Table of Contents

Features

Adaptive Speed Leveling
Data Compression
Error Control
Flow Control/Variable Interface Rates
Software Features
Trellis Encoded Modulation
Link Negotiation Fallback

Compatibility

Additional Standards

Quad Modem Network Application Cards

DIP Switches

Switch Adjustments

Quad Modem Network Interface Cards
Installing the Quad Modems
Rear Panel Connections
Configuring the Quad Modems
Stored Configurations

Power-On Defaults
Permanent Configuration Templates

Loading Configuration Templates

Customizing NVRAM
Stored Commands
Changing Settings Temporarily
Reset Options
Optional NVRAM Lockout (Read-Only)

Interface Controls

Error Control

ARQ Retry Timer
Error Control and Synchronous Mode

Data Compression
Break Handling
EIA/TIA-232 Controls

Data Terminal Ready
Carrier Detect
Data Set Ready (DSR) Operations

Flow Control Commands

Hardware Flow Control
Software Flow Control
Transmit Data Flow Control
Transmit Data Buffer Sizes
Received Data Flow Control

Data Rate Commands

Link Rate Select
Rate-Select Guidelines

S-Registers

User Preferences

Result Codes

Quiet Mode
Response Modes
Result Code Subsets
Additional Result Code Subsets

Local Echo

Command Mode Local Echo (En)
Online Local Echo

Modem Clock Usage
Transmitter Enable/Disable

Quad Modems

After you have configured the AS51 NAC, you can configure the modems in the Cisco Access Server 5100 chassis. This chapter describes the installation and operation of the V.34 and V.32 bisPlus quad modem in the Access Server 5100.

The quad digital and analog/digital modems contain a common microprocessor-based circuit that provides interfaces to the chassis midplane. Digital phone line signals are input directly from the T1 card via the midplane. The quad analog and analog/digital modem accepts input of analog phone signals via RJ-45 jacks on the quad analog/EIA/TIA-232 NIC. The modems output to external EIA/TIA-232 ports on the NIC, which, in turn, connect to the Access Server 5100. See the chapter "AS51 Cards" for cabling information.

The quad analog and analog/digital modem accepts input of analog phone signals via RJ-45 jacks on the quad analog/EIA/TIA-232 NIC. The modem directs its output to external EIA/TIA-232 ports on the NIC, which, in turn, connects to the Access Server 5100. See the chapter "AS51 Cards" for cabling information.

The digital modems can also make use of the dialed number identification string (DNIS) and automatic number indicator (ANI) numbers provided by the public 950 services, feature groups B and D, and enhanced 800 services to customize the configuration of the modem prior to answering a call. For example, the dialed phone number can be associated with specific applications, and the same modem pool can be dynamically configured on a call-by-call basis to adjust to the requirements of the application.

Features

The quad modems are downward com-patible with most installed modems operating at 9600 bps and below. The features and capabilities described in this section ensure superior reliability and performance.

Adaptive Speed Leveling

The rate between a computer and a modem can, depending on equipment and software support, be as high as 115.2-kbps for V.34 modems, and 57.6-kbps for V.32 bisPlus modems.

V.34 modems have a maximum connection rate of 28.8 kbps (if connecting to another V.34 modem). V.32 bisPlus modems have a maximum connection rate of 21.6-kbps (if they are connecting to another V.32 bisPlus modem), and 19.2-kbps with another modem that performs V.32 terbo modulation.

The quad modems monitor line quality and perform adaptive speed leveling (ASL). As necessary, they adjust to the next lower speed when poor line conditions warrant, and adjust to the next higher speed as conditions improve.

Without ASL, there may be so many errors that a modem would disconnect. This feature keeps a modem online, always operating at the highest possible speed, thus ensuring data integrity.

Data Compression

Data compression enables throughput of well over 115.2-kbps on 28.8-kbps connections, and 50 kbps on 19.2-kbps or 21.6 kbps connections. The modems use V.42 bis compression or Level 5 of the MNP protocol. V.42 bis compression is more efficient. V.42 bis recognizes when files are already compressed, and does not expand a compressed file as does MNP compression.

Error Control

Data integrity is ensured when the modems connect with remote modems that use the V.42 (LAPM) or MNP error control protocols. Error control is available on calls at 1200 bps and above.

Flow Control/Variable Interface Rates

Flow control, which is required under error control, also allows the local computer interface rate to be set higher than the link rate, enabling greater throughput. For example, data can be sent from the computer to a modem at 115.2 kbps, regardless of the link rate.

