This article describes how resources are managed in MANETs (mobile ad hoc networks) so that quality of service (QoS) can be achieved to enable service differentiation. The article introduces in detail a QoS routing protocol called admission control enabled on-demand routing (ACOR) protocol. The article also presents the Global framework for functional architecture analysis in telecommunications (GAT) that is used to model ACOR and show its capability to provide different class of service for different mobile customers. For QoS routing protocols, this fashion of modeling is novel and investigates in details the relation between the customer and its provider and the complexity of the domain of MANETs.
QoS is a network performance concept whose definition varies depending on the treatment given to the traffic belonging to a determined user’s profile (Juliet Bates, 2006). For example, video applications require sufficient bandwidth and low packet loss. VoIP services need low latency, but can withstand a limited packet loss.
From a network perspective, QoS is characterized by a number of quantifiable attributes. The following are examples of the QoS commitments that a packet network can give:
Within a call, the packet loss, end-to-end delay and latency are the main parameters. Such parameters can be explicitly specified in the service level agreement, giving rise to “hard” QoS commitments. Alternatively, “soft” QoS commitments may be given that imply priority of a user’s traffic.
The network maintains a model of resources management and decides, with respect to user’s profiles, if it can admit traffic while achieving QoS. This is known as admission control.
For these mechanisms to achieve a quantifiable level of QoS, the profile of each user must be understood. In mobile networks, MANETs should know how to manage resources and meet the QoS commitments. The challenge in these networks consists in delivering the appropriate levels of QoS while ensuring that they can scale to all users and balancing this with the cost and risk of over-provisioning.Top
Admission Control Enabled On-Demand Routing Protocol
Designing an efficient and reliable QoS routing protocol for MANETs is a challenging problem (X. Masip-Bruin, 2006; S.R. DAS, 2000). However, a simple routing mechanism is required to efficiently manage the limited resources while at the same time being adaptable to the changing network conditions.
ACOR (N. Kettaf H. A., 2006) was proposed to efficiently provide end-to-end support for QoS by introducing simple cost functions which represent QoS metrics. Inspired by the colored subgraphs formulation presented in K.M. Konwar (2005), where each link of a MANET is divided potentially to sublinks represented by elementary cost functions for QoS metrics (i.e., bandwidth, delay, packet loss, etc.). For purposes of clarity, we only focus on bandwidth and delay. Firstly, the bandwidth at each node is represented by Fb, which is a ratio of the requested bandwidth B by an application to the supported bandwidth by a link Bmax in addition to the residual bandwidth Bres. Secondly, the delay is represented by Fd which is also a ratio of supported delay D by an application to the accumulated hop-by-hop delays with the upper bound of delay Dmax. The sum of the elementary cost functions (Fb and Fd) at each node is added to the global cost function Fg received in the route request packet during the route discovery to represent a route’s end-to-end cost.
Key Terms in this Chapter
MANET: The mobile ad hoc NETworks is an IETF working group aiming to standardize IP routing protocols for ad hoc applications.
Distributed Coordination Function (DCF): Operation of IEEE802.11MAC provides the distributed medium access mechanism.
Admission Control Enabled On-Demand Routing (ACOR): A QoS routing protocol for MANETs.
SLA: Service level agreement is a part of a service contract in which a certain level of service is agreed between a service provider and a customer.
GAT: The global framework for functional architecture analysis in telecommunications is a model used to analyse telecommunication architectures.
NAV: The network allocation vector is used within IEEE802.11 networks to prevent nodes accessing the medium and causing contention.
Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA): A sensing protocol used to detect the channel state: idle/busy.