Abstract—Wireless channels are characterized by more serious bursty and location-dependent errors. Many packet scheduling algorithms have been proposed for wireless networks to guarantee fairness and delay bounds. However, most existing schemes do not consider the difference of traffic natures among packet flows. This will cause the delay-weight coupling problem. In particular, serious queuing delays may be incurred for real-time flows. In this paper, it is proposed a scheduling algorithm that takes traffic types of flows into consideration when scheduling packets and also it is provided scheduling flexibility by trading off video quality to meet the playback deadline. Keywords—Data communication, Real-time, Scheduling, Video transport. I. INTRODUCTION real-time system is one whose correctness involves both the logical correctness of the outputs and their timeliness. There are many characterizations for ‘‘real-time system’’ and the term is often used ambiguously because real- time systems have such differing time constraints. For example, some real-time systems only need the application to satisfy average time deadlines, with small variability, when processing external events. This might be the case when controlling mixing or heating processes or in the case of display processes. Critical real-time systems, on the other hand, have very strict time deadlines that must be met every time, for example, if a controlled dose of radiation must be delivered to some sample. The application for a critical real- time system must have sufficient time to process an external stimulus, called the response time, within a predetermined value under all possible circumstances [13]. What distinguishes real-time systems are classified as hard, firm, or soft systems. In hard real-time systems, the most critical type, failure to meet its time constraints will lead to system failure (imagine a nuclear reactor control system). In firm real-time systems, the time constraints must be met in most cases, but can tolerate missing a low number of Farzad Abtahi is with Department of Information Technology, Advanced Basic Sciences University, Zanjan, Iran (corresponding author to provide phone: +98 9123411288; fax: +98 241 4152182; e-mail: f_abtahi@iasbs.ac.ir). Sahar Khanmohamadi is with Department of Information Technology, Advanced Basic Sciences University, Zanjan, Iran (e-mail: s_khanmohamadi@iasbs.ac.ir). Bahram Sadeghi Bigham is with Department of Information Technology, Advanced Basic Sciences University, Zanjan, Iran (e-mail: b_sadeghi_b@iasbs.ac.ir). deadlines (consider a food processing plant control system). In soft real-time systems, the performance is degraded when time constraints are not met but the system will not catastrophically fail (this is often the case with real-time animation of visual displays). The real-time traffic is sensitive to delay. When some real- time data is lost during transmission, the lost data will not be retransmitted [11]. Beside real-time systems behave under predefined time constraints, interact with its environments. The development cycle include specification, verification and testing phases. Specification phase define the expected functionalities of the systems. Verification and testing aim checking the system properties in order to make sure of its correctness. Verification works on the system model or specification while testing is faced to the system implementation. Verification analyses the model on general and it can prove some properties on it. Testing is based on the observation of an implementation actually working. Both testing and verification are fundamental steps of communication system design since they contribute to the development of reliable and good quality systems. Standardization issues constitute another important aspect of system design. In order to facilitate the interoperability and the interchangeability between the different parties involved in the telecommunication industry, reference standards as well as methodology frameworks are defined by international institutions [7]. The engineering of time-critical systems poses significant challenges to their correct specification, design and development. In such systems, the time, at which each input is processed or output is produced, is critical. It has been recognized that the use of formal methods, in the development of such systems, is fundamental if ‘‘correctness’’ is to be assured (Typical applications can be found in avionics, robotics, process control, and healthcare). The use of formal approaches increases our understanding of a system by revealing inconsistencies, ambiguities, and incompleteness that might otherwise go undetected. An important aspect in the development of a time-critical system is how to cope with its ‘‘evolution’’. The evolution of a software system could be due to changes in the original requirements, adopting a different hardware platform or to improve its efficiency [10]. The recent increase in the number of soft real-time applications has necessitated the development of protocols which provide real-time services. The large bandwidth requirement of these applications has given rise to the use of the optical fiber with Wavelength Division Multiplexing (WDM) supporting a number of channels (wavelengths) in A New Scheduling Algorithm Based on Traffic Classification Using Imprecise Computation Farzad Abtahi, Sahar Khanmohamadi, and Bahram Sadeghi Bigham A World Academy of Science, Engineering and Technology 21 2008 53