Sangjo Yoo

SIP-based Qos support architecture and session management in a combined IntServ and DiffServ networks

With the development of next-generation convergence networks, the Internet needs to support new network architecture and session management methods that can support various applications requiring differentiated traffic processing and high quality of services, instead of the conventional best-effort service. In next-generation networks based on all-IP, it is expected that SIP will play an important role in session establishment between end-to-end user terminals. Accordingly, this paper proposes a new QoS support SIP-based network architecture that integrates SIP clients, QoS-enabled SIP servers, and policy-based network management in a combined IntServ and DiffServ networks. To control the network access of users and manage network resources, the use of policy servers and QoS extended SIP signaling is presented. Numerical analysis is then used to derive the session establishment delay for the proposed signaling scenarios. Simulations under various environments show appropriate parameter ranges in terms of the server capacity and number of users for the required delay bounds.

Predictive and measurement-based dynamic resource management and QoS control for videos

In this paper, we propose a new dynamic resource allocation and call admission control method for the VBR video sources to meet the users quality of service requirements and at the same time to achieve an efficient resource management in networks. Without any prior knowledge of the users traffic statistics, the proposed mechanism dynamically adjusts the necessary bandwidth by the networks based on the provided quality of service satisfaction degree of each connection in respect to the users requirements in terms of loss ratio and average delay. Using traffic prediction and simple QoS measurements, the next required bandwidth for each video connection is computed. To avoid quality decreasing by new incoming calls, we present a call admission control based on the provided QoS for existing connections. Simulation results show that our proposed dynamic method is able to provide the desired level of quality of service and high network utilization.

Design for testability of protocols based on formal specifications

In this paper, we propose a generic scheme which instruments a formal protocol specification automatically to enhance the testability of the implementation. This approach is a special case of design for testability. It is cost-effective considering the entire cycle of protocol development. The advantage of automatic instrumentation is that the user need not pay special attention to testing problems in the design phase. Unlike most other techniques, our scheme also works with existing protocol specifications since it does not affect the original design. Our models address the problems of controllability and observability, and can handle both sequential and concurrent formal protocol specifications.

Development and Application of ATM Protocol Conformance Test System

This paper presents development and application of ATM Conformance Test Sys-tem (ACTS), an automated test system for ATM protocols. ACTS is a test system that checks conformance of ATM terminal and network equipment implementing either ITU-T or ATM Forum user-network interface. This paper, after presenting the methodology and process used for developing ACTS, conducts case studies of its applications to real ATM equipment. By applying ACTS, we were able to detect numerous problems in protocol implementations of ATM equipment and analyze causes of the problems, thereby demonstrating the efficacy of ACTS as an efficient automated testing tool. Furthermore, by predicting the potential effects of the problems on interoperability, we show how ACTS can be used as a useful tool for ensuring interoperable ATM equipment.

An Approach to Dynamic Protocol Testing

Protocol conformance testing aims at checking if a protocol implementation conforms to the standard (or specification) it is supposed to support. The results of testing can be classified into global verdict showing the tested system is either error-free or faulty, and local verdict indicating whether each element (e.g., a transition in the FSM) of the system is implemented correctly or not. In reality, the conventional protocol test procedure may give wrong local verdicts in the initial stages of testing because the procedure uses predetermined test sequence. In this paper, we propose a dynamic procedure for protocol testing using Test Sequence Tree (TST). The procedure allows us to get local verdicts more correctly than the conventional methods. The TST is reconfigured dynamically to obtain accurate verdicts for the untested elements by feedback of the local verdicts of the tested elements. The proposed technique was tested on the ITU-T Q.2931 signalling protocol. Our results showed that the fault coverage of our test procedure is better than the conventional methods. An extension of the proposed dynamic testing technique to the nondeterministic FSM is also discussed.

A Weighted Random Walk Approach for Conformance Testing of a System Specified as Communicating Finite State Machines

It is very important to test protocol implementations to verify conformance to their specifications (standards) in order to promote interoperability between them. This kind of testing is referred to as conformance testing. For that purpose, a kind of test scenario need prepared in advance and the involved work is called test generation. On the other hand, often a protocol can be specified succinctly and in an understandable way as a collection of communicating finite state machines. In this paper, we propose a test generation scheme called weighted random walk that can be applied to the test generation of communicating finite state machines. The proposed scheme is applied to an example protocol and some results of comparison with existing schemes such as pure random walk and guided random walk are presented. Our scheme is superior to the existing schemes in that it tends to test communicating finite state machines with fewer external test inputs. In an illustrated example in the paper, our scheme shows about 48% improvement over the existing schemes in terms of the number of necessary external test inputs.

Conformance testing of ATM adaptation layer protocol

This paper presents an appropriate testing methodology to check the conformity of an implementation following ATM Adaptation Layer protocol in ATM/B-ISDN communication systems. In this paper, we analyze restrictions of the AAL Type 5 protocol to develop Abstract Test Suites and a test system, and we compare test coverage of applicable test methods to choose the best test method for AAL Type 5 Common Part protocol testing. We decide to apply Distributed Test Method for testing of the protocol because of its larger test coverage. To synchronize the execution of test cases between Upper Tester and Lower Tester in distributed testing environment, we propose a simple and efficient timing synchronization mechanism. To illustrate the effectiveness of our test structure, we give an example of test cases described in Tree and Tabular Combined Notation using the proposed timing synchronization mechanism.

A fair scheduling algorithm for wireless internet differentiated service networks

The recent Internet needs a network structure and traffic engineering that can support various applications requiring differentiated traffic processing and a high quality of service. The extension of the Internet from wired to wireless systems that generate location-dependent and burst errors has made the support of good services more difficult with existing packet scheduling algorithms. Accordingly, this paper troposes a wireless differentiated service packet scheduling (WDSPS) algorithm that can provide reliable and fair services in differentiated wireless internet service networks. As such, the proposed scheduling algorithm solves the HOL blocking problem within a class packet queue that occurs in a wireless network, supports differentiated services for each class defined in a differentiated service network, and facilitates gradual and efficient service compensation not only among classes but also among flows within a class, thereby preventing a monopoly by one class or one flow. Simulations confirmed that the proposed WDSPS scheduling algorithm could provide the required QoS differentiation between classes and enhanced the service throughput under various wireless network conditions.

A dynamic protocol conformance test method

Protocol conformance test is used to promote the interoperability of protocol implementations developed by venders. Noninteroperability between protocol implementations may be caused by ambiguity and/or misinterpretation of protocol specifications by vendors or by different implementations using different options in specifications. The conventional method used for protocol conformance test has been standardized by ISO/IEC JTC1 and ITU-T with the purpose of determining whether a protocol implementation conforms to its specification. However, the conventional method sometimes gives wrong test results because the test is based on static test sequences. This problem is caused by some failed transitions of a protocols finite state machine included in a test sequence, which have an effect on the test result of transitions to be tested. In this paper, an approach called dynamic conformance test method (DCTM) is proposed to solve this problem. DCTM dynamically selects different test sequences during testing depending on whether alternative paths without failed transitions exist. As a result, the fault coverage of DCTM is better than that of the conventional test method. DCTM has been implemented and applied to the TCP protocol in order to demonstrate its improvement in the fault coverage compared to that of the conventional method.