Ilija Basicevic

Comparison of SIP and H.323 Protocols

This paper compares two most important protocols for signaling in voice over IP (VoIP) networks of today, namely SIP and H.323. Several aspects of protocol functionality are covered. We have tried to focus on those aspects that are most important for successful operation of VoIP networks, ranging from characteristics of syntax to functions of infrastructure elements and support for third party call control and other communications applications. Security features and some implementation issues are analyzed as well. Conclusion is that although H.323 appeared earlier, SIP is better adapted to the Internet environment which is the most important reason for its success. Also greater standardization activity related to applications of SIP (e.g. presence services, instant messaging) made it more attractive to developers.

A Task Tree Executor: New Runtime for Parallelized Legacy Software

Building a very large-scale distributed system, such as a power distribution system, was always regarded as a highly demanding undertaking in the area of engineering of computer based systems. Such systems nowadays are managing tens of millions of input variables using rather complex mathematical calculations. Traditionally, these calculations are implemented as sequential software, e.g. in FORTRAN. Under the current circumstances, when the processors are facing the well-known frequency wall, the research community started exploring new technology opportunities brought by the modern symmetric multiprocessors and multicores. One of the most challenging tasks in building modern very large-scale systems is the parallelization of legacy software. This paper contributes to the overall research effort in the area by proposing an original approach to parallelization of legacy sequential software. In the paper we introduce the concept of parallelization based on data slicing and construction of the corresponding task tree. Then we present the new runtime engine referred to as the task tree executor. Finally, we present the results of the performance evaluation based on a series of experiments made on the dual-core symmetric multiprocessor.

An Approach to Parallelization of Legacy Software

The issue of parallelization of large and complex software systems has been widely researched, but no definite solution has been published yet. In the paper we introduce the concept of parallelization based on the identification of mutually independent data sets and refactoring legacy software for the purpose of adjusting it to execution as a task tree. Then we present implementation of the concept on existing distribution management system. Finally, we present the results of the performance evaluation based on a series of experiments made on the dual-core symmetric multiprocessor.

Test case generation for the task tree type of architecture

Context: Emerging multicores and clusters of multicores that may operate in parallel have set a new challenge - development of massively parallel software composed of thousands of loosely coupled or even completely independent threads/processes, such as MapReduce and Java 3.0 workers, or Erlang processes, respectively. Testing and verification is a critical phase in the development of such software products. Objective: Generating test cases based on operational profiles and certifying declared operational reliability figure of the given software product is a well-established process for the sequential type of software. This paper proposes an adaptation of that process for a class of massively parallel software - large-scale task trees. Method: The proposed method uses statistical usage testing and operational reliability estimation based on operational profiles and novel test suite quality indicators, namely the percentage of different task trees and the percentage of different paths. Results: As an example, the proposed method is applied to operational reliability certification of a parallel software infrastructure named the TaskTreeExecutor. The paper proposes an algorithm for generating random task trees to enable that application. Test runs in the experiments involved hundreds and thousands of Win32/Linux threads thus demonstrating scalability of the proposed approach. For practitioners, the most useful result presented is the method for determining the number of task trees and the number of paths, which are needed to certify the given operational reliability of a software product. The practitioners may also use the proposed coverage metrics to measure the quality of automatically generated test suite. Conclusion: This paper provides a useful solution for the test case generation that enables the operational reliability certification process for a class of massively parallel software called the large-scale task trees. The usefulness of this solution was demonstrated by a case study - operational reliability certification of the real parallel software product.

Estimating parallelism of Transactional Memory programs

Transactional Memory (TM), a promising concurrency control mechanism that enables easier and more productive parallel/distributed programming, become a standard part of the latest multicores rolled out by IBM, Intel, AMD, and other IC manufacturers. Many TM aspects have been intensively researched, e.g. semantics of various possible implementations, TM safety and liveness properties, and TM performance. Some researchers suggested some novel measures for the amount of concurrency in TM programs. Alternatively, we in this paper propose an approach to analysis of TM programs by using a well-established methodology, which is based on modeling programs as DAGs, and calculating their work, span, parallelism, and speedup. In the paper we present an approach to application of this methodology in order to calculate the parallelism of a typical TM program for processing a group of transactions on a set of bank accounts. As a result of this approach we established some simple theorems that may be used for analysis of a broader class of TM programs.

