MANET node potentially generates control traffic
Difference with traditional networks (only routers)
Overhead reduction mechanisms are needed

7. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
►Comparison of optimized flooding schemes
Comparison of partial topology schemes
MANET integration in the Internet
MANET scaling to large topologies

8. Overhead Reduction: Optimized Flooding
Def: Reducing the number of (re)transmissions needed to distribute some information network-wide
►Classical flood: every node retransmits once
→ network covered, but redundantly
(especially when the network is dense)
►Optimized flood: only some nodes retransmit
→ network efficiently covered
- reduced bandwidth use
- reduced amount of interferences
- reduced number of packet collision
this node was
covered 4 times

9. Dominating Set Flooding Algorithm: MPR Flooding
MPR (Multi-Point Relay) selection:
each node selects a subset its
neighbors, covering all the
neighbors of its neighbors
MPR
[P. Jacquet, P. Minet, et al. HiperLAN, 1996] S
Flooding: only MPRs retransmit
and the network is efficiently covered
MPR
[L. Viennot, A. Laouiti, A. Qayyum, 2000]

10. Tree Flooding Algorithm: Gateway Flooding
1. Automatic tree formation:
each node selects its neighbor
which has the max number
of neighbors as parent in the tree R
[C. Bonnet, H. Labiod, N. Nikaein, 2000]
2. Network = forest of trees
roots = local degree maxima R
Gateway Flooding: retransmission happens only along tree vertices
(and between trees)

11. Flooding Algorithms Comparison & Analysis
MPR Flooding Simulations (1D)
Gateway Flooding Simulations (1D)
number of nodes in the area
number of retransmitters
MPR flooding
Gateway flooding
classical flooding
the proportion of
retransmitters
is inversely
proportional to the
number of nodes 1
> 2 3
+ o( ) ν
the proportion of
retransmitters
is approx. 70%
of the number
of nodes
Retransmitters % 2 ν ~
→ more efficient
Node density (ν)
[E. Baccelli, P. Jacquet, 2004]
→ analitycal results confirm this
behaviour when the network is dense

12. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
Comparison of optimized flooding schemes
► Comparison of partial topology schemes
MANET integration in the Internet
MANET scaling to large topologies

13. Overhead Reduction: Partial Topology
Def: Reducing the amount of routing information that needs network-wide flooding J K P
Link state routing can still provide routes with partial link state advertizement I C L O A N
MPR G
- using only links towards nodes in
a connected dominating set (CDS) B H M
MPR
→ route stretching
- using only MPR selection links
Note: reactive protocols have
partial topology as main ideal
→ no route stretching
[P. Jacquet, L. Viennot et al., 2002]

14. Partial Topology Algorithm Simulations
Blue: full link state
Purple: CDS links
Light blue: MPR links
MPR topology
reduction is
efficient while
keeping routes
optimal
Number of advertized links
Number of nodes in the network
[E. Baccelli, T. Clausen, P. Jacquet, 2004]

15. Overhead Reduction Summary
MPR flooding and MPR partial topology: simple & efficient
MPR techniques are extracts from OLSR (Optimized Link State Routing):
OLSR = standard (the IETF’s MANET proactive routing protocol)
RFC 3626 [T. Clausen, P. Jacquet, 2003]
Link state routing, enhanced with MPR techniques
Proven, robust MANET routing solution (up to ~70 nodes with )
→focus on OLSR

16. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
►OSPF on wireless
Address Autoconfiguration
MANET scaling to large topologies

17. OSPF: Open Shortest Path First
OSPF is the Internet’s traditional routing protocol
Backbone (Area 0)
Area 3
Area 1
Internet routers
Area 2
Advantages
Scalable: address area hierarchy
Generic: modularity for heterogeneous subnetwork tech.
Drawbacks
Heavy: complexity, overhead
Not dynamic: slow to converge, change in the routing → alarm

18. OSPF Evolution Internet growth: OSPF challenged by:
more links
more mobile wireless devices
OSPF challenged by:
More dynamics
Wired/wireless heterogeneity
→IDEA: design an OLSR-based module for OSPF
FACTS:
1. OLSR is close to OSPF (proactive, link state)
2. OLSR is adapted to wireless & dynamics
3. OSPF is modular

