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Ad-hoc Routing. Michalis Michaelides Dept. of Electrical and Computer Engineering University of Cyprus ECE 654 – Computer Networks Seminar November 12, 2004. Presentation Overview. Motivation Ad-hoc Networks Ad-Hoc Routing Challenges Ad-Hoc Routing protocols DSR- Dynamic Source Routing - PowerPoint PPT Presentation
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Ad-hoc Routing
Michalis MichaelidesDept. of Electrical and Computer Engineering
University of Cyprus
ECE 654 – Computer Networks Seminar
November 12, 2004
Presentation Overview
Motivation Ad-hoc Networks Ad-Hoc Routing Challenges Ad-Hoc Routing protocols DSR- Dynamic Source Routing AODV- Ad-Hoc on Demand Distance Vector DSR vs. AODV comparison Sensor Networks Conclusions
References
Josh Broch, David Johnson, and David Maltz. The Dynamic Source Routing protocol for mobile ad hoc networks. Internet draft (work in progress), Internet Engineering Task Force, October 1999.
Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta Jetcheva. A performance comparison of multi-hop wireless ad hoc network routing protocols. In Proc. ACM/IEEE MobiCom, pages 85–97, October 1998.
David B. Johnson. Routing in ad hoc networks of mobile hosts. In Proc. of the IEEE Workshop on Mobile Computing Systems and Applications, pages 158–163, December 1994.
Charles Perkins, Elizabeth Royer, and Samir R. Das. Ad hoc On demand Distance Vecor (AODV) routing. Internet draft (work in progress), Internet Engineering Task Force, October 1999.
Charles E. Perkins and Pravin Bhagwat. Highly dynamic Destination-Sequenced Distance-Vector routing (DSDV) for mobile computers. In Proc. ACM SIGCOMM Conference (SIGCOMM ’94), pages 234–244, August 1993.
E. M. Royer and C-K. Toh. "A review of current routing protocols for ad-hoc mobile wireless networks." IEEE Personal Communications, April 1999.
D. Braginsky, D. Estrin, Rumor Routing Algorithm For Sensor Networks. WSNA 2002 Karp, B., and Kung. H. T. "GPSR: Greedy Perimeter Stateless Routing for Wireless Networks."
In Proceedings of the 6th Annual International Conference on Mobile Computing and Networking (MobiCom 2000), 243-254, 2000.
W. R. Heinzelman, A. Chandrakasan, and H. Balakrishnan, "Energy-efficient communication protocol for wireless micro-sensor networks" In Proc. IEEE Hawaii Int. Con. on System Sciences, pages 4-7, January 2000.
J. E. Wieselthier, G. D. Nguyen, and A. Ephremides, "On the construction of energy-efficient broadcast and multicast trees in wireless networks" In Proceedings of IEEE INFOCOM, pages 585-594, March 2000.
Motivation
Mobile hosts such as notebook computers featuring powerful CPUs, large main memories and disk space, multimedia capabilities and colour displays are now quite common in everyday business and personal life.
At the same time network connectivity options for use with mobile hosts have increased dramatically, including support for a growing number of wireless networking products based on radio and infrared.
Natural desire and ability to share information between mobile users: Employees in a conference room Friends in an airport terminal Search and rescue teams Military data acquisition operations in inhospitable terrain
Ad-hoc Networks
A collection of wireless mobile hosts dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration.
Due to the limited transmission range of wireless network interfaces, multiple network “hops” may be needed for one node to exchange data with another across the network.
Need a dynamic routing protocol that can efficiently find routes between two nodes.
Ad-hoc Routing
Source
Destination
Ad-hoc Routing Challenges
Correct and efficient route establishment between a pair of nodes so that messages may be delivered in a timely manner.
Keep up with high degree of node mobility. Conserve power- power aware routing Wireless medium challenges:
Links may not be bi-directional High error rates (Hidden Terminal Problem) Redundant paths Limited BW Multicast
Ad-hoc routing protocols history
DARPA (Defence Advanced Research Projects) packet radio networks in early 1970s was the first attempt.
Since then numerous protocols have been developed: Table-driven
Attempt to maintain consistent up-to-date routing information from each node to every other node in the network.
DSDV, CGSR, WRP Substantial traffic and power consumption caused by periodic updates but
routes are always available. Source-initiated On-Demand
When a node requires a route to destination it initiates a route discovery process within the network.
AODV, DSR, TORA, ABR, SSR… MANET (Mobile ad hoc networking) has been formed within the
IETF (Internet Engineering Task Force) to develop a routing framework for IP-based protocols in ad hoc networks.
2 primary candidates: DSR and AODV
Dynamic Source Routing (DSR)
Source routing - The sender knows the complete hop-by-hop route to the destination.
Route cache - Nodes may learn and cache multiple routes to any destination.
Composed of 2 mechanisms: Route Discovery Route Maintenance
Requires no periodic packets of any kind at any level within the network- purely on demand.
Allows uni-directional links. Supports internetworking between different types of
wireless networks and mobile IP.
Route Discovery
RREQ (Route Request packet) Is broadcast when node S needs do send a packet to
D and does not already know a route. Each RREQ includes source and destination address,
unique request id and complete route record of all intermediate nodes.
RREP (Route Reply packet) If a node receives an RREQ for which it is either the
destination or it has a route to the destination in its route cache it responds with a RREP.
