Tainet T-336Cx User manual

USER'S MANUAL
Modem
T-336Cx/Nx/NDx
Version: 1.9
Date: 2008/7/9
P/N: 07008-00027
Headquarters:
No. 25, Alley 15, Lane 120,
SEC.1. NEI-HU RD,
Taipei 114, Taiwan
TEL: [phone]
FAX: [phone]
Beijing Branch:
3F, A Building,
113 Zhi Chun Lu,
HaiDian District,
Beijing, China
Zip Code: 100086
TEL: [phone]~87
FAX: [phone]

T-336Cx/Nx/NDx User’s Manual
-i-
Copyright © 2008 TAINET COMMUNICATION SYSTEM CORP.
All rights reserved
Notice
This document is protected by the international copyright law. No part of this publication may
be reproduced by any means without the expressed permission of Tainet Communication
System Corporation.
TAINET is a registered trademark, and T-336Cx/Nx/NDx is a trademark of Tainet
Communication System Corporation.
Other product names mentioned in this manual are used for identification purposes only and
may be trademarks or trademarks of their respective companies.
The information provided from Tainet Communication System Corporation is believed to be
accurate. Any changes and enhancements to the product and to the information thereof will
be documented and issued as a new release to this manual.
Trademark
All products and services mentioned herein are the trademarks, service marks, registered
trademarks or registered service marks of their respective owners.

T-336Cx/Nx/NDx User’s Manual
ii
About This Manual
This section guides users on how to use the manual effectively. The manual contains
information needed to install, configure, and operate TAINET’s VENUS Series VoIP Gateway.
The summary of this manual is as follows:
Chapter 1: TAINET Modem Introduction
Chapter 2: Installation
Chapter 3: Front Panel and Menu Tree
Chapter 4: General Information and Features
Chapter 5: Instruction Sets
Chapter 6: Maintenance
Appendix A: T-336Cx S-register Table
Appendix B: T-336Cx LCD Menu Quick Reference
Appendix C: T-336Nx LCD Menu Quick Reference

T-336Cx/Nx/NDx User’s Manual
iii
Symbols Used in This Manual
3 types of symbols may be used throughout this manual. These symbols are used to advise
the users when a special condition arises, such as a safety or operational hazard, or to
present extra information to the users. These symbols are explained below:
Warning:
This symbol and associated text are used when death or
injury to the user may result if operating instructions are
not followed properly.
Note:
This symbol and associated text are used to provide the
users with extra information that may be helpful when
following the main instructions in this manual.
Caution:
This symbol and associated text are used when damages
to the equipment or impact to the operation may result if
operating instructions are not followed properly.

T-336Cx/Nx/NDx User’s Manual
iv
LIMITED WARRANTY
TAINET’s DISTRIBUTOR shall be responsible to its customers for any and all warranties,
which it makes relating to Products, and for ensuring that replacements and other
adjustments required in connection with the said warranties are satisfactory. TAINET
warrants to DISTRIBUTOR that the Products to be delivered hereunder will be free of defects
in material and workmanship under normal use and service for a period of twenty-four (24)
months [twelve (12) months in Taiwan] following the date of shipment to DISTRIBUTOR.
If during the warranty period, any component part of the equipment becomes defective by
reason of material or workmanship, and DISTRIBUTOR notifies TAINET of such defect within
seven days after knowing of such defect, TAINET shall, for any Product that TAINET agrees
is defective, at its option, supply a replacement part, request return of equipment to its plant
for repair, or perform necessary repair at the equipment’s location. At TAINET's option,
DISTRIBUTOR shall destroy any Product that TAINET agrees is defective and shall provide
satisfactory proof of such destruction to TAINET. TAINET is not responsible for Products
damaged by misuse, neglect, accident or improper installation, or if repairs or modifications
were made by persons other than TAINET’s own authorized service personnel, unless such
repairs by others were made with the written consent of TAINET.
THE ABOVE WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR
IMPLIED. THERE ARE NO WARRANTIES THAT EXTEND BEYOND THE FACE HEREOF,
INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE, AND IN NO EVENT SHALL TAINET BE LIABLE
FOR CONSEQUENTIAL DAMAGES. If DISTRIBUTOR extends to its customers any
additional warranty with respect to Products that is broader in scope than the warranty
provided by TAINET, DISTRIBUTOR shall be solely responsible for any and all liabilities,
obligations and damages resulting from the extension of such warranty.
TAINET shall not be liable to any person for any special or indirect damages, including, but
not limited to, lost profits, from any cause whatsoever arising from or in any way connected
with the manufacture, sale, handling, repair, maintenance or use of the Products, and in no
event shall TAINET’s liability exceed the purchase price of the Products.
Software Products are provided “as is” and without warranty of any kind. TAINET disclaims
all warranties including the implied warranties of merchantability and fitness for a particular
purpose. TAINET shall not be liable for any loss of use, interruption of business or indirect,
special, incidental or consequential damages of any kind. TAINET shall do its best to provide
end users with Software updates during the warranty period under this Agreement.
TAINET has not been notified of any intellectual property rights or others which may be
infringed by the Products or the promotion, marketing, sale (or resale), or servicing thereof in
the Territory, but TAINET makes NO WARRANTY, EXPRESS OR IMPLIED, WITH RESPECT
THERETO.

