][==================================][
||                                  ||
||     Circuit Switched Digital     ||
||           Capability             ||
||     -------------------------    ||
||            Written by            ||
||                                  ||
||          The Executioner         ||
||                                  ||
||              and the             ||
||                                  ||
||    [+] PhoneLine Phantoms [+]    ||
||        -    -    -               ||
][==================================][

 The Circuit Switched Digital Capability feature provides 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. The CSDC
feature was formerly known as PSDC (Public Switched Digital Capability). Both
terms are used in practice because of translations, set cards and etc.
requiring the PSDC term. The CSDC term is used for customer identification and
explanation. The CSDC feature provides an alternate voice/data capability. If
the loop is a wire loop, CSDC utilizes time compression multiplexing (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 the caller may
alternate between voice and data as many times as desired. CSDC can support
subvariable data rates but a 56 kb/s is used in the network.

    Some applications for CSDC:

     1. Audiographic teleconferencing
     2. Secure voice
     3. Facsimile
     4. Bulk data
     5. Slow scan television

  A typical CSDC call is originated over a 2-wire loops which can be used for
message telecommunications service (MTS) and touch tone is required. Calling
can be done by automatic calling equipment (ACE) or manually. Digit reception,
transmission, and signalling follow the same procedures used for MTS outgoing
calls on CCIS or non-CCIS trunks. However, CSDC calls are always routed over
digital transmission facilities.

=================
=Long term plans=
=================

  The long term plan allows for Equal Access Multi-frequency (EA-MF) signalling
and improved AMA. A CSDC call attempt is screened to ensure that the calling
party has CSDC and the carrier used provides 56 kb/s alternate voice/data at
the office. A blocked call is routed to a special error message. A CSDC call is
routed directly 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 basis.

  The AT is a 1A ESS switch which allows access to carriers form and end office
without requiring direct trunks. Signalling between the end office and the AT
is either EA-MF or CCIS, Trunk groups using EA-MF signalling can have combined
carrier traffic. Separate trunk groups for each carrier are required for CCIS
signalling.

  The SCP is a 1A ESS switch which allows access to carriers using only CCIS
signalling from offices without the CCIS capability. Separate trunk groups for
each are used between the originating end office and the SCP. Separate trunk
groups are optional between the SCP and the terminal end office. Signaling
between the end office and the SCP is MF. The SCP must have direct connection
to the carrier using CCIS.

  CSDC is also available for Centrex/ESS X-1customers. Most of the capabilities
of centrex service can be applied to the CSDC feature. CSDC provides the
following for the centrex group:

   1. Message Network Basis
   2. Intracentrex group basis
   3. Intercentrex group basis
   4. Any combo of above


=========
=Dialing=
=========

  To establish a CSDC call, a user dials the following:

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

  The user dials '#99' to access CSDC and AB is the carrier being used. The '#'
is used optional for end of dialing indicator. The long-term dialing plan is as
follows:

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

  Dialing 56 means 56 kb/s. The 10XXX identifies the carrier. If 10XXX is not
dialed on an Inter-LATA call, the primary subscriber is used. If 10XXX is not
dialed on an Intra-LATA call then the local Telco handles it.

=================
=Switching Modes=
=================

  Suppose Party A wants to switch from voice to data. Party A issues a mode
switch command and then receives a signal called a far end voice (FEV) bipolar
sequence (2031 hz at 60 ipm). Party A can now hang up any time. Party B
receives a far end data tone at 2031 hz at 39 ipm indicating that Party A wants
to do some data transfer. Then Party B must initiate a mode switch command.
Party B then hangs and transmission is possible.

   TO switch back to voice, Party A initiates a mode switch command and this
time receives an FED tone, and B gets an FEV tone. Party B then picks up and
does a switch then the voice is established.

=====================================
= (C) 1985 Sexy-Exy & The PLP       =
=====================================

Dedicated to The Guardian Demon.