CALLING LINE IDENTIFICATION PRESENTATION

(CLIP)

The Way ahead…• Calling-line identification• Operation• Uses it• Blocking• Trapping• Spoofing• Disabling• Enabling

Calling-line identification• The calling number and the billing (or subscriber) name where available.

• When an originating phone switch sends out a phone number as caller ID, the telephone company receiving the call is responsible for looking up the name of the subscriber in a database.

• Cell phone companies must support interconnecting trunks to a significant number of Wireline and PSTN access carriers. – PSTN :- The combination of the interconnected networks and the single numbering plan make it

possible for any phone in the world to dial any other phone.

Operation

• Caller ID information is sent to the called party by the telephone switch as an analog data stream using modulation.

• Database are used to Identify the caller information.• E.g. For 800 numbers, they may report a string such as TOLLFREE

NUMBER if the name is not available in a database.

Uses it

• Telemarketing– Some telemarketers have used caller ID itself for marketing– E.g. an 800 number and the text string "FREE MONEY" or "FREE PLANE

TICKETS" as the name to be displayed on the caller ID.

• ISPs– Some ISPs providing dial-up access require the customer to use CNID to

prevent abuse of the account by unauthorized callers.

• Mobile providers

Blocking

• Blocking is the common term for preventing the display of a calling number.

• By dialing a special code before making a call to block the calling number.

• E.g. code is *67, "PRIVATE" or "WITHHELD

Trapping

• if you block your number, it can still be trapped as it is still sent through the telephone company network.

• When the local number is called by a customer who is blocking their caller ID, the local number is forwarded to a toll-free number, where the number of the calling party is passed on to and the owner of the local number can receive the information.

• When a customer rejects an incoming blocked call it is routed to TrapCall, who in turn traps the number and reroutes the call back to the cellphone user with the Caller ID displayed giving the customer the option to answer the call or reject it once more to send it back to TrapCall where the second call will be sent to voicemail.

Spoofing

• Caller ID is a simple string of data that can be read and generated very simply by small computer programs and even some inexpensive devices.

• VoIP providers use Caller ID replacement to save local plan minutes.• E.g. Skype service provider.

Disabling

• On GSM mobile networks, callers may dial #31# before the number they wish to call to disable it.

Enabling

• On GSM mobile networks, callers may dial *31# before the number they wish to call to enable caller ID.