[*] Latency on VoIP

[LES.NET (1996) INC.]

There was a discussion on asterisk-biz about something, and some people
posted info on the translation time from different codecs..



The discussion on *biz was partly about codec CPU horsepower and
bandwidth.  Because it takes one big machine to do say.. 96 concurrent
ulaw->g729 conversions, and not so much of a machine to keep it ulaw.

Of course, your bandwidth costs go up without g729, but you may be able to
cram more simultaneous channels in a single machine (thus a single amount
of physical space (colocation space costs reduced)) that it may actually
make more economical sense to use ulaw than to use g729 in some cases.

You can see by show translation (below), that converting from ulaw -> g729
takes 27 milliseconds and then 6 milliseconds back to ulaw.   My current
server is a Dual P3 1.13ghz, faster systems should translate quicker..

So I would assume, that having an asterisk box on either end, similarly
equiped, would add about 33 milliseconds to the overall latency

pstn -> ulaw -> g729(+27/27ms) -> internet(+50?/77ms) -> g729 ->
ulaw(+6/86ms) -> pstn

Here is my codec translations listing:
astpbx*CLI> show translation
         Translation times between formats (in milliseconds)
          Source Format (Rows) Destination Format(Columns)

         g723   gsm  ulaw  alaw  g726 adpcm  slin lpc10  g729 speex  ilbc
   g723     -     -     -     -     -     -     -     -     -     -     -
    gsm     -     -     2     2     5     2     1     5    27     -    23
   ulaw     -     5     -     1     5     2     1     5    27     -    23
   alaw     -     5     1     -     5     2     1     5    27     -    23
   g726     -     7     4     4     -     4     3     7    29     -    25
  adpcm     -     5     2     2     5     -     1     5    27     -    23
   slin     -     4     1     1     4     1     -     4    26     -    22
  lpc10     -     7     4     4     7     4     3     -    29     -    25
   g729     -     9     6     6     9     6     5     9     -     -    27
  speex     -     -     -     -     -     -     -     -     -     -     -
   ilbc     -     8     5     5     8     5     4     8    30     -     -

Anyone else want to post their show translations?

Les.