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[c6em]

How does it determine that the presented public CLID is fake?
Surely to do this you need access to the 'real system billing CLID' to compare it with - which I understood only BT as network operator have and will be accessible to them and to the emergency services only.

[Bowdon]

I know on spam emails, if you look at the properties of the email it says something like 'not designated sender'. So the email systems let spam through even though it fails some of the checks. I guess so as not to mistakenly block any genuine emails.

I'm thinking the phone blocking system will be like that. I suspect that instead of enforcing automatic blocks they will have people put it on a block list individually. Then if they get a certain amount of individuals blocking they could move that number on to a nationwide block list.

[aesmith]

If you're talking about a standard analogue line, what information is actually presented with the incoming call?   I wonder if the "fake" designation is actually based on reports from elsewhere, not the properties of the call itself.

[sevenlayermuddle]

It's a while ago now that I actually worked on PSTN protocols.  My memory is hazy and whilst I could dig out the protocol specs I'm not sure I could face it, my recollection is as follows...

When a legitimate user wants to display a number that is not the calling party's number, it gets passed an entirely different parameter, 'presentation number'.  This calling party number is still present all the way to destination exchange, and could be used by BT switches to identify the rogue caller, regardless of 'presentation number'.   

Note also that Calling Party Number is normally present too, even if it has been 'withheld'.  Callers who 'withhold' their number simply cause a bit to be set, indicating it should not be presented to the called subscriber.

[benji09]

  I have used Sipgate's VOIP service for years now. After a year of having the line, I decided to try to change the phone number. Unfortunately I ended up with an additional phone. So I kept both lines, and always give out the original VOIP line to anybody that wants that a phone number to call me. I VERY rarely get junk calls on that number. But I still get an occasional call on my original landline number even now........ But I have found TPS has helped a lot.  Another reason I think that people don't pester me with junk calls is that I am quite abusive to unwanted callers................

[jelv]

There's official fake phone numbers you can give out without the risk of sending nuisance calls to someone else:

http://stakeholders.ofcom.org.uk/telecoms/numbering/guidance-tele-no/numbers-for-drama

[aesmith]

It's a while ago now that I actually worked on PSTN protocols.  My memory is hazy and whilst I could dig out the protocol specs I'm not sure I could face it, my recollection is as follows...

When a legitimate user wants to display a number that is not the calling party's number, it gets passed an entirely different parameter, 'presentation number'.  This calling party number is still present all the way to destination exchange, and could be used by BT switches to identify the rogue caller, regardless of 'presentation number'.   

Note also that Calling Party Number is normally present too, even if it has been 'withheld'.  Callers who 'withhold' their number simply cause a bit to be set, indicating it should not be presented to the called subscriber.

My question was how much of that information is presented down an analogue line.  Not much I suspect, and in fact I suspect it's not presented to the called subscriber on ISDN either.

[WWWombat]

If CLI is to be restricted, it won't be passed out of a signalling connection that goes outside BTs control.

If anyone wants to see the NICC rules, take a look at ND1016
http://www.niccstandards.org.uk/publications/public-net.cfm

[NewtronStar]

I'll just keep the CPR call blocker installed as it seems to be 100% effective and I miss those international Indian calls fake or withheld caller ID's NOT 

[burakkucat]

There's official fake phone numbers you can give out without the risk of sending nuisance calls to someone else:

http://stakeholders.ofcom.org.uk/telecoms/numbering/guidance-tele-no/numbers-for-drama

When pushed, in a not much time to think situation, I have actually quoted the main switchboard number for New Scotland Yard!

(020 7230 1212 is the modern-day equivalent of WHItehall 1212)

[NewtronStar]

Just had a look into BT blocking cost ->

BT has a "Choose to Refuse" service which will cost you £90 a year, whereas the CPR Call Blocker costs just £39.99 as a one off payment. CPR Call Blocker is the most cost effective way to stop any unwanted calls to your home or office.

[sevenlayermuddle]

My question was how much of that information is presented down an analogue line.  Not much I suspect, and in fact I suspect it's not presented to the called subscriber on ISDN either.

The only part of the PSTN that has been analogue, since early 1980s, is the last hop to subscriber.  The terminating exchange would thus make a decision as to which (digital) signalling parameter should be presented...  'Calling party number' or 'presentation number' or neither.   That is then signalled to the called party on the analogue line, with analogue encoding, as a pre-emption to the 'ring' signal.

But the point is, BT are suggesting they will do diversion within their own network and they can do that entirely on digital parameters, the analogue hop to subscriber is not really relevant

I stress again though, I am working from hazy memory here.   My involvement in these issues was quite some time ago.   

[NewtronStar]

I stress again though, I am working from hazy memory here.   My involvement in these issues was quite some time ago.   

VOIP is also blocked in these units if that is were your concern lays ?

[sevenlayermuddle]

I stress again though, I am working from hazy memory here.   My involvement in these issues was quite some time ago.   

VOIP is also blocked in these units if that is were your concern lays ?

Sorry I don't follow, or see the relevance to anything I posted?   

[NewtronStar]

I stress again though, I am working from hazy memory here.   My involvement in these issues was quite some time ago.   

VOIP is also blocked in these units if that is were your concern lays ?

Will need to wait and see how good it is.

But I've no idea how that translates to the modern IP age, and also no idea how much effort BT or other CPs would really want to put into it.

Sorry I don't follow, or see the relevance to anything I posted?   

It can block IP or VOIP calls