Software Features

The quad modems have the following software features:

• Programmable NVRAM.
  
  
• Operational control commands, including error control, data compression, flow control, optionally fixed data terminal equipment (DTE) and link interface rates, and result code subset options.
  
  
• Auto dial and auto-answer capability
  
  
• The modems recognize the AT command set, a superset of the industry standard that is widely used in microcomputer and terminal communications.
  
  
• Three factory-set templates stored in ROM.
  
  
• Programmable S-registers.
  
  
• Link security.
  
  
• Remote access.
  
  
• Synchronous operation.
  
  
• Leased line operation.
  
  
• Modem testing options.
  
  
• Software download of modem firmware
  
  

Trellis Encoded Modulation

Trellis encoded modulation is used for calls at 7200 bps and above. Trellis encoded modulation can tolerate twice the telephone channel noise as con-ventional modulation and is less susceptible to impulse-type noise.

Link Negotiation Fallback

Unless the quad modem cards are set for a fixed link rate, they automatically switch to the highest possible rate at which the remote modem can operate, ensuring compatibility with a greater number of installed modems.

Compatibility

The quad modem NACs adhere to the follow-ing standards, ensuring compatibility with a wide base of installed modems.

• ITU-T V.34, 28.8 kbps, 26.4 kbps, 24 kbps, 21.6 kbps, 19.2 kbps, 14.4 kbps, 12 kbps, 9600 bps, 7200 bps, 4800 bps, 2400 bps
  
  
• V.Fast class, 28.8 kbps, 26.4 kbps, 24 kbps, 21.6 kbps, 19.2 kbps, 14.4 kbps
  
  
• V.32 bisPlus, 21.6 kbps, 19.2 kbps, 16.8 kbps, 14.4 kbps, 12 kbps, 9600 bps, 7200 bps, 4800 bps
  
  
• ITU-T V.32 bis, 14.4 kbps, 12 kbps, 9600 bps, 7200 bps, 4800 bps
  
  
• ITU-T V.32, 9600 bps, 4800 bps
  
  
• Bell 208B, 4800 bps synchronous, half duplex
  
  
• ITU-T V.22 bis, 2400 bps
  
  
• Bell 212A, 1200 bps (also V.22)
  
  
• ITU-T V.23, 1200 bps with 75-bps back channel (British telephone system)
  
  
• Bell 103, 300 bps (also V.21)
  
  
• ITU-T V.25, answer sequence for calls originating outside the U.S. and Canada
  
  
• V.25bis, synchronous
  
  
• ITU-T V.42, LAPM error control, 1200 bps and higher
  
  
• ITU-T V.42 bis, data compression, 1200 bps and higher
  
  
• MNP, Levels 2, 3 and 4 error control, Level 5 data compression, 1200 bps and higher
  
  
• ITU-T V.54, digital and remote digital loopback testing (analog and digital modems); analog loopback testing (analog modems only)
  
  

Additional Standards

The quad modems support the following additional standards:

• EIA/TIA-232 interface
  
  
• Superset of the industry-standard AT command set
  
  

Quad Modem Network Application Cards

Each quad modem NAC contains four modems, numbered 1 through 4. The quad modem NAC front panel is shown in Figure 5-1.

Figure 5-1: Quad Modem NAC Front Panel

Five LEDs on the front panel enable you to monitor performance at all times. Table 5-1 lists the front panel LEDs and their functions.

DIP Switches

One ten-position DIP switch on the quad modem NAC controls the same functions for all four modems. (See Figure 5-2.) When the switch position is away from the front panel, then that switch is on.

Figure 5-2: Quad Modem NAC Switch Location

Table 5-2 lists the factory settings of the ten-position DIP switch on the quad modem NAC.

Switch Adjustments

To change DIP switch settings, remove the quad modem NAC. Reset the switches to the desired setting, then reinstall the NAC in the Access Server 5100 chassis.

Quad Modem Network Interface Cards

The quad modem NICs provide the EIA/TIA-232 serial port interface for all four modems on a quad modem NAC. NICs are available in both analog-only, analog/digital, or digital only versions. Figure 5-3 shows the analog/digital version.

Figure 5-3: Quad Analog/EIA/TIA-232 NIC

Installing the Quad Modems

Perform the following steps to install a quad modem NAC and NIC:

Step 1   Unscrew and remove the cover panels from the desired modem slots. Save the panels and screws.

