Mobile Ad-hoc Networks
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Transcript of Mobile Ad-hoc Networks
![Page 1: Mobile Ad-hoc Networks](https://reader035.fdocuments.us/reader035/viewer/2022062408/5681387b550346895da02af1/html5/thumbnails/1.jpg)
1© 2002, Cisco Systems, Inc. All rights reserved.
ISOC.nlMaster Class
Mobile Ad-hoc Networks
Dr. Muazzam A. Khan
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222© 2002, Cisco Systems, Inc. All rights reserved.
ISOC.nlMaster Class
The manet problem
• Mobile
Random and perhaps constantly changing
• Ad-hoc
Not engineered
• Networks
Elastic data applications which use networks to communicate
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333© 2002, Cisco Systems, Inc. All rights reserved.
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Examples of such networks
• Sensor networks
• Automotive networks
• Military applications
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444© 2002, Cisco Systems, Inc. All rights reserved.
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Sensor networks
• Networks deployed in random distribution
• Low power
• Delivering sensor data to a central site for some purpose
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555© 2002, Cisco Systems, Inc. All rights reserved.
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Traffic networks
• “Smart cars” and “smart roads”
• Onboard systems “talk” to the “road”:
Map obstacles and delays
Obtain maps
Inform the road of its actions
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666© 2002, Cisco Systems, Inc. All rights reserved.
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Military applications
• Combat regiment in the field
Perhaps 4000-8000 objects in constant unpredictable motion…
• Intercommunication of forces
Proximity, function, plan of battle
• Special issues
Low probability of detection
Random association and topology
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777© 2002, Cisco Systems, Inc. All rights reserved.
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Basis of routing:
• Bellman-Ford-Moore proof
In any graph there exists a spanning tree
Ford (1956), Bellman (1958), Moore (1958)
• Spanning tree:
A set of arcs which visits every node in a graph exactly once
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888© 2002, Cisco Systems, Inc. All rights reserved.
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Proof by construction
• Select one node in graph
• Place all arcs connected to that node in set of “available choices”
• Place all other nodes and arcs in set of “unavailable choices”
• Repeatedly select an arc from “available choices”
If it leads to an “unavailable” node,
Add that node and arc to the graph,
Add all other arcs connecting to the new node to “available choices”
Otherwise, discard the arc
• All nodes get included in the graph
Some arcs may be left over
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999© 2002, Cisco Systems, Inc. All rights reserved.
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Issues in routing
• Selection of arcs (metrics and objectives)
• Characteristics of various interfaces
• Convergence
• Algorithms
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101010© 2002, Cisco Systems, Inc. All rights reserved.
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Selection of arcs (metrics)
• Available bandwidth (traffic engineering)
• Link speed (shortest path)
Often measured as duration of a bit, or duration of an operation
• Hop count or other administrative distance
Might be power or S/N ratio for radio
• General policy (BGP)
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111111© 2002, Cisco Systems, Inc. All rights reserved.
ISOC.nlMaster Class
Characteristics of various interfaces
• LAN:
Many to many
• Frame Relay/ATM/MPLS:
1:many circuits
• Serial Lines:
1:1
• Radio:
1:many with inconsistent sets
Often unidirectional
S/N ratio and distance affect connectivity
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121212© 2002, Cisco Systems, Inc. All rights reserved.
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Convergence goals
• Ensuring routing consistency
Algorithms vary by type of properties required
• Managing inconsistency
The backbone is said to never actually converge
Manet networks probably don’t either
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131313© 2002, Cisco Systems, Inc. All rights reserved.
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Common algorithms
• ExplorationNetwork is explored to find possible routes
Of which one is selected
Example: IEEE 802.5 Source Routing
• Bellman-Ford algorithm does this in a distributed mannerCalled "Distance Vector" these days
Generates routes to a node from somewhere else
• Shortest Path First (Ford, CACM, 1968) does this in a databaseDjikstra applied to networks, 1972
Generates routes from a node to somewhere else
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141414© 2002, Cisco Systems, Inc. All rights reserved.
