AOH :: P40-06.TXT

Cellular Telephony, Part II




                                ==Phrack Inc.==

                     Volume Four, Issue Forty, File 6 of 14

  ***************************************************************************
  *                                                                         *
  *                            Cellular Telephony                           *
  *                                 Part II                                 *
  *                                                                         *
  *                                    by                                   *
  *                               Brian Oblivion                            *
  *                                                                         *
  *                                                                         *
  * Courtesy of:       Restricted-Data-Transmissions (RDT)                  *
  *                  "Truth Is Cheap, But Information Costs."               *
  *                                                                         *
  *                                                            June 1, 1992 *
  ***************************************************************************

In Phrack 38, I discussed the history of cellular telephony, monitoring
techniques, and a brief description of its predecessors.  In Part II, I'll
describe the call processing sequences for land-originated and mobile-
originated calls, as well as the signaling formats for these processes.  I
apologize for the bulk of information, but I feel it is important for anyone
who is interested in how the network communicates.  Please realize that there
was very little I could add to such a cut and dried topic, and that most is
taken verbatim from Industry standards, with comments and addendum salt and
peppered throughout.


Call-Processing Sequences


   Call-Processing Sequence for Land-Originated Calls


 MTSO                       Cell Site                     Mobile Unit
 ------------------------------------------------------------------------------
                            1 -- Transmits setup channel data on paging channel
                            2 ----------------------------Scans and locks on
                                                          paging channel
 Receives incoming call --- 3
 and performs translations

 Sends paging message ----- 4
 to cell site
                            5 -- Reformats paging
                                 message
                            6 -- Sends paging message
                                 to mobile unit via
                                 paging channel
                            7 ----------------------------Detects Page
                            8 ----------------------------Scans and locks on
                                                          access channel
                            9 ----------------------------Seizes setup channel
                           10 ----------------------------Acquires sync
                           11 ----------------------------Sends service request
                           12 -- Reformats service request
                           13 -- Performs directional locate
                           14 -- Sends service request to MTSO
 Selects voice channel --- 15
 Sends tx-on command to -- 16
 cell site
                           17 -- Reformats channel designation message
                           18 -- Sends channel designation message to mobile
                                 unit via access channel
                           19 -----------------------------Tunes to voice
                                                           channel
                           20 -----------------------------Transponds SAT
                           21 -- Detects SAT
                           22 -- Puts on-hook on trunk
 Detects off-hook -------- 23
 Sends alert order ------- 24
                           25 -- Reformats alert order
                           26 -- Sends alert order to mobile unit via blank-
                                 and-burst on voice channel
                           27 -----------------------------Alerts User
                           28 -----------------------------Sends 10-kHz tone
                           29 -- Detects 10-kHz tone
                           30 -- Puts on-hook on trunk
 Detects on-hook --------- 31
 Provides audible ring --- 32
                           33 -- Detects absence of 10-kHz tone
                           34 -- Puts off-hook on trunk
 Detects off-hook -------- 35
 Removes audible ring ---- 36
 and completes connection

                         Time


              Call-Processing Sequence for Mobile-Originated Calls

 MTSO                       Cell Site                     Mobile Unit
 ------------------------------------------------------------------------------
                            1 -- Transmits setup channel
                                 data on paging channel
                            2 --------------------------- Scans and locks-on
                                                          paging channel
                            3 --------------------------- User initiates call
                            4 --------------------------- Scans and locks-on
                                                          access channel
                            5 --------------------------- Seizes setup channel
                            6 --------------------------- Acquires sync
                            7 --------------------------- Sends service request
                            8 -- Reformats service request
                            9 -- Performs directional Locate
                           10 -- Sends service request to MTSO
Selects voice channel ---- 11
Sends tx-on command to --- 12
cell site
                           13 -- Reformats channel designation message
                           14 -- Sends channel designation message to mobile
                                 unit via access channel
                           15 --------------------------- Tunes to voice
                                                          channel
                           16 --------------------------- Transponds SAT
                           17 -- Detects SAT
                           18 -- Puts off-hook on trunk
Detects off-hook --------- 19
Completes call through --- 20
network Time

Let me review the frequency allocation for Wireline and non-Wireline systems.
Remember that the Wireline service is usually provided by the area's telephone
company, in my area that company is NYNEX.  The non-Wireline companies are
usually operated by other carriers foreign to the area, in my area we are
serviced by Cellular One (which is owned by Southwestern Bell).  Each company
has its one slice of the electro-magnetic spectrum.  The coverage is not
continuous, remember that there are also 800 MHz trunked business systems that
also operate in this bandwidth.  Voice channels are 30 KHz apart and the Data
channels are 10 KHz apart.


Frequency Range         Use
----------------------------------------------------------------------
870.000 - 879.360       Cellular One (mobile input 825.000 - 834.360)
880.650 - 890.000       NYNEX (mobile input 835.650 - 845.500)
890.000 - 891.500       Cellular One (mobile input 845.000 - 846.500)
891.500 - 894.000       NYNEX (mobile input 846.500 - 849.000)
879.390 - 879.990       Cellular One (data)
880.020 - 880.620       NYNEX (data)

The data streams are encoded NRZ (Non-return-to-zero) binary ones and zeroes
are now zero-to-one and one-to-zero transitions respectively.  This is so the
wideband data can modulate the transmitter via binary frequency shift keying,
and ones and zeroes into the modulator MUST now be equivalent to nominal peak
frequency deviations of 8 KHz above and below the carrier frequency.


   PUTTING IT ALL TOGETHER - Signaling on the Control Channels

The following information will be invaluable to the hobbyist that is monitoring
cellular telephones via a scanner and can access control channel signals.  All
information released below is EIA/TIA -- FCC standard.  There are a lot of
differences between cellular phones, but all phones must interface into the
mobile network and talk fluently between each other and cell sites.  Therefore,
the call processing and digital signaling techniques are uniform throughout the
industry.


   MOBILE CALL PROCESSING

        Calling:

Initially, the land station transmits the first part of its SID to a mobile
monitoring some control channel, followed by the number of paging channels, an
ESN request, then mobile registration, which will either be set to 0 or 1.
When registration is set to one, the mobile will transmit both MIN1 and MIN2
during system access, another 1 for discontinuous (DTX) transmissions, read
control-filler (RCF) should be set to 1, and access functions (if combined with
paging operations) require field setting to 1, otherwise CPA (combined paging
access) goes to 0.

        Receiving:

As the mobile enters the Scan Dedicated Control Channels Task, it must examine
signal strengths of each dedicated control channel assigned to System A if
enabled.  Otherwise System B control channels are checked.  The values assigned
in the NAWC (Number of Additional Words Coming) system parameter overhead
message train will determine for the mobile if all intended information has
been received.  An EDN field is used as a crosscheck, and control-filler
messages are not to be counted as part of the message.  Should a correct BCH
code be received along with a non-recognizable overhead message, it must be
part of the NAWC count train but the equivalent should not try and execute the
instructions.

