==Phrack Magazine==



                  Volume Five, Issue Forty-Six, File 8 of 28



****************************************************************************





                     The Wonderful World of Pagers



                            by Erik Bloodaxe



Screaming through the electromagnet swamp we live in are hundreds of

thousands of messages of varying degrees of importance.  Doctors,

police, corporate executives, housewives and drug dealers all find

themselves constantly trapped at the mercy of a teeny little box:

the pager.



Everyone has seen a pager; almost everyone has one.  Over 20 million

pagers are on the streets in the US alone, sorting out their particular

chunk of the radio-spectrum.  Another fifty-thousand more are

put into service each day.



But what the hell are these things really doing?  What more can we

do with them than be reminded to call mom, or to "pick up dry-cleaning?"



Lots.





** PROTOCOLS **



Pagers today use a variety of signalling formats such as POCSAG, FLEX

and GOLAY.  The most common by far is POCSAG (Post Office Standardization

Advisory Group), a standard set by the British Post Office and adopted

world-wide for paging.



POCSAG is transmitted at three transmission rates--512, 1200 and 2400 bps.

Most commercial paging companies today use at least 1200, although many

companies who own their own paging terminals for in-house use transmit

at 512.  Nationwide carriers (SkyTel, PageNet, MobileComm, etc.) send

the majority of their traffic at 2400 to make the maximum use of

their bandwidth.  In other words, the faster they can deliver pages,

the smaller their queue of outgoing pages is.  Although these

carriers have upgraded their equipment in the field to broadcast at

2400 (or plan to do so in the near future), they still send out

some pages at 1200 and 512 to accommodate their customers with older

pagers.  Most 512 and 1200 traffic on the nationwide services is

numeric or tone-only pages.



POCSAG messages are broadcast in batches.  Each batch is comprised of 8

frames, and each frame contains two codewords separated by a

"synchronization" codeword.  A message can have as many codewords

as needed to deliver the page and can stretch through several batches

if needed.  The end of a complete message is indicated by a "next address"

codeword.  Both addressing and user data are sent in the codewords, the

distinction being the least significant bit of the codeword:

0 for address data, and 1 for user-data.



Standard alphanumeric data is sent in a seven-bit format, with each codeword

containing 2 6/7 characters.  A newer 8-bit alphanumeric format is

implemented by some carriers which allow users to send data such as

computer files, graphics in addition to regular alphanumeric messages.

The 8 bit format allows for 2.5 characters per codeword.



Numeric data is 4 bit, allowing up to 5 numbers to be transmitted per

codeword.  Tone and voice pages contain address information only.



(NOTE:  Pager data uses BCH 32,21 for encoding.  I don't imagine

 very many of you will be trying to decode pager data by building your

 own decoders, but for those of you who may, take my interpretation

 of POCSAG framing with a grain of salt, and try to dig up the

 actual POCSAG specs.)



** THE PAGING RECEIVER **



Paging receivers come in hundreds of shapes and sizes, although the vast

majority are manufactured by Motorola.  Numeric pagers comprise over

fifty percent all pagers in use.   Alphanumeric comprises about thirty

percent, with tone and voice pagers making up the remainder.



Pagers are uniquely addressed by a capcode.  The capcode is usually six

to eight digits in length, and will be printed somewhere on the pager

itself.  Many pager companies assign customers PIN numbers, which are

then cross-referenced to a given capcode in databases maintained by

the service provider.  PIN numbers have no other relationship

to the capcode.



Tone pagers are by far the most limited paging devices in use.

When a specified number has been called, an address only message

is broadcast, which causes the intended receiver to beep.  Wow.

Tone pagers usually have 4 capcodes, which can correspond to

different locations to call back.  Voice pagers are similar, except

they allow the calling party to leave a 15 to 30 second message.

The voice message is broadcast immediately after the capcode of the

receiver, which unsquelches the device's audio.



