Patton electronics NetLink 2701/B User manual

USER
MANUAL
MODEL 2701/B, C, D
G.703/G.704 NTU with
EIA-530, V.35, X.21 Interfaces
SALES OFFICE
[phone]
TECHNICAL SUPPORT
[phone]
http://www.patton.com
Part# 07M2701/x-A
Doc# 086101UA
Revised 02/08/00

1.0 WARRANTY INFORMATION
Patton Electronics warrants all Model 2701/I components to be
free from defects, and will—at our option—repair or replace the prod-
uct should it fail within one year from the first date of shipment.
This warranty is limited to defects in workmanship or materials,
and does not cover customer damage, abuse, or unauthorized modifi-
cation. If this product fails or does not perform as warranted, your sole
recourse shall be repair or replacement as described above. Under no
condition shall Patton Electronics be liable for any damages incurred
by the use of this product. These damages include, but are not limited
to, the following: lost profits, lost savings and incidental or consequen-
tial damages arising from the use of or inability to use this product.
Patton Electronics specifically disclaims all other warranties,
expressed or implied, and the installation or use of this product shall
be deemed an acceptance of these terms by the user.
1.1 RADIO AND TV INTERFERENCE
The Model 2701 generates and uses radio frequency energy, and
if not installed and used properly—that is, in strict accordance with the
manufacturer's instructions—may cause interference to radio and tele-
vision reception. The Model 2701 has been tested and found to com-
ply with the limits for a Class A computing device in accordance with
the specifications in Subpart J of Part 15 of FCC rules, which are
designed to provide reasonable protection from such interference in a
commercial installation. However, there is no guarantee that interfer-
ence will not occur in a particular installation. If the Model 2701 does
cause interference to radio or television reception, which can be deter-
mined by disconnecting the cables, the user is encouraged to try to
correct the interference by one or more of the following measures:
moving the computing equipment away from the receiver, re-orienting
the receiving antenna, and/or plugging the receiving equipment into a
different AC outlet (such that the computing equipment and receiver
are on different branches).
1.2 CE NOTICE
The CE symbol on your Patton Electronics equipment indicates
that it is in compliance with the Electromagnetic Compatibility (EMC)
directive and the Low Voltage Directive (LVD) of the Union European
(EU). A Certificate of Compliance is available by contacting Technical
Support.
1
1.3 SERVICE
All warranty and nonwarranty repairs must be returned freight pre-
paid and insured to Patton Electronics. All returns must have a Return
Materials Authorization number on the outside of the shipping contain-
er. This number may be obtained from Patton Electronics Technical
Services at:
tel: [phone];
email: [email protected]; or,
www: http://www.patton.com.
NOTE: Packages received without an RMA number will not be
accepted.
Patton Electronics' technical staff is also available to answer any
questions that might arise concerning the installation or use of your
Patton Model 2701. Technical Service hours: 8AM to 5PM EST,
Monday through Friday.
2

2.0 GENERAL INFORMATION
Thank you for your purchase of this Patton Electronics product.
This product has been thoroughly inspected and tested and is warrant-
ed for One Year parts and labor. If any questions or problems arise
during installation or use of this product, please do not hesitate to con-
tact Patton Electronics Technical Support at [phone].
2.1 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
• X.21, V.35, and EIA-530
• Switch-selectable AMI or HDB3 line encoding options
• Switch-selectable DTE/DCE modes for X.21 version
• 75-ohm dual coax and 120-ohm twisted-pair G.703 connections
• Local and remote loopback diagnostics
• Internal and G.703 network timing
• CE and BABT approvals
• 90-260VAC & 48VDC power options
• Conforms to ONP requirements CTR 12 and CTR 13 for connec-
tion to international Telecom networks
2.2 DESCRIPTION
The Model 2701 receives channelized G.704 (n x 64kbps) or clear
channel E1/G.703 (2.048-Mbps) data from the telco's digital data net-
work. The Model 2701 terminates the G.703 telco interface and con-
verts the data for transmission to a user-oriented serial [X.21, V.35,
and EIA-530 (V.36/RS422)]. The 2701 can connect to a Router, FRAD,
PABX or Multiplexer over its serial interface at nx64kbps data rates up
to 2.048 Mbps.
3
3.0 CONFIGURATION
The Model 2701 features configuration capability via hardware DIP
switches. This section describes all possible DIP switch configurations
of the Model 2701.
3.1 DIP SWITCH CONFIGURATION
The Model 2701 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 2701. Figure 1 (below) shows the
location of the DIP switches on the bottom of the printed circuit board.
The Model 2701 DIP switches (Switch Sets 1-2) can be configured
as either “ON” or “OFF”. Figure 2 (below) shows the orientation of the
DIP switches with respect to ON/OFF positions.
4
Figure 1. Underside of Model 2701, Showing Location of DIP Switches
Front
Rear
ON
S2
S1
OFF
OFF
12345678
DHS-8
Figure 2. Close up of configuration switches
OFF
ON
ON

