Black Box G.703/G.704 NTU w/V35 User manual

CUSTOMER
SUPPORT
INFORMATION
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FREE technical support, 24 hours a day, 7 days a week: Call 724-746-5500 or fax [phone]
Mail order: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
Web site: www.blackbox.com • E-mail: [email protected]
BLACK BOX
NETWORK SERVICES
®®
G.703/G.704
NTU w/V35
511/E
Normal
511
G.703/G.704 NTU w/V35
Local
Normal
Remote
Test Modes
TMERRDTDE1 Link LOS
MARCH 2006
MT335A

G.703/G.704 NTU W/V35
2
CE NOTICE
The CE symbol on your Black Box equipment indicates that it is in compliance
with the Electromagnetic Compatibility (EMC) directive and the Low Voltage
Directive (LVD) of the European Union (EU). A Certificate of Compliance is
available by contacting Technical Support.
RADIO AND TV INTERFERENCE
The Multi-Rate Ethernet Extender generates and uses radio frequency energy,
and if not installed and used properly-that is, in strict accordance with the manu-
facturer’s instructions-may cause interference to radio and television reception.
The Multi-Rate Ethernet Extender has been tested and found to comply with the
limits for a Class A computing device in accordance with specifications in Sub-
part B of Part 15 of FCC rules, which are designed to provide reasonable protec-
tion from such interference in a commercial installation. However, there is no
guarantee that interference will not occur in a particular installation. If the Ether-
net Extender does cause interference to radio or television reception, which can
be determined by disconnecting the unit, the user is encouraged to try to correct
the interference by one or more of the following measures: moving the comput-
ing equipment away from the receiver, re-orienting the receiving antenna and/or
plugging the receiving equipment into a different AC outlet (such that the com-
puting equipment and receiver are on different branches).

G.703/G.704 NTU W/V35
3
FCC PART 68
TRADEMARKS USED IN THIS MANUAL
All applied-for and registered trademarks are the property of their respective owners.
NORMAS OFICIALES MEXICANAS (NOM) ELECTRICAL SAFETY STATEMENT
Instrucciones De Seguridad
1. Todas las instrucciones de seguridad y operación deberán ser leídas antes
de que el aparato eléctrico sea operado.
2. Las instrucciones de seguridad y operación deberán ser guardadas para ref-
erencia futura.
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones de
operación deben ser respetadas.
4. Todas las instrucciones de operación y uso deben ser seguidas.
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo, cerca
de la tina de baño, lavabo, sótano mojado o cerca de una alberca, etc.
6. El aparato eléctrico debe ser usado únicamente con carritos o pedestales
que sean recomendados por el fabricante.
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como sea
recomendado por el fabricante.
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico más
allá a lo descrito en las instrucciones de operación. Todo otro servicio
deberá ser referido a personal de servicio calificado.
9. El aparato eléctrico debe ser situado de tal manera que su posición no interfi-
era su uso. La colocación del aparato eléctrico sobre una cama, sofá, alfombra
o superficie similar puede bloquea la ventilación, no se debe colocar en libre-
ros o gabinetes que impidan el flujo de aire por los orificios de ventilación.
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de calor
como radiadores, registros de calor, estufas u otros aparatos (incluyendo
amplificadores) que producen calor.
Caution
The MT335A is not intended to be connected to the pub-
lic telephone network.

G.703/G.704 NTU W/V35
4
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo del tipo
descrito en el instructivo de operación, o como se indique en el aparato.
12. Precaución debe ser tomada de tal manera que la tierra fisica y la polarización
del equipo no sea eliminada.
13. Los cables de la fuente de poder deben ser guiados de tal manera que no sean
pisados ni pellizcados por objetos colocados sobre o contra ellos, poniendo
particular atención a los contactos y receptáculos donde salen del aparato.
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las recomen-
daciones del fabricante.
15. En caso de existir, una antena externa deberá ser localizada lejos de las lineas
de energia.
16. El cable de corriente deberá ser desconectado del cuando el equipo no sea
usado por un largo periodo de tiempo.
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean derra-
mados sobre la cubierta u orificios de ventilación.
18. Servicio por personal calificado deberá ser provisto cuando:
A. El cable de poder o el contacto ha sido dañado; u
B. Objectos han caído o líquido ha sido derramado dentro del aparato; o
C. El aparato ha sido expuesto a la lluvia; o
D. El aparato parece no operar normalmente o muestra un cambio en su
desempeño; o
E. El aparato ha sido tirado o su cubierta ha sido dañada.