Under normal circumstances, mobiles are to tune to the strongest dedicated
control channel, receive a system parameter transmission, and, within 3
seconds, set up the following:

        o  Set SID's 14 most significant bits to SID1 field value.

        o  Set SID's least significant bit to 1, if serving system status
           enables, or to zero if not.

        o  Set paging channels N to 1 plus the value of N-1 field.

        o  Set paging channel FIRSTCHP as follows:
                If SIDs = SIDp then FIRSTCHPs = FIRSTCHPp (which is an 11-bit
                paging channel).
                If SIDs = SIDp and serving system is enabled, set FIRSTCHPs to
                initial dedicated channel for system B.
                If SIDs = SIDp and serving system is disabled, set FIRSTCHPs to
                first dedicated control channel for system B.

        o  Set LASTCHPs to value of FIRSTCHPs + Ns -1.

        o  Should the mobile come equipped for autonomous registration, it
           must:

                o Set registration increment (REGINCRs) to its 450 default
                  value.

                o Set registration ID status to enabled.

I know that was a little arcane sounding but it's the best you can do with
specifications.  Data is data, there is no way to spruce it up.  From here on
out a mobile must begin the Paging Channel Selection Task.  If this cannot be
completed on the strongest dedicated channel, the second strongest dedicated
channel may be accessed and the three second interval commenced again.
Incomplete results should result in a serving system status check and an
enabled or disabled state reversed, permitting the mobile to begin the Scan.
Dedicated control Channels Task when channel signal strengths are once more
examined.

Custom local operations for mobiles may be sent and include roaming mobiles
whose home systems are group members.  A new access channel may be transmitted
with a new access field set to the initial access channel.  Autonomously
registered mobiles may increment their next registered ID by some fixed value,
but the global action message must have its REGINCR field adequately set.
Also, so that all mobiles will enter the Initialization Task and scan dedicated
control channels, a RESCAN global action message must be transmitted.

Mobile stations may be required to read a control-filler message before
accessing any system on a reverse control channel.

System access for mobiles is sent on a forward control channel in the following
manner.  Digital Color Code (DCC) identifies the land is carried with the
system parameter overhead message overload class fields are set to zero among
the restricted number, and the remainder set to 1.  Busy-to-idle status (BIS)
access parameters go to zero when mobiles are prevented from checking on the
reverse control channel and the message must be added to the overhead.  When
mobiles can't use the reverse control channel for seizure messages attempts or
busy signals, access attempt parameters must also be included in the overhead.
And when a land station receives a seizure precursor matching its digital color
code with 1 or no bit errors, busy idle bits signals on the forward control
channel must be set to busy within 1.2 milliseconds from the time of the last
bit seizure.  Busy-idle bit then must remain busy until a minimum of 30 msec
following the final bit of the last word of the message has been received, or a
total of 175 msec has elapsed.

        Channel Confirmation

Mobiles are to monitor station control messages for orders and respond to both
audio and local control orders even though land stations are not required to
reply.  MIN bits must be matched.  Thereafter, the System Access Task is
entered with a page response, as above, and an access timer started.

This time runs as follows:

        o  12 seconds for an origination
        o  6 seconds for page response
        o  6 seconds for an order response
        o  6 seconds for a registration

The last try code is then set to zero, and the equipment begins the Scan Access
Channels Task to find two channels with the strongest signals which it tunes
and enters the Retrieve Access Attempts Parameters Task.

This is where both maximum numbers of seizure attempts and busy signals are
each set to 10.  A read control-filler bit (RCF) will then be checked:  If the
RCF equals zero, the mobile then reads a control-filler message, sets DCC and
WFOM (wait for overhead message train before reverse control channel access) to
the proper fields and sets the proper fields and sets the appropriate power
level.  Should neither the DCC field nor the control-filler message be received
and access time has expired, the mobile station goes to Serving System
Determination Task.  But within the allowed access time, the mobile station
enters the Alternate Access Channel Task.  BIS is then set to 1 and the WFOM
bit is checked.  If WFOM equals 1, the station enters the Update Overhead
Information Task; if WFOM equals 0, a random delay wait is required of 0 to 200
msec, +/- 1 msec.  Then, the station enters the Seize Reverse Control Channel
Task.

Service Requesting is next.  This task requires that the mobile continue to
send is message to the land station according to the following instructions:

        o Word A is required at all times.
        o Word B has to be sent if last try access LT equals 1 or if E requires
          MIN1 and/or MIN2, and the ROAM status is disabled, or if the station
          has been paged with a 2-word control message.
        o Word C is transmitted with S (serial number) being 1
        o Word D required if the access is an origination
        o Word E transmitted when the access is an origination and between 9
          and 16 digits are dialed.  When the mobile has transmitted its
          complete message, an unmodulated carrier is required for another 25
          milliseconds before carrier turnoff.  After words A through E have
          been sent, the next mobile task depends on the type of access.

Order confirmation requires entry into the Serving System Determination Task.

     Origination means entry into the Await Message Task.
     Page response, is the same as Origination.

Registration requires Await Registration Confirmation, which must be completed
within 5 seconds or registration failure follows.  The same is true for Await
Message since an incomplete task in 5 seconds sends the mobile into the Serving
System Determination Task.  Origination or Page response requires mobile update
of parameters delivered in the message.  If R equals 1, the mobile enters the
Autonomous Registration Task, otherwise, it goes to the Initial Voice Channel
Confirmation Task.  Origination access may be either an intercept or reorder,
and in these instances, mobiles enter the Serving System Determination Task.
The same holds true for a page response access.  But if access is an
origination and the user terminates his call during this task, the call has to
be released on a voice channel and not control channel.

If a mobile station is equipped for Directed Retry and if a new message is
received before all four words of the directed retry message, it must go to the
Serving System Determination Task.  There the last try code (LT) must be set
according to the ORDQ (order qualifier) field of the message as follows:

                If 000, LT sets to 0
                If 0001, LT sets to 1

Thereafter, the mobile clears the list of control channels to be scanned in
processing Directed Retry (CCLIST) and looks at each CHANPOS (channel position)
field contained in message words three and four.  For nonzero CHANPOS field,
the mobile calculates a corresponding channel number by adding CHANPOS to
FIRSTCHA minus one.  Afterwards, the mobile has then to determine if each
channel number is within the set designated for cellular systems.  A true
answer requires adding this/these channel(s) to the CCLIST.


        Awaiting Answers

Here, an alert timer is set for 65 seconds (0 to +20 percent).  During this
period the following events may take place:

        o Should time expire, the mobile turns its transmitter off and enters
          the Serving System Determination Task.
        o An answer requires signaling tone turnoff and Conversation Task 
          entry.

        o If any of the messages listed hereafter are received within 100
          milliseconds, the mobile must compare SCC digits that identify stored
          and proper SAT frequencies for the station to the PSCC (present SAT
          color code).  If not equivalent, the order is ignored.  If correct,
          then the following actions taken for each order:

        Handoff:  Signaling extinguished for 500 msec, signal tone off,
        transmitter off, power lever adjusted, new channel tuned, new SAT, new
        SCC field, transmitter on, fade timer reset, and signaling tone on.
        Wait for an answer.

          Alert:  Reset alert timer for 65 seconds and stay in
                  Waiting for Answer Task.

     Stop Alert:  Extinguish signaling tone and enter Waiting for Order Task.

        Release:  Signaling tone off, wait 500 msec, then enter Release Task.

          Audit:  Confirm message to land station, then stay in
                  Waiting for Answer Task.

    Maintenance:  Reset alert timer for 65 seconds and remain in
                  Waiting for Answer Task.

