Advice: one way multinational voice mail server

Hello forumites,

A newbie question. We are building an application that will process inbound SMSes and voice mails (sometimes automatically, sometimes manually), and send back replies to the originall callers via SMS.

The service is to be provided in several countries, however, all the calls will be forwarded to one server (or a cluster of servers). That is, most of the phone numbers will be used simply as "gateways".

The SMS sending and receiving is handled by an external provider (Clickatell in our case).


We plan using Asterisk (or equivalent) in order to process the voice mails, and we need a forwarding service with wide coverage and low rates.

We do not plan employing a dedicated telephony specialist, as our needs are quite modest (simple inbound voice mail). And obviously, the costs should be kept as low as possible (cheap hardware or no special hardware).

1. Do you think Asterisk can handle this?
2. Can you recommend a forwarding service?

Any advice is much appreciated.

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1. Do you think Asterisk can handle this?

Yes, but bear in mind Asterisk's weak points are high availability and scaling

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2. Can you recommend a forwarding service?

You mean a call forwarding service? so that asterisk can answer the calls and record the call as a voicemail? Not sure what you're after here.. is it just pstn origination?

x-console :

Quote: 2. Can you recommend a forwarding service? You mean a call forwarding service? so that asterisk can answer the calls and record the call as a voicemail? Not sure what you're after here.. is it just pstn origination?

Yes, exactly: for example, a call originates in France, and a call forwarding service forwards it to a telephony server in UK, which automatically records the call (and then our application retrieves the WAV file).

Generally, the application is mobile oriented (we're not interested in SIP on this stage), so yes, just PSTN origination.

If Asterisk is not scalable enough, how about a public API such as http://web21c.bt.com ?

We want to reduce the management and support hassle as much as possible.

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Generally, the application is mobile oriented (we're not interested in SIP on this stage), so yes, just PSTN origination.

Why would SIP be a problem? user calls number (via gsm or pstn), origination partner connects call and broadcasts sip to your server. Caller needs never know SIP is involved. SIP is useful for these kinds of circumstances where a) you can have multiple channels concurrently active without significant cost (90 channels == 3 E1's == expensive). When you dial out from your asterisk box (if you need to), your partner turns it back into pstn/gsm traffic. Plus, you can get one provider that does all your international numbers and origination. If you are strictly pstn, you will likely need a more complicated setup involving more suppliers

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If Asterisk is not scalable enough, how about a public API such as http://web21c.bt.com

Define 'not scalable enough'? what are your projected numbers? concurrent calls? bhca? bhcc? call duration, message storage etc etc.

Aside from that, then sure; I'm a big fan of what they are doing at BT re: 21Cn. However, will they provide you with an SLA? what if you need some custom callback they don't currently offer? Are you happy with the fact that they may make changes to the API without notice which breaks your code? It all depends on your business drivers

x-console, thanks for your informative replies.

x-console :

Quote: Generally, the application is mobile oriented (we're not interested in SIP on this stage), so yes, just PSTN origination. Why would SIP be a problem? user calls number (via gsm or pstn), origination partner connects call and broadcasts sip to your server. Caller needs never know SIP is involved. SIP is useful for these kinds of circumstances where a) you can have multiple channels concurrently active without significant cost (90 channels == 3 E1's == expensive). When you dial out from your asterisk box (if you need to), your partner turns it back into pstn/gsm traffic. Plus, you can get one provider that does all your international numbers and origination. If you are strictly pstn, you will likely need a more complicated setup involving more suppliers

OK. I meant that we were not interested in SIP as a frontend.

But the way you describe it, this possibility is certainly more promising.

Are there any suppliers you can recommend in the field?

x-console :

Quote: If Asterisk is not scalable enough, how about a public API such as http://web21c.bt.com Define 'not scalable enough'?

You mentioned earlier that Asterisk's weak points are high availability and scaling (maybe I misunderstood what you meant here).

x-console :

what are your projected numbers? concurrent calls? bhca? bhcc? call duration, message storage etc etc.

Tens of thousands calls per country a day, which translates at least to 1,000+ calls per hour per country. Call duration is very short, normally under 1 minute. Message storage does not have to be large - most of the voicemail will be retrieved and deleted by the human staff minutes after it's there.

x-console :

Aside from that, then sure; I'm a big fan of what they are doing at BT re: 21Cn. However, will they provide you with an SLA?

That's a big question.

x-console :

what if you need some custom callback they don't currently offer?

We don't need that. Just the voicemail, and SMS send / receive (these ones are optional, because Clickatell is already good enough).

x-console :

Are you happy with the fact that they may make changes to the API without notice which breaks your code?

Not happy, but we're in software business, it happens all the time. Necessary evil we learned to live with .

x-console :

It all depends on your business drivers

For now, we are interested in quick and relatively painless start.

Later, we can go for more complex and reliable solutions (obviously, in-house server is a better idea, but it requires a deployment specialist or team).

It's just we were expecting to find an equivalent of Clickatell for voice mails, but it looks like the closest thing is Web21C BT (and it's the only one).

So, to sum it up: do you think it's OK to use Web21c with needs like ours?

And - can you please recommend any of the SIP-based providers?

Thx again.

I'm not sure. I've not used the bt 21cn api for any production work as yet, and dont know anyone else that has (in telephony apps). i would suggest you do some research on that. Likewise for PSTN termination/origination partners.. it specific to what you want.. quality vs price.. specific codec's, specific routes, SLA's, secure links etc etc.

OK, I guess there is only way to find out with BT . And asking is one of the ways doing research, no?

Know any place where I can start looking for the PSTN origination partners with good value? Codecs, routes, secure links don't matter, SLA is secondary.

I found a couple via Google ads, but not sure whom to ask about their quality. It's all good on paper, you know.

I hope it's still in your field and I'm not drifting off-topic.

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I hope it's still in your field and I'm not drifting off-topic.

my field? yes, forum-topic? meh.. close enough Have a look on some of the mailing lists for pbx's like asterisk. For the UK (my domestic market) there are a handful of well known ones.. eSMS, gradwell, magrathea and gamma telecom, but you are normally better of going with someone reasonably local so you minimize your latency.