Switch SW1-1 through SW1-5
A detailed description of each switch (SW1-1 through SW1-5) setting
follows the summary table below.
Use Switches SW1-5 to set the DTE data rate.
SW1 SW2 SW3 SW4 SW5 Speed
ON ON ON ON ON 64kbps
OFF ON ON ON ON 128kbps
ON OFF ON ON ON 192kbps
OFF OFF ON ON ON 256kbps
ON ON OFF ON ON 320kbps
OFF ON OFF ON ON 384kbps
ON OFF OFF ON ON 448kbps
OFF OFF OFF ON ON 512kbps
ON ON ON OFF ON 576kbps
OFF ON ON OFF ON 640kbps
ON OFF ON OFF ON 704kbps
OFF OFF ON OFF ON 768kbps
ON ON OFF OFF ON 832kbps
OFF ON OFF OFF ON 896kbps
ON OFF OFF OFF ON 960kbps
OFF OFF OFF OFF ON 1024kbps
ON ON ON ON OFF 1088kbps
OFF ON ON ON OFF 1152kbps
ON OFF ON ON OFF 1216kbps
OFF OFF ON ON OFF 1280kbps
ON ON OFF ON OFF 1344kbps
OFF ON OFF ON OFF 1408kbps
ON OFF OFF ON OFF 1472kbps
OFF OFF OFF ON OFF 1536kbps
ON ON ON OFF OFF 1600kbps
OFF ON ON OFF OFF 1664kbps
5
ON OFF ON OFF OFF 1728kbps
OFF OFF ON OFF OFF 1792kbps
ON ON OFF OFF OFF 1856kbps
OFF ON OFF OFF OFF 1920kbps
ON OFF OFF OFF OFF 1984kbps
OFF OFF OFF OFF OFF Clear Channel 2048kbps
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.
SW1-6 and SW1-7 CLOCK MODES
Use Switches SW1-6 and SW1-7 to configure the 2701 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 tim
ing.
SW1-8: Enable/Disable Loop Tests from DTE
Use Switch SW1-8 to allow Model 2701 to enter loopback tests when
the DTE raises the appropriate loop request pin.
S1-8 Setting
Off Response to DTE Loopback Request Enabled
On Response to DTE Loopback Request Disabled
6
SWITCH SET 1 SUMMARY TABLE
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
}SW1-6 SW1-7 Clock Mode
On On Network (Recieved Recovered)
On Off Internal
Off On External
Off Off Network (Recieved Recovered)