G.703/G.704 NTU W/V35
5
CONTENTS
CE Notice .................................................................................................... 2
Radio and TV Interference.......................................................................... 2
FCC Part 68................................................................................................. 3
Trademarks Used In This Manual............................................................... 3
Normas Oficiales Mexicanas (NOM) Electrical Safety Statement............. 3
1. General Information ....................................................................................7
1.1 Features ...............................................................................................7
1.2 Description ......................................................................................... 7
2. Configuration............................................................................................... 8
2.3 DIP Switch Configuration.................................................................. 8
2.3.1 Switch SW1-1 through SW1-5................................................ 9
2.3.2 SW1-6 and SW1-7 Clock Modes .......................................... 10
2.3.3 SW1-8: Enable/Disable Loop Tests from DTE..................... 11
2.3.4 Switch SW2-1 Line Coding: HDB3 (default) ....................... 11
2.3.5 Switch SW2-2: CRC-4 Multiframe....................................... 12
2.3.6 Switch SW2-3 Data Inversion............................................... 12
2.3.7 Switch SW2-4: Remote Digital Loopback Type................... 13
2.3.8 Switch SW2-5 Front Panel Switches..................................... 13
2.3.9 Switch SW2-6: V.54 Response Disabled (default)................ 13
3. Installation................................................................................................. 14
3.4 Connecting to the G.703 Network.................................................... 14
3.4.10 Opening the Case.................................................................. 14
3.4.11 Connecting the Twisted Pair (120 ohm) to the
G.703 Network ...................................................................... 15
3.5 Connecting the Serial Port................................................................ 15
3.5.12 Connecting to a “DTE” Device............................................ 15
3.5.13 Connecting to a “DCE” Device............................................ 15
3.6 Power Connection ............................................................................ 16
4. Operation................................................................................................... 17
4.7 Power-up........................................................................................... 17
4.8 LED Status Monitors........................................................................ 17
4.9 Loop (V.54 & Telco) Diagnostics.................................................... 18
4.9.14 Operating Local Loopback (LL) .......................................... 18
4.9.15 Operating Remote Digital Loopback (RL)........................... 19
4.9.16 CSU Loop............................................................................. 20

G.703/G.704 NTU W/V35
6
4.9.17 Using the V.52 (BER) Test Pattern Generator..................... 21
A. Specifications ............................................................................................ 22
A.1 Network Data Rate ...........................................................................22
A.2 Network Connector ..........................................................................22
A.3 Nominal Impedance ..........................................................................22
A.4 Line Coding ......................................................................................22
A.5 Line Framing ....................................................................................22
A.6 CRC-4 Multiframing ........................................................................22
A.7 Clocking ...........................................................................................22
A.8 Time Slot Rate ..................................................................................22
A.9 Network Data Rates ..........................................................................22
A.10 Distance ............................................................................................22
A.11 Configuration ....................................................................................23
A.12 Power Supply ....................................................................................23
A.13 Humidity ...........................................................................................23
A.14 Temperature ......................................................................................23
A.15 Dimensions .......................................................................................23
B. Interface Pin Assignment........................................................................... 24

G.703/G.704 NTU W/V35
7
1. General Information
Thank you for your purchase of this Black Box product. If any questions arise
during installation or use of the unit, contact Black Box Tech Support at
[phone].
1.1 Features
•
Terminates G.703 and G.704, E1/fractional E1 service
•
Available in low-cost standalone or rack-mountable versions
•
n x 64 kbps data rates to 2 Mbps
•
V.35
• Switch-selectable AMI or HDB3 line encoding options
•
75-ohm dual coax and 120-ohm twisted-pair G.703 connections
•
Local and remote loopback diagnostics
•
Internal, external, and G.703 network timing
•
CE and BABT approvals
•
100–240 VAC
•
Conforms to ONP requirements CTR 12 and CTR 13 for connection to interna-
tional Telecom networks
1.2 Description
The Model 2701 receives channelized G.704 (n x 64 kbps) or clear channel
E1/G.703 (2.048-Mbps) data from the Telco’s digital data network. The Model
2701 terminates the G.703 telco interface and converts the data for transmission
to a user-oriented serial. The 2701 can connect to a Router, FRAD, PABX or
Multiplexer over its serial interface at nx64kbps data rates up to 2.048 Mbps.

