Comdial Dxp Plus Instructions Manual

							Installing The DXPT1 Digital Carrier Transmission Option
In The DXP Plus Digital Communications System
1.0 Introducing The DXPT1 Option
The digital carrier transmission option (DXPT1) gives the DXPPlusdigital communications system the
capability to handle up to 24 channels of voice and/or data transmissions over a single four-wire cable using
multiplexing techniques in superframe (SF) or extended superframe (ESF) format. The DXPT1 board includes a
customer service unit (CSU) to eliminate the need for a CSU external to the DXPPlus.
Since the DXPPlussupports a maximum of 240 lines, and each DXPT1 board handles up to 24 channels, you can
install up to 10 DXPT1 boards in the DXPPlussystem. You can install these 10 boards in any available universal
board slot in the main or expansion cabinets. Of course, any other line boards that you install, such as loop start,
DID or multipurpose, reduce the number of lines available for T1 service and thus reduces the number of DXPT1
boards that you can install.
Whenever you install one or more DXPT1 boards, and the DXPPlusis receiving its timing signals from an
external source, you must install one synchronization card (DXOPT–SYN) on the services board. When you
connect the system to central office (CO) lines, you must include a synchronization card, and the DXPPlusmust
be controlled by CO signalling. In installations where the DXPPlussupplies the clock signal for the distant
system, there is no requirement for DXOPT–SYN cards.
If you plan to use tone dial configured DID or E&M lines with the T1 digital carrier transmission option, you will
need to install one or more DTMF receiver cards to the DXPPlus. Typically, you will need one DTMF receiver
for every six lines. This ratio indicates that you need to add one DTMF receiver card for each DXPT1 board that
is configured for 24 DID or E&M lines. In high traffic situations, you may need additional DTMF receiver cards.
For information on DTMF receiver card installation, see IMI89–186,Installing A DTMF Receiver In The DXP
Plus Digital Communications System.
NOTE: The DTMF receiver cards that you add for this purpose are in addition to any you may add to the system
to support industry-standard telephone station boards
If you are unfamiliar with the terms and component names associated with the T1 digital carrier transmission
option, refer to glossary of terms presented inSection 8located at the end of this publication.
CAUTION
For operation with the DXP Plus, the T1 board must be Revision B or higher. If the T1 board that you are
installing is a lower revision, contact Comdial Technical Services (1–800–366–8224) for advice before
you proceed with the installation..
R
This manual has been developed by Comdial Corporation (the “Company”) and is intended for the use of its customers and service personnel. The information in this manual is subject to change
without notice. While every effort has been made to eliminate errors, the Company disclaims liability for any difficulties arising from the interpretation of the information contained herein.
The information contained herein does not purport to cover all details or variations in equipment or to provide for every possible contingency to be met in connection with installation, operation, or
maintenance. Should further information be desired, or should particular problems arise which are not covered sufficiently for the purchaser’s purposes, contact Comdial, Inside Sales Department,
Charlottesville, Virginia 22906.
Printed in U.S.A.IMI89-193.01
7/95 
						

							1.1 Understanding The DXPT1 Board
Through time division multiplexing, the DXPT1 board greatly increases the efficiency and economy of the DXP
Plussystem by providing up to 24 channels on two twisted metallic pairs. This multiplexing technique allows
two-way voice or data communications at 1.544 Mbps (million bits per second) with either a central office (CO),
public branch exchange (PBX), or another digital communications system (DXPPlus). The DXPT1 board
includes a built-in customer service unit (CSU) but there is no restriction on adding an external CSU.
When you connect two DXPPlussystems together using E&M protocol through the T1 lines, designate one DXP
Plus as the master and the other one as the slave. In this application, only the slave DXP Plussystem requires a
DXOPT–SYN card.
When the T1 option is installed, the DXPPlussupports the following signaling protocols per channel.
