Estimation on quality of service for real-time communications in IP networks IPネットワークにおけるリアルタイム系通信サービス品質の推定法
Estimation on quality of service for real-time communications in IP networks
Packet communication is considered one of the key technologies to transport various kinds of information over the networks because of its effective and flexible transporting capability. However, they have issues to be solved to apply to multimedia communications, especially real-time communications. The issues include how to measure/estimate transmission characteristics such as transmission delays (variations), losses, which are experienced in packet communications networks, implementation of high-speed protocol processing, and so on. The thesis consists of four study subjects aiming at realization of real-time packet communications. First, a scheme to estimate one-way delay variations is described. The one-way delay variations (OWDV), which is a key item for evaluating communications quality but is hard to be measured without external clock synchronization function. The new approach to estimate OWDV is proposed so that it is able to easily estimate OWDV anywhere in IP networks. Second, the study about a practical scheme that can estimate ADSL link rates is depicted. The proposed scheme allows us to estimate ADSL link rate measurements from the network operation center (NOC) using existing communications protocols and network node facilities. It is applied to estimate ADSL link rates in actual IP network, and shown that the down- and up-link rates can be obtained in a simple manner. Third, an experimental study of speech quality of conversational packetized voice communications is presented. There are many degradation factors such as transmission delays, packet losses to be considered. Since speech quality is affected by combination of plural factors, the experiment of speech quality of packetized voice communications was carried out under the condition of packet length, voice codec (PCM and ADM), and compensatory methods when packets are lost, in addition to transmission delays and packet losses. Fourth, protocol processing for high-speed packet switching systems is presented. Packet switching networks were required to process packet switching functions at higher speed for applying packet switching networks to multimedia communications. The communications protocol processing based on parallelism of transmission and receipt, layers 2 and 3 are proposed. Employing 1.5 μm VLSI technology, the data rates are estimated one hundred times as much as the previous X.25 data packet switching systems, which could process at most 64 kb/s. These research works contribute to improve real-time packet communications services and network facilities.