[Asterisk-Users] Is transcoding a bad thing?

[Philipp von Klitzing]

Hi there,

up till now I had this two-box setup in mind:

* no.1: public IP
* no.2: private IP, registers with no.1, serves a small office with 
clients behind NAT

See we'd get something like this:
SIP client (GSM) --> *1 --> IAX2 (iLBC) --> *2 --> G.711 --> MGCP UA

The codec of the SIP client (on the Internet) I don't have full control 
over, that depends on the capabilities of the client, so it can be GSM 
(preferably) or something else. iLBC appears to be great for inter-* 
connections when bandwidth is an issues (from what I read). G.711 finally 
is required since that is the only common protocol between * and the IP 
phone available.

But then I stumbled across the passage I quoted below. Should I 
reconsider the setup to at least remove one of the transcodings? Or is 
the document's author simply wrong?

Greetings, Philipp


2) Transcoding: To be avoided at all times

Transcoding is the conversion of a voice stream with one codec to a voice 
stream with another codec (e.g. G.729 to G.7.23). Transcoding 
dramatically degrades the voice quality. It has to be avoided at all 
times.  

Comment:
Stay with G.711 until the cost of bandwidth becomes an issue, then stick 
to one choice of your trade-off decision.


The above was taken from:
http://www.beltug.be/pages/Pdfs/Checklist_VoIP.pdf