Step 2   If your system has come from the factory assembled, and you want to change any of the quad modem NAC switch settings, you must remove the NAC. Loosen the captive screws and push the ejector tabs away from each other. The NAC pops out slightly. Use the tabs or grasp the front panel to slide the NAC toward you and remove it from the chassis.

Step 3   To change any of the modem's software settings, you must have DIP switch 8 on (the factory setting for smart mode in which the modem recognizes AT commands, and DIP switch 4 off to echo commands to the local screen). Use the tip of a pen or other small instrument to change applicable DIP switch settings.

After you customize the software settings, you may need to remove the quad modem NAC and reset one or more of the DIP switch settings. See the section "DIP Switches" earlier in this chapter.

Step 4   Install the quad modem NAC in the upper and lower card guides of the slot. Lift the top ejector tab while sliding the NAC toward the rear until it is firmly plugged into the connector on the chassis midplane.

Step 5   Remove the safety panel of the selected slots at the back of the chassis by unscrewing the top and bottom screws of each panel.

Step 6   With the 50-pin connector toward the top of the NIC, slide the NIC into the slot's upper and lower card guides until its rear connector is firmly positioned in the connector on the chassis midplane.

Step 7   Tighten the thumb screws that are attached to the rear panel.

Rear Panel Connections

A 50-pin female EIA/TIA-232 connector is located on the quad modem NIC. This connector controls the serial ports for the four modems on the quad modem card. The analog and analog/digital NICs also have four RJ-45 phone jacks for incoming telephone lines.

A breakout cable is provided that connects modems to the AS51 NIC. See the chapter "AS51 Cards" for more information.

The four 8-pin RJ-45 modular phone jacks located on the rear panel of the modem NIC are only for use with quad analog modems or quad analog/digital modems in analog mode. The jacks connect the NIC to the telephone network and are labeled CH1, CH2, CH3, and CH4.

Configuring the Quad Modems

Perform the following steps to configure each modem on a quad modem NAC:

Step 1   Power on the system, if it is not already operating.

Step 2   Connect a terminal to the console port of the AS51 NAC. For information on connecting a console, see the section "Booting the AS51 NAC for the First Time" in the chapter "AS51 Cards."

Step 3   Telnet to the desired modem port from the AS51 console. The following shows an example of connecting to one of the quad modems.

You can now issue AT commands to the modem.

When a quad modem NAC is powered on, each of the four modems automatically loads a default configuration template. This template, and several others stored in RAM, can be used to configure the modem. To access these templates, use the &Fn command, where n = 0, 1, or 2, corresponding to a template number.

By using Figure 5-4 as an example, and referring to Table 5-3, you can determine exactly which quad modem card and channel you are connected to based on the telnet port number. In this example, telnet port 2011 corresponds to quad modem card 3, channel 3.

You can also see that this modem port communicates with the AS51 NIC port labeled 9-16 through connector 2 on the breakout cable.

Figure 5-4: Example of a Quad Modem NIC Connected to an AS51 NIC

Stored Configurations

This section describes the settings that can be stored in the modem's NVRAM.

Power-On Defaults

Each quad modem is equipped with NVRAM, which is used to store default configuration information. The defaults that are factory-stored in NVRAM are based on the &F1 template. They are the most efficient, and offer enhanced performance. The defaults include the following:

• Transmit hardware flow control is set to Clear to Send (CTS)
  
  
• Receive hardware flow control is set to Request to Send (RTS)
  
  
• The serial port rate is fixed—it does not switch to match the connection rate
  
  
• Extended result codes are enabled, including full protocol reporting for those systems that have enabled result codes (DIP switch 3 is on).
  
  

The command that corresponds to these settings is as follows:

Permanent Configuration Templates

Each quad modem has three permanent templates. Only one may be loaded into active memory at a time. Each template corresponds to an AT&Fn command that can be used to change the active settings. Table 5-4 lists the permanent configuration templates.

Loading Configuration Templates

To load a template other than the default hardware flow control template (&F1) and save it as the power-on or reset default, enter the following command, where n = 0, 1, or 2:

Customizing NVRAM

To modify the active configuration in NVRAM, enter your changes and then save them to NVRAM, as in the following example. The original factory template remains intact, but your power-on default will reflect your changes.

You can load a new configuration template and modify it at the same time, as shown below. When writing changes to a configuration template in NVRAM, insert your changes after the &Fn command but before &W, or the changes will be overwritten by &Fn.

