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VEHICLE AD HOC NETWORKS: APPLICATIONS AND RELATED TECHNICAL ISSUES. A summary. Applications. Classification in two types: Safety applications Goal: decrease the number of accidents User applications Examples: Internet, P2P. Table on Content. Physical / Mac layer Routing
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Classification in two types:
Safety applications Goal: decrease the number of accidents
User applications Examples: Internet, P2P
Physical / Mac layer
Three main problems in VANETs (on these layers)
Robust transmission and efficient sharing of the radio medium
Large variation in node density
300m – 1km
Like 802.11a but doubled physical parameters
Controlled access (e.g. TDMA)
Random access (e.g. Aloha) Preferred for VANETs
DSRC, a short-medium technology using IEEE 802.11 access technology @ 5.9 GHz.
DSRC is standardized as IEEE 802.11p as part of WAVE.
Topic is studied before in wired context but VANETs add more complexity due to spatial reuse.
Dividing the road in small segments
Using power control
Using directional antennas Low gain in VANETs due to linear networks
Quality of Service is important, for instance, for safety applications.
Safety messages need to be send immediately and efficiently.
Intelligently change the number and rate at which vehicles send messages
Change the transmission range
VANET specific properties and issues:
VANETs are usually linear networks
Mobility is high but movements are predictable
Connectivity is a challenge due to the high mobility
Mobility may improve network performance
VANETs require broadcast protocols to disseminate information is a certain area
MANET unicast protocols (AODV, DSR, OLSR)
Geocast routing for VANETs
Forward based on geographical destination packet
Reduced routing state at each node
Requires location service
Predict radio link breakage
Heavy initial investments
Multi-home vehicle based
Vehicles act as mobile gateways
Share bandwidth and processing power
What is the incentive?
Combination of both!
Broadcast protocols are required
Reactive protocols have unacceptable delays
Proactive protocols consume a considerable part of the bandwidth
Traditional multicast are inefficient for broadcasting.
Three described techniques:
Pure flooding (high bandwidth, high success, low delay)
Multipoint relay (MPR) diffusion technique of OLSR (lowest bandwidth, too high delay)
Geographic aware flooding
Data dissemination is the transport of data to theintended recipients while satisfying certain requirements such as delays, reliability, etc.
Safety applications require the limitation of dissemination:
Vehicle location information
The problem of high mobility makes locating data very difficult in VANETs
Network partition can render data unavailable for some time
Using multi-home vehicles (requires infrastructure)
Adaptive, content-driven routing and data dissemination algorithm for intelligently routing search queries in a peer-to-peer network
TCP/IP is not well suited for VANETs
Unfairness in wireless networks cause unfairness in transport layer
Transmission errors are interpreted as congestion
Connection loss is interpreted as congestion
Many TCP extension were proposed (TCP-F,TCP-ELFN,etc.)end-to-end extensions to determine the cause of packet loss
Some completely new transport protocols were designed (ACTP, ATP)
Security is extremely important in VANETs
Ensuring anonymity and privacy in a VANET while maintaining access control and liability is difficult
A requirement of cryptographic techniques used in VANETs must have low traffic and processing overheads
IEEE 802.11p proposes using asymmetric cryptography to sign safety messages
Pseudonyms to make communication anonymous
Requires changing pseudonyms periodically
Certification revocation might be handled
Certificate Revocation List (CRL)
Neighborhood detection of misbehaving vehicles
The random waypoint model (RWM) may be suitable for VANETs
Two simulation approaches:
Feeding a network simulator with traces that are generated from traffic simulators
Integrated traffic and network simulator
Network on Wheels
The subject of VANETs is still immature
Many studies try to solve one solution in VANET
Hardly ever, a general architecture is proposed (though probably a key success factor for VANETs)
A cross layer solution might be more likely for solving issues of VANETs instead of the OSI model