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Specific issues in manet networks
• Dynamic Connections
Constant change (motion)
Random interconnection
• Radio Characteristics
Unidirectional Links
Varying S/N Ratio
Overlapping connectivity
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151515© 2002, Cisco Systems, Inc. All rights reserved.
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Overview of Proposals
• Reactive (on-demand) Protocols
Overview of DSR
Overview of AODV
• Proactive (pre-calculated) Protocols
Overview of TBRPF
Overview of OLSR
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16© 2002, Cisco Systems, Inc. All rights reserved.
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Dynamic Source Routing
“IEEE 802.5 Source Routing” in wireless networks
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171717© 2002, Cisco Systems, Inc. All rights reserved.
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Route Discovery
• A route between two nodes is found by sending an Route Request
• Route Request builds a source route on every path through the network
• First Route Request to arrive is accepted; target responds on that path and tells initiator what the source route is
• Source route is used on subsequent data traffic
B
H I J
GFE
D
A
C
K
Detected Source Route:(A, B, F, J, K)
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181818© 2002, Cisco Systems, Inc. All rights reserved.
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Link reliability
• Passing source routes cached
To know how to send routing error messages
• Network layer acknowledgements watched
To ensure delivery
To detect failed routing nodes
• After several retransmissions,
Neighboring routing node declared dead
Route Error sent to senders using the node
Packets flushed
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191919© 2002, Cisco Systems, Inc. All rights reserved.
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Route Maintenance
• When routing node/routing node link changes, existing source routes no longer work
• routing nodes respond to source routes with a Route Error, triggering a new route discovery
• routing nodes may attempt to change source route and re-forward on a cached route
B
H I J
GFE
D
A
C
K
RouteError
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202020© 2002, Cisco Systems, Inc. All rights reserved.
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Status of testing
• Simulations and some operational testing
• Testing shows some documented features in use of route cache don’t work properly
• Ongoing research, seeking experimental status
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21© 2002, Cisco Systems, Inc. All rights reserved.
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Ad-hoc On-Demand Distance Vector
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222222© 2002, Cisco Systems, Inc. All rights reserved.
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Target networks
• Targets networks in which
Routing churn is high enough that maintaining routes is unproductive, and
Can absorb a network wide broadcast rate
• Modified on-demand Distance Vector routing
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232323© 2002, Cisco Systems, Inc. All rights reserved.
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Messages
• Route Request: “I need a route”
• Route Response: “Route advertisement”
• Route Error: “Withdraw route”
• Periodic route response to neighbors acts as “hello”, installing and refreshing route
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242424© 2002, Cisco Systems, Inc. All rights reserved.
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Route Discovery
• A route between two nodes is found by sending an Route Request to a locality
Initial locality small, grows with failure
After that, a little larger than the locality target last found in
• Route Response sent
By target if necessary
By neighboring routing node if possible to “join” existing route
• Network stores the route
d
j k l
ihg
f
A
e
C
B
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252525© 2002, Cisco Systems, Inc. All rights reserved.
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Route Errors
• Routes expire if not refreshed
• routing nodes log recent downstream users of a route
• When routes expire or are flushed, downstream users are notified to flush
• New route request triggered d
j k l
ihg
f
A
e
C
B
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262626© 2002, Cisco Systems, Inc. All rights reserved.
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Status of testing
• Simulations and some operational testing
• Not perfect, but few major problems
• Ongoing research, seeking experimental status
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27© 2002, Cisco Systems, Inc. All rights reserved.
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Topology Broadcast Based on Reverse-Path Forwarding
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282828© 2002, Cisco Systems, Inc. All rights reserved.
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Target networks
• Targets networks in which
Routing churn is consistent with pre-calculated routes, and
Capable of supporting fairly intelligent device
• Modified Shortest Path First routing
Routing by “need to know”
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292929© 2002, Cisco Systems, Inc. All rights reserved.