To complete the configuration, perform the following steps:

Step 1   If you changed any of the switch settings, remove the quad modem NAC, reset the switches, and reinstall the modems.

Step 2   When the quad modems are correctly installed and configured, tighten the captive screws on the front panel.

Step 3   Reinstall the safety pan-els on any unused slots at the front and the rear of the chassis.

Stored Commands

In addition to configuration information, a modem can store up to four dial strings in NVRAM, store the last dialed number, and do an inquiry of stored phone numbers. The dial string can be up to 40 characters long, and can include any valid dial command options, but no other commands. (See Table 5-5.)

Changing Settings Temporarily

Any setting can be changed just for the current session. You may want to experiment with this feature if you are experiencing performance difficulties. If the change does not achieve the effect you want, reset the modem to return it to its previous saved configuration. The following example changes the result code setting, but the power-on or reset default remains intact.

Reset Options

If you have changed a setting and have not saved it to NVRAM, you can restore the modem to its original settings by entering the Z or S13 commands.

When the modem is in smart mode (DIP switch 8 on), it resets when you enter the fol-lowing command:

If bit 0 of register S13 is on (S13 = 1 or greater), the modem automatically resets when data terminal ready (DTR) drops and the modem hangs up. Unlike the ATZ command that only resets the modem if it is in smart mode, the following command will reset the modem if it is in either smart or dumb mode and DTR drops:

Optional NVRAM Lockout (Read-Only)

The NVRAM lockout option makes the NVRAM settings and stored phone numbers read-only. The modem displays these settings and numbers if it is in smart mode and receives the ATI5 command.

To prevent the NVRAM configuration from being changed by an unauthorized person, enter the following command:

OK is then displayed. If the &W command is issued a second time, an error message is displayed.

To disable the lock-out and make NVRAM programmable by anyone, perform the following steps:

Step 1   Remove the quad modem NAC from the Access Server 5100 chassis and set DIP switch 10 on to clear the lockout setting.

Step 2   Reinsert the quad modem NAC in the Access Server 5100 and enter the following command:

Step 3   Remove the quad modem NAC from the Access Server 5100 again and set DIP switch 10 off.

Step 4   Reinsert the quad modem NAC in the Access Server 5100. The NVRAM feature is disabled and you can now send the modem NVRAM configuration commands.

Interface Controls

The commands explained in the section control operating characteristics at the computer-to-modem and modem-to-modem interfaces. The terminal or computer is referred to as the DTE. The DTE rate is the rate at which the DTE and modem (or DCE) communicate, for example, 19.2-kbps.

Figure 5-5 shows the relationship between the local DTE interface, the link interface, and the remote DTE interface. Table 5-6 indicates which commands control modem operations at the DTE and link interfaces.

Figure 5-5: Interface Control Commands

Error Control

Automatic repeat request (ARQ), or retransmission, is the term used by U.S. Robotics in error control commands and response codes. An ARQ connection indicates a call under error control.

While error control is optional, it is required for data compression and should always be selected for connec-tions above 2400 bps. Cyclic redundancy checking is used to detect errors. Automatic repeat requests are issued for retransmission of corrupted data frames.

ARQ Retry Timer

A retransmission request for the same frame may occur repeatedly, because of a serious disturbance in the phone connection. The retry maximum is 12, after which the modem automatically hangs up. If the modem hangs up for no apparent reason, and it is operating in smart mode, check the link diagnostics screen by sending the modem the ATI6 command. The modem displays the reason for the last disconnect along with other call information. If the modems reach the retry timeout and hang up, the call should be placed again.

Error Control and Synchronous Mode

The modems first try for a V.42 connection and then an MNP connection, depending on the capabilities of the remote modem.

Assuming the modems are set for data compression with the &Kn command, once they establish error control for a call they also attempt to use data compression. Table 5-7 lists the error control and synchronous mode options.

Data Compression

When data compression is enabled, the transmitting modem detects redundant information and recodes it. The receiving modem decompresses the redundant data units before passing them to the receiving DTE.

Compression does not take place unless the modems are able to establish an error control connection. In addition, the modem should be set for flow control (&H1, &H2, or &H3), as described in the section "Flow Control Commands" later in this chapter.

The modem tries first for V.42 bis compression, which is more efficient than MNP Level 5 compression. If V.42 bis is not feasible, the modem tries for MNP Level 5 com-pression. If MNP Level 5 is also not feasible, the error-controlled connection continues without compression.

Table 5-8 lists the data compression options.

