QoS provisioning in wireless IP networks

This paper deals with quality of service (QoS) provision in wireless IP networks. QoS provision is particularly challenging in wireless networks, where network resources are generally limited, variable over time and shared. In the design of possible measures to assure QoS one should consider that standardization is well established for the network layer Internet Protocol and for many underlying technologies of frequent use (e.g. IEEE 802.11, BLUETOOTH or HIPERLAN II). Therefore, as far as research on QoS is concerned, there is little room in both the IP and the link-layers for improved IP over wireless interfaces. In this paper we illustrate a solution in which an intermediate Wireless Adaptation Layer (WAL) is transparently interposed between the IP layer and specific link-layer technologies as a solution to provide QoS. The WAL addresses two main issues: (i) compensation for channel impairments in different platforms in order to enhance wireless channel reliability and (ii) implementation of traffic control and packet scheduling mechanisms to satisfy bandwidth and delay requirements, as well as to enforce a general principle of fairness among the IP associations contending for network resources and achieve optimal exploitation of transmission capacity. The WAL consists of a set of modules, each one in charge of a specific task, which can be enabled or disabled depending on the specific network environment. The novelty of the WAL approach is its capability of adapting itself to different wireless interfaces selecting performance enhancing modules for specific networks. This requires to modify the standard TCP/IP protocol stack by introducing an intermediate layer between the IP layer and the Data Link layer, with performance enhancement purposes. This paper focuses on two modules in particular, namely a traffic control module, which is in charge of performing congestion control and channel state dependent scheduling (CSD) packet scheduling, and a forward error correction (FEC) module, which compensates for channel impairments. This paper presents the proposed architecture provided with these modules and reports some measurements and simulations highlighting benefits resulting from the use of such modules.