Numeric pagers, although seemingly limited by their lack of display

options have proven otherwise by enterprising users.  Most numeric

data sent is obviously related to phone numbers, but numerous users

have developed codes relating to various actions to be carried out

by the party being paged.  The most prolific users of this have

been the Chinese who have one of the most active paging networks

in the world.  I suppose the next biggest users of code-style numeric

paging would be drug dealers.  (2112 0830 187 -- get to the fucking

drop site by 8:30 or I'll bust a cap in your ass!)  :)



Alphanumeric pagers are most often contacted through a dedicated

service that will manually enter in the message to be sent onto the

paging terminal.  One such service, NDC, offers its phone-answering

and message typing services to various pager companies.  Next time

you are talking to a pager operator, ask him or her if they are at

NDC.  They probably are.



In addition to the capcode, pagers will have an FCC ID number, a serial

number, and most importantly, the frequency that the device has been

crystaled for imprinted on the back of the device.  Although technology

exists that would allow pagers to listen on a number of frequencies

by synthesizing the frequency rather than using a crystal, pager

manufacturers stick to using crystals to "keep the unit cost down."



Pagers may have multiple capcodes by which they can be addressed by.

Multiple capcodes are most often used when a person has subscribed to

various services offered by their provider, or when the subscriber is

part of a group of individuals who will all need to receive the same

page simultaneously (police, EMTs, etc.).



Most low-cost pagers have their capcode stored on the circuit board

in a PAL.  Most paging companies will completely exchange pagers

rather than remove and reprogram the PAL, so I don't think

it's worth it for any experimenter to attempt.  However, like most

Motorola devices, many of their paging products can be reprogrammed

with a special serial cable and software.  Reprogramming software

is usually limited to changing baud rates, and adding capcodes.



Additionally, some units can be reprogrammed over the air by the

service provider.  Using a POCSAG feature known as OTP (over the air

programming) the service provider can instruct the paging receiver to

add capcodes, remove capcodes, or even shut itself down in the case

of non-payment.



** SERVICES **



With the growing popularity of alphanumeric pagers, many service providers

have decided to branch out into the information business.  The most

common of these services is delivery of news headlines.  Other services

include stock quotes, airline flight information, voice mail and

fax reception notification, and email.  Of course, all of these services

are available for a small additional monthly premium.



Email is probably the single coolest thing to have sent to your

alpha pager.  (Unless you subscribe to about a zillion mailing lists)

Companies like SkyTel and Radiomail give the user an email address

that automatically forwards to your paging device.

IE: [email protected]  Several packages exist for forwarding

email from a UNIX system by sending stripping down the email to

pertinent info such as FROM and SUBJECT lines, and executing a script

to send the incoming mail out via a pager terminal data port.

One such program is IXOBEEPER, which can be found with an archie

query.



Radiomail's founder, (and rather famous ex-hacker in his own right - go

look at ancient ComputerWorld headlines), Geoff Goodfellow had devised

such a method back in the late 70's.  His program watched for incoming

email, parsed the mail headers, and redirected the FROM and SUBJECT

lines to his alphanumeric pager.  Obviously, not many people had

alphanumeric pagers at all, much less email addresses on ARPANET

back in the 70's, so Geoff's email pager idea didn't see much

wide-spread use until much later.



Two RFC's have been issued recently regarding paging and the Internet.

RFC 1568, the Simple Network Paging Protocol, acts similarly to SMTP.

Upon connecting to the SNPP port the user issues commands such as:



        PAGE followed by pager telephone number

        MESS followed by the alpha or numeric message

        SEND

      & QUIT



RFC 1568 has met with some opposition in the IETF, who don't consider

it worthwhile to implement a new protocol to handle paging, since it

can be handled easily using other methods.



The other RFC, number 1569, suggests that paging be addressed in a rather

unique manner.  Using the domain TPC.INT, which would be reserved for

services that necessitate the direct connection to The Phone Company,

individual pagers would be addressed by their individual phone numbers.