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Messages
• “Hello”
Neighbor discovery and relationship maintenance
• Topology Update
Distributes subset of interconnectivity information
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303030© 2002, Cisco Systems, Inc. All rights reserved.
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Topology Update Distribution
• Therefore every routing node effectively calculates all routes from all nodes for which it has information
• Topology information distributed to the set of systems that are deemed to need it.
You need information about a routing node if your routing would use it…
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313131© 2002, Cisco Systems, Inc. All rights reserved.
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Status of testing
• Simulations and some operational testing
Boeing and SRI actively promoting
Not all algorithms publicly documented
• Not perfect
Needs operational experience to debug
• Ongoing research, may seek experimental status
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32© 2002, Cisco Systems, Inc. All rights reserved.
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Optimized Link State Routing
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333333© 2002, Cisco Systems, Inc. All rights reserved.
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Target networks
• Targets networks in which
Routing churn is consistent with pre-calculated routes, and
Capable of supporting fairly intelligent device
• Modified Shortest Path First routing
Level 1/Level 2 routing distinction
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343434© 2002, Cisco Systems, Inc. All rights reserved.
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Messages
• “Hello”
Neighbor discovery and relationship maintenance
• Topology Update
Distributes subset of interconnectivity information
![Page 35: Mobile Ad-hoc Networks](https://reader035.fdocuments.us/reader035/viewer/2022062408/5681387b550346895da02af1/html5/thumbnails/35.jpg)
353535© 2002, Cisco Systems, Inc. All rights reserved.
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Neighbor relationships
• Each device emits a periodic “Hello”
Advertise itself to its neighbors
Determine who else is there
Select some systems to act as Multi-Point Relays
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363636© 2002, Cisco Systems, Inc. All rights reserved.
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Multi-Point Relays
• Passes Topology Information
Acts as router between hosts, in wired parlance
Minimizes information retransmission
Forms a routing backbone
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373737© 2002, Cisco Systems, Inc. All rights reserved.
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Structure of an OLSR Network
• MPRs form routing backbone
Other nodes act as “hosts”
• As devices move
Topological relationships change
Routes change
Backbone shape and composition changes
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383838© 2002, Cisco Systems, Inc. All rights reserved.
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Status of testing
• Simulations and some operational testing
Inria in active research
Not all algorithms publicly documented
• Not perfect
Needs operational experience to debug
• Ongoing research, may seek experimental status
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39© 2002, Cisco Systems, Inc. All rights reserved.
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Status of research
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404040© 2002, Cisco Systems, Inc. All rights reserved.
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Open problems
• Behavior of applications in manet networks
TCP likely to not work well if loss leads to congestion avoidance
ECN (RFC 3168) allows separation of the concepts
Various other research proposals
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414141© 2002, Cisco Systems, Inc. All rights reserved.
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Open problems in DSR
• Route Maintenance as specified results in problems in routing
Man-in-the-middle issues
• Requires protocol number from IANA
Small number space
We don’t give those to just anybody
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424242© 2002, Cisco Systems, Inc. All rights reserved.
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Open problems in TBRPF
• High computational overhead
• High messaging overhead
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434343© 2002, Cisco Systems, Inc. All rights reserved.
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Open problems in OLSR
• Selection and dynamic minimization of MPR set
• Operational testing of protocol
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444444© 2002, Cisco Systems, Inc. All rights reserved.
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Open problems in AODV
• Protocol needs operational experience to discover further issues
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454545© 2002, Cisco Systems, Inc. All rights reserved.
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Directions for manet working group
• Probably will take several protocols to “experimental” status
RFC is an archive, not a standard
• Likely to standardize
One reactive protocol
One proactive protocol
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46© 2002, Cisco Systems, Inc. All rights reserved.
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Mobile Ad-hoc Networks