·Loop Start (subscriber end only)
·Ground Start (subscriber end only)
·E&M two- or four-wire tie lines
·DID (direct inward dial)
Loop Start and Ground Start will support synchronized ring, hook flash, and pause. Dialing can be DTMF (tone)
or dial pulse. For E&M and DID tone operation, check the number of DTMF receiver cards needed in the system
E&M and DID will support wink start, delay dial, and immediate dial (dial pulse only). Dialing can be tone or dial
pulse.
1.2 Understanding The DXOPT-SYN Synchronization Card
The DXOPT–SYN card uses a reference timing frequency of 8 KHz that it derives from the 1.544 MHz frequency
supplied to the DXPT1 board by the central office (CO) or other external source. By referencing this 8 KHz with
8 KHz timing derived internally, the master 16.384 MHz voltage-controlled oscillator (VCO) can be
synchronized. The T1 transmit clock (1.544 MHz) is derived from the 16.384 MHz frequency on the DXPT1
board. If the 1.544 MHz received frequency is incorrect (not within a 200 Hz tolerance), the system may loose
synchronization with the CO or other external source. The DXOPT–SYN card reports this condition by turning on
the appropriate alarms on the  DXPT1 board and DXOPT–SYN card. A loss of clock synchronization causes
frame slips that result in data communications errors.
The DXOPT–SYN card allows two timing references ( primary and secondary) to be selected. You can select
either automatic or manual (for maintenance mode). In the automatic mode, a loss of primary timing causes the
system to switch to the secondary timing reference. If both the primary and secondary timing references are lost,
the VCO oscillator on the DXOPT–SYN card is defaulted to the fixed 16.384 MHz oscillator on the services
board. This results in the loss of T1 clock synchronization.
IMI89–193 Installing The DXPT1 Line Board
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							2.0 Installing Circuit Boards In The Equipment Cabinet
CAUTION
Circuit boards are susceptible to damage caused by electrostatic discharge, and you must keep this fact in
mind as you handle the circuit boards. Refer to the Comdial publication IMI01-005,Handling Of
Electrostatically Sensitive Components, for general information. Specific handling precautions are also
included in this installation instruction.
2.1 Creating A Static Safe Work Area
When servicing the common equipment cabinet at the installation location, it is a good practice to place a
conductive mat in front of the cabinet area and ground the mat to a good earth ground. (The third wire ground of
the AC power line is also an acceptable grounding point.) The grounded conductive mat provides a safe static
electric discharge path.
When removing the common equipment cabinet from the installation location for servicing, it is a good practice to
prepare a static-safe work area on which to place the cabinet.
You should supply yourself with a static discharge wrist strap, and wear it every time you handle electronic circuit
boards either at the cabinet mounting location or at your work area.
Backboard
Earth
Ground 1 Meg Ohm
Resister Conductive
MatStatic Discharge
Wrist Stap Common
Equipment
Cabinet
PLUS034
Providing Static Protection At The Cabinet
Mounting Location
Typical Earth
Ground
Static
Wrist
Strap
ESD Protective
Mat ESD Protective
Mat
ESD Protective
Worksurface
Static 2
Common Point Ground
Creating A Static Safe Work Area
Installing The DXPT1 Line Board IMI89–193
Installing The DXPT1 Line Board – 3 
						

							3.0 Configuring The DXPT1 Board
Before you install the DXPT1 board, determine if you must meet special system requirements such as fractional
service (8 or 16 channel operation). If you do have special system requirements, use the dual in-line pin (DIP)
switches provided on the board to re-configure the DXPT1 board.
The DXPT1 board contains 28 DIP switches (three 8-position modules and one 4-position module). Rectangular
cutouts in the front-edge panel provide access to these switches.
The eight DIP switches nearest the bottom of the panel are accompanied by eight green LED indicators.
NOTE: These eight switches and their associated indicators are for factory diagnostic purposes only.