19. Designing OSPF’s Mobile Ad Hoc Module
Area 2
Area 1
OSPF shortcomings on wireless:
Overhead scalability
Database synchronization
Acknowledgements
Database exchange
Cross-area mobility
wOSPF C
ACK B D A
PACKET
B retransmits in vain
Heavy: new neighbors exchange whole databases
Not adapted to wired/wireless heterogeneous synch. needs
OSPF control traffic is too big,
overhead saturates wireless links
Positive ACK fails
If A entered a new area, reconfiguration
of the node is needed → new address
B sends a packet to A
A moves
[J. Ahrenholz, E. Baccelli et al., IETF 2003] designs a new OSPF extension (called wOSPF) based on OLSR techniques using:
- MPR flooding and partial topology
- A new database synchronization mechanism

20. Wired/Wireless Heterogeneity
wOSPF: potential mix of large numbers of fixed & mobile nodes in the Internet
Heterogeneous needs for synchronization in the network
Mobile wireless nodes generate frequent updates (~1 second): synchronization is wasteful
Traditional fixed nodes do not generate frequent updates (30min): synchronization is desireable
→ Need for a new heterogeneous synchronization scheme

21. Database Signatures (DbX) Synchronization
[E. Baccelli, T. Clausen, P. Jacquet, 2004]
1. Each node periodically emits hash of different parts of its link state database (signature)
SYNCH A
2. Neighbors compare their respective signatures & detect discrepancies B
Signature = ?
New node
Db exchange
Context
Independent
ACK
Signature ≠
3. Nodes synchronize when discrepancies are detected
Light-weight synchronization mechanism, for:
Packet loss recovery (replacing ACK)
Heterogeneous database synchronization

22. Analytical Performance Evaluation of DbX
traditional OSPF
database scanning
proportional to n
→light
weight
synch.
number of exchanged IP addresses
database signatures
proportional to log(n)
Size of the database (n) size of the network
[E. Baccelli, T. Clausen, P. Jacquet, 2004]

23. wOSPF in a Nutshell wOSPF supports MANET techniques in OSPF framework
MPR flooding & partial topology provides efficient overhead reduction
DbX provides an efficient database synchronization scheme adapted to the wired/wireless heterogeneity
wOSPF
OSPF
overhead
scalability
ACK issue
solved
Wired/wireless
synchronization
Area
mobility

24. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
OSPF on wireless
►Address Autoconfiguration
MANET scaling to large topologies

25. IP Address Autoconfiguration
Prior to routing: nodes should be uniquely identified
In the Internet: identity is given by IP address
MANET characteristics challenge Internet addressing
a “new” node must be configured
traditional autoconf. tools fail
server(s) may be unreachable
no fully shared medium = issue
Nodes
MANET
Internet N
New node.
Address?
→ Need for new autoconfiguration
schemes, adapted to MANETs

26. Light Autoconf for OLSR
[E. Baccelli, T. Clausen, 2005]
1. Configured nodes advertize
ADDR-BEACON periodically
2. A new node listens for
ADDR-BEACON
OLSR Nodes C
ADDR-CONFIG
3. A new node registers with
a configurating node
Proxy
Autoconf
HELLO N N N
NOA-OLSR
[K. Mase, C. Adjih, 2005]
4. Temporary address assignment
+ HELLO tracking
Light
OLSR
Autoconf
new
OLSR
node
New Node
5. The configurating node uses OLSR
connectivity to act as autoconf proxy
Auto.
DHCP
6. Permanent address assignment, the
new node can take part in the network
Manual
config
Connected
with
DHCP
Connected
without
DHCP
Disconnected
with one node
configured
Partition
Merge

27. Conclusions on MANET Integration in the Internet
A suite of new protocols is needed to integrate MANETs in the Internet
{wOSPF or OLSR} + autoconfiguration provides a solution for local MANET mobility integration
MANET
integration
standalone
MANET
connected
MANET
connected
scalable
MANET

28. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
MANET scaling to large topologies
►Introduction to MANET scaling
Horizontal scaling with OLSR Fisheye
Vertical Scaling with OLSR Trees

29. Scaling with Mobility in the Internet
Internet scaling: tied to IP address location & low mobility
Integrating mobile devices: a challenge for Internet scaling
MANETs can integrate fixed & wireless mobile devices
But MANETs do not scale yet
MANET
testing
(802.11)
theoretical
OLSR
limit
practical
Internet
scalability
theoretical
size of the
Internet 1
~26
~212
~230
~2128
nodes
nodes
nodes
nodes

30. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
MANET scaling to large topologies
Introduction to MANET scaling
►Horizontal scaling with OLSR Fisheye
Vertical Scaling with OLSR Trees