T-336Cx/Nx/NDx User’s Manual
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INFORMATION TO THE USER
NOTE: This equipment has been tested and found to comply with the limits for a Class A
digital device. Pursuant to Part 15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a residential installation. This
equipment generates, uses and if not installed and used in accordance with the instructions
may cause harmful interference will not occur in a particular installation. If this equipment
does cause harmful interference to radio or television reception, which can be determined by
turning the equipment off and on. The user is encouraged to try to correct the interference by
one or more of the following measures:
Reorient or relocate the receiving antenna.
Increase the separation between the equipment and receiver.
Connect the equipment into an outlet on a circuit different from that to which the receiver is
connected.
Consult the dealer or an experienced radio/TV technician for help.
This booklet is available from the US government Printing Office, Washington, DC 20402,
Stock NO. 004-000-00345-4.
The shielded RS-232 cable is to be used in order to ensure compliance with FCC Part 15,
and it is the responsibility of the user to provide and use shielded RS-232 cable from
MODEM to personal computer.
CAUTION: Any changes of modifications not expressly approved by the
grantee of this device could void the user's authority to operate the
equipment.

T-336Cx/Nx/NDx User’s Manual
vi
FCC REQUIREMENTS
This equipment complies with Part 68 of the FCC Rules. On the base unit of this equipment
is a label that contains, among other information, the FCC Registration Number and Ringer
Equivalence Number (REN) for this equipment. IF REQUESTED, THIS INFORMATION
MUST BE GIVEN TO THE TELEPHONE COMPANY.
The REN is useful to determine the quantity of devices you may connect to your telephone
line and still have all of those devices ring when your telephone number is called. In most,
but not all areas, the sum of the REN's of all devices connected to one line should not
exceed five (5.0). To be certain of the number of devices you may connect to your line, as
determined by the REN you should contact your local telephone company to determine the
maximum REN to your calling area.
If your equipment causes harm to the telephone network, the telephone company may
discontinue your service temporarily. If possible, they will notify you in advance. But the
advance notice isn't practical, you will be notified as soon as possible. You will be informed of
your right to file a complaint with the FCC. Your telephone company may make changes in its
facilities, equipment, operations or procedures that could affect the proper functioning of your
equipment. If they do, you will be notified in advance to give you an opportunity to maintain
uninterrupted telephone service.
If you experience trouble with this telephone equipment, please contact the following address
and phone number for information on obtaining service or repairs.
The telephone company may ask that you disconnect this equipment from the network until
the problem has been corrected or until you are sure that the equipment is not malfunctioning.
This equipment may not be used on coin service provided by the telephone company.
Connection to party lines is subject to state tariffs.
COMPANY: SUMMIT MICRO DESIGN, INC.
ADDRESS: 485 MACARAAVE., SUITE 901 SUNNYVALE, CA 94086 USA
TEL NO: [phone]