   Change Power:  Adjust transmitter to power level required and send
                  confirmation to land station.  Remain in
                  Waiting for Answer Task.

  Local Control:  If local control is enabled and order received, examine LC
                  field and determine action.

                  Orders other than the above for this type of action are
                  ignored.

        Conversation

In this mode, a release-delay timer is set for 500 mSec.  If Termination is
enabled, the mobile sets termination status to disabled and waits 500 mSec
before entering Release Task.  The following actions may then execute:

        o  Upon call termination, the release delay timer has to be checked.
           If time has expired, the Release Task is entered; if not expired,
           the mobile must wait until expiration and then enter Release Task.

        o  Upon user requested flash, signaling tone turned on for 400 mSec.
           But should a valid order tone be received during this interval,
           the flash is immediately terminated and the order processed.  The
           flash, of course, is not then valid.

        o  Upon receipt of the following listed orders and within 100 mSec,
           the mobile must compare SCC with PSCC, and the order is ignored
           if the two are not equal.  But if they are the same, the following
           can occur:

        Handoff:  Signaling tone on for 50 mSec, then off, transmitter off,
        power level adjusted, new channel tuned, adjust new SAT, set SCC to SCC
        field message value, transmitter on, fade timer reset, remain in
        Conversation Task.

    Send Called Address:  Upon receipt within 10 seconds of last valid flash,
                  called address sent to land station.  Mobile remains in
                  Conversation Task.  Otherwise, remain in Conversation Task.

          Alert:  Turn on signaling tone, wait 500 mSec, then enter
                  Waiting for Answer Task.

        Release:  Check release delay timer.  If time expired, mobile enters
                  Release Task; but if timer has not finished, then mobile must
                  wait and then enter Release Task when time has expired.

          Audit:  Order confirmation sent to land station while remaining in
                  Conversation Task.

    Maintenance:  Signaling tone on, wait 500 mSec, then enter Waiting for
                  Answer Task.

   Change Power:  Adjust transmitter to power level required by order
                  qualification code and send confirmation to land station.
                  Remain in Conversation Task.

  Local Control:  If local control in enabled and local control order received,
                  the LC field is to be checked for subsequent action and
                  confirmation.

Orders other than the above for this type of action are ignored.


        Release

In the release mode the following steps are required:

        o  Signaling tone sent for 1.8 sec.  If flash in transmission when
           signaling tone begun, it must be continued and timing bridged so
           that action stops within 1.8 sec.
        o  Stop signaling tone.
                o  Turn off transmitter.
                o  The mobile station then enters the Serving System
                   Determination Task.

The above is the Cellular System Mobile/Land Station Compatibility
Specification.  The following shall be Signaling Formats which are also found
in the above document.  I converted all these tables by HAND into ASCII so
appreciate them.  It wasn't the easiest thing to do.  But I must say, I
definitely understand the entire cellular operation format.


   There are two types of continuous wideband data stream transmissions.  One
is the Forward Control Channel which is sent from the land station to the
mobile.  The other is the Reverse Control Channel, which is sent from the
mobile to the land station.  Each data stream runs at a rate of 10 kilobit/sec,
+/- 1 bit/sec rate.  The formats for each of the channels follow.


      - Forward Control Channel

The forward control channel consists of three discrete information streams.
They are called stream A, stream B and the busy-idle stream.  All three streams
are multiplexed together.  Messages to mobile stations with the least
significant bit of their MIN number equal to "0" are sent on stream A, and
those with a "1" are sent on stream B.

The busy-idle stream contains busy-idle bits, which are used to indicate the
status of the reverse control channel.  If the busy-idle bit = "0" the reverse
control channel is busy, if it equals "1" it is idle.  The busy-idle bit is
located at the beginning of each dotting sequence, word sync sequence, at the
beginning of the first repeat of word A and after every 10 message bits
thereafter.

Mobile stations achieve synchronization with the incoming data via a 10 bit
dotting sequence (1010101010) and an 11 bit word sync sequence (11100010010).
Each word contains 40 bits, including parity and is repeated 5 times after
which it is then referred to as a "block".  For a multiword message, the second
word block and subsequent word blocks are formed the same as the first word
block including the dotting and sync sequences.  A "word" is formed when the 28
content bits are encoded into a (40, 28; 5) BCH (Bose-Chaudhuri-Hocquenghem)
code.  The left-most bit shall be designated the most-significant bit.

        The Generator polynominal for the (40, 28;5) BCH code is:

                        12    10    8    5    4    3    0
              G (X) =  X   + X   + X  + X  + X  + X  + X
               B

Each FOCC message can consist of one or more words.  Messaging transmitted over
the forward control channel are:

                - Mobile station control message
                - Overhead message
                - Control-filler message

Control-filler messages may be inserted between messages and between word
blocks of a multiword message.

Message Formats:  Found on either stream A or B

     -  Mobile Station Control Message

The mobile station control message can consist of one, two, or four words.

        Word 1 (abbreviated address word)

   +--------+-------+---------------------------------------+-----------+
   | T   t  |       |                                       |           |
   |  1   2 |  DCC  |    Mobile Identification Number 1     |     P     |
   |        |       |                      23-0             |           |
   +--------+-------+---------------------------------------+-----------+
 bits:  2       2                      24                         12


         Word 2 (Extended Address Word)


     +------+-----+-----------+------+--------+-------+----------+-----+
     | T  T |SCC =|           | RSVD | LOCAL  | CRDQ  |   ORDER  |     |
     |  1  2| 11  |  MIN2     | = 0  |        |       |          |     |
     |   =  +-----+     3-24  +------+-----+--+-------+----------|  P  |
     |  10  |SCC =|           |    VMAC    |       CHAN          |     |
     |      | 11  |           |            |                     |     |
     +------+-----+-----------+------------+---------------------+-----+
         2     2       10           3               11              12


        Word 3 (First Directed-Retry Word)


     +------+-----+-----------+-----------+-----------+-------+--------+
     | T  T | SCC |           |           |           | RSVD  |        |
     |  1  2|  =  |  CHANPOS  |  CHANPOS  |  CHANPOS  |  =    |        |
     |   =  |     |           |           |           | 000   |    P   |
     |  10  | 11  |           |           |           |       |        |
     +------+-----+-----------+-----------+-----------+-------+--------+
        2      2        7           7           7         3       12


        Word 4 (Second Directed-Retry Word)

     +------+-----+-----------+-----------+-----------+-------+--------+
     | T  T | SCC |           |           |           | RSVD  |        |
     |  1  2|  =  |  CHANPOS  |  CHANPOS  |  CHANPOS  |  =    |        |
     |   =  |     |           |           |           | 000   |    P   |
     |  10  | 11  |           |           |           |       |        |
     +------+-----+-----------+-----------+-----------+-------+--------+
        2      2        7           7           7         3        12


The interpretation of the data fields:

        T  T   - Type field.  If only Word 1 is send, set to 00 in Word 1.
        SCC    - SAT color code (discussed previously)
        ORDER  - Order field.  Identifies the order type (see table below)
        ORDQ   - Order qualifier field.  Qualifies the order to a specific
                 action
        LOCAL  - Local control field.  This field is specific to each system.
                 The ORDER field must be set to local control for this field to
                 be interpreted.
        VMAC   - Voice Mobile Attenuation Code field.  Indicates the mobile
                 station power level associated with the designated voice
                 channel.
        CHAN   - Channel number field.  Indicates the designated voice channel.
        CHANPOS- CHANnel POSition field.  Indicates the position of a control
                 channel relative to the first access channel (FIRSTCHA).
        RSVD   - Reserved for future use, all bits must be set as indicated.
        P      - Parity field.