Usernames would be limited to pager-alpha or pager-numeric to represent

the type of pager being addressed.  For example, an alpha-page being sent to

1-800-555-1212 would be sent as [email protected]



** PAGING TERMINAL DATA PORTS **



Many services offer modem connections to pager terminals so that

computer users can send pages from their desks using software packages

like WinBeep, Notify! or Messenger.  All of these services connect to

the pager terminal and speak to it using a protocol known as

IXO.



Upon connection, a pager terminal identifies itself with the following:



ID=



(I bet you always wondered what the hell those systems were)

Paging terminals default to 300 E71, although many larger companies

now have dialups supporting up to 2400.



Many such systems allow you to manually enter in the appropriate information

by typing a capital "M" and a return at the ID= prompt.  The system will then

prompt you for the PIN of the party you wish to page, followed by a prompt

for the message you wish to send, followed by a final prompt asking if you

wish to send more pages.  Not every pager terminal will support a manual

entry, but most do.



All terminals support the IXO protocol.  As there are far too many

site specific examples within the breadth of IXO, we will concentrate on

the most common type of pager services for our examples.



[  Sample IXO transaction of a program sending the message ABC to PIN 123

   gleened from the IXOBeeper Docs                                         ]



Pager Terminal                          YOU

--------------------------------------------------------------

                                        

ID=

                                        PG1

Processing - Please Wait

                                        



ACK 

[p 

                                        123

                                        ABC

                                        17;



ACK 

                                        

EOT 





The checksum data came from:



STX     000 0010

1       011 0001

2       011 0010

3       001 0011

    000 1101

A       100 0001

B       100 0010

C       100 0011

    000 1101

ETX     000 0011

----------------

     1 0111 1011

----------------

     1    7    ;  Get it?  Get an ASCII chart and it will all make sense.





Note:  Everything in the paging blocks, from STX to ETX inclusive are used

       to generate the checksum.  Also, this is binary data, guys...you can't

       just type at the ID= prompt and expect to have it recognized as IXO.

       It wants specific BITS.  Got it?  Just checking...





** PAGER FREQUENCIES - US **



[Frequencies transmitting pager information are extremely easy to

 identify while scanning.   They identify each batch transmission

 with a two-tone signal, followed by bursts of data.  People with

 scanners may tune into some of the following frequencies to

 familiarize themselves with this distinct audio.]