T-336Cx/Nx/NDx User’s Manual
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CONTENTS
CHAPTER 1.TAINET MODEM INTRODUCTION...........................................1
1.1PRODUCT OVERVIEW .............................................................................................1
1.2TECHNICAL SPECIFICATIONS ..................................................................................2
1.3ORDERING INFORMATION.......................................................................................7
CHAPTER 2.INSTALLATION ..............................................................................9
2.1DESCRIPTION .........................................................................................................9
2.2UNPACKING..........................................................................................................10
2.3SITE REQUIREMENTS ...........................................................................................11
2.4SITE SELECTION...................................................................................................12
2.5AC ELECTRICAL OUTLET CONNECTION...............................................................13
2.6CONNECTING WITH DIAL LINE ............................................................................14
2.7CONNECTING WITH LEASED LINE........................................................................15
CHAPTER 3.FRONT PANELAND MENU TREE............................................17
3.1THE FRONT PANEL DESCRIPTION .........................................................................17
3.2THE REAR PANEL DESCRIPTION ...........................................................................18
3.3OPERATING THE TAINET NETWORK SERIES MODEM..........................................19
3.4THE MENU TREE..................................................................................................22
3.5DETAILED DESCRIPTION OF THE MENU TREE.......................................................27
3.5.1STATUS MENU.............................................................................................................27
3.5.2DIAL MENU..................................................................................................................29
3.5.3PROTOCOL MENU ......................................................................................................31
3.5.43.5.4 TEST MENU.........................................................................................................33
3.5.53.5.5 CONFIG MODEM MENU...................................................................................34
3.5.6CONFIG DTE MENU....................................................................................................38
3.5.7COMMAND MENU......................................................................................................40
3.5.8LINE SETUP MENU.....................................................................................................41
3.5.9PROFILE MENU...........................................................................................................42
CHAPTER 4.GENERAL INFORMATION AND FEATURES.........................45
4.1PREVIEW..............................................................................................................45
4.2DIAL LINE VS. LEASED LINE...............................................................................46
4.32W/4WLEASED LINE..........................................................................................47
4.4ANSWER MODE VS. ORIGINATE MODE................................................................48
4.5SYNCHRONOUS VS.ASYNCHRONOUS ..................................................................49
4.6ERROR CORRECTION AND DATA COMPRESSION...................................................50
4.7CONFIGURATION PROFILE SET-UP........................................................................51
4.8REMOTE ACCESS..................................................................................................53
4.9MULTI-STANDARD HANDSHAKE...........................................................................54
4.10AUTO DIAL BACK-UP..........................................................................................55
4.11AUTO FALLBACK AND FALL FORWARD ................................................................56
4.12LINE STATUS MONITORING ..................................................................................57
4.13B.E.R TEST..........................................................................................................59
4.14INTELLIGENT DIAL...............................................................................................60
4.15FRONT PANEL LOCK AND PASSWORD PROTECT....................................................61
4.16ITU-TV.13/ V.23 SIMULATED CARRIER CONTROL IN HALF DUPLEX...................62
4.17PASSWORDAND CALLBACK FUNCTIONS ................................................63

T-336Cx/Nx/NDx User’s Manual
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4.17.1Dynamic Password/CallBack:........................................................................................63
4.17.2Extension Code for Stored Phone Numbers (‘+’+<char>):............................................63
4.17.3Additional Information:..................................................................................................63
4.18INTELLIGENT DIAL POLLING................................................................................65
CHAPTER 5.INSTRUCTION SETS ...................................................................67
5.1AT COMMAND SET...............................................................................................67
5.2DIAL MODIFIERS..................................................................................................74
5.3RESULT CODES.....................................................................................................75
5.4V.25BIS AUTO CALL UNIT ....................................................................................77
CHAPTER 6.MAINTENANCE............................................................................79
6.1DESCRIPTION .......................................................................................................79
6.2INSTRUMENTS......................................................................................................80
6.3PERIODIC MAINTENANCE.....................................................................................81
6.4TROUBLESHOOTING .............................................................................................82
6.5RETURN PROCEDURES .........................................................................................83
APPENDIX AT-336CX S-REGISTER TABLE....................................................85
APPENDIX BT-336CX LCD MENU QUICK REFERENCE............................96
APPENDIX CT-336NX LCD MENU QUICK REFERENCE............................125H99

