[asterisk-users] Maximum number of users

Brian LaVallee b.lavallee at globaltank.jp
Wed Dec 18 23:19:47 CST 2013

Hi Bilal,

Assuming you have the latest hardware, sufficient memory, cpu, etc...
The key to determine the maximum number of users comes down to the 
office type, RTP path, network interface, and primary codec used.

First we need to determine the over-subscription rate, how many people 
will be using the phones at any given time.

For a call center, the ratio is 1:1.
For a normal office, the industry standard is 4:1.
{This ratio is also used to determine the number of PSTN channels you 
will need too}

Will the PSTN connections be Digium card(s) in your server or external 
Assuming Diguim card(s), the RTP will be going through your server.

Determine the network interface.  10/100/1000baseT
Then we need to consider the largest codec used, and divide the 
available bandwidth by the typical packet size.

µ-law/A-law is roughly 80 kbps, so we can support 128/1280/13107 audio 
Divide that by 2 (just to be safe) and allow RTP in both directions. 

Now multiple the result by the over-subscription ratio.  4:1 = 

So we see that the maximum number of users is 2560 for a normal office 
when there is a 100baseT NIC in your Asterisk server.
You would also need to have 640 channels (28 T1 PRI's) connecting to the 
/Using SIP trunks to connect to the PSTN through the same 100baseT NIC 
will reduce the maximum number of users you can support./

The real challenge is not supporting thousands of users (IP Phones), 
it's connecting a sufficient number of PSTN connections to support those 

Brian LaVallee

On 12/18/13, 11:45 PM, bilal ghayyad wrote:
> Hello;
> Can someone advise me what is the maximum number of users (IP Phones) 
> that can be supported by asterisk 1.8 or later?
> Regards
> Bilal

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