The remaining 20 DIP switches labeled SW1, SW2. and LIU are for configuring the DXPT1 board to meet
specific operating requirements. See Figure 2. The default setting for all of these switches is 0 (on the left as you
face the front edge of the board). This is the standard superframe (SF) configuration for most customer
applications. However, special customer needs may require that you reset one or more of these switches using the
procedure given below.
1. Obtain a static discharge wrist strap (supplied with the main DXP cabinet) and attach it to one of your wrists.
Make sure to adjust the strap for a snug fit against your skin; do not apply the strap over any of your clothing.
2. Connect one end of the wrist strap-cord to the wrist strap and the other end to earth ground.
NOTE: With the DXP cabinet in the installed position, the ground lug on the right side of the cabinet is normally
a good grounding point since this lug should have a heavy ground wire connected between it and a good
earth ground.
3. Remove the DXPT1 board from its static protection bag and set it on a static-safe work area.
4. Using a ball-point pen or similar object, move the DIP switches from left (0 position) to right (1 position) as
needed. All DIP switches are facing left for typical applications. See Tables 1, 2, and 3 for descriptions of the
DIP switches.
IMI89–193 Installing The DXPT1 Line Board
4 – Installing The DXPT1 Line Board 
						

							Locating The DIP Switches
T1002A
Reset Pushbutton
(Behind Hole)
LIU
SW1
SW2
00
011
1
(Default)
1
2
3
4(Default)
1
2
3
4
5
6
7
8
(Default)
1
2
3
4
5
6
7
8
(See Table 3)
(See Table 1)
(See Table 2)
Diagnostic
Switches and LEDs
For Factory
Use Only
Installing The DXPT1 Line Board IMI89–193
Installing The DXPT1 Line Board – 5 
						

							3.1 Understanding The T1 Options (SW1–1 Through SW1–8)
The following T1 operating modes are described to help you understand the many options that you can select with
DIP switches SW1–1 through SW1–8 on the DXPT1 board.
3.1.1 T1 General Operation
T1 is the digital two-way transmission of telecommunications over a single high-speed circuit. Up to 24 separate
voice or data transmissions form digital pulses that are transferred at the rate of 1.544 million bits per second
(Mb/s) over the T1 trunk. At the receiving end, the digital pulses are decoded into 24 separate circuits.
Pulse characteristics such as repetition rate, pulse width, pulse amplitude, and average ones density ((ratio of one
(1) bits to zero (0) bits)) are as specified by digital signal level 1 (DS-1) described in American National
Standards Institute Specification, ANSI T1.403-1989.
3.1.2 Framing Modes
Digital data is handled most efficiently when it is organized into frames. A frame of digital information consists
of 193 bits (24 channels x one eight-bit word + one framing or control bit). The framing bit is used for frame
identification when multiple frames are used.
The frame repetition rate is eight thousand frames per second (8 Kf/s).
This option uses either of two framing formats—superframe (SF) and extended superframe (ESF).
The superframe format contains 12 frames. In the 6th and 12th frames, the voice information in the eighth (least
significant) bit positions is overwritten with signaling information. This signaling method is called robbed-bit
signaling. The robbed bits in the 6th and 12th frames are designated signaling bit A and B respectively.
The extended superframe format extends the framing boundaries to include 24 frames . The ESF format provides
improved maintenance capability over the SF format. In this format, 24 framing bits (or 8 Kb/s) are available to
provide the following:
·framing synchronization (2 Kb/s)
·facility data link (FDL) (4 Kb/s)
·CRC-6 error check (2 Kb/s)
The robbed bits from the 6th, 12th, 18th, and 24th frames are used for signaling. Therefore, two additional
signaling paths are available—signaling bits C and D (future).
3.1.3 Signaling  Type
Channel associated signaling (CAS) is a signaling method employing robbed bits. The signals using the robbed
bits are related to the same channel as the one carrying the information. CAS is currently the only signaling-type
option available for this equipment.