Chapter 1 Tainet Modem Introduction
-1-
Chapter 1. Tainet Modem Introduction
1.1 Product Overview
The TAINET Network Series Modem T-336Cx/Nx/NDx is high performance,
synchronous and asynchronous, full duplex multi-standard modems designed for
use on 2-wire dial circuits and 2/4 wire leased lines.
The MODEM series fully comply with ITU-T V.34、V.32bis/V.32、V.22bis、V.22、
V.23、V.21 and BELL 212A/103，speed: 115200 - 300bps Asynch，33600 -
1200bps Synchronization。
In V.34 and V.32bis/ V.32 modes, echo cancellation provides 2-wire full duplex
operation over all PSTN circuits including those with satellite sections.
Compatibility is also provided with Bell 212Aand Bell 103 operating standard.
V.34 mode provide full duplex operation at up to 33.6 kbps speed, with line
probing, symbol rate and carrier frequency selection technologies.
V.34 mode also use other advance technologies such as Adaptive
Precoding, Non-Linear Encoding (Warping), Constellation Expansion,
Multidimensional Trellis coding and Shell Mapping ,Tx power back off(Power
Reduction).
There are 10 factory default profiles and 10 user's profiles for your easiest
configuration setting.
Allow up to 16 modem cards (T-336Nx) with 16 port on a rack shelf (TRS-16).
Allow up to 16 modem cards (T-336NDx), with 32 port on a rock shelf (TRS-
32).
A 2 by 16 characters LCD display on the front panel with back lighted control
for configuration set-up and monitoring conveniently.
Line status monitoring including transmit/receive signal level, S/N ratio, EQM
(eye quality monitoring), signal quality, frequency shift, delay, echo, retrain
count, phase jitter, Tx/Rx baud rate, Tx/Rx carrier frequency, Tx/Rx DCE
speed, TX power back-off ..., etc.
Front panel lock and password protect features prevents from the operation
of unauthorized person.
Enable remote configuration through secondary channel.
V.13& V.23 simulated carrier control for half duplex application.
2 wires or 4wires automatic or manual dial back-up and restore.

Chapter 1 Tainet Modem Introduction
2

1.2 Technical Specifications
T-336Cx/Nx/NDx fully comply with ITU-T recommendations V.34, V.32bis, V.32,
V.22bis, V.22, V.21, V.23, V.24, V.26bis,V.28, V.25, V.25bis, V.52, V.54, V.42,
V.42bis, V.8, and BELL 212A/103 operating standards.
Modulation type : Refer to table 1-1A,1-1B.
Clock tolerance
Synchronous: ±0.01%
Asynchronous:Basic range + 1% to - 2.5%
Extended overspeed range + 2.3% to - 2.5%
DTE speed
Synchronous: 33600/31200/28800/26400/24000/21600/19200/1680
/14400/12000/9600/7200/4800/2400/1200 bps
Asynchronous : 15200/76800/57600/38400/33600/32000/31200/28800/
26400/24000/21600/19200/16800/14400/12000/9600/7200/4800/3600/2
400/1200/600/300 bps with speed conversion.
•Total bit length : 8, 9, 10, 11 bits
•Parity bit : odd, even, none
•Stop bit : 1, 1.5, 2 bits
Error Correction : MNP 4/ITU-T V.42
Data Compression : MNP 5/ITU-T V.42bis
Flow Control : Hardware CTS/RTS, CTS only, Software X-ON/X-OFF
Dial Command : Extended AT and ITU-T V.25bis command set.

Chapter 1 Tainet Modem Introduction
3
Table 1-1A : Modem operating mode (4 wires/2wires L-L or D-L)
Operating Mode MOD. Carrier Symbol rate Constellation points
V.34+ 33600
V.34+ 31200
V.34 28800
V.34 26400
V.34 24000
V.34 21600
V.34 19200
V.34 16800
V.34 14400
V.34 12000
V.34 9600
V.34 7200
V.34 4800
V.34 2400
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
(Table 1-1c) (Table 1-1c)
4 to 1024
Depends on the
combination of data
rate, symbol rate and
constellation expansion
chosen.
V.32bis 14400
T TCM 1800 2400 128
V.32bis 12000
T TCM 1800 2400 64
V.32 9600
T TCM 1800 2400 32
V.32 9600 QAM 1800 2400 16
V.32bis 7200
T TCM 1800 2400 16
V.32 4800 QAM 1800 2400 4
V.26bis 2400 DPSK 1800 1200 4
V.26bis 1200 DPSK 1800 1200 4
V.22bis 2400 QAM 1200/2400 600 16
V.22 1200 DPSK 1200/2400 600 4

