A large amount of the existing research work that has been carried in mobile networking are mainly based on the assumption that there is an existence of a path between the sender and the receiver. Decentralized mobile systems are however exemplified by network partitions and this has been one of the main driving factors towards the study and implementation of the fully context-aware protocols. This protocol is mainly based on the fact that nodes can be exploited as carrier of messages in the network partitions in order to attain delivery of network components. The nodes in context aware protocol can be used to compute delivery probabilities and then disseminate them into their respective ad hoc cloud. In this protocol, the context information is then exploited so as to appraise the probabilities for the destinations of each of the nodes. In this section, we will lay more focus on the defining algorithms to combine the context information to compute the probabilities of delivery. We can therefore present a way in which the context based information can be used to route data in a specific class of the opportunistic networks.
Opportunistic networks commonly refered to as (Oppnets) is one of the ways through which mobile devices are able to transmit messages by exploiting the direct contacts without establishing and end-to-end infrastructure. When using the opportunistic networks, high churn rates and disconnections are usually a common occurrence. Therefore routing becomes one of the main challenges in this kind of environment. In this paper we are going to take a look at the opportunistic networks which are used in routing of different messages to various destinations. The opportunistic networks can be further subdivided into three main classes which include; context-oblivious, mobility-based and the social-context-aware routing protocols. Each of the classes has their own advantages and disadvantages and can be applied in different environments. We are going to lay more focus on the context-aware protocol which is used in forwarding data in the opportunistic networks and then evaluate the relative performance of the above three routing techniques.
In this case, fully context-aware routing protocol has been picked as our class of choice. This class takes into account the context of the messages being routed and then uses the context information to determine the routing path that the messages are to take. The context information being considered in this case can cover various ranges which entirely depend on the specific routing protocols. The context information is used in this case to help in making decisions to route the messages. This class involves the use of two approaches namely the naïve and the intelligent approaches. This class puts more focus on the role of the context information and the interactions taking place when the messages are being routed. The fully ware-context information involves the amalgamation of two protocols which include the mobility based protocols and the social context-based protocols.
The mobility based protocols takes into account the mobility patterns of the nodes while the social based context protocol takes into consideration the interactions taking place during message routing. When the two protocols are combined together, we are able to achieve the fully ware context-based protocol which is very instrumental during message routing as the routing of the messages is mainly done using the context information.
There are various algorithms that can be used in the opportunistic networks. However, for this case, we are mainly going to lay more emphasis on the following three algorithms: PROPICMAN (Probabilistic Routing Protocol for Intermittently Connected Mobile Ad hoc Networks), HiBOp (History-Based Opportunistic routing) and CAR (Context-aware Adaptive Routing). These algorithms play a very important role towards the determination and establishment of the routing channels that different types of messages follow.
2. Literature Review
2.1 PROPICMAN (Probabilistic Routing Protocol for Intermittently Connected Mobile Ad hoc Networks)
PROPICMAN is one of the best algorithms which are used to determine the routing sequence of different sets of messages. It allows the sender of a given set of information to select the neighbor in such a way that the message has the highest probability of reaching the intended destination. When using this method, message is simply sent to the neighbor which has the best and shortest route to the destination. The message is sent to a single node since the reliability of the path is usually considered to be very high. When using this algorithm, the delivery probability of messages can be considered to be quasi-static. Therefore the mobility of a node does not affect the validity of the propicman selection. It can therefore e established that Propicman effectively exploits the mobility while at the same time reducing the number of nodes which are involved in the process of forwarding messages. The propicman algorithm also takes into account the privacy of information. The main goals of this algorithm includes: distributing messages through the opportunistic mobile ad hoc networks in a probabilistic fashion, minimizing the amount of resources consumed during the delivery of any single message and maximizing on the percentage of the messages that are eventually delivered to various destinations. In order to achieve the above goals, probability nodes can be used in order to ensure that the nodes meet the destinations.
2.2 HiBOp (History-Based Opportunistic routing)
This algorithm is mainly used when handling networks which have simultaneous paths between senders and receivers. This algorithm is very instrumental when dealing with networks which involves high resource consumption. When properly implemented, this method can help to reduce the amount of resource consumed during message trafficking. It also reduces the rate of message loss and also helps in preserving the performance of the system in terms of message delay.
2.3 CAR (Context-aware Adaptive Routing)
The context information is usually considered to be available. The context aware protocols may not only be used to exploit some kinds of context information in the mobility based protocols but can also be used into account the social aspects of the nodes to route the messages. This can be attributed to the fact that the mobility of the nodes is usually decided by the carriers. Therefore the social aspect of the nodes becomes of utmost importance which can then help in the establishment of how each of the nodes interacts with each other. This protocol has several advantages over the traditional mobility-based approaches as it is more general hence can be used with different types of traffic. It can be used with any kind of context information thus making it easy to be customized in order to suit a particular environment.
3. Comparison of the protocols
Different protocols can be used in different environments depending on the nature of information to be delivered and the destination that the message is supposed to be delivered to. Each protocol has its own unique advantage and disadvantage. For instance, HiBOp (History-Based Opportunistic routing) protocol is very proficient in environments that require controlled resource consumption. PROPICMAN also on the other side helps in controlling the amount of resource consumption while at the same time helps in minimizing message loss and also in reducing error rate in messages. The CAR routing protocol takes into consideration the context of the messages being delivered and then help in determining the destination of the messages. This helps in ensuring that similar messages but with different contexts are channeled towards their right destinations.
The opportunistic networks have several difficulties especially when routing information to various destinations. Therefore it is necessary to determine the types of messages being delivered and the paths that they are supposed to follow. In order to accurately determine the path, there is need to choose the right algorithm. Using the fully context aware algorithm helped in ensuring that similar messages but with different contexts are channeled towards their right destinations. The chosen algorithm also ensured that resource consumption are minimized and that message error rates were also minimized.
A. Vahdat and D. Becker, “Epidemic Routing for Partially Connected Ad Hoc Networks,” Technical Report CS-2000-06, Dept. Computer Science, Duke Univ., 2000.
Hoang Anh Nguyen, Silvia Giordano. Routing in Opportunistic Networks Networking Lab - ISIN, University of Applied Sciences (SUPSI) 2007
Hoang Anh Nguyen, Silvia Giordano. Spatiotemporal Routing Algorithm in Opportunistic Networks ISIN-DTI, University of Applied Sciences, Switzerland. 2008
Hoang Anh Nguyen, Silvia Giordanot, Alessandro Puiatti. Probabilistic Routing Protocol for Intermittently Connected Mobile Ad hoc Network* PROPICMAN). 2007
K. Fall, “A Delay-Tolerant Network Architecture for Challenged Internets,” Proc. ACM SIGCOMM ’03, Aug. 2003.
M.Conti, S.Giordano, Multi-hop Ad Hoc Networking, IEEE Communication Magazine, April 2007.
Marco Conti, Jacopo Jacopini, Andrea Passarella. HiBOp: a History Based Routing Protocol for Opportunistic Networks, 2007
Mirco Musolesi and Cecilia Mascolo, CAR: Context-Aware Adaptive Routing for Delay-Tolerant Mobile Networks IEEE TRANSACTIONS ON MOBILE COMPUTING, VOL. 8, NO. 2, FEBRUARY 2009
S. Jain, K. Fall, and R. Patra, “Routing in a Delay Tolerant
V. Zhao, M. Ammar, and E. Zegura, “A Message Ferrying Approach for Data Delivery in Sparse Mobile Ad Hoc Networks,” Proc. ACM MobiHoc ’04, May 2004.