SWITCH SW2-1 LINE CODING: 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 Model 2701s together as
short range modems, set both units to HDB3.
SW2-1 Line Encoding
OFF HDB3
ON AMI
OPTIONS: HDB3, AMI
HDB3: In this line coding, the transmitter substitutes a deliberate
bipolar violation 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 requirements. 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 connec-
tion, signals are transmitted as a sequence of ones and zeros.
Ones are sent as pulses, and zeros 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
7
equipment connected to the unit provides a minimally accept-
able 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 require-
ments.
SWITCH SW2-2: CRC-4 MULTIFRAME
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.
SW2-2 Option
Off CRC-4 Disabled
On CRC-4 Enabled
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.
SWITCH SW2-3 DATA INVERSION
Set Switch S2-3 to determine whether or not the data stream from the
local DTE is inverted within the Model 2701 before being passed to the
G.703/G.704 network. An inverted data stream may be required when
you use the Model 2701 to communicate with a G.703 device (that
inverts the data) on the remote end. In typical installations, data inver-
sion is not necessary.
SW2-3 Option
Off Data not inverted
On Data inverted
SWITCH SW2-4: REMOTE DIGITAL LOOPBACKTYPE
The user can set this switch to select the type of remote loop that
will be initiated by the Model 2701. If set to V.54, the Model 2701 will
initiate a V.54 loop when Remote Loop is selected by the front panel
switches. If set to CSU, the Model 2701 will initiate a CSU loop when
Remote Loop is selected by the front panel switches.
8
SWITCH SET 2 SUMMARY TABLE
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 OFF Enabled
SW2-7 Not Used N/A N/A
SW2-8 Not Used N/A N/A

S2-4 RDL Type
Off Initiate a V.54 RDL loop when selected
On Initiate a CSU loopback when selected
SWITCH SW2-5 FRONT PANEL SWITCHES
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.
SW2-5 Option
Off Front Panel Switches Enabled
On Front Panel Switches Disabled
SWITCH SW2-6: V.54 RESPONSE ENABLED
(DEFAULT)
V.54 Response is a special in-band loopback facility that sends a pseu-
do-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 the V.54
loopback command, and the whole process 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 duration of the
loopback is limited by the loopback timeout setting.
SW2-6 Option
Off V.54 Response Enabled
On V.54 Response Disabled
9
44..00 IINNSSTTAALLLLAATTIIOONN
Once the Model 2701 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.
4.1 CONNECTING TO THE G.703 NETWORK
The Power, G.703/G.704 and serial Line connections are located
on the rear panel of the Model 2701. The following sections describe
operation of these connections.
4.1.1 Connecting the 2701/D (X.21 version) Dual Coaxial Cable (75
ohm) to the G.703 Network
The Model 2701/D (X.21 version) is equipped with dual female
BNCs (TX and RX) for connection to a 75 ohm dual coax G.703 net-
work interface. If your G.703/G.704 network terminates via dual coaxial
cable, use the diagram below to make the proper connections. See
Figure 3 below.
NOTE: The outer conductor of the coax cables are isolated from
system earth ground.
When using the 75 Ohm interface, jumper straps JP3, JP6, JP7,
and JP8 must be installed over the jumpers. The jumpers are located
next to the BNC connectors. Refer to the following section to open the
case. Open the case and install jumper straps for JP3, JP6, JP7, and
JP8.
4.1.2 Opening the Case
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.
10
Data TO
Network Data
FROM
Network
Figure 3: Rear Panel, Showing Location of Connectors.
TX RX