3.1.4 Yellow Alarm
A yellow alarm is a signal transmitted by a digital communications system when that system has lost
synchronization to the incoming signal. Communications can be restored if a a yellow alarm lasts less than four
seconds. After four seconds, a red alarm (out-of-service) is issued and all calls are set to on-hook. When the
system is using the superframe format, the transmitted yellow alarm signal contains binary zeros (0s) in the
second bit positions of all 24 channels. This is the default setting for DIP switch SW1–4.
The 12th frame method (used in Japan) forces the framing bit for the 12th channel to a binary one (1). This is
detected by the receiving system as a yellow alarm.
In the extended superframe format, the system that has lost synchronization to the incoming signal will transmit a
16-bit pattern consisting of eight one (1) bits followed by eight zero (0) bits over the facility data link (FDL) to
represent a yellow alarm.
IMI89–193 Installing The DXPT1 Line Board
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							3.1.5 Zero Suppression
There are two ways to avoid system timing problems when eight or more successive zero (0) bits are transmitted.
One method is B7 suppression and the other is bipolar 8-zero substitution (B8ZS). For pulse modulated voice
(PCM), eight consecutive zero (0) bits should never occur.
B7 suppression is a technique that forces a one (1) bit in the 7th bit position when all of the bits in a binary word
are zero (0). The resulting distortion in a voice circuit is negligible. However, this technique could induce errors if
it was used in digital data transmissions.
Digital information transmitted over T1 trunks is bipolar; that is, the binary ones (1s) pulses (marks) alternate
between a positive and a negative voltage level. The bipolar 8-zero substitution (B8ZS) method substitutes four
bits in bit positions four, five, seven, and eight when eight zero (0) bits occur in a binary word. The substituted
bits are inserted in a unique pattern that causes a bipolar error. The B8ZS binary words containing the deliberate
bipolar errors are detected at the receiving terminal where the errant bipolar pulses are removed and substituted
with all zero (0) bits. Because the received binary words are returned to their original bit patterns (all binary zero
bits), a clear channel is provided for error-free digital data transmission. Both ends of the communications link
must be configured to use B8ZS. (B8ZS is a feature designed for future requirements.)
3.1.6 Fractional T1
Fractional T1 is when you use only a portion of a T1 trunk, as needed. On the DXP Plus you must set DIP
switches SW1–7 and SW1–8 for 24 channel operation. This setting allows the system to pass error information
end-to-end when operating fractional T1 with the ESF format.
Setting The SW1 DIP Switches
Switch
NumberSwitch
PositionFunction
1 (top) 0 (default)
1FRAME MODE
superframe mode (SF)
extended superframe mode (ESF)
2 0 (default)
1SIGNALING TYPE
channel associated signaling (CAS)
reserved
3 0 (default)
1RESERVED FOR FUTURE USE
reserved
reserved
40 (default)
1YELLOW ALARM TYPE
bit 2 of all channels method
12 frame method (Japanese)
5,60, 0 (default)
0,1
1,0
1,1ZERO SUPPRESSION
B7 suppression
B8ZS suppression (digital data)
no suppression
no suppression
7,8
0,0 default)CHANNEL CAPACITY
24 channel capacity
NOTE: SW1–1 through SW1–8 switches are read only when you apply power to the board or do a manual reset.
With power on, manually reset the board by inserting a slender object, such as a straightened-out paper
clip, into the small hole located between the Yellow and Syn LEDs on the front-edge panel. You can also
reset the board remotely from a video display terminal or personal computer. A reset causes a T1 service
disruption.
Installing The DXPT1 Line Board IMI89–193
Installing The DXPT1 Line Board – 7 
						

							3.2 Understanding The T1 Options
(SW2–1 Through SW2–8 And LIU–1 Through LIU–4)
The following T1 operating modes are described to help you understand the many options that you can select with
DIP switches SW2–1 through SW2–8 and LIU–1 through LIU–4 on the DXPT1 board. DIP switches designated
LIU are associated with the DXPT1 board’s line interface unit.