        Coded Digital Color Code
      +--------------------------------------------+
      | Received DCC           7-bit Coded DCC     |
      |     00                     0000000         |
      |     01                     0011111         |
      |     10                     1100011         |
      |     11                     1111100         |
      +--------------------------------------------+


        Order and Order Qualification Codes

  +-------+-------------+---------------------------------------------------+
  | Order |    Order    |                                                   |
  | Code  |Qualification|                     Function                      |
  |       |    Code     |                                                   |
  +-------+-----------------------------------------------------------------+
  | 00000      000      page (or origination)                               |
  | 00001      000      alert                                               |
  | 00011      000      release                                             |
  | 00100      000      reorder                                             |
  | 00110      000      stop alert                                          |
  | 00111      000      audit                                               |
  | 01000      000      send called-address                                 |
  | 01001      000      intercept                                           |
  | 01010      000      maintenance                                         |
  |                                                                         |
  | 01011      000      charge power to power level 0                       |
  | 01011      001      charge power to power level 1                       |
  | 01011      010      charge power to power level 2                       |
  | 01011      011      charge power to power level 3                       |
  | 01011      100      charge power to power level 4                       |
  | 01011      101      charge power to power level 5                       |
  | 01011      110      charge power to power level 6                       |
  | 01011      111      charge power to power level 7                       |
  |                                                                         |
  | 01100      000      directed retry - not last try                       |
  | 01100      001      directed retry - last try                           |
  |                                                                         |
  | 01101      000      non-autonomous registration - don't reveal location |
  | 01101      001      non-autonomous registration - make location known   |
  | 01101      010      autonomous registration - don't reveal location     |
  | 01101      011      autonomous registration - make location known       |
  |                                                                         |
  | 11110      000      local control                                       |
  |                                                                         |
  |      All other codes are reserved                                       |
  |                                                                         |
  +-------------------------------------------------------------------------+


        Forward Voice Channel

The forward voice channel (FVC) is a wideband data stream sent by the land
station to the mobile station.  This data stream must be generated at a 10
kilobit/Sec +/- .1 bit/Sec rate.  The Forward Voice Channel format follows:

  +-----------+------+--------+-----+------+--------+-----+------+------
 ||           |      | Repeat |     |      | Repeat |     |      |
 ||           | word |        |     | word |        |     | word |
 ||  Dotting  | sync |  1 of  | dot | sync |  2 of  | dot | sync |
 ||           |      |        |     |      |        |     |      |
 ||           |      |  Word  |     |      |  Word  |     |      |
  +-----------+------+--------+-----+------+--------+-----+------+------
      101        11      40      37    11      40      37    11

       -----+--------+-----+------+--------+-----+------+--------+
            | Repeat |     |      | Repeat |     |      | Repeat ||
            |        |     | word |        |     | word |        ||
            |  9 of  | dot | sync | 10 of  | dot | sync | 11 of  ||
            |        |     |      |        |     |      |        ||
            |  Word  |     |      |  Word  |     |      |  Word  ||
       -----+--------+-----+------+--------+-----+------+--------+
                40      37    11      40      37    11      40

A 37-bit dotting sequence and an 11-bit word sync sequence are sent to permit
mobile stations to achieve synchronization with the incoming data, except at
the first repeat of the word, where the 101-bit dotting sequence is used.  Each
word contains 40 bits, including parity, and is repeated eleven times together
with the 37-bit dotting and 11-bit word sync; it is then referred to as a word
block.  A word block is formed by encoded the 28 content bits into a (40, 28)
BCH code that has a distance of 5 (40, 28; 5).  The left-most bit (as always)
is designated the most-significant bit.  The 28 most significant bits of the
40-bit field shall be the content bits.  The generator polynominal is the same
as that used for the forward control channel.

The mobile station control message is the only message transmitted over the
forward voice channel.  The mobile station control message consists of one
word.


        Mobile Station Control Message:

      +-------+-------+------+-----------+-------+------+-------+------+
      | T  T  | SCC = |      |  RSVD =   | LOCAL | ORDQ | ORDER |      |
      |  1  2 |   11  |      | 000 ... 0 |       |      |       |      |
      |   =   +-------| PSCC +-----------+-------+------+-------+   P  |
      |       | SCC = |      |  RSVD =   |  VMAC |    CHANNEL   |      |
      |  10   |   11  |      | 000 ... 0 |       |              |      |
      +-------+-------+------+-----------+-------+--------------+------+
          2       2       2        8         3          11         12

      Interpretation of the data fields:

        T  T   - Type field.  Set to '10'.
         1  2

       SCC     - SAT color code for new channel (see SCC table)
       PSCC    - Present SAT color code.  Indicates the SAT color code
                 associated with the present channel.
       ORDER   - Order field.  Identifies the order type.  (see Order table)
       ORDQ    - Order qualifier field.  Qualifies the order to a specific
                 action (see Order table)
       LOCAL   - Local Control field.  This field is specific to each system.
                 The ORDER field must be set to local control (see Order table)
                 for this field to be interpreted.
       VMAC    - Voice mobile attenuation code field.  Indicates the mobile
                 station power level associated with the designated voice
                 channel.
       RSVD    - Reserved for future use;  all bits must be set as indicated.
       P       - Parity field.


        Reverse Control Channel

The Reverse Control Channel (RECC) is a wideband data stream sent from the
mobile station to the land station.  This data stream runs at a rate of 10
kilobit/sec, +/- 1 bit/sec rate.  The format of the RECC data stream follows:

     +---------+------+-------+------------+-------------+-----------+-----
     | Dotting | Word | Coded | first word | Second word | Third word|
     |         | sync |  DCC  | repeated   |   repeated  |  repeated |
     |         |      |       | 5 times    |   5 times   |  5 times  |
     +---------+------+-------+------------+-------------+-----------+-----
  bits:  30       11      7        240           240          240

                         Dotting = 01010101...010101

                       Word sync = 11100010010


All messages begin with the RECC seizure precursor with is composed of a 30 bit
dotting sequence (1010...101), and 11 bit word sync sequence (11100010010), and
the coded digital color code.

Each word contains 48 bits, including parity, and is repeated five times after
which it is referred to as a word block.  A word is formed by encoding 36
content bits into a (48, 36) BCH code that has a distance of 5, (48 36; 5).
The left most bit shall be designated the most-significant bit.  The 36 most
significant bits of the 48 bit field shall be the content bits.

The generator polynomial for the code is the same for the (40,28;5) code used
on the forward channel.

