Quality of service on ad-hoc wireless networks

Over the last years, Mobile Ad-hoc Networks (MANETs) have captured the attention of the research community. The flexibility and cost savings they provide, due to the fact that no infrastructure is needed to deploy a MANET, is one of the most attractive possibilities of this technology. However, along with the flexibility, lots of problems arise due to the bad quality of transmission media, the scarcity of resources, etc. Since real-time communications will be common in MANETs, there has been an increasing motivation on the introduction of Quality of Service (QoS) in such networks. However, many characteristics of MANETs make QoS provisioning a difficult problem.In order to avoid congestion, a reservation mechanism that works together with a Connection Admission Control (CAC) seems to be a reasonable solution. However, most of the QoS approaches found in literature for MANETs do not use reservations. One reason for that, is the difficulty on determining the available bandwidth at a node. This is needed to decide whether there are enough resources to accommodate a new connection.This thesis proposes a simple, yet effective, method for nodes in a CSMA-based MANET to compute their available bandwidth in a distributed way. Based on this value, a QoS reservation mechanism called BRAWN (Bandwidth Reservation over Ad-hoc Networks) is introduced for multirate MANETs, allowing bandwidth allocation on a per flow basis. By multirate we refer to those networks where wireless nodes are able to dynamically switch among several link rates. This allows nodes to select the highest possible transmission rate for exchanging data, independently for each neighbor.The BRAWN mechanism not only guarantees certain QoS levels, but also naturally distributes the traffic more evenly among network nodes (i.e. load balancing). It works completely on the network layer, so that no modifications on lower layers are required, although some information about the network congestion state could also be taken into account if provided by the MAC (Medium Access Control) layer. The thesis analyzes the applicability of the proposed reservation mechanism over both proactive and reactive routing protocols, and extensions to such protocols are proposed whenever needed in order to improve their performance on multirate networks. On mobile scenarios, BRAWN also achieves high QoS provisioning levels by letting the nodes to periodically refresh QoS reservations. This extension of the protocol for mobile nodes is referred as BRAWN-R (BRAWN with Refreshments).Summarizing, the outstanding features of the reservation mechanism proposed by this thesis are: (i) Multirate, i.e. it allows wireless nodes to choose among different transmission rates, in order to accommodate to different channel conditions. (ii) Targeted to CSMA-based wireless MAC protocols, e.g. 802.11. (iii) Reservation based, allowing the network nodes to pro-actively protect ongoing QoS flows, and applying an effective CAC. (iv) Adaptive to topology changes introduced by the mobility of the nodes, re-routing QoS flows to more efficient paths. (v) Feasible and simple to implement over existing MANET routing protocols (as it is shown by the prototype presented at the end of the study).