3.2.1 Loopback
Loopback is the maintenance routine used to verify the receive function (local or remote) and to isolate system
problems. When using the superframe format, the customer interface (CI) loopback option from the network, if
provided, can be activated from the network via in-band signaling (per ANSI T1.403, 1989, SECTION 8.3.1.1).
Framed code words activate and deactivate loopback routines when the option is enabled with DIP switch
SW2–1. The default setting is off, but many central offices will support SF loopback. See your central office
representative to ensure that you are complying with their requirements.
You access remote and payload loopback operation via the facility data link when using the extended superframe
format.
You can manually make three different types of loopback requests depending on the option you select using DIP
switches SW2–7 and SW2–8. These are: local, remote, and payload loopback. When using payload loopback
(ESF format only), all channel bits maintain bit-sequence integrity but the framing bit is re-established.
3.2.2 Customer Service Unit (CSU) Identification Bit
You can set the message-oriented (C/R) bit transmitted over the ESF data link by DIP switch SW2-2 to be a zero
(0) bit or a one (1) bit. The C/R bit is used to identify the T1 signal origin as being either from customer premise
equipment (CPE) or carrier equipment such as a CSU.
Set C/R to be a zero (0) bit for customer premise equipment (CPE) or when using an external CSU (default).
Set C/R to be a one (1) bit if the network requires the T1 internal CSU to be classified as carrier equipment.
3.2.3 Cyclic Redundancy Check (CRC-6)
This is a method for checking the accuracy of data transmissions when using the ESF format. This method uses a
polynomial algorithm based on the content of a superframe of data. When CRC-6 checking is enabled via DIP
switch SW2–4, an alarm will be activated whenever a CRC code (checksum) is received over the ESF data link
that does not match the locally calculated code (checksum).
3.2.4 Yellow Alarm During ANSI Messages On The Facility Data Link
When using the ESF format, the facility data link is available for reporting transmission performance information
once a second. Normally, these transmissions are inhibited by yellow alarms. However, you can set DIP switch
SW2-5 to allow these transmissions during yellow alarms.
3.2.5 Green B8ZS/COFA LED Definition
The green LED on the DXPT1 board’s edge-panel labeled “B8ZS/COFA” indicates either that B8ZS code words
are being received or that a change of frame alignment (COFA) occurred during the last synchronization by the
external T1 source or carrier equipment. You can determine which condition you want reported by how you set
DIP switch SW2–6. The default setting is for “COFA” reporting.
3.2.6 Receive  Sensitivity
The equalizer gain logic (EGL) determines how sensitive the receive circuits are to the incoming signals. You set
the level for -26 dB or -36 dB by using DIP switch LIU-1. (Normally, the -26 dB level setting is the better choice.)
IMI89–193 Installing The DXPT1 Line Board
8 – Installing The DXPT1 Line Board 
						

							3.2.7 Transmit Level Attenuation
You can manually set the transmit level for a particular value (0, -7.5, -15, or -22.5 dB) or select the automatic
feature that sets the transmit level automatically depending on the receive signal. A weak receive signal causes a
strong transmit signal and vice versa. Use DIP switch LIU–2 to select either the manual or the automatic setting.
If you select the manual setting, set the desired value with DIP switches LIU–3 and LIU–4. Normally, 0 dB is
used when connecting to a network interface box.
