Asterisk Scalability - How many extentions

I am new to Asterisk and am considering installing it in a fairly large company. Can anybody tell me how it is working in large installations and the number of extentions?

Much appreciated

You can have as many extensions on the system as you want how ever the limit is placed on the box. What kind of set up are you looking at ? If it is large I would recommend that you set it up with a SIP proxy (such as OpenSer) and use load balancing and heart beat for redundancy.

Asterisk has been installed in many large companies. The answer of how many extensions per server gets the usual “it depends”!

Will the servers be doing any transcoding? recording? will they have analog\digital connections directly on the server? how many simultaneous calls do you expect?

The last one is one of the more important. You can have a company with 1000 extensions but due to the nature of the business only have 200 active calls, or you could have a call center where you have 100 agents but have 300 active calls (calls on hold\in queue are considered active and need to be counted as load).

Thanks for your responses. The whole installation will be VOIP on a campus network. The last hop will be 2.4GHz WiFi. We will grow to 800+ extensions with 3 to 4 Primary Rate circuits. We expect at any given time to have a max of 100 simultaneous calls. My concern is voice quality – echo. Can a quality SIP handset cancel echo? Or is there other echo canceling hardware for the Asterisks server? What else can we do to make sure we have the best quality voice?


This is the part that scares me. Is that how each endpoint will connect or is that how you connect from build to building?

VOIP uses a fair amount of bandwith and there are calculators on the wiki that can help you determine what you need. I will tell you that if you come close to saturating the link quality will suffer.

VOIP calls rarely suffer from echo - echo is a PSTN problem. That said you can sometimes get echo over SIP but is usually caused by the endpoint (usually because the speakers are so sensitive they pick up even the faintest noises). VOIP calls can and will suffer from other mjor issues though and 99% of those are either caused by overloaded servers or network links.

You absolutely should segregate your voice and data traffic either through a physically seperate network or by a VLAN and QoS. The network is as important as anything else in VOIP.

You could probably get away with one server but I would not recommend it. I think the max recommeded is about 4 T1’s per server.