G.703/G.704 NTU W/V35
8
2. Configuration
The MT335A features configuration capability via hardware DIP switches. This
section describes all possible DIP switch configurations of the MT335A.
2.3 DIP Switch Configuration
The MT335A has two sets of internal DIP switches that allow configuration for a
wide range of applications. The sets of switches are accessed from the underside
of the MT335A. Figure 1 shows the location of the DIP switches on the bottom
of the printed circuit board.
Figure 1. Underside of MT335A, Showing Location of DIP Switches
The MT335A DIP switches (Switch Sets 1–2) can be configured as either “ON”
or “OFF”. Figure 2 shows the orientation of the DIP switches with respect to
ON/OFF positions.
Figure 2. Close-up of configuration switches
8 7 6 5 4 3 2 1
8 7 6 5 4 3 2 1
Front
Rear
ON
S2
S1
OFF

G.703/G.704 NTU W/V35
9
2.3.18 S
WITCH
SW1-1
THROUGH
SW1-5
A detailed description of each switch (SW1-1 through SW1-5) setting follows the
summary table below.
Table 1: Switch Set 1 Summary Table
SW1 SW2 SW3 SW4 SW5 Speed
On On On On On 64 kbps
Off On On On On 128 kbps
On Off On On On 192 kbps
Off Off On On On 256 kbps
On On Off On On 320 kbps
Off On Off On On 384 kbps
On Off Off On On 448 kbps
Off Off Off On On 512 kbps
On On On Off On 576 kbps
Off On On Off On 640 kbps
On Off On Off On 704 kbps
Off Off On Off On 768 kbps
On On Off Off On 832 kbps
Off On Off Off On 896 kbps
On Off Off Off On 960 kbps
Off Off Off Off On 1024 kbps
On On On On Off 1088 kbps
Off On On On Off 1152 kbps
On Off On On Off 1216 kbps
Off Off On On Off 1280 kbps
Use Switches SW1-5 to set the DTE data rate.
Position Function Factory Default Selected Option
SW1-1 DTE Rate OFF
SW1-2 DTE Rate OFF
SW1-3 DTE Rate OFF
SW1-4 DTE Rate OFF
SW1-5 DTE Rate OFF
SW1-6 Clock Mode OFF Receive Recovered
SW1-7 Clock Mode OFF Receive Recovered
SW1-8 TM from DTE OFF Enabled
2.048 Mbps
Clear
Channel
}

G.703/G.704 NTU W/V35
10
Note When the data rate is set to 2.048Mb/s, the unit is forced into G.703
mode, and it transmits user data on all 32 time-lots. There is no framing
information; therefore, the CRC4 MF (SW2-2) switch is ignored. In all
other rate settings, the unit employs G.704 framing; TS0 is reserved
for signaling.
2.3.19 SW1-6
AND
SW1-7 C
LOCK
M
ODES
Use Switches SW1-6 and SW1-7 to configure the MT335A for internal, external,
or receive recover clock mode.
Network Clock —Transmitter timing is derived using the received line signal
(received recovered) from the network.
Internal Clock —Transmitter timing is derived from an internal clock source.
External Clock —Transmitter timing is derived from DTE terminal timing.
On On Off On Off 1344 kbps
Off On Off On Off 1408 kbps
On Off Off On Off 1472 kbps
Off Off Off On Off 1536 kbps
On On On Off Off 1600 kbps
Off On On Off Off 1664 kbps
On Off On Off Off 1728 kbps
Off Off On Off Off 1792 kbps
On On Off Off Off 1856 kbps
Off On Off Off Off 1920 kbps
On Off Off Off Off 1984 kbps
Off Off Off Off Off Clear Channel 2048 kbps
SW1-6 SW1-7 Clock Mode
On On Network (Received Recovered)
On Off Internal
Off On External
Off Off Network (Received Recovered)
SW1 SW2 SW3 SW4 SW5 Speed