Setting The SW2 DIP Switches
Switch
NumberSwitch
PositionFunction
1 (top)0 (default)
1superframe NETWORK IN-BAND loopback
disabled
enabled
20 (default)
1CSU ID (C/R) BIT (ESF MODE)
C/R bit = 0 designates customer premise equipment  (CPE)
C/R bit = 1 designates carrier equipment
30 (default)
1RESERVED FOR FUTURE USE
reserved
reserved
40 (default)
1CRC (CYCLIC REDUNDANCY CHECK) FOR ESF MODE
disabled
enabled
50 (default)
1FDL YELLOW ALARM DURING ANSI MESSAGES
disabled
enabled
60 (default)
1B8ZS/COFA LED DEFINITION
COFA (change of frame alignment)
B8ZS detect
7,80,0 (default)
0,1
1,0
1,1MANUAL loopback REQUEST
no loopback
local loopback request
remote loopback request
payload loopback request (ESF only)
NOTE: When changing DIP switch SW2–2 or SW2–5, you must reset the board before the switch is read. With
power on, manually reset the board by inserting a slender object, such as a straightened-out paper clip,
into the small hole located between the Yellow and Syn LEDs on the front-edge panel. You can also reset
the board remotely from a video display terminal or personal computer. A reset causes a T1 service
disruption.
Setting The LIU DIP Switches
Switch
NumberSwitch
PositionFunction
1 (top)
0 (default)
1RECEIVE SIGNAL SENSITIVITY
-26 dB
-36 dB
20 (default)
1TRANSMIT LEVEL MODE
Automatic (level set by receive signal)
Manual (level set by switches 3 and 4 below)
3,40,0 (default)
0,1
1,0
1,1TRANSMIT LEVEL ATTENUATION
(LIU-2 must be “1)
0 dB
-7.5 dB
-15 dB
-22.5 dB
Installing The DXPT1 Line Board IMI89–193
Installing The DXPT1 Line Board – 9 
						

							4.0 Installing The DXPT1 Board
1. Normally you should disconnect the AC power cord from the AC outlet and disconnect the optional battery
back-up assembly from the main cabinet power supply; however, when necessary, you can install a DID line
board in an operating system. If you must do this, connect one end of a standard telephone handset coil cord
to the precharge port on the power supply. During step 6, you will connect the other end of this coil cord to
the precharge jack on the line board.
2. Install your static discharge wrist strap on your bare wrist; adjust it for a snug fit. Be sure that the strap is
touching bare skin and is not isolated by clothing. Connect the wrist strap cord between the wrist strap and an
AC or earth ground
3. Loosen the retaining hardware and lift the front panel away from the common equipment cabinet.
NOTE: With the common equipment in the installed position, the ground lug on the side of the cabinet is an
appropriate grounding point since it should have a heavy ground wire connected between it and a good
earth ground.
4. Each DXPT1 line board is supplied in a static protection bag for safe keeping. When you are ready to install
the board, remove it from its static protection bag.
5. Locate the proper board slot.
·On DXP Plus systems the DXPT1 line boards connect to any universal slot.
NOTE: On DXP Plus systems, do not install a DXPT1 line board at the right-most board slot in the second (or
lower) expansion cabinet. The system reserves this slot for internal use.
6. If you are installing the DXPT1 line board in an operating system, connect the free end of the precharge cord
that you installed in step 1 to the precharge jack on the line board.
7. Orient the DXPT1 line board with its top and bottom guides in main cabinet board cage, and press the board
firmly until its board edge connection properly mates with the connector on cabinet’s backplane. If you
connected a handset cord between the pre-charge port on DXP Plus power supply and the jack on DXPT1 line
board (as directed in step 6), disconnect it after installing board.
CAUTION
When pressing circuit boards into place, press them only at the extractor lever locations.
If you apply pressure at other locations you may damage the board assembly.
8. Repeat steps 3 and 4 until all DXPT1 line boards are installed.
9. Make a final inspection to ensure that all boards are, oriented correctly and mated properly.
10. Install and tighten the supplied screws to secure the circuit boards to the board cage. Do not neglect this step!
It is important because it helps in providing a protective ground condition for the board thus ensuring RFI
(radio frequency interference) and lightning protection.
IMI89–193 Installing The DXPT1 Line Board
10 – Installing The DXPT1 Line Board