Search This Blog

Wednesday, February 18, 2009

TrapCall: Old Wine in a new Bottle (Caller ID unblocking is not Voodo)

I noticed quite a flutter on several blogs and news sites on a new service from Trapcall that allows you to "see" Caller ID even if the caller blocks the caller ID.

A layman description: Jack is an agressive sales person who loves calling his prospective customer Bob with his caller ID blocked, so that Bob will be forced to pick up the phone and have a chat with Jack.  This is a good ploy, because Bob may otherwise ignore the call if he recognizes Jack's number. (There are of course more serious situations like domestic abuse etc. reported on other sites)

So what does Bob do ? Well, Bob sets 'Call Forwarding on No Answer' and/or 'Call Forward Busy' etc. on his phone to point to a Trapcall 1-800 number. That's all.

So what happens ? Jack calls Bob. Bob gets an incoming call without an ID. He ignores it. This makes the call route to Trapcall's 1-800 # which does  its 'Voodoo' and routes the call back to Bob, who gets an incoming call again,  but this time with Bob's caller ID !! So he can now really ignore it.

How does this work ?

The SS7 protocol (that is used between almost all telephony switches these days) has 2 fields where calling information is recored. The first is CNID (Calling # Identification). This field stores the number of the caller. When you block Caller ID,  your number is masked and this field contains generic information (like Private, Anonymous) depending on the carrier.

However, there is another field, ANI (Automatic Number Identification) that will still retain the 'calling party' information. ANI is not normally exposed to users or businesses, unless you are authorized. What could be an example of authorized agencies? Well, 911 could be one. Caller ID can be spoofed easily, but ANI usually can't.  What could be another example of authorized agencies? 1-800 subscribers! Why ? Well, think about it. If I set up a 1-800 number, I am telling the carrier that I will pay for incoming calls. So even if a caller has blocked its identity, when I get the bill from the carrier, I should be able to see who called me (so the carrier can justifiably ask you for the fees). That is where ANI comes in. The carrier uses this information to present you with charges you owe them. Also, since you are a 1-800 provider, you get access to the ANI information when the call gets routed to you for similar reasons.

So that is basically what Trapcall does. It set's up a 1-800 number. When you route a call to them, it extracts ANI information (the carrier needs to authorize them to do this - so it will not always work across all carriers), places that information as 'Caller ID' information and places a call to you. Voila. You get your caller id.

But here is the catch. If most telemarketers use VoIP services like Skype,Vonage, Ribbit, Jajah or others that act as a Back to Back and place outgoing calls on behalf of the users, this trick will be useless because at best, you will get the VOIP provider's ANI and not the person making the VoIP call. Actually, it is not only restricted to B2B agents. My guess is most VoIP intermediaries will mess this information up, since they will put their own ANI (since they terminate a PSTN call and originate a new leg VoIP call)


1 comment:

  1. افضل شركة تنظيف منازل بالمدينة المنورة شركة تنظيف منازل بالمدينة المنورة
    شركة غسيل خزانات بالمدينة المنورة شركة تنظيف خزانات بالمدينة المنورة