Use of Finite State Machine Based Framework in Implementation of Communication Protocols A Case Study

In this paper we present a finite state machine (FSM) based implementation of SIP protocol stack for SIP user agent. Design decisions made during the development process, and the resulting characteristics of software product are discussed. Some characteristics of FSM-based framework that has been used in development are presented. We compare quantitatively our implementation with a well known open source SIP implementation, resiprocate. Comparison is focused on the following parameters: lines of code (LOC) and cyclomatic complexity. Results show viability of FSM-based approach, most importantly its support for modularization.

Use of Tsallis entropy in detection of SYN flood DoS attacks

In this paper, we present results of application of Tsallis entropy in detection of denial of service attacks. Two detectors, one based on Tsallis and the other one based on Shannons entropy, have been applied in several attack simulations, and their properties have been compared. The simulated attack is Synchronize packet SYN flood. A simple packet distribution, that is, entropy of source addresses are considered. In both cases, cumulative sum control chart algorithm is used for change point detection. Properties of two detectors that are compared are detection delay and rate of true and false positives. The results show that Tsallis entropy-based detector can outperform with respect to false positive rate Shannon-based one but that requires careful tuning of Tsallis Q parameter that depends on characteristics of network traffic. The detection delay of two detectors is approximately the same. Copyright

A model-based statistical usage testing of communication protocols

In this paper, we present our original approach to the model-based statistical usage testing of a class of communication protocol implementations that are based on the state design pattern and Java programming environment augmented with the class FSMSystem. The approach is based on the working environment that has been proven on a number of real-world projects. The working environment is created with the following set of tools: generic modeling environment with the operational profile model paradigm registered to it, operational profile model interpreter, generic test case generator, test case compiler, and the unit testing framework JUnit extended with the class TestBed that acts as both test driver and stub thus providing the complete test harness. In the paper, we present the methodology of the model-based statistical usage testing of a class of communication protocol implementations, the tools that support this methodology, and the case study - the model based statistical usage testing of SIP INVITE client transaction, a part of the SIP protocol stack

On the application of fuzzy-based flow control approach to High Altitude Platform communications

Most of the research effort in the field of HAP communications until now has been invested in the physical layer of the protocol stack, and in the radio related issues in particular. However, the overall system throughput is limited by the performance of the transport layer. Since HAPs will be used in networks with different topological complexity, various kinds of wireless communications links, bit error rates, and various mixtures of multimedia traffic, the control flow in such networks may present itself as a non-linear and stochastic process. Therefore we introduced a fuzzy control of the throughput in the TCP. Our approach is based on the off-line synthesis of the Takagi-Sugeno fuzzy controller based on the simulation data and on-line flow control by the synthesized controller that is built in the conventional TCP. In the paper we present the ns2-based simulation results.

A Host Based Method for Data Leak Protection by Tracking Sensitive Data Flow

This paper describes a method for data leak protection (DLP) based on tracking sensitive information as it flows inside file system on a host. The method is based on the idea that every flow from sensitive to non-sensitive object increases the security level of the target object to that of the source object. Any process which reads an object that contains sensitive data automatically itself becomes tagged as sensitive. When a process gets tagged, all subsequent write operations to any object make target objects also tagged. Any process created by a tagged process is also tagged. By spreading tags over all objects touched by a sensitive process, we have a guarantee that no one bit of sensitive information resides in a non-sensitive objects. Using any software tool to process a sensitive object results in a new sensitive object, this prevents bypassing security mechanisms. All objects tagged as sensitive are checked before being transferred out of the host according to security policy. The main goal of this method is to prevent covert channels for information leakage which use steganography, data modification, compression or encryption. It is implemented in Linux OS as a kernel module. It works with legacy applications, since all changes are on OS level.