Each Reverse Control Channel message can consist of one of the five words.  The
types of messages to be transmitted over the reverse control channel are as
follows:

        o  Page Response Message
        o  Origination Message
        o  Order Confirmation Message
        o  Order Message

These messages are made up of combination of the following five words:

        Word A - Abbreviated Address Word

   +---+------+---+---+---+------+---+-----------------------------------+---+
   | F |      |   |   |   | RSVD | S |                                   |   |
   |   |      |   |   |   |      |   |                                   |   |
   | = | NAWC | T | S | E |  =   | C |          MIN 1                    | P |
   |   |      |   |   |   |      |   |                23 - 0             |   |
   | 1 |      |   |   |   |  0   | M |                                   |   |
   +---+------+---+---+---+------+---+-----------------------------------+---+
     1     3    1   1   1    1     4                   24                  12


        Word B - Extended Address Word

   +---+------+-------+------+-------+----+------+-----------------------+---+
   | F |      |       |      |       |    | RSVD |                       |   |
   |   |      |       |      |       |    |      |                       |   |
   | = | NAWC | LOCAL | ORDQ | LOCAL | LT |  =   |      MIN 2            | P |
   |   |      |       |      |       |    |      |            33-24      |   |
   | 0 |      |       |      |       |    | 00..0|                       |   |
   +---+------+-------+------+-------+----+------+-----------------------+---+
     1    3       5      3       5     1      8              10            12


        Word C - Electronic Serial Number Word

   +---+--------+--------------------------------------+---------------+
   | F |        |                                      |               |
   |   |        |                                      |               |
   | = |  NAWC  |             SERIAL (ESN)             |       P       |
   |   |        |                                      |               |
   | 1 |        |                                      |               |
   +---+--------+--------------------------------------+---------------+
     1     3                      32                           12


        Word D - First Word of the Called-Address

    +---+------+-------+-------+-----+-----+-----+-----+-------+-------+---+
    | F |      | 1st   | 2nd   |     |     |     |     | 7th   | 8th   |   |
    |   |      |       |       |     |     |     |     |       |       |   |
    | = | NAWC | DIGIT | DIGIT | ... | ... | ... | ... | DIGIT | DIGIT | P |
    |   |      |       |       |     |     |     |     |       |       |   |
    | 1 |      |       |       |     |     |     |     |       |       |   |
    +---+------+-------+-------+-----+-----+-----+-----+-------+-------+---+
      1    3       4       4      4     4     4     4      4       4     12


        Word E - Second Word of the Called-Address

    +---+------+-------+-------+-----+-----+-----+-----+-------+-------+---+
    | F | NAWC | 9th   | 10th  |     |     |     |     | 15th  | 16th  |   |
    |   |      |       |       |     |     |     |     |       |       |   |
    | = |  =   | DIGIT | DIGIT | ... | ... | ... | ... | DIGIT | DIGIT | P |
    |   |      |       |       |     |     |     |     |       |       |   |
    | 0 | 000  |       |       |     |     |     |     |       |       |   |
    +---+------+-------+-------+-----+-----+-----+-----+-------+-------+---+
      1    3       4       4      4     4     4     4      4       4     12


The interpretation of the data fields is as follows:

        F      - First word indication field.  Set to '1' in first word and '0'
                 in subsequent words.

        NAWC   - Number of additional words coming field.
        T      - T field.  Set to '1' to identify the message as an origination
                 or an order; set to '0' to identify the message as an order
                 response or page response.
        S      - Send serial number word.  If the serial number word is sent,
                 set to '1';  if the serial number word is not sent, set to
                 '0'.
        SCM    - The station class mark field
        ORDER  - Order field.  Identifies the order type.
        ORDQ   - Order qualifier field.  Qualifies the order confirmation to a
                 specific action.
        LOCAL  - Local control field.  This field is specific to each system.
                 The ORDER field must be set to locate control for this field
                 to be interpreted.
        LT     - Last-try code field.
        MIN1   - Mobile Identification number field part one.
        MIN2   - Mobile Identification number field part two.
        SERIAL - Electronic Serial Number field.  Identifies the serial number
                 of the mobile station.
        DIGIT  - Digit field (see table below)
        RSVD   - Reserved for future use; all bits must be set as indicated.
        P      - Parity field.


        Called-address Digit Codes
   +------------------------------------------------------------------------+
   |    Digit           Code            Digit           Code                |
   |                                                                        |
   |      1             0001              7             0111                |
   |      2             0010              8             1000                |
   |      3             0011              9             1001                |
   |      4             0100              0             1010                |
   |      5             0101              *             1011                |
   |      6             0110              #             1100                |
   |                                    Null            0000                |
   |                                                                        |
   |    NOTE:                                                               |
   |    1.  The digit 0 is encoded as binary 10, not binary zero.           |
   |    2.  The code 0000 is the null code, indicated no digit present      |
   |    3.  All other four-bit sequences are reserved, and must not be      |
   |        transmitted.                                                    |
   |                                                                        |
   +------------------------------------------------------------------------+

Examples of encoding called-address information into the called address words
follow:

If the number 2# is entered, the word is as follows:

   +------+------+------+------+------+------+------+------+------+---------+
   | NOTE | 0010 | 1100 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 |    P    |
   +------+------+------+------+------+------+------+------+------+---------+

If the number 13792640 is entered, the word is as follows:

   +------+------+------+------+------+------+------+------+------+---------+
   | NOTE | 0001 | 0011 | 0111 | 1001 | 0010 | 0110 | 0100 | 1010 |    P    |
   +------+------+------+------+------+------+------+------+------+---------+

As you can see the numbers are coded into four bits and inserted sequentially
into the train.  Notice that when the number is longer than 8 numbers it is
broken into two different Words.

If the number 6178680300 is entered, the words are as follows:

        Word D - First Word of the Called-Address

   +------+------+------+------+------+------+------+------+------+---------+
   | NOTE | 0110 | 0001 | 0111 | 1000 | 0110 | 1000 | 1010 | 1010 |    P    |
   +------+------+------+------+------+------+------+------+------+---------+
       4      4      4      4      4      4      4      4     4        12

        Word E - Second Word of the Called-Address

   +------+------+------+------+------+------+------+------+------+---------+
   | NOTE | 0010 | 1010 | 1010 | 0000 | 0000 | 0000 | 0000 | 0000 |    P    |
   +------+------+------+------+------+------+------+------+------+---------+
       4      4      4      4      4      4      4      4     4        12

       NOTE = four bits which depend on the type of message


        Reverse Voice Channel

The reverse voice channel (RVC) is a wideband data stream sent from the mobile
station to the land station.  This data stream must be generated at a 10
kilobit/second +/- 1 bit/sec rate.  The format is presented below.

