LRS Reference Manual

9 - Modems

9.1 - Introduction

9.2 - Modem Profiles

9.2.1 - Using a Profile

9.2.2 - Editing a Profile

9.2.2.1 - Examine the Profile

9.2.2.2 - If Necessary, Edit the Init String

9.2.2.3 - Edit Other Settings

9.2.2.4 - Enable Modem Control

9.2.2.5 - Initialize the Modem

9.2.3 - Profile Settings

9.2.3.1 - Answer

9.2.3.2 - Answer String

9.2.3.3 - Attention String

9.2.3.4 - Busy Response String

9.2.3.5 - Carrierwait

9.2.3.6 - Command Prefix String

9.2.3.7 - Compression

9.2.3.8 - Compression String

9.2.3.9 - Connect Response String

9.2.3.10 - Dial String

9.2.3.11 - Error Correction

9.2.3.12 - Error Correction String

9.2.3.13 - Error Response String

9.2.3.14 - Get Setup String

9.2.3.15 - Initialization String

9.2.3.16 - No Carrier Response String

9.2.3.17 - No Dialtone Response String

9.2.3.18 - OK Response String

9.2.3.19 - Reset & Reload String

9.2.3.20 - Ring String

9.2.3.21 - Save String

9.2.3.22 - Speaker

9.2.3.23 - Speaker String

9.2.3.24 - Statistics String

9.3 - How the LRS Interacts with the Modem

9.3.1 - Initialization

9.3.2 - Outgoing Calls

9.3.3 - Incoming Calls

9.3.4 - When a Port is Logged Out

9.3.5 - Compression

9.3.6 - Error Correction

9.3.7 - Security

9.3.8 - Autostart

9.3.9 - Dialback

9.4 - Wiring

9.5 - Examples

9.5.1 - Typical Modem Configuration

9.5.2 - Modem Configuration Using Generic Profile

9.5.3 - Editing Modem Strings

9.6 - Troubleshooting

9.7 - Quick Reference

9.1 Introduction

9.2 Modem Profiles

In order to communicate appropriately with a modem (this varies from modem to modem) the LRS consults a compilation of appropriate commands and responses for that modem. This compilation is called a modem profile.

9.2.1 Using a Profile

A modem profile must be chosen from this list and copied to the port that the modem is attached to. Examine this list. If your modem is listed, copy it to the port using the Define Port Modem Type command.

Figure 9-1: Associating Modem Profile With a Port

Local>> DEFINE PORT 3 MODEM TYPE 5

All configurations in the modem profile will be applied to the specified port. The port's flow control will be changed to RTS/CTS, Autobaud will be disabled if it's enabled, and the port's baud rate will be changed to the highest rate the modem can support.

If your modem isn't in the list of profiles, use a modem profile that's similar to your modem type (for example, a modem from the same manufacturer). If there isn't a similar modem listed, use the Generic profile.

Be sure to verify the provisions mentioned in Security.

To verify that the changes have been made, use the List Port Modem command:

Figure 9-2: Verifying Modem Configuration

Local>> LIST PORT 3 MODEM

9.2.2 Editing a Profile

Very few modems can use all commands in the generic modem profile. This is a starting point only.

To edit a modem profile, complete the following steps.

9.2.2.1 Examine the Profile

Figure 9-3: Displaying Modem Configuration

Local>> LIST PORT 3 MODEM

A series of settings will be displayed. For example, the Attention string may currently be set to at, and Error Correction may be enabled. Read through the configuration options discussed in Profile Settings and determine which options you'll need to enable or disable to meet your needs. Consult your modem's documentation for the appropriate strings.

9.2.2.2 If Necessary, Edit the Init String

Table 9-1: Commands in Initialization String

Command	Example String (Not for all modems: consult your documentation for appropriate commands)
Set modem to factory defaults	&f
Set modem to ignore any character that may force it to return to command mode (for example, +++)	s2=128
Set carrier detect (DCD) to "follow carrier"	&c1
Set modem to hang up phone and reload its configuration when DTR signal is dropped	&d2
Set modem to return as many result codes as possible (known as "all progress"). Result codes will be returned in text (rather than numbers)	w2
Set modem to use hardware flow control	&k3
Set modem to determine its serial speed from the Attention command (rather than using a constant serial speed).	s20=0

If the Init string in your profile needs to be edited, use the Define Port Modem Init command:

Figure 9-4: Sending Initialization String

Local>> DEFINE PORT 3 MODEM INIT "&fs2=128&c1&d3w2"

Often, initialization commands are sent individually, prefaced by the modem's Command Prefix string (commonly "at"). In order for the LRS to correctly send the information to your modem, all commands must be sent in one string. Do not include the Command Prefix string in this string.

If you configure a modem profile that is not available on the list, please mail it to support@lantronix.com.

9.2.2.3 Edit Other Settings

Figure 9-5: Configuring a String

Local>> DEFINE PORT 3 MODEM DIAL "DT"

9.2.2.4 Enable Modem Control

Figure 9-6: Enabling Modem Control

Local>> DEFINE PORT 3 MODEM CONTROL ENABLED

9.2.2.5 Initialize the Modem

Figure 9-7: Initializing the Modem

Local>> LOGOUT PORT 2

9.2.3 Profile Settings

9.2.3.1 Answer

9.2.3.2 Answer String

9.2.3.3 Attention String

9.2.3.4 Busy Response String

9.2.3.5 Carrierwait

9.2.3.6 Command Prefix String

9.2.3.7 Compression

See Compression for a complete description of compression.

