Wednesday, June 28, 2006

Question on VOIP

Hey CEG guys and others, I'm not sure how familiar with VOIP are the readers here, but am just posting to see if anyone has some fundamental knowledge to help me out.

Have you seen or used one of Skype-In, Netzero Private Phone, AIM or the service from any other VOIP provider which gives its users a private phone number that the user can share with his world of friends. If I call my friend on his Skype-In number from say my landline phone or cell phone, the call will be first routed to the Skype servers and then be packet-switched to the user's IP address provided he is online. So, something at the Skype server side should do a PBX to IP translation. My question is, what is that? Is that like a PBX-IP gateway that supports SIP or H.323 ? Is that the only way it can be done, or does anyone know of any software alternatives? Or could it be something as simple like a normal phone system that records the incoming call and transfers it to the user's machine through a cable or something?

Also, when I call a Skype-In number, how does my telecom provider route it to the Skype's system? Does the PBX-IP translation happen before it reaches the Skype's system itslef or at the Skype's gateway? I'm clear with what happens after the voice is received at the Skype's system, but am a little confused on how exactly it gets there. Any insight is appreciated.


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Blogger Srinath said...

One option is, Skype would buy these numbers from a PSTN provider. The PSTN provider would typically route the call to a Skype's location, which would have an IP-PBX gateway which is capable of converting VoIP to PSTN and vice-versa. Once it is converted to a IP protocal oriented call, then Skype would send it to the particular user.

The other option is to buy these numbers from VoIP providers ( like nuphone, voipjet ), who would do the above said job.

On conversion hardware / software, there are many vendors who provide such hardware / software. There cannot be a pure software based approach, ( at the very least you need a card that gets the PSTN input into your computer ). There is a nice open source tool called asterisk that acts as a PBX for you ( once you have a digium card that you can fit to your computer ). And, there are lots of hardware options supplied by various vendors starting from Avaya ( for large scale systems ), Cisco to small ones like Quintum.

5:58 AM  
Blogger Padmanaban Kumar (paddu) said...

Thanks Srinath, that makes better sense. I didn't know about the digium card at all, worth exploring for my purpose, definitely.

9:08 AM  
Blogger Srinath said...

Dei Paddu - JFYI
You can reach me at or the following msgrs:

1:22 PM  
Blogger Padmanaban Kumar (paddu) said...

Thanks Srinath, I'll try to catch you online this weekend.

9:45 AM  
Anonymous Sheetal C said...

Great,nifty explanation Srinath. Was excited to comment abt something I have been playing with.. but seeing your answer, there is nothing more I can add!

9:47 AM  
Anonymous Anonymous said... that all ur queries are spares me the time....hi sheetal how are u?
Paddu do u think he will remember me?
Dai, en da eppidi blade panare. Ethume puriyale :S

4:16 PM  
Blogger Padmanaban Kumar (paddu) said...

It will be nice if the anonymous folks can identify themselves.

2:18 AM  

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