G.703/G.704 NTU W/V35
11
2.3.20 SW1-8: E
NABLE
/D
ISABLE
L
OOP
T
ESTS FROM
DTE
Use Switch SW1-8 to allow MT335A to enter loopback tests when the DTE
raises the appropriate loop request pin.
2.3.21 S
WITCH
SW2-1 L
INE
C
ODING
: HDB3 (
DEFAULT
)
Use Switch SW2-1 to control the Network Line Coding options. Set these
options to be the same as the Line Coding given to you by your Service Provider.
If you are using two MT335As together as short range modems, set both units to
HDB3.
Options: HDB3, AMI
HDB3 In this line coding, the transmitter substitutes a deliberate bipolar viola-
tion when excessive zeros in the data stream are detected.The receiver
recognizes these special violations and decodes them as zeros.This
method enables the network to meet minimum pulse density require-
ments.Unless AMI is required in your application, HDB3 should be used
whenever possible.
AMI Alternate Mark Inversion defines a pulse as a “mark,” a binary one, as
opposed to a zero. In an E1 network connection, signals are transmitted
as a sequence of ones and zeros. Ones are sent as pulses, and zeros
S1-8 Setting
Off Response to DTE Loopback Request Enabled
On Response to DTE Loopback Request Disabled
Position Function Factory Default Selected Option
SW2-1 Line Coding Off HDB3
SW2-2 CRC-4 multiframe Off Disabled
SW2-3 Data Inversion Off Data Not Inverted
SW2-4 V.54/CSU select Off V.54 RDL loop
SW2-5 FPS enabled Off Enabled
SW2-6 V.54 Response On Disabled
SW2-7 Not Used N/A N/A
SW2-8 Not Used N/A N/A
SW2-1 Line Encoding
Off HDB3
On AMI

G.703/G.704 NTU W/V35
12
are sent as spaces, i.e., no pulse. Every other pulse is inverted from the
previous pulse in polarity, so that the signal can be effectively transmit-
ted.This means, however, that a long sequence of zeros in the data
stream will cause problems, since the NTU receiving the signal relies on
the signal to recover the 2.048 Mb/s clock.
If you must use AMI, you should ensure that the data terminal equipment
connected to the unit provides a minimally acceptable pulse density. For
this reason, there are advantages to using HDB3 instead.AMI coding
does not inherently account for ones density.To meet this requirement,
the user should ensure that the data inherently meets pulse density
requirements.
2.3.22 S
WITCH
SW2-2: CRC-4 M
ULTIFRAME
In framed mode, SW2-2 is used for CRC-4 MF. When CRC-4 is enabled, the unit
monitors the incoming data stream for CRC-4 errors. It transmits CRC-4 error
counts to the transmitting unit. When using timeslot zero (TS0), excessive errors
may cause loss of frame or loss of sync. If CRC-4 MF is used, both units must be
set for set for CRC-4 MF. Otherwise, the one using CRC-4 MF will detect loss of
sync.
Note When the data rate is set to 2.048Mb/s, then the unit is forced into G.703
mode, and it transmits user data on all 32 time-lots. There is no framing
information; therefore, the CRC4 MF (SW2-2) switch is ignored. In all
other rate settings, the unit employs G.704 framing; TS0 is reserved for
signaling.
2.3.23 S
WITCH
SW2-3 D
ATA
I
NVERSION
Set Switch S2-3 to determine whether or not the data stream from the local DTE
is inverted within the MT335A before being passed to the G.703/G.704 network.
An inverted data stream may be required when you use the MT335A to commu-
nicate with a G.703 device (that inverts the data) on the remote end. In typical
installations, data inversion is not necessary.
SW2-2 Option
Off CRC-4 Disabled
On CRC-4 Enabled
SW2-3 Option
Off Data not inverted
On Data inverted

G.703/G.704 NTU W/V35
13
2.3.24 S
WITCH
SW2-4: R
EMOTE
D
IGITAL
L
OOPBACK
T
YPE
The user can set this switch to select the type of remote loop that will be initiated
by the MT335A. If set to V.54, the MT335A will initiate a V.54 loop when
Remote Loop is selected by the front panel switches. If set to CSU, the MT335A
will initiate a CSU loop when Remote Loop is selected by the front panel
switches.
2.3.25 S
WITCH
SW2-5 F
RONT
P
ANEL
S
WITCHES
As the Front Panel Switches may be inadvertently toggled, or in the event that the
end-user may not need to use the switches, the installer may disable the front
panel switches. Set Switch S2-5 to determine whether the front-panel toggle
switches are active or inactive.
2.3.26 S
WITCH
SW2-6: V.54 R
ESPONSE
D
ISABLED
(
DEFAULT
)
V.54 Response is a special in-band loopback facility that sends a pseudo-random
pattern over the data stream. This is the only loopback that the unit can initiate.
This is useful for campus applications when you need to put a remote unit in
loopback. The unit responds to theV.54 loopback command, and the whole pro-
cess takes only a few seconds to complete. When V.54 Loopback is disabled, the
unit will not be able to send or respond to V.54 loopback commands. The dura-
tion of the loopback is limited by the loopback timeout setting.
S2-4 RDL Type
Off Initiate a V.54 RDL loop when selected
On Initiate a CSU loopback when selected
SW2-5 Option
Off Front Panel Switches Enabled
On Front Panel Switches Disabled
SW2-6 Option
Off V.54 Response Enabled
On V.54 Response Disabled

