Configuring Client Modems to Work with Cisco Access ServersPrintable Pdf
Document ID: 9284
Introduction Prerequisites
Requirements
Components Used
Conventions Examine the Client Modems
Identify the Client Modem Type
Upgrade the Client Modem Code
Reconfigure the Client Modem Example HyperTerminal Session Log Dialin Events and Use Custom Parameters Log PPP Events NetPro Discussion Forums - Featured Conversations Related Information
Introduction
When you troubleshoot modem connections, it is important to evaluate three main areas: the client modem,
the telco network and the Network Access Server (NAS). You must ensure that the modems on either side,
and the telco network work properly, because problems with any of those factors can affect modem
connectivity. This document discusses how to optimize and troubleshoot client modem related issues.
Prerequisites
Requirements
Readers of this document should have knowledge of these topics:
How to troubleshoot the NAS and the telco.
For information on how to troubleshoot the NAS and the telco, refer to these documents:
Troubleshooting Modems
Overview of General Modem and NAS Line Quality
Recommended Modemcaps for Internal Digital and Analog Modems on Cisco Access Servers
Components Used
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the
devices used in this document started with a cleared (default) configuration. If your network is live, make sure
that you understand the potential impact of any command.
Conventions
For more information on document conventions, refer to the Cisco Technical Tips Conventions.
Examine the Client Modems
After you examine the server side of the connection, look at the modem or connection of the client as a
possible cause of difficulty. In many cases, a particular client modem on a particular phone line can have
problems when it is connected to a digital modem. Problems can include failure to train up, or a successful
train-up but poor throughput or premature disconnection.
Based on the assumption that the phone circuit works, and holds the server modem constant, you can fix the
problem with the client modem. To do so, you must improve the code of the client modem, or reconfigure the
client modem.
First, determine what kind of modem the client uses. Find out the vendor, the hardware model, the software
(firmware) version, and the underlying modem chipset. Although there are hundreds of different modem
vendors, there are only a dozen or so different chipsets.
For more information, refer to the document Client Modem Firmware Overview.
Identify the Client Modem Type
Details about the modem vendor and hardware model must appear on the modem and its packaging. For
modems sold in the United States, see the FCC ID and Part 68 registration number found on the modem
packaging. Refer to the FCC ID Search Help Page for more information.
To determine which chipset you have, use the ATI commands. Use HyperTerminal to connect to the COM
port of the modem, and issue the ATI0 through ATI11 commands. Some of these commands can yield errors,
but they usually provide enough information for an educated guess.
These links will help determine your modem type:
Client Modem Firmware Overview
Unknown Modem Search by Modem Help
Who Manufactured My Modem?
Upgrade the Client Modem Code
To upgrade the modem code, refer to the modem vendor, not the chipset manufacturer. For modem code
upgrades, visit these web sites of modem manufacturers:
www.56k.com (Click the Modem Makers and Firmware Updates links for relevant information.)
Modem-Help: Home Page
windrivers.com
56K Modem Troubleshooting (includes the Interactive Modem Troubleshooter )
For LT winmodems (Mars/Apollo controllerless modems), use the common code, regardless of the vendor.
Warning: There is no guarantee that the problem will be solved if you upgrade the client modem code.
In some cases, an attempt to upgrade the modem can render the modem useless.
Reconfigure the Client Modem
If a client modem has performance problems, it is useful to configure it to use slower modulations, or to use
slower rates within the chosen modulation.
For example:
Problem 1: A client connects in V.90 at 49333, but suffers from a premature disconnect after two
minutes.
Solution 1: Configure the client to cap its V.90 receive speed at a lower speed (for example,
44000). If the client still suffers from erratic performance, configure it to use V.34 or below.
Problem 2: A client attempts to train up in V.90, but fails to train up at all.
Solution 2: Configure the client to use K56Flex, V.34 or below. If the train up still fails,
configure the client to connect at a maximum V.34 rate of 21600. If that still fails, configure
the client to use only V.32bis or below. If that fails, configure the client to use only V.22bis
or below. If that fails, get a new modem and phone line.
The modem vendor must supply documentation with the modem. If this is not available, refer to these links
for more information:
56k.com Modem Manuals ·
56k Modem Troubleshooting - INIT STRINGS / EXTRA SETTINGS for your modem ·
While you try to reconfigure the client modem, use HyperTerminal (or some other terminal program) instead
of Windows Dial Up Networking (DUN). This is because, DUN does not generally display details of the call
placed.
If necessary, temporarily reconfigure the NAS lines to permit terminal dialin. That is, if the async
interfaces have async mode dedicated configured, change them to async mode interactive, and put
autoselect ppp on the lines. If you use Authentication, Authorization, and Accounting (AAA), the
AAA server can require adjustment to allow interactive logins.
On the client PC, start the terminal program. If you use HyperTerminal, create a new connection.
Create a name and icon. In the Connect To panel, select Connect using COM port.
In this case, the COM port refers to the COM port on which the modem is. In the COM Properties
panel, set 115200 bps, 8 databits, no parity, 1 stopbit, flowcontrol hardware (see the Example
HyperTerminal Session section for details). Enter the AT command, and ensure that an OK response
appears. If no response appears, there could be a cable problem or, on an older modem, the speed has
to be slower in the COM properties.
Reset the modem to the factory defaults (use the hardware flow control template, if it is available).
This will typically be AT&F or AT&F1. If the factory default does not use these settings, set the
modem to provide data communications equipment (DCE) rate information at connect time (typically
TW2), and ensure that the speaker is on, until carrier detect (typically ATM1).
