Preface

An Ad Hoc network is an autonomous system made up by a set of nodes (mobile or fixed) which use wireless bonds to communicate. These nodes constitute a temporal network with‐ out the necessity of a centralized administration, nor the standard group of regular services usually offered by the conventional networks (address assignment, safety, name services, etc). In the case of MANETs (Mobile Ad Hoc networks), the network nodes can move on an aleatory way to organize itself arbitrarily. Therefore, the network's topology can change in an incredibly fast, dynamic and unpredictable way.

Ad Hoc wireless network properties must be taken into account when considering propos‐ als for service improvement and protocol designs. Some of these properties include: node mobile capacity, which promotes dynamic topology (referring to the MANETs), the routing network's demeanor, which shows multiple hops, a broadband's limited restrictions, opera‐ tional power restrictions, limited physical security, and limited scalability. Some advantages of Ad Hoc wireless networks include: quick deployment, dynamic topology, a high failure tolerance, an easy way for connectivity, mobility, deployment costs, and a chance to re-use the spectrum. Some issues related to the use of Ad Hoc wireless networks are: broadband restrictions, processing capability, power restrictions, a high-rate of latency, transmission er‐ rors, a lack of security, location and roaming (only occurs with MANETs).

Ad Hoc wireless networks are useful in multiple situations including: at conferences and meetings where people use laptops, at home with the use of smart household appliances, in search and rescue operations, in cases of natural disasters, or on a battlefield. In these situa‐ tions, the benefits of the system can truly be utilized due to the system's versatility and abili‐ ty of quick deployment.

A systematic review of Ad Hoc wireless networks allows for the consideration of the follow‐ ing issues:

a) Operative Characteristics: This type of network does not rely on an infrastructure, instead, it has a broadcast information channel, with some restrictions in the use of resources (storage power and broadband) which derive from its precarious‐ ness. With MANETs, node dynamics display a variable topology, there is no cen‐ tral place to connect or coordinate the allocation and the use of resources. This fact promotes the establishment of distributed schemes for the assignment and use of resources, favoring the spontaneous appearance of a global coordination mechanism, called self-organization, resulting from l ocal interactions between the initially disordered components. This type of distributed organization is very robust and allows them to survive and self-repair in the event of operational damage or disruption.


particular, dynamic spectrum allocation and resource allocation schemes consid‐ ering channel behavior.

robust and allows them to survive and self-repair in the event of operational

b) Its modeling: The complex operation of this type of network, derived from the permanent change in the channel and its topology, requires the development of models that allow characterization of its behavior. Four major types of models must be developed: the behavior model of the channel, which tries to predict the behavior of the signal propagating; the mobility model of the nodes, which estab‐ lishes the way each node moves in the geographical area where the MANET is deployed; the traffic pattern generation model, which describes how information is generated at each of the nodes; and the model of energy consumption, which establishes the effect of the mobility of the nodes and the traffic patterns on the

c) Network's routing type: The characteristics described for a network's routing type are particularly complex in this type of network. Two types of approaches have been proposed, the proactive and reactive approach. A proactive approach establishes and updates routes in tables before the need to deliver information to a destination arises. The changing nature of the network topology causes, in many cases, a loss in the effort to maintain the trajectories. The reactive approach establishes and updates the routes in the tables only at the moment in which the need to take information to a destination arises. In this case, a little delay is gener‐ ated as a consequence of the need to determine the path to the destination when the need arises. Some other important criteria are also taken into account when proposing a routing protocol, including: resilience, overload, security, perform‐ ance, delay, resource utilization and, ultimately, energy consumption. Also, pro‐ posals are developed considering other key characteristics in the routing: the mobility of the nodes (network dynamics), the quality of service in the routing, security, the consideration of the state of the channel and energy consumption. Also, dynamic addressing schemes need to be considered when using both the

d) Evaluation of benefits: Development of metrics that allow the evaluation of the following metrics: throughput, end-to-end delay, packet delivery rate, network load level and packet loss rate. These metrics are affected by the type of routing, the behavior of the nodes (their dynamics and their speed), the size of the net‐

e) The key aspects associated with operation are related to: offering quality service to deployed applications, the allocation schemes of resources within this type of network, power management, seeking energy efficiency, and security in the ex‐ change of information. In terms of quality of service, this type of network offers significant challenges that require the development of models, protocols and met‐ rics that allow the evaluation and guarantee of the service levels expected by the applications and services that are deployed in this type of network. In terms of resource allocation schemes, it is important to note that the variable behavior of these networks requires dynamic mechanisms for the allocation of resources. In

work, and the number of traffic sources, among other factors.

damage or disruption.

VIII Preface

energy consumption of the battery.

IPv4 protocol and the IPv6 protocol.

In terms of security, it is necessary to develop architectures and models that guar‐ antee the safe provision of services in these types of networks. To get this, the risks must being identified to establish the strategies that allow mitigating them and surviving the different types of attacks.

f) Simulation tools and test scenarios: The complex nature of the behavior of this type of network forces the development of behavioral models and test scenarios to validate hypotheses and to show how the nodes and the network will behave.

In conclusion, the universe of Ad Hoc networks is complex, full of great challenges and problems to be solved. This book presents a perspective of different applications, in differ‐ ent areas of knowledge.

> **Jesús Hamilton Ortiz, PhD** Santiago de Cali University Columbia

## **Álvaro Pachón de la Cruz, PhD** ICESI University Columbia

**Section 1**
