[Asterisk-Users] g729 and latency measures

[Rich Adamson]

Erick Perez wrote:
> Hi, we have set up a small project in a school the following way:
> SITE_A(4 port analog to ip
> g729)------ADSL_ISP1-------ISP2--------Asterisk-----PSTN
> Site A has 1 Megabit of bandwith (up 512kilobit down 1 megabit)
> The asterisk box gets internet service via a wireless antenna. 1 Mbit
> of up/down bandwith
> 
> Comments:
> So far, this means that I will need licenses for the 729.
> asterisk only supports 20ms sampling on g729 so 4 channels will need
> 96 kilobits at 20ms sampling (or is it kilobytes??) for the internet
> bandwith.
> i cannot use CRTP because i cant be sure if the ISP's routers are CRTP aware.
> Installing ADSL from ISP1 on the asterisk place will give a clear advantage
> 
> Please correct any of my prior statements if wrong.
> 
> should I maintain packet latency below 300ms or 150ms?

The objective should be to keep latency as low as possible, however some 
folks do run asterisk via satellite which as a very lengthy latency.

> How can I measure this latency all the way to the asterisk? 

Several ways depending on how accurate a measurement you want. A simple 
ping would give a starting point. A much more expensive way is to use 
VoIP analysis software to measure it, but be prepared to spend at least 
$1,500 (US) to do that.

> Should I ping from SITE_A to the asterisk box with 8k packets?

If you want to emulate a sip/iax packet, use a packet size of about 200 
bytes.

> If I can't install ADSL for the moment, will the above setup work?

Probably a bigger issue to address relates to what "other" traffic might 
be passing across the dsl and/or wireless channel that might be 
consuming bandwidth and impacting the rtp packets.  Broadcasts 
originating from devices outside your control (other isp users), hackers 
attempting to access your ip addresses (at both ends), data traffic 
between your two endpoints, etc, are just some thoughts of items using a 
portion of the bandwidth available.

Might also think about jitter (eg, variations in latency) and what that 
might do to your end to end communications.

There are other low bandwidth codecs available that could be used 
instead of g729. Some include ilbc, g726, gsm, etc. Each consumes 
different bandwidths, and each provide a slightly different quality of 
audio. See the wiki for more detail on what each consumes for bandwidth 
on the wire.