Voice Quality Assessment of SIP-PBX Softphone Extension in 3G Cellular Service Environment

Abstract

Voice Communications is still playing important role in business activities. Large companies generally use PBX to handle corporate communications both internally and externally. PBXs have rich features that can fulfil corporate voice communications requirements. Internet changed the corporate communications importance from voice centric to data communications. Intranet becomes the strategic data infrastructure for internal communications and its connection to Internet is an absolute must to have global reach. Voice over IP (VOIP) is the technology that capitalizes the ubiquitous presence of data network in corporates. VOIP provides efficiency in business communications. Naturally, traditional PBX evolves to IP-PBX that use data network which is currently based on TCP/IP for certain connections. The acceptance of SIP (Session Initiation Protocol) as the protocol for VOIP resulted in improvement of IP-PBX to become SIP-PBX. One of the SIP-PBX that is Open Source is called Asterisk. It has rich features found in high end corporate PBX. In this research Asterisk is used as the basic PBX for small corporates in fulfilling corporate voice communications. Sometimes small companies have to operate in locations that have no proper and reliable fixed or cable infrastructure for Internet connection. The only economic viable choice is 3G or 4G cellular service. The problem is whether the service quality is suitable. ITU has recommendation for planning of telephony transmission quality. The parameter is known as MOS. The recommendation shows detailed variables to reach the MOS. Based on the ITU recommendations; this research provides a novel technique to quickly assess the voice quality of internal voice corporate communications using SIP-PBX that is located in the Internet. The data used for evaluating MOS can be directly obtained using Wireshark as the tool. The resulting MOS used only to assess whether the 3G or 4G service in that particular location is suitable for small corporate communications or other solution should be found. This research result showed that based on MOS, 3G access line quality is inadequate for VOIP based voice communication.