**2. Related work**

The following section provides an overview of what has been done by other researchers, related to the chapter's topic. Only a part of the most relevant and most recent work has

for clarity and accuracy in the telecommunication standards, but the last aspect is commonly

The formal methods are always advised for the development process when early functional error detection is needed. Formal Descriptive Techniques (FDTs) provide corrective actions in the more abstract phases by introducing formal syntax and what is more important, precise semantics. In combination with the computer-aided software engineering, FDTs offer a delivery of better communication protocols and systems, sooner. The introduction of the FDTs has brought correctness and reliability into the protocol development, which has been recognized long time ago (Wing, 1990), (Hall, 1990). Today there are many formal languages and tools used in the protocol development process: Specification and Description Language-SDL (SDL, 2011), Simple ProMeLa Interpreter (Spin), Estelle (Estelle, 1989), Language of Temporal Ordering Specifications (LOTOS, 2000), Petri Nets (Petri, 1996), Uppaal (Larsen, 1997), Message Sequence Chart (MCS, 2001) and Unified Modelling Language (Booch, 2000). Among them, SDL has achieved widespread success because of its friendly graphical notation, its standardization by the International Telecommunication Union (ITU-T) as the major specification tool for standards and protocols, and because of its support for other popular notations such as ASN.1 (ASN.1, 1993), MSC and TTCN (TTCN, 2006). The effectiveness of SDL and its ability to develop unambiguous protocols have won it a widespread popularity and have led the standardization institutes, such as ETSI (European Telecommunications Standards Institute) (ETSI), 3GPP (Third Generation Partnership Project) (3GPP) and IEEE (The Institute of Electrical and Electronics Engineers) (IEEE) to include SDL diagrams in their protocols specification. SDL also provides powerful analysis of communication protocols, along with design, comprehensive modelling, protocol prototyping, exhaustive validation and verification, and all that by a user-friendly graphical notation. Along with Message Sequence Chart (MSC) description language, SDL is the most widely used FDT not only in the communication protocol specification area, but also in the industry systems engineering domain. Because of the previously stated advantages, SDL was selected as a protocol description method for the purpose of this chapter's analysis.

The aim of this chapter is to emphasize the importance of conducting an early performance evaluation of the communication protocols and systems, and to suggest an appropriate solution for carrying out such an activity. Performance evaluation activity denotes the actions to evaluate the protocol under development regarding its performance. This process can take place in different phases of the development, and can be based on modelling or measurements. If the designer can control the performance of the product, rather than just manage its functionality, the result will be a much superior creation. This problem is treated

The chapter is organized as follows. Section 2 presents the most relevant and most recent work which relates to the target topic of the chapter. In Section 3, the proposed and used methodology is elaborated in details. This methodology is demonstrated in Section 4, where a real engineering problem is provided, involving an IEEE 802.16 wireless communication

The following section provides an overview of what has been done by other researchers, related to the chapter's topic. Only a part of the most relevant and most recent work has

in this chapter through a tangible wireless communication protocol example.

protocol. Section 5 contains the conclusions of the chapter.

**2. Related work** 

avoided or even neglected.

been selected, which is needed for proper introduction of the proposed methodology in Section 3 and for presentation of the example in Section 4.

Engineering of a communication system means to describe, to analyze and to optimize the dynamic, time dependent behavior of the system and its inherent communication protocols. However, as it says in (Mitschele-Thiel, 2001) it is common for a system to be fully designed and functionally tested before an attempt is made to determine its performance characteristics. But it is a necessity to integrate the performance engineering into the design process from the very beginning. In (Mitschele-Thiel, 2001) the author addresses an improvement of the run-time properties by taking into account the characteristics of the applications (communication protocols) and different process scheduling and management strategies. The author concentrates on efficient implementation of behavioural concepts. For the treatment of issues arising from object-oriented concepts the author applies the traditional flattening approach of the language standard. Finally, it is obvious that the book lacks of actual communication system engineering examples, through which the engineering process would have been successfully explained.

The usage of FDT for protocol development has also arisen as a promising way of dealing with the increasing complexity of next generation mobile protocols. In (Showk, 2009) a rudimentary version of the Long Term Evolution (LTE) protocol for the access stratum user plane is modelled using SDL. The LTE radio communication is the upgrade of the current 3G mobile technology with a more complex protocol in order to enable very high data rates. This related work presents a tool which shows easy understanding of the model as well as easy testing of its functionality by simulation in cooperation with Message Sequence Chart. The simulation result presented in (Showk, 2009) shows that the implemented SDL guarantees a good consistency with the target scenarios. The system implementation is mapped to multiple threads and integrated with the operating system to enable execution in multi core hardware platforms. The only obvious drawback of the work is the usability of the created model, as it is only used for functional validation and not for performance evaluation of the analyzed communication protocol.

When developing modern communication systems, the energy consumption is a major concern, especially in the case of wireless networks consisting of battery-powered nodes. In (Gotzhein, 2009) the authors study possibilities of specifying energy aspects in the system a designing phase, with SDL as design language. In particular, they strive for suitable abstractions, by establishing a design view that is largely platform-independent. This objective is achieved by identifying and realizing energy mode signalling and energy scheduling as two complementary approaches to incorporate energy aspects into SDL. A case study illustrates the use of both approaches in a wireless networked control system. These approaches are applied and tested on a hardware platform, but again, the paper does not provide in a sufficient manner any performance metrics of the implemented wireless network.

The security of communication systems is another important aspect which must be considered in the protocol development. In order to study this aspect, (Lopez 2005) have developed a methodology for application of the formal analysis techniques, commonly used in communication protocols, to the analysis of cryptographic protocols. In particular, (Lopez, 2005) have extended the design and analysis phases with security properties. This related work uses a specification notation based on one of the most commonly used standard requirement languages HMSC/MSC, which can be automatically translated into a generic SDL specification. The obtained SDL system can then be used for the analysis of the addressed security properties, by using an observer process scheme. Besides the main goal to provide a notation for describing the formal specification of security systems, (Lopez, 2005) studies the possible attacks to the system, and the possibility of re-using the produced specifications to describe and analyse more complex systems.

The related work (Chen Hui, 2010) analyzes a Networked Control System (NCS), which governs the communication activities and directly affects the communication Quality of Service (QoS). Full or partial reconfiguration of protocol stack offers both optimized communication service and system performance. (Chen Hui, 2010) proposes a formal approach for the design and implementation of reconfiguration protocol stack based on Specification and Description Language for NCS. In Telelogic TAU environment, detail SDL models to support communication and reconfiguration functions of communication link layer, network transmission layer and application layer are discussed respectively. Similarly to the most of the presented related papers, only MSC verification results validate the effectiveness of the reconfiguration concepts of the protocol implementation for NCS.

The methodology which is presented in the following section differs from all previously presented work, as it extends the performance evaluating aspect of the communication systems engineering process. The methodology tries to maintain the functional correctness efforts regarding developing communication entity (similarly to the most of the related work), but at the same time provides the developers with a realistic insight of its performance capabilities.