DSR
N1
N2
N5
N6
N4
N8
N3
N7Source
Destination
RREQ
RREP
N1
N1
N1-N3
N1-N2
N1-N3-N4N1-N3-N4
N1-N3-N4
N1-N3-N4-N6
N1-N2-N5
N1-N3-N4-N7
N1-N2-N5-N8
N1-N2-N5-N8
N1-N2-N5-N8
Route Maintenance
Hop-by-hop acknowledgement Link-level acknowledgement IEEE 802.11 Passive acknowledgement (Overhearing) DSR specific acknowledgement
RERR (Route Error packet) Informs the source of any broken link. Source removes any routes containing broken link from route cache.
Additional Optimizations
Packet Salvaging An intermediate node can use an alternate route from its own cache in case of a
failed link. Gratuitous route repair
A source node receiving an RERR packet piggybacks the RERR in the following RREQ.
Helps clean up cashes of other nodes in network. Promiscuous listening
When a node overhears packet checks to see whether it could be routed via itself to gain a shorter route and sends a gratuitous RREP to source.
Learn different routes without participating in routing process.
Ad-hoc On-Demand Distance Vector Routing (AODV)
Discovers routes on-demand. Uses traditional routing tables, one entry per destination
that are dynamically established at each intermediate node.
Use ‘hello’ messages for local connectivity management. Sequence numbers maintained at each destination to
determine freshness of routing information and to prevent rooting loops.
Timer-based states in each node regarding utilization of individual routing table entries.
Expanding ring search optimization.
Path Discovery
Every node maintains two separate counters: Node sequence number – Maintain freshness information of route Broadcast id – Incremented for every new RREQ
RREQ (Route Request packet) <Source and destination address ,source and destination sequence
number, broadcast id, hop count> Each node that cannot satisfy the RREQ rebroadcasts to its own
neighbours after increasing hop count. Each node keeps expiration timers to remove old RREQ and routes
from its cache. RREP (Route Reply packet)
Unicast back to the neighbour from which it received the first RREQ. <Source and destination address, destination sequence number, hop
count, lifetime>
AODV
N1
N2
N5
N6
N4
N8
N3
N7Source
Destination
RREQ
RREP
Path Maintenance
Detecting link failures Periodic ‘hello’ messages Link Layer acknowledgements (LLACKS) Attempts to forward packet to next hop fail
RERR (Route Error packet) Created when next-hop link breaks. Propagated to all predecessors until all sources using
the failed link are informed. Sources restart discovery process if they still need the
route to destination.
DSR vs. AODV
Source routing More routing overhead No periodic routing
advertisements Route caching
More routing information Fast recovery from failure More RREP
Supports uni-directional links Only broadcast No mechanism to expire stale
routes or prefer ‘fresher’ routes RERR backtracks the data
packet
Dynamic routing tables Only next-hop information Periodic “hello” messages for
local connectivity One entry per destination
Limited routing information New RREQ for every failure More RREQ
Only bi-directional links Multicast capability Expiration timers remove stale
routes and sequence numbers RERR informs all predecessor
nodes of link failure
DSR-AODV performance comparison
Simulation model ns-2 model for simulating multihop wireless networks Virtual carrier sense with RTS/CTS to reduce hidden terminal problem. 802.11 Link layer acknowledgements for each packet transmission. Send buffer with FIFO and routing packets getting higher priority than
data packets. Continuous bit rate (CBR) sources and destinations randomly spread in
rectangular field. Nodes move with randomly chosen speed, pause and then move again. Vary number of sources, node mobility, traffic load
Performance metrics Packet delivery fraction (Throughput)
Ratio of packets delivered to destination to those generated by the CBR Routing load
Routing packets transmitted per data packet delivered Path optimality or Delay (QoS)
DSR-AODV performance comparison simulation results
DSR authors DSR has the lowest routing overhead. Both DSR and AODV exhibit similar good
performance compared to DSDV,TORA.
AODV authors DSR outperforms AODV in less stressful situations-
small number of nodes and lower mobility. AODV outperforms DSR in more stressful situations.
DSR consistently generates less routing load than AODV.
Sensor Networks
Sensor networks are a special class of Ad-Hoc Networks
DIFFERENCES Number of nodes- scalability Densely deployed Prone to failure (power outage) Topology may change frequently Limited power, computational capability and memory Broadcasting vs. point-to-point Sensor nodes may not have global identification ID
because of the large amount of overhead and large number of sensors
What are sensor networks?
Sink
Internet or Satellite network
Internet or Satellite network
Task Manager Node
sensor field
sensor nodes
Ad-hoc routing for sensor networks
Geographic routing GPSR (Greedy perimeter stateless routing) uses positions of immediate
neighbours and a packet’s destination to make greedy forwarding decisions.
Outperforms DSR and demonstrates scalability on densely deployed networks.
Probability routing Gossip- Each node forwards a message with some probability to reduce
overhead of routing protocol. Adding gossiping to AODV results in significant performance
improvement. Minimum Energy
LEACH (Low Energy Adaptive Clustering Hierarchy)- Clustering based protocol that uses randomization to distribute energy dissipation.
BIP (Broadcast Incremental Power)- Uses Wireless Multicast Advantage
Conclusions
Mobile Ad hoc Networks are becoming part of our everyday lives.
DSR and AODV both provide simple on-demand routing solutions for ad-hoc networks.
They fail however to scale to large networks with limited energy resources so further enhancements are possible using position, probability, clustering, power management…
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