  +-------------+------+----------+-----+------+----------+-----+------+----
 ||             |      | Repeat 1 |     |      | Repeat 2 |     |      |
 ||             | word |          |     | word |          |     | word |
 ||   Dotting   | sync |    of    | Dot | sync |    of    | Dot | sync |
 ||             |      |          |     |      |          |     |      |
 ||             |      |  Word 1  |     |      |  Word 1  |     |      |
  +-------------+------+----------+-----+------+----------+-----+------+----
      101         11       48      37     11       48       37    11

 ---+----------+-----+------+----------+-----+------+----------+-----+----
    | Repeat 3 |     |      | Repeat 4 |     |      | Repeat 5 |     |
    |          |     | word |          |     | word |          |     |
    |    of    | Dot | sync |    of    | Dot | sync |    of    | Dot |
    |          |     |      |          |     |      |          |     |
    |  Word 1  |     |      |  Word 1  |     |      |  Word 1  |     |
 ---+----------+-----+------+----------+-----+------+----------+-----+----
        48       37     11      48        37    11       48       37

        ---+------+----------+--------    -------+----------+
           |      | Repeat 1 |                   | Repeat 5 ||
           | word |          |                   |          ||
           | sync |    of    |   ...             |    of    ||
           |      |          |                   |          ||
           |      |  Word 2  |                   |  Word 2  ||
        ---+------+----------+--------    -------+----------+

A 37-bit dotting sequence and an 11-bit word sync sequence are sent to permit
land stations to achieve synchronization with the incoming data, except at the
first repeat of word 1, where a 101-bit dotting sequence is used.  Each word
contains 48 bits, including parity, and is repeated five times together with
the 37-bit dotting and 11-bit word sync sequences; it is then referred to as a
word block.  For a multi-word message, the second word block is formed the same
as the first word block including the 37-bit dotting and 11-bit word sync
sequences.  A word is formed by encoding the 36 content bits into a (48, 36)
BCH code that has a distance of 5, (48, 36; 5).  The left-most bit (earliest in
time) shall be designated the most-significant bit.  The 36 most-significant
bits of the 48-bit field shall be the content bits.  The generator polynomial
for the code is the same as for the (40, 28; 5) code used on the forward
control channel.

Each RVC message can consist of one or two words.  The types of messages to be
transmitted over the reverse voice channel are as follows:

        o Order Confirmation Message
        o Called-Address Message

The message formats are as follows:


        Order Confirmation Message:

     +---+------+---+-------+------+-------+-----------+---------+
     | F | NAWC | T |       |      |       |    RSVD   |         |
     |   |      |   |       |      |       |           |         |
     | = |  =   | = | LOCAL | ORDQ | ORDER |     =     |    P    |
     |   |      |   |       |      |       |           |         |
     | 1 |  00  | 1 |       |      |       | 000 ... 0 |         |
     +---+------+---+-------+------+-------+-----------+---------+
       1    2     1     5       3      5        19         12


        Called-Address Message

        Word 1 - First Word of the Called-Address

  +---+------+---+-------+-------+-----+-----+-----+-----+-------+-------+---+
  | F | NAWC | T |       |       |     |     |     |     |       |       |   |
  |   |      |   |  1st  |  2nd  |     |     |     |     |  7th  |  8th  |   |
  | = |  =   | = | Digit | Digit | ... | ... | ... | ... | Digit | Digit | P |
  |   |      |   |       |       |     |     |     |     |       |       |   |
  | 1 |  01  | 0 |       |       |     |     |     |     |       |       |   |
  +---+------+---+-------+-------+-----+-----+-----+-----+-------+-------+---+
    1    2     1     4       4      4     4     4     4      4       4     12

        Word 2 - Second Word of the Called-Address

  +---+------+---+-------+-------+-----+-----+-----+-----+-------+-------+---+
  | F | NAWC | T |       |       |     |     |     |     |       |       |   |
  |   |      |   |  9th  |  10th |     |     |     |     |  15th |  16th |   |
  | = |  =   | = | Digit | Digit | ... | ... | ... |  .. | Digit | Digit | P |
  |   |      |   |       |       |     |     |     |     |       |       |   |
  | 0 |  00  | 0D|       |       |     |     |     |     |       |       |   |
  +---+------+---+-------+-------+-----+-----+-----+-----+-------+-------+---+
    1    2     1     4       4      4     4     4     4      4       4     12


The fields are descriptions a the me as those for the Reverse Control channel
above.

        Overhead Message

A three-bit OHD field is used to identify the overhead message types.  Overhead
message type codes are listed in the table below.  They are grouped into the
following functional classes:

        o System parameter overhead message
        o Global action overhead message
        o Registration identification message
        o Control-filler message

Overhead messages are send in a group called an overhead message train.  The
first message of the train must be the system parameter overhead message.  The
desired global action messages and/or a registration ID message must be
appended to the end of the system parameter overhead message.  The total number
of words in an overhead message train is one more than the value of the NAWC
field contained in the first word of the system parameter overhead message.
The last word in the train must be set to '0'.  For NAWC-counting purposes,
inserted control-filler messages must not be counted as part of the overhead
message train.

The system parameter overhead message must be sent every .8 +/- .3 seconds on
each of the following control channels:

        o combined paging-access forward channel.
        o Separate paging forward control channel
        o Separated access forward control channel when the control-filler
          message is sent with the WFOM bit set to '1'.

The global action messages and the registration identification message are sent
on an as needed basis.

        o The system parameter for overhead message consists of two words.


    0  Word 1

        +-------+-----+----------+------+------+-----+------------+
        | T  T  |     |          | RSVD |      | OHD |            |
        |  1  2 |     |          |      |      |     |            |
        |   =   | DCC |   SID1   |  =   | NAWC |  =  |     P      |
        |       |     |          |      |      |     |            |
        |  11   |     |          | 000  |      | 110 |            |
        +-------+-----+----------+------+------+-----+------------+
            2      2       14        3      4     3        12


        Word 2

       +-------+-------+-----+-----+------+------+-----+------+---
       | T  T  |       |     |     |      |      |     | RSVD |
       |  1  2 |       |     |     |      |      |     |      |
       |   =   |  DCC  |  S  |  E  | REGH | REGR | DTX |  =   |
       |       |       |     |     |      |      |     |      |
       |   11  |       |     |     |      |      |     |  0   |
       +-------+-------+-----+-----+------+------+-----+------+---
           2       2      1     1     1       1     1      1

       ---+-------+-----+-----+----------+-----+-------+-----------+
          |       |     |     |          |     |  OHD  |           |
          |       |     |     |          |     |       |           |
          | N - 1 | RCF | CPA | CMAX - 1 | END |   =   |     P     |
          |       |     |     |          |     |       |           |
          |       |     |     |          |     |  111  |           |
       ---+-------+-----+-----+----------+-----+-------+-----------+
              5      1     1        7       1      3         12


                Overhead Message Types
    +----------------------------------------------------------+
    |   Code    Order                                          |
    +----------------------------------------------------------+
    |   000     Registration ID                                |
    |   001     Control-filler                                 |
    |   010     reserved                                       |
    |   011     reserved                                       |
    |   100     global action                                  |
    |   101     reserved                                       |
    |   110     Word 1 of system parameter message             |
    |   111     Word 2 of system parameter message             |
    +----------------------------------------------------------+

        The interpretation of the data fields:

        T  T    - Type field. Set to '11' indicating an overhead word.
         1  2
        OHD     - Overhead message type field.  The OHD field of Word 1 is set
                  to '110' indicating the first word of the system parameter
                  overhead message.  The OHD field of Word 2 is set to '111'
                  indicating the second word of the system parameter overhead
                  message.
        DCC     - Digital Color Code field.
        SID1    - First part of the system identification field
        NAWC    - Number of Additional Words Coming field.  In Word 1 this
                  field is set to one fewer than the total number of words in
                  the overhead message train.
        S       - Serial number field.
        E       - Extended address field.
        REGH    - Registration field for home stations.
        REGR    - Registration field for roaming stations.
        DTX     - Discontinuous transmission field.
        N-1     - N is the number of paging channels in the system.
        RCF     - Read-control-filler field.
        CPA     - Combined paging/access field
        CMAX-1  - CMAX is the number of access channels in the system.
        END     - End indication field.  Set to '1' to indicate the last word
                  and '0' if not the last word.
        RSVD    - Reserved for future use, all bit must be set as indicated.
        P       - Parity field.