G.703/G.704 NTU W/V35
14
3. Installation
Once the MT335A is properly configured, it is ready to connect to the
G.703/G.704 interface, to the serial port, and to the power source. This section
describes how to make these connections.
3.4 Connecting to the G.703 Network
The MT335A is equipped with a single RJ-48C jack for connections to a 120
ohm twisted pair G.703/G.704 network interface (see Figure 3).
Figure 3. Rear Panel, Showing Location of Connectors.
If your G.703/G.704 network terminates via RJ-48C, use the connection diagram
(Figure 4) following the pinout and signals chart below to connect the 120 ohm
G.703/G.704 network channel.
3.4.27 O
PENING THE
C
ASE
Open the case by inserting a screwdriver into the slots and twist the screwdriver
head slightly. The top half of the case will separate from the lower half of the
case. Take caution not to damage any of the PC board mounted components.
Made in the USA
Interface
Power
Line
Power
V.35 Interface
Line

G.703/G.704 NTU W/V35
15
3.4.28 C
ONNECTING THE
T
WISTED
P
AIR
(120
OHM
)
TO THE
G.703 N
ETWORK
Figure 4. G.703/G.704 170 ohm Connection.
3.5 Connecting the Serial Port
The MT335A supportsV.35 serial port connections, this section describes how to
connect the serial ports to your terminal equipment.
3.5.29 C
ONNECTING TO A
“DTE” D
EVICE
The serial port on the MT335A is hard-wired as a DCE. Therefore these modules
“want” to plug into a DTE such as a terminal, PC or host. When making the con-
nection to your DTE device, use a straight through cable of the shortest possible
length—we recommend 6 feet or less. When purchasing or constructing an inter-
face cable, please refer to the pin diagrams in Appendix D as a guide.
3.5.30 C
ONNECTING
TO A“DCE” DEVICE
If the MT335A serial interface is hard-wired as a DCE, you must use a null
modem cable when connecting to a modem, multiplexer or other DCE device.
RJ-45 Cable (8-Wire)
G.703/G.704
NETWORK SIGNAL SIGNAL
PIN#
RX+ 1-----------------------TX+
RX- 2-----------------------TX-
TX+ 5-----------------------RX+
TX- 4-----------------------RX
Shield 3-----------------------Shield
Shield 6-----------------------Shield
(No Connection) 8
(No Connection) 7
(No Connection) 6
(TX+) 5
(TX-) 4
(No Connection) 3
(RX-) 2
(RX+) 1
8
7
6
5
4
3
2
1
MT335A

G.703/G.704 NTU W/V35
16
This cable should be of the shortest possible length—we recommend 6 feet
or less.
3.6 Power Connection
The MT335A uses a 5VDC, 2A universal input 100–240 VAC, power supply
(center pin is +5V). The universal input power supply has a male IEC-320 power
entry connector. This power supply connects to the MT335A by means of a barrel
jack on the rear panel. Many international power cords are available for the uni-
versal power supply.
The MT335A powers up as soon as it is plugged into an AC outlet--there is no
power switch.
WARNING
There are no user-serviceable parts in the
power supply section of the MT335A.
Contact Black Box technical support at
[phone] for more information.

G.703/G.704 NTU W/V35
17
4. Operation
When the MT335A has been properly configured and installed, it should operate
transparently. This sections describes power-up, LED status monitors, and the
built-in loopback test modes.
4.7 Power-up
Before applying power to the MT335A, please read “Power Connection” on
page 16 and verify that the unit is properly connected to the appropriate power
source.
4.8 LED Status Monitors
The MT335A features six front panel LEDs that monitor connections on the
G.703/G.704 and signaling, error and test modes. Figure 5 shows the front panel
location of each LED. Descriptions of each LED follow Figure 5.
Figure 5. MT335A Front Panel
E1 Link (Active Green) Solid green (On) indicates that the end to end E1 Link is
G.703/G.704 NTU w/V35
E1 Link
TD RD LOS
TM
ER