31. MANET Horizontal Scaling
Theory: optimal network capacity is O(√n)
Real protocols: network capacity tends to crumble when the numbers of nodes/users increases in the network
[P. Gupta, P. Kumar, 1999]
OLSR
Total network capacity
Network population (n)
[E. Baccelli, P. Jacquet, C. Adjih et al, 2004]
→ overhead limits the number of nodes in a MANET

32. Fisheye
OLSR
Fisheye: a simple function periodically updating the scope of flooded messages [G. Pei, M. Gerla, T. Chen, 2000]
[C. Adjih, E. Baccelli, P. Jacquet et al, 2004] combines OLSR with a simple Fisheye strategy → Fisheye OLSR
with Fisheye OLSR routing:
network capacity continues to grow
with more nodes in the network!!!! S

33. Analysis of Fisheye OLSR Capacity
capacity continues to grow!!
with Fisheye OLSR
O(√n)
Total network capacity (nominal)
OLSR
Network size (n)
[C. Adjih, E. Baccelli, P. Jacquet et al, JCN 2004]

34. ZOOM: why does Fisheye OLSR scale? Where does √n come from?
Fisheye bounding overhead
Basic OLSR’s overhead proportional to n
Fisheye strategy bounds OLSR’s overhead
Similar to Gupta & Kumar minus overhead “tax”
Overhead
Distance (hop count)

35. Agenda Background on Mobile Ad Hoc Networks
MANET routing overhead reduction schemes
MANET integration in the Internet
MANET scaling to large topologies
Introduction to MANET scaling
Horizontal scaling with OLSR Fisheye
►Vertical Scaling with OLSR Trees

36. MANET Vertical Scaling
OLSR Trees
MANET Vertical Scaling
Fact: the main MANET solutions don't use clustering, hierarchical networking
→ Clustering and hierarchical routing can scale R
[E. Baccelli, 2005] tree-based dynamic clustering (similar to Gateway trees)
Hierarchical routing R
“super” OLSR
between trees
(between roots)

37. Short on MANET Scaling
Currently: MANETs are limited in the number of nodes they can manage
OLSR + specific scaling techniques (OLSR Trees, Fisheye OLSR) can scale to much bigger topologies
Fisheye OLSR
+ trees scalability 1 26
2128 ?
nodes
nodes

38. Perspective on Internet & Wireless
ubiquitous
wireless
Internet
We can anticipate:
Massive ad hoc topologies
Hybrid networks
Ubiquitous network
traditional
Internet
fixed
core
mobile
ad hoc
nodes
►A new suite of protocols is needed for ubiquitous wireless Internet
Research challenges:
MANET Scalability
MANET Security
MANET Multicast
MANET Integration

39. Related Publications IETF Publications: Academic Publications:
E. Baccelli, T. Clausen, P. Jacquet, ``Ad-hoc and Internet Convergence: Adapting OSPF-style Database Exchanges for Ad-hoc Networks,'' HET-NET, 2004.
C. Adjih, E. Baccelli, P. Jacquet, ``Link State Routing in Wireless Ad Hoc Networks,'' MILCOM, 2003.
E. Baccelli, R. Rajan, ``Monitoring OSPF Routing,'' IM, 2001.
E. Baccelli, P. Jacquet, ``Diffusion Mechanisms for Multimedia Broadcasting in Mobile Ad Hoc Networks,'' IMSA, 2004.
E. Baccelli, ``OLSR Trees: A Simple Clustering Mechanism for OLSR,'' MED-HOC-NET, 2005.
C. Adjih, E. Baccelli, T. Clausen, P. Jacquet, R. Rodolakis, ``Fish Eye OLSR Scaling Properties,'' IEEE Journal of Communication and Networks, 2004.
IETF Publications:
J. Ahrenholz, E. Baccelli, T. Clausen, T. Henderson, P. Jacquet, P. Spagnolo, ``OSPFv2 Wireless Interface Type,'' IETF I-draft, 2004.
E. Baccelli, F. Baker, M. Chandra, T. Henderson, J. Macker, R. White, ``Problem Statement for OSPF Extensions for Mobile Ad Hoc Routing,'' IETF I-draft, 2003.
E. Baccelli, T. Clausen, R. Wakikawa, ``NEMO Route Optimisation Problem Statement,'‘ IETF I-draft, 2004.
E. Baccelli, T. Clausen, P. Jacquet, ``DB Exchange for OSPFv2 Wireless Interface Type,'‘ IETF I-draft, 2004.
E. Baccelli, T. Clausen, ``Simple MANET Address Autoconfiguration,'‘ IETF I- draft, 2005.

40. Thank you.