4.1.3 Connecting the Twisted Pair (120 ohm) to the G.703
Network
The Model 2701 is equipped with a single RJ-48C jack for connec-
tions to a 120 ohm twisted pair G.703/G.704 network interface. If your
G.703/G.704 network terminates via RJ-48C, use the connection dia-
gram (Figure 4) following the pinout and signals chart below to connect
the 120 ohm G.703/G.704 network channel.
RJ-45 Cable (8-Wire)
G.703/G.704 2701
NETWORK SIGNAL SIGNAL
PIN#
RX+ 1-----------------------TX+
RX- 2-----------------------TX-
TX+ 5-----------------------RX+
TX- 4-----------------------RX
Shield 3-----------------------Shield
Shield 6-----------------------Shield
11
4.2 Connecting the Serial Port
The Model 2701/B, C, D supports RS-530, V.35, X.21 serial port
connections. This section describes how to connect the serial ports to
your terminal equipment.
4.2.1 Connecting to a “DTE” Device
The serial port on the 2701/B (RS-530 version) and 2701/C (V.35
version) 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
connection to your DTE device, use a straight through cable of the
shortest possible length—we recommend 6 feet or less. When pur-
chasing or constructing an interface cable, please refer to the pin dia-
grams in Appendix D as a guide.
4.2.2 Connecting to a “DCE” Device
If the Model 2701 serial interface is hard-wired as a DCE (all
except the X.21 version), you must use a
null modem cable when con-
necting to a modem, multiplexer or other DCE device. This cable
should be of the shortest possible length—we recommend 6 feet or
less.
4.2.3 Configuring the X.21 Interface (2701/D)
The serial port on the X.21 interface is default wired as a DCE, but
may be switched to a DTE. This is done by reversing the orientation of
the DCE/DTE strap, as described below:
To reverse DCE/DTE orientation, remove the top case. Refer to
section 4.1.2.
The DCE/DTE strap is located near the DB15 connector on the
top side of the board. The arrows on the top of the strap indicate the
configuration of the X.21 port (for example, if the DCE arrows are
pointing toward the DB-15 connector, the X.21 port is wired as a DCE).
Reverse the DCE/DTE orientation by pulling the strap out of its socket,
rotating it 180º, then plugging the strap back into the socket. You will
see that the DCE/DTE arrows now point in the opposite directions,
showing the new configuration of the X.21 port.
NOTE: If the 2701/D is configured as a DTE, the clocking mode
must be set for external clock.
12
(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
Figure 4: G.703/G.704 170 Ohm Connection.

13
4.4 POWER CONNECTION
Universal AC Power (100-240VAC)
The Model 2701 uses a 5VDC, 2A universal input 100-240VAC,
power supply (center pin is +5V). The universal input power supply
has a male IEC-320 power entry connector. This power supply con-
nects to the Model 2701 by means of a barrel jack on the rear panel.
Many international power cords are available for the universal power
supply.
The Model 2701 powers up as soon as it is plugged into an AC
outlet--there is no power switch.
DC Power
The 36-60 VDC DC to DC adapter supplied with the DC version of
the Model 2701 plugs in a DC source (nominal 48VDC) and plugs into
the barrel power supply jack on the rear of the 2701. Please refer to
Figure 5, below, to make the proper connection.
14
55..00 OOPPEERRAATTIIOONN
When the Model 2701 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.
5.1 POWER-UP
Before applying power to the Model 2701, please read Section
4.3 and ensure that the unit is properly connected to the appropriate
power source.
5.2 LED STATUS MONITORS
The Model 2701 features six front panel LEDs that monitor con-
nections on the G.703/G.704 and signaling, error and test modes.
Figure 6 (below) shows the front panel location of each LED.
Descriptions of each LED follow Figure 6.
E1 Link (Active Green) Solid green (On) indicates that the
end to end E1 Link is up, signifying that the link is
active. The E1 Link LED is Off when the link is
down.
TD & RD Glows yellow to indicate an idle condition of Binary
“1” data on the respective terminal interface sig-
nals. 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 moni
tors the status of the transmit clock.
ER The error LED indicates various error conditions,
including framing bit errors, excessive zeros, con-
trolled slips, severe errors, or bit errors (when
sending V.52 test patterns). When sending a test
Figure 6: 2701 Front Panel
WARNING! There are no user-serviceable parts in the
power supply section of the Model 2701. For more informa-
tion, please contact Patton Electronics Technical support at
[phone] , via our web site at http://www.patton.com, or
by e-mail at [email protected].
Figure 5: Connecting DC Power to the 2701 DC Power Supply.
+ Vin
To Power
Supply Jack
- Vin
To -48VDC
Source