G.703/G.704 NTU W/V35
18
up, signifying that the link is active.The E1 Link LED is Off when the link
is down.
TD & RDGlows yellow to indicate an idle condition of Binary “1” data on the
respective terminal interface signals. Green indicates Binary “0” data.
LOS The Loss of Sync LED lights when the unit loses synchronization with the
incoming signal.This may happen when there is a framing mismatch or a
loss of signal.In unframed mode, the LOS LED monitors the status of the
transmit clock.
ER The error LED indicates various error conditions, including framing bit
errors, excessive zeros, controlled slips, severe errors, or bit errors
(when sending V.52 test patterns).When sending a test pattern, the LED
will remain lit if the unit does not receive the identical pattern.When it
receives the correct pattern, the LED will turn off. If error insertion is on,
the LED will blink once a second if everything is operating properly.
TM (ActiveYellow) SolidYellow indicates an ActiveTest Mode.The unit may
be placed in test mode by the local user or by the remote user.
4.9 Loop (V.54 & Telco) Diagnostics
The MT335A offers three V.54 loop diagnostics. Use these diagnostics to test the
NTU and any communication links. These tests can be activated via the front
panel switches or via signals on the MT335A serial port interface.
4.9.31 OPERATING LOCAL LOOPBACK (LL)
The Local Loopback (LL) test checks the operation of the local MT335A, and is
performed separately on each unit.Any data sent to the local MT335A in this test
mode will be echoed (returned) back to the user device (i.e., characters typed on
the keyboard of a terminal will appear on the terminal screen).

G.703/G.704 NTU W/V35
19
Figure 6. Local Loopback for a NetworkTermination Application
To perform a LL test, follow these steps:
1. Activate LL. This may be done in one of two ways:
— Place the switch on the front panel in the “Local” position.
— Activate the “LL” signal on the DTE. If you are not sure which lead is
the “LL” signal, please refer to Appendix B.
2. Verify that the data terminal equipment is operating properly and can be
used for a test.
3. Perform a V.52 BER (bit error rate) test as described in section “Using the
V.52 (BER) Test Pattern Generator” on page 21. If the BER test equipment
indicates no faults, but the data terminal indicates a fault, follow the manu-
facturer’s checkout procedures for the data terminal. Also, check the inter-
face cable between the terminal and the MT335A.
4.9.32 OPERATING REMOTE DIGITAL LOOPBACK (RL)
The Remote Digital Loopback (RL) test checks the performance of both the local
and remote MT335A, as well as the communication link between them. Any
characters sent to the remote MT335A in this test mode will be returned back to
the originating device (i.e, characters typed on the keyboard of the local terminal
will appear on the local terminal screen after having been passed to the remote
MT335A and looped back).
Serial
Device
Serial
Device
MT335A
Receive
Recover
Clocking
Internal
Clocking
Cable Span
G.703/G.704 NTU
MT335A
G.703/G.704 NTU
MT335A
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
MT335A

G.703/G.704 NTU W/V35
20
Figure 7. Remote Loop in a Network Extension Application
There are two Remote Loops that can be initiated from the MT335A: (1) V.54
Loop, and; (2) CSU Loop. The user can select the type of loop that can be initi-
ated by Switch S2-4. When a loopback is initiated this is the type of loop that the
unit uses to loop up the remote unit and which type of loop the unit will
respond to.
To perform an RDL test, follow these steps:
1. Activate RDL. This may be done in two ways:
— Activate the “RL” signal on the DTE. If you are not sure which lead is
the “RL” signal, please refer to Appendix B.
— Set the front panel switch to “Remote”.
2. Perform a bit error rate test (BERT) using the internal V.52 generator (as
described in section “Using the V.52 (BER) Test Pattern Generator”), or
using a separate BER Tester. If the BER test indicates a fault, and the
Local Line Loopback test was successful for both devices, you may have
a problem with the twisted pair line connection.
4.9.33 CSU LOOP
Although CSU Loop is predominantly a T1 function, the MT335A responds to
central office initiated loop commands. Customers can use this facility when the
Central Office network switch supports CSU loops over an E1 interface.
When CSU Loop is selected, the MT335A will implement the “loop up” com-
mand when it recognizes the pattern “10000” in the data stream for a minimum
of 5 seconds. The “loop down” command is implemented by the pattern “100” in
the data stream for a minimum of 5 seconds.
Serial
Device
Serial
Device
Receive
Recover
Clocking
Internal
Clocking
Cable Span
G.703/G.704 NTU
MT335A
G.703/G.704 NTU
MT335A
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data