To establish a performance baseline, dial manually into the NAS with the ATDTnnnnnnn command.
See the AS5x00 Case Study in the Verifying Modem Performance documentation for an example.
Example HyperTerminal Session
Here is a sample session to connect HyperTerminal to a COM port to a modem. The progression described in
this section works on most Windows systems.
From the Start menu, point to Programs > Accessories, and select HyperTerminal.
Note: If HyperTerminal does not appear in the menu, you need to install it from the Windows
CD-ROM.
Double-click the Hypertrm.exe file. The Connection Description dialog box is displayed (see Figure
1).
Figure 1 The Connection Description Dialog Box
Select an appropriate name and icon.
Click OK.
The Phone Number dialog box is displayed (see Figure 2). HyperTerminal assumes that you want to
make a call, so it prompts for the phone number. From the drop-down list, select the desired COM
port.
Figure 2 The Phone Number Dialog Box
When you make a selection, the relevant Port Properties dialog box is displayed.
Set the COM port to 115200 bits per second, because that is the fastest speed modems can
communicate over the data terminal equipment (DTE) link (see Figure 3).
Figure 3 Set the COM Port to 115200 Bits Per Second
Note: This speed is not the connection speed the modems use to talk to each other. This is the speed
that goes across the async modem cable between the PC and its modem.
Click OK.
A terminal window is displayed.
Here is an example session that uses the ATI commands numbered 3 through 11. This example includes what
was entered and the responses from a modem in one of Cisco's labs:
at
OK
ati3
U.S. Robotics 56K FAX V4.6.6
OK
ati4
US Robotics 56K FAX Settings...
B0 E1 F1 M1 Q0 V1 X1 Y0
BAUD=38400 PARITY=N WORDLEN=8
DIAL=TONE ON HOOK CID=0
Precoding ON/ON
Shaping ON/ON
Preemphasis (-dB) 8/6
Recv/Xmit Level (-dBm) 32/10
Near Echo Loss (dB) 32
Far Echo Loss (dB) 49
Carrier Offset (Hz) 294
Round Trip Delay (msec) 7
Timing Offset (ppm) -1440
SNR (dB) 32
Speed Shifts Up/Down 0/0
Status :
OK
Here is the output from a connection to one of Cisco's test systems. First, enable the speaker and DCE rate
information reporting:
atw2m1
ERROR
As it turns out, w2 is not necessary on US Robotics modems.
atm1
OK
Next, dial into a static lab:
at
OK
atdt914085703932
NO CARRIER
The normal connection seems to fail. In this case, it is a noisy line, so set the modem to factory defaults (&f),
turn on the speaker (m1), and cap the modem at 28.8 (&n14) with the at&fm1&n14 command:
Try to dial again. If the connection is successful you will see:
atdt914085703932
CONNECT 28800/ARQ
Welcome! Please login with username cisco, password
cisco, and type the appropriate commands for your test:
ppp - to start ppp
slip - to start slip
arap - to start arap
access-3 line 29 MICA V.90 modems
User Access Verification
Username: cisco
Password:
access-3>
Note: For more information, refer to:
Customer Dial-in Lab (San Jose, USA)
Customer Dial-in Lab (Australia)
Log Dialin Events and Use Custom Parameters
You have determined that the connection seems to work with the new settings. Now you must update the
configuration of the modem for dialup networking to reflect the changes.
To help troubleshoot modem problems, configure Windows to create a modemlog (\windows\modemlog.txt).
The configuration setting only works with Telephone Application Programmable Interface (TAPI)-enabled
programs, such as, DUN and HyperTerminal.
Complete these steps to set up modem logging or customer parameters on a Windows 95/98 system:
From the Start menu, point to Control Panel, and select Modems.
The Modems Properties dialog box is displayed.
Select your modem, and click the Properties button (see Figure 4).
Figure 4 Select Your Modem
The Modem type Properties dialog box is displayed.
Select the Connection tab, and click the Advanced button (see Figure 5). Figure 5 Specify Advanced Connention Settings
The Advanced Connention Settings dialog box is displayed.
Check the Record a log file check box to enable the modem logging feature (see Figure 6).
If any additional settings are needed for the modem connection to succeed, enter those commands in
the Extra settings text box. Based on the previous example from the Example HyperTerminal
Session section, the &n14 command has been added.
Figure 6 Specify Extra Settings and Enable Modem Logging
Click OK.
The procedure for modem logging and custom settings for Windows NT 4.0 comprises similar steps. The file
will be called modemlog_modemname.txt. The file appears in the system root directory (which is usually the
winnt directory, unless set otherwise). Modify the Registry Editor to enable modem logging and settings on
Windows NT 3.x.
Log PPP Events
When you attempt to diagnose premature disconnect problems on a PC, it is helpful to know the type of
information that was sent over the link at the PPP level. Windows 95/98 is able to create a PPP log file
whenever the PPP adapter is used (/windows/ppplog.txt)
From the Start menu, point to Control Panel,and select Network.
The Network dialog box is displayed.
From the list of network components, select Dial-Up Adapter, and click the Properties button (see
Figure 7).
Figure 7 The Network Dialg Box
The Dial-Up Adapter Properties dialog box is displayed.
Select the Advanced tab. From the Properties list, select Record a log file. From the Value
drop-down list, select Yes (see Figure 8).
Figure 8 Enable PPP Logging for the Dial-Up Adapter
Click OK to complete the operation.
Reboot the system.
For Windows NT, edit the registry to turn on PPP logging.
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