Going through the tweets and notes of last week’s HD Communications Summit / HD Comm ’09, there’s another reason why transcoding isn’t the best solution to moving between AMR-WB and G.722 — added latency.
While transcoding processes may be very fast, the process is not a non-zero one and adds some amount of latency into both sides of the conversation. While transcoding is relatively transparent with existing low-bit rate codecs and VoIP, the additional information and bandwidth for HD calls is going to add some number of milliseconds to each voice media stream.
Will it add up to 150 milliseconds of delay? Right now, vendors aren’t talking transaction times, but down the road there will likely be more discussions of how better (software) optimization and CPU horsepower can minimize/mitigate trandcoding between HD codecs.
France Telecom and the DECT Forum CAT-iq group might have the best idea — one codec from end to end, no transcoding required. Avoiding transcoding allows for “slack” in other potential overhead areas (SBCs, routing).