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.:: Circuit Switched Digital Capability ::.

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Current issue : #10 | Release date : 1987-01-01 | Editor : Taran King
Introduction to Phrack 10Taran King
Pro-Phile on Dave StarrTaran King
The TMC Primer by Cap'n CraxCap'n Crax
A Beginner's Guide to the IBM VM/370Elric of Imrryr
Circuit Switched Digital CapabilityThe Executioner
Hacking Primos Part IEvil Jay
Automatic Number IdentificationDoom Prophet & Phantom Phreaker
Phrack World News 9 Part IKnight Lightning
Phrack World News 9 Part IIKnight Lightning
Title : Circuit Switched Digital Capability
Author : The Executioner
                               ==Phrack Inc.==

                     Volume Two, Issue Ten, Phile #5 of 9

                 ^                                         ^
               [<+>]                                     [<+>]
               /|-|\                                     /|-|\
                |h|           ^                 ^         |h|
                |a|          ]+[The Executioner]+[        |a|
                |n|                                       |n|
                |t|      Call Phreak Klass, Room 2600     |t|
                |o|            [806][799][0016]           |o|
                |m|                                       |m|
                |s| [Circuit Switched Digital Capability] |s|
                |-|  -----------------------------------  |-|
                |S|                                       |S|
                |e|  Part I of II in this series of files |e|
                |x|                                       |x|
                |y|      Written for PHRACK, Issue 10.    |y|
               /|-|\                                     /|-|\
               [<+>]                                     [<+>]

=Part I=

The Circuit Switch Digital Capability (CSDC) allows for the end to end digital
transmission of 56 kilobits per second (kb/s) data and, alternately, the
transmission of analog voice signals on a circuit switched basis.

=Network Perspective=

The CSDC feature was formerly known as PSDC (Public Switched Digital
Capability). These two terms can be used synonymously. The CSDC feature
provides an alternate voice/data capability. If a SLC Carrier System 96 is
used, digital signals are transmitted by T1 signal. If the loop is a two wire
loop, the CSDC feature utilizes time compression multi-plexing (TCM) which
allows for the transmission of digital signals over a common path using a
separate time interval for each direction. During a CSDC call an end user may
alternate between the voice and data modes as many times as desired. The CSDC
feature can support sub-variable data rates from customer premises equipment,
but a 56 kb/s rate is utilized in the network. Some possible applications of
the CSDC feature are:

     1. Audiographic Teleconferencing.
     2. Secure Voice.
     3. Facsimile.
     4. Bulk Data.
     5. Slow scan television.

The ESS switch provides end user access and performs signalling, switching,
and trunking functions between the serving ESS switch and other CSDC offices.
End users of CSDC require a network channel terminating equipment circuit
(NCTE) which is the SD-3C476 or its equivalent. End user access is over 2-wire
metallic loops terminating at the metallic facility terminal (MFT) or SLC
Carrier System. End users not served directly by a direct CSDC ESS office, can
access CSDC equipment through a RX (Remote Exchange) access arrangement via
use of a D4 Carrier System and if required, a SLC Carrier System. The
T-Carrier trunks serve for short haul transmissions while long haul
transmissions are served by digital microwave radio and other digital systems.

If the NCTE interface is used with customer premises equipment, a miniature
8-position series jack is used to connect the NCTE to other equipment. The
jack pins are paired off; data transmit pair, data receive pair, a voice pair,
and a mode switch pair. The data pairs support the simultaneous transmission
and reception of digital data in a bipolar format at 56 kb/s. The data pairs
also provide for the xmission of control information to and from the network.
The voice pairs supports analog signal transmission and provides for call
setup, disconnect and ringing functions. The mode control pair provides
signals to the network when a change in mode (voice to data/data to voice) is
requested by the customer.

A CSDC call is originated over a 2-wire loop which can also be used for
Message Telecommunication Service (MTS) calls. Lines may be marked (MTS/CSDC
or CSDC only). Touch tone is needed to originate a CSDC call. Originations may
be initiated manually or with Automatic Calling Equipment (ACE) if available.
Digit reception, transmission and signalling follow the same procedures used
for a MTS outgoing call on CCIS or non-CCIS trunks. However CSDC calls are
ALWAYS routed over digital transmission facilities.

The long term plan also allows for EA-MF (Equal Access-Multi Frequency)
signalling and improved automatic message accounting (AMA) records. A CSDC
call is screened to ensure that the originating party has CSDC service and
that the carrier to be used provides 56 kb/s voice/data capability. A blocked
call is routed to a special service error announcement. Non-CSDC calls are not
allowed to route over CSDC-only carriers. Non-payer screening is not allowed
for CSDC calls using CCIS signalling.

