Outline
■ Introduction
■ Assumptions■ Basic Operation
Route Discovery
Route Maintenance
■ Optimizations■ Performance Evaluation■ Conclusion
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Introduction (1/3)
Ad hoc network A collection of mobile hosts with wireless network interfaces may
form a temporary network
Without the aid of any established infrastructure or centralizedadministration
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Introduction (2/2)
Dynamic Source Routing The sender of a packet determines the complete sequence of
nodes through which to forward the packet
The sender explicitly lists this route in the packet’s header
DSR offers a number of advantages Uses no periodic routing advertisement messages
Network bandwidth overhead
Battery power
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Assumptions
n Each host should be willing to forward packets for other hosts
The diameter of the ad hoc network may be greater than one
Hosts move at any time without notice, but the speed withwhich hosts move is moderate
Hosts can enable a promiscuous receive mode on theirwireless network interface hardware
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Basic Operation
The sender constructs a source route in the packet’s header
Each host in the ad hoc network maintains a route cache
When a host sends a packet to another host A route is found
Use this route to transmit the packet
Use the route discovery
No route is found
The route should fail The correct operation of a route in use we call route maintenance
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Basic Operation – Route Discovery (1/3)
A host initiating a route discovery Broadcasts a route request packet
Each route request packet contains Route record
Initiator address Request id
If the route discovery is successful The Initiating host receives a route reply packet
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Basic Operation – Route Discovery (2/3)
When any host receives a route request packet, it processesthe request according to the following steps: If <initiator address, request id> is found in this host
Discard the route request packet
If this host’s address is already listed in the route record
Discard the route request packet
If the target of the request matches this host’s address
Return a copy of this route in a route reply packet to the initiator
Otherwise, append this host’s address to the route record, andre-broadcast the request
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Basic Operation – Route Maintenance (1/2)
Conventional routing protocols integrate route discovery withroute maintenance by continuously sending periodic routingupdates
There are no periodic message of any kind from any of themobile hosts
It monitors the operation of the route and inform the sender ofany routing errors
The host sends a route error packet to the original sender
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OptimizationsFull Use of the Route Cache (1/2)
A host can add entries to its route cache any time it learns anew route
A host may use its route cache to avoid propagating a routerequest packet received from another host
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OptimizationsFull Use of the Route Cache (2/2)
There are two problems can occur
Collision
Delay for a period of d
d=Hx(h – 1 + r)
h : the length of network hops for the route to be returned
r : a random number between 0 and 1
H : a small constant delay to be introduced per hop (4 msec)
Loop The host instead discards the request if the route in its reply
would contain a loop
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OptimizationsReflecting Shorter Routes
While two hosts are communicating with each other usingcached routes it is desirable for the hosts to begin using shorter routes if the
hosts move sufficiently closer together
Network interfaces operate in promiscuous receive mode
Use an unsolicited route reply packet
It has not yet added this method to simulator
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Performance Evaluation (1/3)
The Simulation The area in which the host move is square, 9 meters on a side
Each host moves with a velocity between 0.3 ~ 0.7 meters / s Each transceiver has a range of 3 meters Packet lengths
70% of the packets are long packets (1000 bytes)
The remainder are short packets (32 bytes)
Transmissions to a host that is out of range always fail whiletransmissions to a host in range fail with a probability of 5%
The bandwidth for transmitting data is 100 Kbytes / s
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