1. Information Transport Protocols
Yaroslav (Kobi) Hayat
Gadi Israeli

2. Information Transport
After obtaining information from different sensors, a local view of a car’s surrounding can be created. However, not only the car that obtained this information will need this data, but also other vehicles should be able to adapt their behavior based on this information. It is thus important to distribute the information to the cars interested in it.

3. Information Transport Methods
In this presentation we will present different methods for information transport in VANET.

4. A Few Basics
Broadcasting: a single-hop transmission of a packet to all nodes within radio range of the sending node.

5. A Few Basics
Flooding: Distributing a packet over a range spanning multiple wireless hops. The receiving nodes rebroadcast the packet and thereby deliver it to all nodes in the network or to a subset, for instance the nodes within a limited geographical region

6. A Few Basics Beaconing:
periodic transmission of information to all neighbors within radio range. In a sense beaconing is periodic broadcasting. One single packet transmitted by beaconing is called a beacon.

7. Protocols for information transport
We will present a few protocols for information transport in VANET’s:
Flooding and Geocasting
Request/Reply
Sharing
Clustering
Beaconing
Every protocol has its own advantages and disadvantages.

8. Flooding and Geocasting
One way to propagate information very fast within MANET's is to use flooding. In a naive implementation every node that receives information will simply rebroadcast it. To avoid infinite packet duplication, each node will broadcast a given packet at most once. In addition a time to live (TTL) counter may be used to limit the area where the packet is distributed. This naive approach will transmit a large amount of redundant packets, potentially leading to severe congestion.

9. Flooding and Geocasting
Geocasting functionality means that messages containing information about specific geographic location, for instance road condition in a certain area are disseminated only within this specific region.

10. Request/Reply Request/Reply:
As opposed to the previous protocol, this protocol is based on the notion that the information isn't needed by many of the nodes. Therefore, some reactive or on-demand protocols were developed. In this protocol a vehicle will ask explicitly for specific information by transmitting a request message. The final destination of this packet may be known. for instance, if the user requests the current gas prices from the next gas station.

11. Request/Reply Example

12. Sharing
Sharing:
Based on the publish/subscribe paradigm. Messages are disseminated and kept in a predefined area. If a node is interested in any type of message it can subscribe to this event locally. If a message is received by that node it can easily check if this matches its subscription or not.
It resembles the “likes” on Facebook.
After pressing “like” to a certain subject, you’ll get incoming updates and news about that subject.

13. Sharing (Contd.)
Information is duplicated and these replicas are transmitted to some nodes within this area. If a node leaves this area, the information is then transferred to a node which moves into the area or remains within this area. The main difference of this approach compared to the approaches above is that information should remain in a specific area.

14. Clustering What is clustering?
clustering is the task of assigning a set of objects into groups (called clusters) so that the objects in the same cluster are more similar to each other than to those in other clusters.

15. Clustering (Contd.) Motivation
In some situations it becomes obvious that flooding a message into a whole network is not appropriate and will cause a high level of congestion. At the same time request / reply schemes might not be appropriate, since the information is needed by many nodes at the same time. It has therefore been proposed to replace the unstructured flooding of packets by some sort of hierarchical distribution using clustering.

16. Clustering (Contd.) Example of Vehicular Clustering
Notice that usually the size of the cluster changes only during unavoidable situations like sudden increase in the number of vehicles moving in a particular road due to traffic changes.

17. Clustering (Contd.)
We will demonstrate 3 approaches for the clustering protocol in information transport:
DPP – Directional Propagation protocol by Little and Agarwal
Chang approach
Chennikara-Varghese approach

18. Clustering (Contd.) DPP – Directional Propagation Protocol
DPP is a method presented by Little and Agarwal (2005). In this approach we consider information dissemination along a highway. When the traffic is dense, nodes (vehicles) within some region form a cluster. Within this cluster, messages are shared with all nodes of this cluster.
Every car in the figure is illustrated by two letters: C stands for car and E,W,S,N stands for East, West, South and North accordingly.

19. Clustering (Contd.) DPP – Directional Propagation Protocol
In order to propagate a message in one direction, overlapping clusters are used to transmit the message. Clusters in the opposing direction are considered as well to propagate the message. If there is no overlapping cluster the propagation of messages is done simply by the movement of vehicles.

20. Clustering (Contd.)
DPP Example

21. Clustering (Contd.) Chang approach
A dissemination approach that also makes use of clustering techniques is proposed by Chang (2008).
If a car needs some information, it forms a cluster.
This initiates the clustering process. In order to transmit data to other clusters relay vehicles connect two clusters. In a first phase, information within one cluster is gathered. After the first – collection phase, all cluster heads own the information of all vehicles within their cluster. In the second – retrieval phase this information is then sent back to the initiator of the first cluster, i.e., the requesting node.

22. Clustering (Contd.) Chennikara-Varghese approach
Another cluster-based approach is presented by Chennikara-Varghese (2007).
In this approach, cars within a small region autonomously form a cluster. Owing to the close vicinity, direct communication between those cars is possible. However, communication to other vehicles or clusters has to be performed by relaying vehicles that are part of several clusters.

23. Beaconing
In many VANET applications, time-varying data is announced periodically by each node in form of a beacon. In this way the network load is limited to a fixed level determined by the density of the nodes and the beaconing frequency.
When receiving such a one-hop broadcast, nodes do not react to it with a new transmission directly. They instead integrate the content of the message into their local knowledge base. The information will be further distributed with the next beacon.
Here is a movie simulates the beaconing process in VANET’s:

24. Beaconing (Contd.) Maximizing the information dissemination
The main purpose is to maximize the information dissemination without causing congestion in the network. One of the approaches in to adapt the rate of the beacons. With increasing distance and depending on the average velocity of vehicles along a road, the frequency of beacons to be transmitted is adapted.
Another approach analyzes the environment of the vehicle. If a new neighboring vehicle appears, a beacon is sent to update their local knowledge base.

25. Beaconing (Contd.) Maximizing the information dissemination
One approach proposes to use a TDMA (Time Division Multiple Access) approach where one second is divided into 10 slots. The used slot depends on the current speed of a node. The idea is that if there is a traffic jam, the current speed will be slow and thus less beacons need to be sent.

26. Beaconing (Contd.) Maximizing the information dissemination
There is another approach that suggests to control the channel load used by safety beacons and to provide a more reliable information transmission to receivers close to the sender. Instead of varying the frequency of beacons as in the above-mentioned studies they propose adjusting the transmission power of beacons. The goal is to diminish the risk of packet collisions through congestion and thereby increasing the likelihood that beacons are successfully received.

27. Summary
Today we have learned about the various information transport protocols in VANET’s. We saw different implementations and approaches used in those protocols.
We want to emphasize that nowadays in Israel, those implementations aren’t functional, but in the near future, we believe that most of the cars will have some sort of information transport technology.
There are already some organizations (Car 2 Car Consortium, Visteon) that work towards the implementation of those technologies.

28. The End