Chapter 1 Tainet Modem Introduction
4
V.23
1200/75 FSK 1700/420 1200 N/A
V.21 0-300 FSK 1080/1750 300 N/A
BELL 212A 1200 DPSK 1200/2400 600 4
BELL 103 0-300 FSK 1175/2125 300 N/A
Table 1-1B : V.34 Symbol Rate and Carrier Frequency
Symbol Rate (Baud) Low Carrier (Hz) High Carrier (Hz)
2400 1600 1800
3000 1800 2000
3200 1829 1920
3429 1959 1959
Transmit Level Lease-Line: 0~-31 dBm 1 dB stepadjustable.
Dial-Line: 0~-15 dBm 1 dB step adjustable.
Line requirement : 4/2 wires L-L or D-L
Line Impedenance : Balance 600Ω±10 %
Return Loss : > 20 dB, 300 - 3400 Hz
Longitude Balance : > 60 dB
Dial Line Characteristics :
Maximum Current : 120 mA
Holding Resistance : 50 ~ 220 Ω
Holding Current : 25 ~ 110 mA
Ring Detect Range :
•ON - > 27 Vrms
•OFF - < 13 Vrms
Ring Detect Frequency : 16 - 50 Hz
DTMF Characteristics
•O/P Lowband -8 ±1 dBm
•O/P Highband -6 ±1 dBm
•Frequency Tolerance ≤±1 %
•TONE Duration and Spacing 95 ms (adjustable)
Pulse Per Sec : 10 ±0.5 PPS

Chapter 1 Tainet Modem Introduction
5
Make/Break Ratio : 33/67, 39/61 ±3 %
Auto Answer
V.32bis/V.32/V.22bis/V.22 comply with ITU-T V.25 & V.25bis
V.34 Comply with ITU-T V.8, V.25/V.25bis
Answer Tone : 2100±15Hz
Calling Tone : Comply with ITU-T V.8, V.25
Receive Range : -12 ~ -44 dBm, -2 ~ -35 dBm
Dynamic Range : 0 ~ -44 dBm
Equalization : Automatic Adaptive Equalizer
Frequency Shift : Compensation cancel at least of ±7Hz offset
Far-end Echo Coverage : Maximum 1.2 seconds.
Scrambler & Descrambler: Comply with ITU-T V.34,V.32bis,V.32,V.22bis,
V.22
Data And Control Signal:
Output Voltage ±(6 ~ 12)V
(ITU-T V.28) Input Voltage±(3 ~ 25)V
Output Impedance ≧330 Ω
Input Impedance 3000 ~ 7000 Ω
Tx Clock Source
Internal/External/Loopback
Freq. Tolerance : ±0.01 %
Duty Cycle : 50 ±1 %
Test Features
V.54/V.52 , LAL/DL/RDL
Test Patterns - 511
Power Requirement
90 ~ 265 VAC Auto Range, 47 ~ 63 Hz
DC Power Input : -36 ~ -72 VDC option(Chassis type)
Operating Temperature : 0 °C ~ 50 °C
Storage Temperature : -25 °C ~ 70 °C
Relative Humidity :95 % (non-condensing)
Physical Size
Stand alone ÖW - 180mm, H - 48mm, D - 262mm, Weight 0.9kg
Rack mount card ÖW - 220mm, H - 26mm, D - 328mm, Weight 0.6kg
Rack mount shelf ÖW - 19", H - 6RU, D - 380mm, Weight 8kg

Chapter 1 Tainet Modem Introduction
6
Full shelf Equipped ÖWeight 16kg
DTE Interface: EIA RS-232C, CCITT V.24/V.28
Pin V.24 DESCRIPTION Source
1 101 (PG) Protective Ground —
2 103 (TXD) Transmit Data DTE
3 104 (RXD) Receive Data MODEM
4 105 (RTS) Request To Send DTE
5 106 (CTS) Clear To Send MODEM
6 107 (DSR) Data Set Ready MODEM
7 102 (SG) Signal Ground —
8 109 (DCD) Data Carrier Detect MODEM
9 +12 VDC MODEM
10 -12 VDC MODEM
15 114 (TXC)Transmit Clock MODEM
17 115 (RXC) Receive Clock MODEM
18 141 (AL) Local Analog Loopback DTE
20 108 (DTR) Data Terminal Ready DTE
21 140 (RDL) Remote Digital Loopback DTE
22 125 (RING) Ring Detect MODEM
24 113 (XTC) External Clock DTE
25 142 (TST) Test Mode MODEM