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 inser-
tion is on, the LED will blink once a second if
everything is operating properly.
TM (Active Yellow) Solid Yellow indicates an Active
Test Mode. The unit may be placed in test mode
by the local user or by the remote user.
5.3 LOOP (V.54 & TELCO) DIAGNOSTICS
The Model 2701 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
Model 2701/B and C serial port interface.
5.3.1 Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local
Model 2701, and is performed separately on each unit. Any data sent
to the local Model 2701 in this test mode will be echoed (returned)
back to the user device (i.e., characters typed on the keyboard of a ter-
minal will appear on the terminal screen).
To perform a LL test, follow these steps:
1. Activate LL. This may be done in one of two ways:
a. Place the switch on the front panel in the “Local” position.
b. Activate the “LL” signal on the DTE (2701/B and 2701/C
only). If you are not sure which lead is the “LL” signal,
please refer to Appendix D.
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 5.3.4. If the BER test equipment indicates no faults,
but the data terminal indicates a fault, follow the manufactur-
er’s checkout procedures for the data terminal. Also, check
the interface cable between the terminal and the Model 2701.
5.3.2 Operating Remote Digital Loopback (RL)
The Remote Digital Loopback (RL) test checks the performance of
both the local and remote NetLink-E1™, as well as the communication
link between them. Any characters sent to the remote NetLink-E1™ in
this test mode will be returned back to the originating device (i.e, char-
acters typed on the keyboard of the local terminal will appear on the
local terminal screen after having been passed to the remote NetLink-
E1™ and looped back).
There are two Remote Loops that can be initiated from the
NetLink-E1 unit: (1) V.54 Loop, and; (2)CSU Loop. The user can
select the type of loop that can be initiated 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 (refer to a. and
b. on the following page:
Figure 7. Local Loopback for a Network Termination Application
Serial
Device
Serial
Device
Model 2701 Serial
Receive
Recover
Clocking
Internal
Clocking
Cable Span
G.703/G.704 NTU
Model 2701 Serial G.703/G.704 NTU
Model 2701 Serial
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
Model 2701 Figure 8. Remote Loop in a Network Extension Application
Serial
Device Ethernet
Device
Model 2701/I
Receive
Recover
Clocking
Internal
Clocking
Cable Span
G.703/G.704 NTU
Model 2701 Serial G.703/G.704 NTU
Model 2701 Serial
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
Model 2701/I
15 16

a. Activate the “RL” signal on the DTE (2701/B and 2701/C
only). If you are not sure which lead is the “RL” signal, please
refer to Appendix B or C, depending on the version you are
using.
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 5.3.4), or using a separate
BER Tester. If the BER test indicates a fault, and the Local
Line Loopback test was successful for both NetLink™s, you
may have a problem with the twisted pair line connection.
5.3.3 CSU Loop
Although CSU Loop is predominantly a T1 function, the NetLink-
2701 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 NetLink 2701 will implement the
“loop up” command 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.
The NetLink 2701 will respond to Universal Loopback De-activate
to clear all central office loops.
5.3.4 Using the V.52 (BER) Test Pattern Generator
To use the V.52 BER tests in conjunction with the Remote Digital
Loopback tests (or with Local Line Loopback tests), follow these
instructions:
1. Locate the “511/511E” toggle switch on the front panel of the
2701 and move it UP. This activates the V.52 BER test mode
and transmits a “511” test pattern into the loop. If any errors are
present, the local modem’s red “ER” LED will will illuminate.
2. If the above test indicates no errors are present, move the V.52
toggle switch DOWN, activating the “511/E” test with errors pre
sent. If the test is working properly, the local modem's red “ER”
LED will blink once every second. A successful “511/E” test will
confirm that the link is in place, and that the Model 2701’s built-in
“511” generator and detector are working properly.
NOTE: The above V.52 BER tests can be used independent-
ly of the Remote Digital Loopback tests. This requires two
operators: one to initiate and monitor the tests at the local
Model 2701, and one to do the same at the remote Model
2701. In this case, the test pattern sent by each Model 2701
will not be looped back, but will be transmitted down the line
to the other Model 2701. While one operator initiates test, the
other monitors for errors.
17 18