Break Handling

The &Yn command allows a break to be sent to end data transfer without disconnecting from the data link. Table 5-9 lists the break handling options.

EIA/TIA-232 Controls

This section describes EIA/TIA controls DTR, CD, and DSR.

Data Terminal Ready

The &Dn command is another way to control the DTR signal the DTE sends the modem. The modem is factory-set with DIP switch 1 off. The DTE must provide DTR for the modem to accept commands; dropping DTR terminates a call. The &Dn command overrides the switch setting until the modem is reset. Table 5-10 describes the DTR options.

Carrier Detect

The &Cn command is another way to control the CD signal the modem sends to the DTE. The modem is shipped with DIP switch 6 off. The modem sends CD when it connects with a remote modem, and drops CD when one of the modems dis-connects. The &Cn command overrides the switch setting until the modem is reset. Table 5-11 describes the CD options.

Data Set Ready (DSR) Operations

The DSR function on the EIA/TIA-232 inter-face is required by some systems to enable the modem to signal the DTE when the modem is ready to answer a call. Typically, DSR signaling is overridden. Table 5-12 lists the DSR options.

Flow Control Commands

Flow control prevents data loss by controlling the amount of data in the modem's transmit and received data buffers. The modem is shipped with hardware flow control enabled to allow the greatest performance.

Hardware Flow Control

Hardware flow control refers to signaling over the EIA/TIA-232 interface. The DTE raises or lowers the RTS signal, and the modem raises or lowers the CTS signal to control the flow of data. Both RTS and CTS require com-munications software support.

Software Flow Control

The modem sends the DTE the conventional ASCII transmit on/off (XON/XOFF) characters. This requires software support of XON/XOFF signaling. (See Table 5-13.)

You can select ASCII characters. See regis-ters S22 and S23.

---

Note Hardware flow control is required when transferring binary files under XMODEM-type protocols. If this is not possible because CTS is not supported, disable flow control when you use XMODEM-type protocols and set the modem to &B0 and &N0 so that the DTE and link rates are equal.

---

Caution In normal operation, the only characters the modem recognizes during a call are the three pluses (+++) of the escape code. But when software flow control is enabled, the modem also looks for Ctrl-S or Ctrl-Q characters. If these characters occur in a file or as part of a protocol, the modem reads them as XON/XOFF characters and acts on them. Use software flow control of received data only if the system does not support hardware flow control (&R2), and only for text files without XMODEM-type protocols.

Transmit Data Flow Control

Transmit data refers to the data from the computer that the modem is to transmit over the phone line.

The modem monitors the transmit buffer as data comes from the DTE and, as the buffer approaches 90 percent capac-ity, signals the DTE to stop sending. Once enough data has been transmitted over the phone link to empty half the buffer, the modem signals the DTE to resume sending.

Transmit data flow control is required in either of the following situations:

1. The modem is set for error control (at rates of 1200 bps and above), with or without data compression. If problems on the line cause a number of retrans-missions, continued input from the DTE may cause the modem's transmit buffer to overflow.

2. The rate at the DTE interface is higher than the link rate; for example, the DTE is sending at 115.2 kbps, 57.6 kbps, 38.4 kbps, or 19.2 kbps and the link rate is 14.4 kbps. This setup offers the greatest throughput, but the modem must be able to signal the DTE when the modem's buffer is reaching capacity.

Transmit Data Buffer Sizes

The size of the transmit data buffer depends on whether or not the connection is under error control, as follows:

• ARQ connections: 3.25 KB
  
  
• Non-ARQ connections: 1.5 KB, allowing error control file transfer protocols such as XMODEM and YMODEM to be used without flow control
  
  

If bit 3 of register S15 is turned on, the non-ARQ buffer size is reduced to 128 bytes for the conven-ience of people at remote sites using slower modems. Limiting the buffer size allows these users to send an XOFF to the remote DTE without causing the data that is already in the modem's buffer, or in transit, to exceed the size of their screens. See register S15.

Table 5-14 lists the transmit data flow control commands.

Received Data Flow Control

Separate commands, &Rn (hardware) and &In (software), control the flow of received data passed by the modem to the DTE. The received data refers to the data the modem has received over the phone link, which the modem is to pass on to its attached computer. The size of this buffer remains constant at 2 KB.

This type of flow control is optional. For example, if the data rate at the DTE inter-face is 9600 bps or higher, you may need to signal the modem to temporarily stop passing data in order to read what is on the screen.

As with transmit data flow control, you should select the default hardware control, not software control.