Each global action overhead message consists of one word.  Any number of global
action messages can be appended to a system parameter overhead message.

Here are the global action command formats:


    Rescan Global Action Message

    +-------{-------+------+---------------+-------+-------+-------------+
    | T  T  |       |  ACT |    RSVD =     |       |  OHD  |             |
    |  1  2 |       |      |               |       |       |             |
    |   =   |  DCC  |   =  |               |  END  |   =   |      P      |
    |       |       |      |   000 ... 0   |       |       |             |
    |  11   |       | 0001 |               |       |  100  |             |
    +-------+-------+------+---------------+-------+-------+-------------+
        2       2       4          16          1       3          12

    Registration Increment Global Action Message

    +-------+-----+------+---------+--------+-------+-------+------------+
    | T  T  |     |  ACT |         |        |       |  OHD  |            |
    |  1  2 |     |      |         | RSVD = |       |       |            |
    |   =   | DCC |   =  | REGINCR |        |  END  |   =   |      P     |
    |       |     |      |         |  0000  |       |       |            |
    |  11   |     | 0010 |         |        |       |  100  |            |
    +-------+-----+------+---------+--------+-------+-------+------------+
        2      2     4       12        4        1       3         12

    New Access Channel Set Global Action Message

    +-------+-------+-------+--------+----------+-------+-------+----------+
    | T  T  |       |  ACT  |        |          |       |  OHD  |          |
    |  1  2 |       |       |        |  RSVD =  |       |       |          |
    |   =   |  DCC  |   =   | NEWACC |          |  END  |   =   |     P    |
    |       |       |       |        |  00000   |       |       |          |
    |   11  |       | 0110  |        |          |       |  100  |          |
    +-------+-------+-------+--------+----------+-------+-------+----------+
        2       2       4       11         5        1       3        12


    Overload Control Global Action Message

    +-------+-----+-------+---+---+---+--   --+---+---+---+-----+-----+------+
    | T  T  |     |  ACT  | O | O | O |       | O | O | O |     | OHD |      |
    |  1  2 |     |       | L | L | L |       | L | L | L |     |     |      |
    |   =   | DCC |   =   | C | C | C |  ...  | C | C | C | END |  =  |   P  |
    |       |     |       |   |   |   |       |   |   |   |     |     |      |
    |   11  |     |  0110 | 0 | 1 | 2 |       | 13| 14| 15|     | 100 |      |
    +-------+-----+-------+---+---+---+--   --+---+---+---+-----+-----+------+
        2      2      4     1   1   1           1   1   1    1     3     12


    Access Type Parameters Global Action Message

    +-------+-----+------+-------+-----------+-------+-------+-----------+
    | T  T  |     | ACT  |       |           |       |  OHD  |           |
    |  1  2 |     |      |       |   RSVD =  |       |       |           |
    |   =   | DCC |  =   |  BIS  |           |  END  |   =   |     P     |
    |       |     |      |       | 0 ... 000 |       |       |           |
    |  11   |     | 1001 |       |           |       |  100  |           |
    +-------+-----+------+-------+-----------+-------+-------+-----------+
        2      2      4      1        15         1       3         12


    Access Attempt Parameters Global Action Message

     +-------+-------+---------+-----------+-----------+-----------+---
     | T  T  |       |   ACT   |           |           |           |
     |  1  2 |       |         |  MAXBUSY  |  MAXSZTR  |  MAXBUSY  |
     |   =   |  DCC  |    =    |           |           |           |
     |       |       |         |   - PGR   |   - PGR   |  - OTHER  |
     |  11   |       |   1010  |           |           |           |
     +-------+-------+---------+-----------+-----------+-----------+---
         2       2        4           4           4           4

     ------+-----------+-------+-------+-----------+
           |           |       |  OHD  |           |
           |  MAXSZTR  |       |       |           |
           |           |  END  |   =   |     P     |
           |  - OTHER  |       |       |           |
           |           |       |  100  |           |
     ------+-----------+-------+-------+-----------+
                 4         1       3         12


     Local Control 1 Message

     +-------+-------+-------+-----------------+-------+-------+----------+
     | T  T  |       |  ACT  |                 |       |  OHD  |          |
     |  1  2 |       |       |                 |       |       |          |
     |   =   |  DCC  |   =   |  LOCAL CONTROL  |  END  |   =   |     P    |
     |       |       |       |                 |       |       |          |
     |   11  |       |  1110 |                 |       |  100  |          |
     +-------+-------+-------+-----------------+-------+-------+----------+
         2       2       4            16           1       3        12


     Local Control 2 Message

     +-------+-------+-------+-----------------+-------+-------+----------+
     | T  T  |       |  ACT  |                 |       |  OHD  |          |
     |  1  2 |       |       |                 |       |       |          |
     |   =   |  DCC  |   =   |  LOCAL CONTROL  |  END  |   =   |     P    |
     |       |       |       |                 |       |       |          |
     |   11  |       |  1111 |                 |       |  100  |          |
     +-------+-------+-------+-----------------+-------+-------+----------+
         2       2       4            16           1       3        12


        The interpretation of the data fields are as follows:

        T  T    - Type field.  Set to '11' indicating overhead word.
         1  2
        ACT     - Global action field (see table below).
        BIS     - Busy-idle status field.
        DCC     - Digital Color Code.
        OHD     - Overhead Message type field.  Set to '100' indicating the
                  global action message.
        REGINCR - Registration increment field.
        NEWACC  - News access channel starting point field.
        MAXBUSY - Maximum busy occurrences field (page response).
        - PGR
        MAXBUSY - Maximum busy occurrences field (other accesses).
        - OTHER
        MAXSZTR - Maximum seizure tries field (page response).
        - PRG
        MAXSZTR - Maximum seizure tries field (other accesses).
        - OTHER
        OLCN    - Overload class field (N = 0 to 15)
        END     - End indication field.  Set to '1' to indicate the last word
                  of the overhead message train; set to '0' if not last word.
        RSVD    - Reserved for future use, all bits must be set as indicated.
        LOCAL   - May be set to any bit pattern.
        CONTROL
        P       - Parity field.

The registration ID message consists of one word.  When sent, the message must
be appended to a system parameter overhead message in addition to any global
action messages.

        +-------+-------+-------------+-------+-------+-----------+
        | T  T  |       |             |       |  OHD  |           |
        |  1  2 |       |             |       |       |           |
        |   =   |  DCC  |    REGID    |  END  |   =   |     P     |
        |       |       |             |       |       |           |
        |   11  |       |             |       |  000  |           |
        +-------+-------+-------------+-------+-------+-----------+
            2       2          20         1       3         12

        The interpretation of the data fields:

        T  T    - Type field.  Set to '11' indicating overhead word.
        DCC     - Digital color code field.
        OHD     - Overhead message type field.  Set to '000' indicating the
                  registration ID message.
        REGID   - Registration ID field.
        END     - End indication field.  Set to '1' to indicate last word of
                  the overhead message train;  set to '0' if not.
        P       - Parity field.