A CSDC call is routed directed to the carrier or indirectly via the Access
Tandem (AT) or Signal Conversion Point (SCP). The call is terminated directly
from the carrier to the end office or indirectly via the AT or SCP. Signalling
for direct routing is either CCIS or EA-MF and is assigned on a trunk group

The AT is an ESS switch which allows access to carriers from an end office
without requiring direct trunks. Signalling between end offices and the AT is
either EA-MF or CCIS. Trunks groups using EA-MF signalling can have combined
carrier traffic.  Separate trunk groups for each carrier are required for CCIS

The SCP is an ESS switch which allows access to carriers using only CCIS
signalling from offices without the CCIS capability. Separate trunk groups for
each carrier are used between the originating end office and the SCP. Separate
trunk groups are optional between the SCP and the terminating end office and
the terminating end office. Signalling between the end office and the SCP is
MF. The SCP must have direct connection to the carrier using CCIS signalling.

=Remote Switching System=

The RSS can be used as a remote access point for CSDC. The compatibility of
RSS and CSDC improves the marketability of both features. The RSS design
allows a provision for the support of D4 special service channel bank
plug-ins. This provision allows for such applications as off premises
extensions, foreign exchanges lines, and private lines. Thus the RSS can be
used as a CSDC access point in a configuration similar to the CSDC RX


The CSDC feature is optionally available to Centrex/ESSX-1 customers. Most of
the capabilities of Centrex service can be applied to Centrex lines that have
been assigned the CSDC feature. In voice mode, the Centrex/CSDC line can
exercise any of the Centrex group features that have been assigned to the
line. In the voice/data mode, several Centrex features are inoperable or
operate only on certain calls. The CSDC feature can be provided for a Centrex
group as follows:

     1. Message Network Basis (MTS)
     2. IntraCentrex group basis
     3. InterCentrex group basis
     4. Any combination of the above

=User Perspective for the CSDC=

To establish a CSDC call, a CSDC user goes off hook, receives dial tone and
dials. The dialing format for the CSDC/MTS is as follows for interim plan:

     #99 AB (1+) 7 or 10 digits (#)

The customer dials '#99' to access the CSDC feature. The 'AB' digits are the
carrier designation code. No dial tone is returned after the 'AB' digits. The
1+ prior to the 7 or 10 digit directory number must be used if it is required
for MTS calls.  The '#' at the end is optional, if it is not dialed, end of
dialing is signalled by a time-out.

The long term dialing format for the CSDC/MTS is as follows:

     #56 (10XXX) (1+) 7 or 10 digits (#)

Dialing '#56' indicates 56kb/s alternate voice/data transmission. the '10XXX'
identifies the carrier to be used for the call. If '10XXX' is not dialed on an
inter-LATA call, the primary carrier of the subscriber is used. If '10XXX' is
not dialed on an intra-LATA call, the telco handles the call. The long term
plan also allows for several abbreviated forms. Dialing '#56 10XXX #' is
allowed for routing a call which prompts the customer to dial according to the
carrier dialing plan. Dialing '#56 10XXX' followed by a speed call is also
allowed. If a customer has pre-subscribed to a carrier which can carry CSDC
calls and the CSDC access code is stored as part of the speed calling number,
the customer dials the speed calling code to make a CSDC call.

Regular ringing is applied to the called line and audible ringing is applied
to the calling terminal. Once the voice connection is established, either
party can initiate the switch to data mode, if desired. To initiate a change
in mode a CSDC user must initiate a mode switch command via a closure of the NCT

An example of a mode switch:

     Suppose party A wants to switch to data. Party A issues a mode switch
command and receives a signal called far end voice (FEV) which is a bipolar
sequence (2031 hz at 60 ipm). Party A may now hang up the handset at any time
after initiating the mode switch command. Party B receives a far end data
(FED) tone (2031 Hz at 39 ipm) indicating party A wants to switch to data. If
party B agrees to switch to data, party B must initiate a mode switch command.
Party B may nor hang up the handset. Data transmission is now possible.
     To switch to the voice mode, anyone can initiate it. To switch, party A
would pick up the handset and initiate a mode switch command and will receive
the FED tone. Party B receives the FEV tone indicating that party A wants to
go voice. Party B must now pick up the hand set and initiate a mode switch
command. To terminate a call, either party may just leave the handset on and
indicate a mode switch. If termination is issued during a mode conflict, time
out will disconnect the call, usually about 10 or 11 seconds.

Centrex/ESSX-1 customers may utilize the CSDC service in several ways if they
have CSDC terminals with the necessary on premises equipment. The standard
CSDC call is initiated by dialing the message network access code, (9). The
dialing sequence is then identical to the plan for MTS:

     #99 AB (1+) 7 or 10 digits (interim plan)

     #56 (10XXX) (1+) 7 or 10 digits (#) (long term plan)

The dialing pattern to establish interCentrex or intraCentrex CSDC calls is as

     CSDC access code + extension

An intraCentrex/CSDC call is initiated by dialing the trunk access code
assigned to route a loop-around Centrex/CSDC trunk group. Next, the extension
of the desired station is dialed. To establish an interCentrex call a
different trunk access code must be used to route the CSDC calls to another
Centrex group instead of a station.

The CSDC maintenance circuit has a dialable digital loopback. This loopback is
very useful in CSDC testing. A customer can check their access line by dialing
the test DN. The loop is automatically activated when the call is answered.

=End of Part I.=

Part II: The CSDC hardware, and office data structures.

= (c) 1986 The Executioner and The PhoneLine Phantoms =
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