Voice Pager Ranges:      152.01   - 152.21

                         453.025  - 453.125

                         454.025  - 454.65

                         462.75   - 462.925



Other Paging Ranges:      35.02   -  35.68

                          43.20   -  43.68

                         152.51   - 152.84

                         157.77   - 158.07

                         158.49   - 158.64

                         459.025  - 459.625

                         929.0125 - 931.9875



** PAGER FREQUENCIES - WORLD **



Austria         162.050  - 162.075         T,N,A

Australia       148.100  - 166.540         T,N,A

                411.500  - 511.500         T,N,A

Canada          929.025  - 931-975         T,N,A

                138.025  - 173.975         T,N,A

                406.025  - 511.975         T,N,A

China           152.000  - 172.575           N,A

Denmark                    469.750           N,A

Finland                    450.225         T,N,A

                146.275  - 146.325         T,N,A

France          466.025  - 466.075         T,N,A

Germany         465.970  - 466.075         T,N,A

                           173.200         T,N,A

Hong Kong                  172.525           N,A

                           280.0875        T,N,A

Indonesia       151.175  - 153.050             A

Ireland         153.000  - 153.825         T,N,A

Italy                      466.075         T,N,A

                           161.175         T,N

Japan           278.1625 - 283.8875         T,N

Korea           146.320  - 173.320         T,N,A

Malaysia        152.175  - 172.525           N,A,V

                           931.9375          N,A

Netherlands     156.9865 - 164.350         T,N,A

New Zealand     157.925  - 158.050         T,N,A

Norway          148.050  - 169.850         T,N,A

Singapore                  161.450           N,A

                           931.9375          N,A

Sweden                     169.8           T,N,A

Switzerland                149.5           T,N,A

Taiwan                     166.775           N,A

                           280.9375          N,A

Thailand                   450.525           N,A

                172.525  - 173.475           N,A

UK              138.150  - 153.275         T,N,A

                454.675  - 466.075         T,N,A



T = Tone

N = Numeric

A = Alphanumeric

V = Voice





** INTERCEPTION AND THE LAW **



For many years the interception of pages was not considered an

invasion of privacy because of the limited information provided

by the tone-only pagers in use at the time.  In fact, when

Congress passed the Electronic Communications Privacy Act in 1986

tone-only pagers were exempt from its provisions.



According to the ECPA, monitoring of all other types of paging signals,

including voice, is illegal.  But, due to this same law, paging

transmissions are considered to have a reasonable expectation to

privacy, and Law Enforcement officials must obtain a proper court

order to intercept them, or have the consent of the subscriber.



To intercept pages, many LE-types will obtain beepers programmed with

the same capcode as their suspect.  To do this, they must contact

the paging company and obtain the capcode associated with the person

or phone number they are interested in.  However, even enlisting

the assistance of the paging companies often requires following

proper legal procedures (warrants, subpoenas, etc.).



More sophisticated pager-interception devices are sold by a variety

of companies.  SWS Security sells a device called the "Beeper Buster"

for about $4000.00.  This particular device is scheduled as

a Title III device, so any possession of it by someone outside

a law enforcement agency is a federal crime.  Greyson Electronics

sells a package called PageTracker that uses an ICOM R7100

in conjunction with a personal computer to track and decode pager

messages.  (Greyson also sells a similar package to decode

AMPS cellular messages from forward and reverse channels called

"CellScope.")



For the average hacker-type, the most realistic and affordable option

is the Universal M-400 decoder.  This box is about 400 bucks and

will decode POCSAG at 512 and 1200, as well as GOLAY (although I've never

seen a paging service using GOLAY.)  It also decodes CTCSS, DCS, DTMF,

Baudot, ASCII, SITOR A & B, FEC-A, SWED-ARQ, ACARS, and FAX.  It

takes audio input from any scanners external speaker jack, and

is probably the best decoder available to the Hacker/HAM for the price.



Output from the M400 shows the capcode followed by T, N or A (tone, numeric

or alpha) ending with the message sent.  Universal suggests hooking

the input to the decoder directly to the scanner before any de-emphasis

circuitry, to obtain the true signal.  (Many scanners alter the audio

before output for several reasons that aren't really relevant to this

article...they just do. :) )



Obviously, even by viewing the pager data as it streams by is of little

use to anyone without knowing to whom the pager belongs to.  Law Enforcement

can get a subpoena and obtain the information easily, but anyone else

is stuck trying to social engineer the paging company.  One other alternative

works quite well when you already know the individuals pager number,

and need to obtain the capcode (for whatever reason).



Pager companies will buy large blocks in an exchange for their customers.

It is extremely easy to discover the paging company from the phone number

that corresponds to the target pager either through the RBOC or by paging

someone and asking them who their provider is when they return your call.

Once the company is known, the frequencies allocated to that company

are registered with the FCC and are public information.  Many CD-ROMs

are available with the entire FCC Master Frequency Database.

(Percon sells one for 99 bucks that covers the whole country -

716-386-6015)  Libraries and the FCC itself will also have this information

available.



With the frequency set and a decoder running, send a page that will be

incredibly easy to discern from the tidal wave of pages spewing

forth on the frequency.  (6666666666, THIS IS YOUR TEST PAGE, etc...)

It will eventually scroll by, and presto!  How many important people

love to give you their pager number?



** THE FUTURE **



With the advent of new technologies pagers will become even more

present in both our businesses and private lives.  Notebook computers

and PDAs with PCMCIA slots can make use of the new PCMCIA pager cards.

