NTT Research and Development 2008 Review of Activities

The spread of optical fiber and ADSL^*1 broadband access networks has led to a rapid increase in IP-based telephony services. For next-generation IP telephony services, NTT Laboratories have developed a scalable wideband speech coding, UEMCLIP^*2, which provides high-quality speech communication on a 7-kHz frequency bandwidth and interoperability with conventional telephones equipped with ITU-T^*3 G.711 codecs.

For deployment of wideband speech communication, NTT Laboratories have taken the initiative in standardization of a new wideband speech coding based on the same concept as UEMCLIP in ITU-T. We proposed a coding algorithm in which the technologies from four other organizations are merged. The algorithm met the quality requirements of ITU-T and was approved as ITU-T standard G.711.1 in March, 2008.

The advantages of the G.711.1 are as follows:

• (1)Clear and real-sounding voice can be transmitted by using a wideband speech (50 Hz - 7 kHz) capability with twice the bandwidth of telephone-band speech (300 Hz - 3.4 kHz).
• (2)To connect terminals equipped with the G.711 codec and those with the wideband speech codec, it is necessary to transcode the bitstream of the wideband codec into that of the G.711. (The transcoding includes both decoding and re-encoding.) However, since the G.711 bitstream is involved in the G.711.1 bitstream, the transcoding only extracts the G.711 bitstream part and it causes no quality degradation.

NTT Laboratories will implement the standard in VoIP^*4 chips and PC software phones and provide it in our customers. It will also continue to participate in standardization activities on the 14-kHz bandwidth and stereo extensions to G.711.1 at ITU-T.

• *1 ADSL: Asymmetric Digital Subscriber Line
• *2 UEMCLIP: mU-law Embedded Coder for Low-delay IP communication
• *3 ITU-T: International Telecommunication Union-Telecommunication standardization sector
• *4 VoIP: Voice over Internet Protocol