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Before the Dawn of IP Telephony - Part 6
Originality and ingenuity for establishing voice quality
These contents translated a serialization article carried by ITPro IP telephony ONLINE published by Nikkei Business Publications, Inc. Jump to the original (Japanese).
(continued from previous page)
Selection of a codec
A codec is a method used to convert voice to digital data. Various methods have been researched and standardized.
LD-CELP and CS-ACELP were the remaining candidates as the selection of codec when considering compression of bandwidth and latency.
At the time, LSI for 8kbit/sec LD-CELP was already completed at OKI. If my memory serves me correct, the standardization of CS-ACELP was only at the drafting stage.
In the case of IP networks, there is great possibility of packet loss. Even if processing requires more time, jittering on the network side is much, much greater. We decided that CS-ACELP was more suitable for our concept of no sound intermittence.
Selection of a codec was a crucial theme requiring many hours of deliberation with the integrator. Fortunately, there were many engineers familiar with encoding in our Transmission Department, Semiconductor Department and research laboratory that the right decision was made over a short period of time while exchanging opinions with them. Since CS-ACELP became the standard in the world of IP later on, I assume we made the right decision at the time.
Photo 2 "OKI Technical Review" issue 174 announcing the technology for the first time.
English version is available.
After the shipment of BS1100 in December 1996, a thesis on the concept and technology of this product was completed and announced outside the company (photo 2). At the time, we didn't think that the technology would be widely recognized. Actually, the technology probably gained very little recognition here in Japan. However, surprising news came in.
... To be continued