Chapter 1 Tainet Modem Introduction
7
1.3 Ordering Information
T-336Cx Stand alone V.34 33.6kbps modem
T-336Nx Rack-mounted V.34 33.6kbps modem card(TRS16)
T-336NDx Rack-mounted V.34 33.6kbps modem card(TRS32)
T-336Cx-t Stand alone V.34 33.6kbps modem
T-336Nx-t Rack-mounted V.34 33.6kbps modem card(TRS16)
T-336NDx-t Rack-mounted V.34 33.6kbps modem card(TRS32)
NMC16 NMS Control unit(TRS16)
NMC32 NMS Control unit(TRS32)
TRS16 19inch rack (up to 16 modem card)
TRS32 19inch rack (up to 32 modem card)
PW-130AC 90 ~ 265 VAC 130W power unit for rack
PW-130DC -36 ~ -72 VDC 130W power unit for rack
PW-132A 90 ~ 265 VAC 130W power unit for rack
PW-132D -36 ~ -72 VDC 130W power unit for rack
A50 50 pin cable with standard centronic connector for (TRS32)
TB32 The rear panel terminal block module board of the TRS32
for 2/4-wire Leased and Dial line connection
TAINET MANAGER®Network Management System

Chapter 2 Installation
-9-
Chapter 2. Installation
2.1 Description
This chapter provides the information needed to install the TAINET Network
Series Modem and to ensure that it is working properly. You may obtain more
information about this subject for rack-mount modem shelf from the User's
Manual of TAINET TRS16 or TRS32 rack-mount modem shelf.

Chapter 2 Installation
10
2.2 Unpacking
Save the carton and protective packing material in which your TAINET Network
Series Modem was shipped; you might need them for repackaging if you have to
store or ship the modem in the future. The following items are shipped with your
modem:
One Modem User's Manual.
One 7-feet (2.13m) modular telephone cable for connection to RJ45 8-pin
jack.or one site is RJ-45 and the other site is Ｕtype(option).
One 7-feet (2.13m) modular telephone cable for connection to an RJ11 4-pin
jack.
One 8-pin RJ-45 box for leased line application.
One 6-feet power cord.
Rough handling during shipping causes most early modem failure; after you
unpack the modem, check carefully for shipping damage. Contact the shipper if
you notice any damage. Direct any additional questions about damaged or
missing parts to the nearest sales representative.

Chapter 2 Installation
11
2.3 Site Requirements
The FCC requires telecommunications equipment to withstand electrical surges
that may result from lightning strikes; the TAINET Network Series Modem meet
the requirements set forth by the FCC. Make sure the electrical service in your
building is properly grounded as described in article 250 of the National Electrical
Code (NEC) handbook. The following procedure outlines some common practices
that can minimize the risk of damage to computer equipment from electrical
surges:
Verify that a good copper wire of the appropriate gauge, as described in
Tables 250-94/95 of the NEC Handbook, is permanently connected between
the electrical service panel in the building and a proper grounding device
such as:
A ground rod buried outside the building at least 8 feet (2.44 meters)
deep in the earth. Several ground rods, connected together, buried
outside the building at least 8 feet (2.44 meters) deep in the earth.
If you are unsure whether the electrical service in your building is
properly grounded, have it examined by your municipal electrical
inspector.
Install a surge protector between the modem and AC power outlet. Any
additional computer equipment you have connected to the modem
(directly or through another device), such as a terminal or printer, should
also be plugged into the same surge protector. Make sure that the surge
protector is properly rated for the devices you have connected to it.
Call your telephone company and ask them if your telephone line is
equipped with a circuit surge protector.
If you are operating the modem in an area where the risk of electrical
surges form lightning is high, disconnect the modem form the telephone
line at the modem's rear panel when it is not in use.