Hardware and software must support RTS at the EIA/TIA-232 interface, with RTS not overridden (not always high). The modem set to &R2 stops passing data to the DTE when the DTE lowers RTS, and resumes passing data to the DTE when RTS is raised. Table 5-15 lists the hardware flow control commands.

As noted earlier, you can select the ASCII XON/XOFF definitions by changing the settings of registers S22 and S23. Table 5-16 lists the software flow control commands.

Data Rate Commands

The modem can be set to a fixed or variable serial port rate. A fixed rate sets the modem for the highest possible throughput and provides the best performance. A variable rate allows the modem to switch to match the more limited rate on the phone connection. Most communications programs support variable rates, but not all software supports fixed rates. Table 5-17 lists the DTE rate select commands.

Link Rate Select

The link rate should never be set higher than the DTE rate. Table 5-18 lists the link rate select commands.

Table 5-19 lists the allowable data rates for the DTE rate and link rate select commands.

Rate-Select Guidelines

Use the following rate select guidelines:

1. For maximum throughput, set the DTE rate to 57.6 kbps or 115.2 kbps if the computer and software support one of these higher rates. Use the default hardware flow control template, &F1. The template includes the following commands.

• &B1 (fixed DTE interface rate)
  
  
• &N0 (variable link rate)
  
  
• &H1 (transmit data hardware flow control)
  
  
• &M4 (error control enabled)
  
  
• &K1 (data compression enabled)
  
  

2. Online fallback ensures that the modem stays online during poor connections, and requires a variable link rate, &N0, enabled by the &F1 template. Setting a fixed link rate, for example, &N6, disables online fallback.

3. Some software does not support a fixed DTE rate. In this case, set the modem to &B0.

4. Some systems require the DTE and link rates to be fixed with both the &Bn and &Nn commands.

S-Registers

The S-registers are used to set various timing parameters, redefine selected ASCII char-acters, and other configuration options. See the appendix "This appendix contains the following information:" for a summary of the S-registers.

User Preferences

The commands described in this section define how to customize the local modem's operating characteristics.

Result Codes

Modems compatible with the AT command set send result codes, such as OK and CONNECT messages, to the DTE. The Qn, Vn, Xn and &An commands allow format and other result code options, as described in the following sections.

Quiet Mode

The Qn command enables or disables result codes sent to the DTE by the modem. The Qn command overrides the default setting of DIP switch 3 until the modem is reset. Table 5-20 lists the quiet mode commands.

Response Modes

When result codes are enabled they are sent to the screen in either words (written mode) or numbers (numeric mode). The modem is factory set to written mode (DIP switch 2 is off). The Vn command over-rides the default setting of DIP switch 2 until the modem is reset. Table 5-21 lists the response mode commands.

Result Code Subsets

Eight optional result code subsets are listed in Table 5-22. Most of the subsets combine various call-progress mes-sages. The default setting, X7, includes all the result code mes-sages except 12/VOICE.

Additional Result Code Subsets

Use the &An command to enable or disable one of the subsets—error control, modulation, or protocol result codes—listed in Table 5-25.

Local Echo

Two commands control what the modem displays on the screen. The command mode local echo (En) command applies when the modem is in command mode. The online local echo (Fn) command applies when the modem is online with another system.

Command Mode Local Echo (En)

The En command enables or disables the display of entered commands. If double characters appear on the screen, both the modem's local echo and the software's local echo are on. The modem is shipped with DIP switch 4 on, disabling the echo. The En command over-rides DIP switch 4 until the modem is reset. Table 5-26 lists the local echo commands.

Online Local Echo

The Fn command causes the modem to display a copy of the data it is transmitting to another system. Many systems, however, return a copy of received data, which is called a remote echo. If the modem's online echo is on and there is remote echoing, double characters appear on the screen. (See Table 5-27.)

Modem Clock Usage

The modem clock is used as a call duration timer or as a real-time clock. Used in conjunction with the Inquiry (In) command, the modem returns the duration of the last call in hours, minutes, and seconds or the actual time. See Table 5-28.

Transmitter Enable/Disable

If an additional DTE and modem share the phone line for monitoring purposes, the second modem is placed in the receive only state by disabling its transmitter. Use this feature only at 1200 bps or 300 bps. See Table 5-29.

Posted: Tue Oct 1 04:02:32 PDT 2002
All contents are Copyright © 1992--2002 Cisco Systems, Inc. All rights reserved.
Important Notices and Privacy Statement.