Blue Box courtesy of the Jolly Roger

To quote Karl Marx, blue boxing has always been the most noble form of

phreaking. As opposed to such things as using an MCI code to make a free

fone call, which is merely mindless pseudo-phreaking, blue boxing

is actual interaction with the Bell System toll network.

It is likewise advisable to be more cautious when blue boxing, but the

careful phreak will not be caught, regardless of what type of switching

system he is under.

In this part, I will explain how and why blue boxing works, as well as

where. In later parts, I will give more practical information for blue

boxing and routing information. To begin with, blue boxing is simply

communicating with trunks. Trunks must not be confused with subscriber

lines (or "customer loops") which are standard telefone lines. Trunks are

those lines that connect central offices. Now, when trunks are not in

use (i.e., idle or "on-hook" state) they have 2600Hz applied to them. If

they are two-way trunks, there is 2600Hz in both directions. When a trunk

IS in use (busy or "off-hook" state), the 2600Hz is removed from the side

that is off-hook. The 2600Hz is therefore known as a supervisory

signal, because it indicates the status of a trunk; on hook (tone) or

off-hook (no tone). Note also that 2600Hz denoted SF (single frequency)

signalling and is "in-band." This is very important. "In-band" means that

is within the band of frequencies that may be transmitted over normal

telefone lines. Other SF signals, such as 3700Hz are used also. However,

they cannot be carried over the telefone network normally (they are

"out-of-band" and are therefore not able to be taken advantage of as

2600Hz is. Back to trunks. Let's take a hypothetical phone call. You pick

up your fone and dial 1+806-258-1234 (your good friend in Amarillo, Texas).

For ease, we'll assume that you are on #5 Crossbar switching and not in the

806 area. Your central office (CO) would recognize that 806 is a foreign

NPA, so it would route the call to the toll centre that serves you.

[For the sake of accuracy here, and for the more experienced readers,

note that the CO in question is a class 5 with LAMA that uses out-of-band

SF supervisory signalling]. Depending on where you are in the country,

the call would leave your toll centre (on more trunks) to another toll

centre, or office of higher "rank". Then it would be routed to central

office 806-258 eventually and the call would be completed.





A.... you

CO1=your central office

TC1.. your toll office.

TC2.. toll office in Amarillo.

CO2.. 806-258 central office.

B.... your friend (806-258-1234)


In this situation it would be realistic to say that CO2 uses SF

in-band (2600Hz) signalling, while all the others use out-of-band signal-

ling (3700Hz). If you don't understand this, don't worry. I am pointing

this out merely for the sake of accuracy. The point is that while you

are connected to 806-258-1234, all those trunks from YOUR central office

(CO1) to the 806-258 central office (CO2) do *NOT* have 2600Hz on them,

indicating to the Bell equipment that a call is in progress and the trunks

are in use.

Now let's say you're tired of talking to your friend in Amarillo, so you

send a 2600Hz down the line. This tone travels down the line to your

friend's central office (CO2) where it is detected. However, that CO thinks

that the 2600Hz is originating from Bell equipment, indicating to it

that you've hung up, and thus the trunks are once again idle (with 2600Hz

present on them). But actually, you have not hung up, you have fooled the

equipment atyour friend's CO into thinking you have. Thus,it disconnects

him and resets the equipment to prepare for the next call. All this happens

very quickly (300-800ms for step-by-step equipment and 150-400ms for other

equipment). When you stop sending 2600Hz (after about a second), the

equipment thinks that another call is coming towards

--> on hook, no tone -->off hook.

Now that you've stopped sending 2600Hz, several things happen:


1) A trunk is seized.

2) A "wink" is sent to the CALLING end from the CALLED end indicating that

the CALLED end (trunk) is not ready to receive digits yet.

3) A register is found and attached to the CALLED end of the trunk within

about two seconds (max).

4) A start-dial signal is sent to the CALLING end from the CALLED end

indicating that the CALLED end is ready to receive digits.

Now, all of this is pretty much transparent to the blue boxer. All he

really hears when these four things happen is a <beep><kerchunk>. So,

seizure of a trunk would go something like this:


1> Send a 2600Hz

2> Terminate 2600Hz after 1-2 secs.

3> [beep][kerchunk]


Once this happens, you are connected to a tandem that is ready to obey your

every command. The next step is to send signalling information in order to

place your call. For this you must simulate the signalling used by

operators and automatic toll-dialing equipment for use on trunks. There are

mainly two systems, DP and MF. However, DP went out with the dinosaurs, so

I'll only discuss MF signalling. MF (multi-frequency) signalling is the

signalling used by the majority of the inter- and intra-lata network. It is

also used in international dialing known as the CCITT no.5 system.

MF signals consist of 7 frequecies, beginning with 700Hz and separated by

200Hz. A different set of two of the 7 frequencies represent the digits 0

thru 9, plus an additional 5 special keys. The frequencies and uses are as



Frequencies (Hz) Domestic Int'l


700+900 1 1

700+1100 2 2

900+1100 3 3

700+1300 4 4

900+1300 5 5

1100+1300 6 6

700+1500 7 7

900+1500 8 8

1100+1500 9 9

1300+1500 0 0

700+1700 ST3p Code 1

900+1700 STp Code 1

1100+1700 KP KP1

1300+1700 ST2p KP2

1500+1700 ST ST

The timing of all the MF signals is a nominal 60ms, except for KP, which

should have a duration of 100ms. There should also be a 60ms silent period

between digits. This is very flexible however, and most Bell equipment will

accept outrageous timings. In addition to the standard uses

listed above, MF pulsing also has expanded usages known as "expanded

inband signalling" that include such things as coin collect, coin return,

ringback, operator attached, and operator attached, and operator

released. KP2, code 11, and code 12 and the ST_ps (STart "primes" all have

special uses which will be mentioned only briefly here.

To complete a call using a blue box once seizure of a trunk has been

accomplished by sending 2600Hz and pausing for the <beep><kerchunk>, one

must first send a KP. This readies the register for the digits that follow.

For a standard domestic call, the KP would be followed by either 7 digits

(if the call were in the same NPA as the seized trunk) or 10 digits (if the

call were not in the same NPA as the seized trunk). [Exactly like dialing

normal fone call]. Following either the KP and 7 or 10 digits, a STart is

sent to signify that no more digits follow. Example of a complete call:


1> Dial 1-806-258-1234

2> wait for a call-progress indication (such as ring,busy,recording,etc.)

3> Send 2600Hz for about 1 second.

4> Wait for about ll-progress indication (such as ring,busy,recording,etc.)

5> Send KP+305+994+9966+ST

The call will then connect if everything was done properly. Note that if a

call to an 806 number were being placed in the same situation, the are code

would be omitted and only KP + seven digits + ST would be sent.

Code 11 and code 12 are used in international calling to request

certain types of operators. KP2 is used in international calling to route a

call other than by way of the normal route, whether for economic or

equipment reasons. STp, ST2p, and ST3p (prime, two prime, and three prime)

are used in TSPS signalling to indicate calling type of call (such as

coin-direct dialing.


It all started here................... Exodus