The control-filler message consists of one word.  It is sent whenever there is
no other message to be sent on the forward control channel.  It may be inserted
between messages as well as between word blocks of a multiword message.  The
control-filler message is chosen so that when it is sent, the 11-bit word
sequence will not appear in the message stream, independent of the busy-idle
bit status.

The control-filler message is also used to specify a control mobile
attenuation code (CMAC) for use by mobile stations accessing the system on the
reverse control channel, and a wait-for-overhead-message bit (WFOM) indicating
whether or not mobile stations must read an overhead message train before
accessing the system.

  +-------+-----+------+------+------+--+------+---+------+----+-----+-----+
  | T  T  |     |      |      | RVSD |  | RVSD |   |      |    | OHD |     |
  |  1  2 |     |      |      |      |  |      |   |      |    |     |     |
  |   =   | DCC |010111| CMAC |  =   |11|  =   | 1 | WFOM |1111|  =  |  P  |
  |       |     |      |      |      |  |      |   |      |    |     |     |
  |   11  |     |      |      |  00  |  |  00  |   |      |    | 001 |     |
  +-------+-----+------+------+------+--+------+---+------+----+-----+-----+
      2      2      6      3     2     2    2    1     1     4    3     16

        Interpretation of the data fields:

        T  T    - Type field.  Set to '11' indicating overhead word.
         1  2
        DCC     - Digital color code field.
        CMAC    - Control mobile attenuation field.  Indicates the mobile
                  station power level associated with the reverse control
                  channel.
        RVSD    - Reserved for future use; all bits must be set as indicated.
        WFOM    - Wait-for-overhead-message field.
        OHD     - Overhead message type field.  Set to '001' indicating the
                  control-filler word.
        P       - Parity field.


        Data Restrictions

The 11-bit sequence (11100010010) is shorter than the length of a word, and
therefore can be embedded in a word.  Normally, embedded word-sync will not
cause a problem because the next word sent will not have the word-sync sequence
embedded in it.  There are, however, three cases in which the word-sync
sequence may appear periodically in the FOCC stream.  They are as follows:

        o the overhead message
        o the control-filler message
        o Mobile station control messages with pages to mobile stations with
          certain central office codes.

These three cases are handled by:

        1. Restricting the overhead message transmission rate to about once per
           second
        2. designing the control-filler message to exclude the word-sync
           sequence, taking into account the various busy-idle bits
        3. Restricting the use of certain office codes


If the mobile station control message is examined with the MIN1 separated into
NXX-X-XXX as described earlier (where NXX is the central office code, N
represents a number from 2 - 9, and X represents a number from 0-9) the order
and order qualifications table can be used to deduce when the word-sync word
would be sent.  If a number of mobile stations are paged consecutively with the
same central office code, mobile stations that are attempting to synchronize to
the data stream may not be able to do so because of the presence of the false
word sync sequence.  Therefore, the combinations of central office codes and
groups of line numbers appearing in the following table must not be used for
mobile stations.


        RESTRICTED CENTRAL OFFICE CODES
  +-------------------------------------------------------------------------+
  |                                                   Central               |
  |  T  T       DCC        NXX         X     XXX      Office      Thousands |
  |   1  2                                             Code         Digit   |
  +-------------------------------------------------------------------------+
  |  01         11    000100(1)0000   ...    ...       175         0 to 9   |
  |  01         11    000100(1)0001   ...    ...       176         0 to 9   |
  |  01         11    000100(1)0010   ...    ...       177         0 to 9   |
  |  01         11    000100(1)0011   ...    ...       178         0 to 9   |
  |  01         11    000100(1)0100   ...    ...       179         0 to 9   |
  |  01         11    000100(1)0101   ...    ...       170         0 to 9   |
  |  01         11    000100(1)0110   ...    ...       181         0 to 9   |
  |  01         11    000100(1)0111   ...    ...       182         0 to 9   |
  |  0Z         11    100010(0)1000   ...    ...       663         0 to 9   |
  |  0Z         11    100010(0)1001   ...    ...       664         0 to 9   |
  |  0Z         11    100010(0)1010   ...    ...       665         0 to 9   |
  |  0Z         11    100010(0)1011   ...    ...       666         0 to 9   |
  |  0Z         Z1    110001(0)0100   ...    ...       899         0 to 9   |
  |  0Z         Z1    110001(0)0101   ...    ...       800         0 to 9   |
  |  0Z         ZZ    111000(1)0010   ...    ...       909         0 to 9   |
  |  00         ZZ    011100(0)1001   0ZZZ   ...       568         1 to 7   |
  |  00         ZZ    111100(0)1001   0ZZZ   ...       070         1 to 7   |
  |  00         ZZ    001110(0)0100   10ZZ   ...       339          8,9,0   |
  |  00         ZZ    011110(0)0100   10ZZ   ...       595          8,9,0   |
  |  00         ZZ    101110(0)0100   10ZZ   ...       851          8,9,0   |
  |  00         ZZ    111110(0)0100   10ZZ   ...       007          8,9,0   |
  |  0Z         ZZ    000011(1)0100   0010   ...       150            2     |
  |  0Z         ZZ    000111(1)0001   0010   ...       224            2     |
  |  0Z         ZZ    001011(1)0001   0010   ...       288            2     |
  |  0Z         ZZ    001111(1)0001   0010   ...       352            2     |
  |  0Z         ZZ    010011(1)0001   0010   ...       416            2     |
  |  0Z         ZZ    010111(1)0001   0010   ...       470            2     |
  |  0Z         ZZ    011011(1)0001   0010   ...       544            2     |
  |  0Z         ZZ    011111(1)0001   0010   ...       508            2     |
  |  0Z         ZZ    100011(1)0001   0010   ...       672            2     |
  |  0Z         ZZ    100111(1)0001   0010   ...       736            2     |
  |  0Z         ZZ    101011(1)0001   0010   ...       790            2     |
  |  0Z         ZZ    101111(1)0001   0010   ...       864            2     |
  |  0Z         ZZ    110011(1)0001   0010   ...       928            2     |
  |  0Z         ZZ    110111(1)0001   0010   ...       992            2     |
  |  0Z         ZZ    111011(1)0001   0010   ...       056            2     |
  |  0Z         ZZ    111111(1)0001   0010   ...       ...            2     |
  +-------------------------------------------------------------------------+


1. In each case, Z represents a bit that may be 1 or 0.
2. Some codes are not used as central office codes in the US at this time.
   They are included for completeness.
3. The bit in parentheses is the busy-idle bit.

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

Well there is your signaling in a nutshell.  Please note I hardly have the most
up-to-date signalling data.  Basically what was presented here was a skeleton,
the bare bones without all the additions.  There are some additions that are
system specific.  As I get updates I'll be sure to share them with the rest of
you.  I would be interested in any feedback, so, if you have something to say,
send it to:

                        oblivion@atdt.org


In the last article I said that there would be a listing of SID codes
accompanying the article.  Well, I forgot to edit that line out, but if you
would like a copy of it, just mail me at the above address an you shall receive
one.

In the next article I will be going in-depth on the actual hardware behind the
Mobile telephone, the chip sets, and its operation.  I will also publish any
updates to the previous material I find, as well as information on the
transitory NAMPS system that will be used to bridge the existing AMPS cellular
network over to the ISDN compatible fully digital network.
_______________________________________________________________________________



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