Some of these cards have actual screens that allow for use without the

computer, but most require a program to pull message data out.  These

cards also have somewhat large storage capacity, so the length of

messages have the option of being fairly large, should the service

provider allow them to be.



With the advent of 8-bit alphanumeric services, users with PCMCIA pagers

can expect to receive usable computer data such as spreadsheet

entries, word processing documents, and of course, GIFs.  (Hey, porno

entrepreneurs:  beeper-porn!  Every day, you get a new gif sent to your

pagecard!  Woo Woo.  Sad thing is, it would probably sell.)



A branch of Motorola known as EMBARC (Electronic Mail Broadcast to A

Roaming Computer) was one of the first to allow for such broadcasts.

EMBARC makes use of a proprietary Motorola protocol, rather than

POCSAG, so subscribers must make use of either a Motorola NewsStream

pager (with nifty serial cable) or a newer PCMCIA pager.  Messages are

sent to (and received by) the user through the use of special client

software.



The software dials into the EMBARC message switch accessed through

AT&T's ACCUNET packet-switched network.  The device itself is used

for authentication (most likely its capcode or serial number)

and some oddball protocol is spoken to communicate with the switch.



Once connected, users have the option of sending a page out, or

retrieving pages either too large for the memory of the pager, or

from a list of all messages sent in the last 24 hours, in case the

subscriber had his pager turned off.



Additionally, the devices can be addressed directly via x.400

addresses.  (X.400: The CCITT standard that covers email address

far too long to be worth sending anyone mail to.)  So essentially,

any EMBARC customer can be contacted from the Internet.



MTEL, the parent company of the huge paging service SkyTel, is

implementing what may be the next generation of paging technologies.

This service, NWN, being administrated by MTEL subsidiary Destineer,

is most often called 2-way paging, but is more accurately Narrowband-PCS.



The network allows for the "pager" to be a transceiver.  When a page

arrives, the device receiving the page will automatically send back

an acknowledgment of its completed reception.  Devices may also

send back some kind of "canned response" the user programs.  An example

might be:  "Thanks, I got it!" or "Why on Earth are you eating up my

allocated pages for the month with this crap?"



MTEL's service was awarded a Pioneers Preference by the FCC, which gave them

access to the narrowband PCS spectrum before the auctions.  This is a big

deal, and did not go unnoticed by Microsoft.  They dumped cash into the

network, and said the devices will be supported by Chicago.  (Yeah,

along with every other device on the planet, right?  Plug and Pray!)



The network will be layed out almost identically to MTEL's existing paging

network, using dedicated lines to connect towers in an area to a central

satellite up/downlink.  One key difference will be the addition of

highly somewhat sensitive receivers on the network, to pick up the ACKs

and replies of the customer units, which will probably broadcast at

about 2 or 3 watts.  The most exciting difference will be the

speed at which the network transmits data:  24,000 Kbps.  Twenty-four

thousand.  (I couldn't believe it either.  Not only can you get your

GIFs sent to your pager, but you get them blinding FAST!)  The actual

units themselves will most likely look like existing alphanumeric pagers

with possibly a few more buttons, and of course, PCMCIA units will

be available to integrate with computer applications.



Beyond these advancements, other types of services plan on offering

paging like features.  CDPD, TDMA & CDMA Digital Cellular and ESMR

all plan on providing a "pager-like" option for their customers.

The mere fact that you can walk into a K-Mart and buy a pager

off a rack would indicate to me that pagers are far to ingrained into

our society, and represent a wireless technology that doesn't scare

or confuse the yokels.  Such a technology doesn't ever really go away.





** BIBLIOGRAPHY **



Kneitel, Tom, "The Secret Life of Beepers," _Popular Communications_,

         p. 8, July, 1994.



O'Brien, Michael, "Beep! Beep! Beep!," _Sun Expert_, p. 17, March, 1994.



O'Malley, Chris, "Pagers Grow Up," _Mobile Office_, p. 48, August, 1994.