9.2.3.8 Compression String

9.2.3.9 Connect Response String

9.2.3.10 Dial String

9.2.3.11 Error Correction

See Error Correction for a complete description of error correction.

9.2.3.12 Error Correction String

9.2.3.13 Error Response String

9.2.3.14 Get Setup String

When most modems receive the Get Setup string, they'll return one page that lists their configuration. The LRS will not function properly if more than one page of configuration information is sent (prompting the user to press a key to continue to the next page); if your modem is configured in this manner, the Get Setup string will need to be set to "". When Get Setup is set to "", the modem will not be queried for its configuration; instead, the LRS will write the modem's NVR each time the LRS is booted.

The AT&T Paradyne Compshere and AT&T Dataport pose this problem.

9.2.3.15 Initialization String

9.2.3.16 No Carrier Response String

9.2.3.17 No Dialtone Response String

9.2.3.18 OK Response String

9.2.3.19 Reset & Reload String

9.2.3.20 Ring String

9.2.3.21 Save String

9.2.3.22 Speaker

9.2.3.23 Speaker String

9.2.3.24 Statistics String

9.3 How the LRS Interacts with the Modem

9.3.1 Initialization

The modem will then be asked for its current configuration. The Init string will be sent followed by a request for the modem's configuration. If the current modem profile on that port does not match the configuration sent from the modem, it will be assumed that the modem's setup has changed. The Save string will be sent, and the setup contained in the profile will be saved in the modem's permanent memory (NVR).

The NVR on some modems will wear out with repeated use. This limitation is avoided by only writing the setup to the modem if it has changed.

9.3.2 Outgoing Calls

To set the telephone number, refer to Assign A Telephone Number to the Port or Site.

9.3.3 Incoming Calls

When the modem asserts the DCD signal, the incoming call will be permitted.

If more than 60 seconds pass between ring signals or before the assertion of DCD, the LRS will assume that the caller hung up or that the connect failed. (60 seconds is the default wait period; this can be configured using the Define Port Modem Carrierwait command). The port will then be available for outgoing calls.

9.3.4 When a Port is Logged Out

When the modem receives the Reset string, it will read its configuration from NVR. Any temporary configuration (for example, changes that an outbound modem user made) will be cleared at this point.

If a user made changes during an outbound call and saved them to the modem's NVR, the modem will be returned to this state.

9.3.5 Compression

Data compression enables a modem to transfer a larger amount of data in the same amount of time. When compression is used, uncompressed data arrives on the modem's serial port and the modem compresses the data before sending it over the phone line. The advantage of compression is increased throughput. For example, a modem might compress data to 1/2 its original size, doubling the modem's throughput; twice the data could be sent in the same amount of time required to send uncompressed data.

The disadvantage of compression is increased latency. Latency is the delay before data transfer occurs, caused by the additional time the modem requires to compress the data before it is sent. In situations where the delay is annoying (for example, during interactive use over a long distance line), compression should not be used.

The "compressibility" of data depends on what is being compressed. Some data can be compressed to half its original size, while other data cannot be compressed at all. As the data to be sent changes, the modem's throughput will change.

Before enabling compression, flow control must be enabled. In addition, the modem's serial speed must be set higher than the line speed. This enables the LRS to keep the modem's internal data buffer filled with data to compress. As lower compression ratios decrease the effective line speed, the modem will flow control the LRS more often. When compression ratios and the effective line speed rise, the modem will flow control the LRS less often.

To configure flow control, see Flow Control.

Figure 9-8: Enabling Modem Compression

Local>> DEFINE PORT 2 MODEM COMPRESSION ENABLED

When modem compression is enabled on a port, the LRS will send a string to the modem to instruct it to enable modem compression. When compression should be disabled, a disable string may be sent. The default enable and disable strings vary, dependent upon the modem profile used. To display the default strings for a particular modem profile, use the List Modem command:

Figure 9-9: Displaying a Modem Profile's Strings

Local>> LIST MODEM 11

To modify these strings, use the Define Port Modem Compression command. The first string specified is the disable string; the second is the enable string.

Figure 9-10: Changing the Disable and Enable Strings

Local>> DEFINE PORT 2 MODEM COMPRESSION "s46=136" "q5"

The compression mode used varies from modem to modem, however, the most common mode is V.42bis. This is the recommended method of data compression.

V.42bis encoding offers an automatic 20% savings on all data sent, regardless of how compressible it is. Some text files can be compressed down to 1/4 or less of their original size. In addition, V.42bis will enable or disable compression according to whether or not it's required.

Other compression modes, such as MNP, may not give the same results as V.42bis. To obtain the best results, experiment with different modes of compression.

On many modems, error correction must be enabled in order to use data compression.

9.3.6 Error Correction

Error correction modes enable modems to ensure data integrity in the presence of telephone line noise. These modes work by checking the data for errors at the receiving modem. If an error is detected, the receiving modem requests that the sending modem retransmit the data.

When errors are not detected, data flows through the modem at a normal rate. If an error occurs, requiring the sending modem to retransmit the data, new data will not be permitted through the connection. The sending modem must be able to flow control the LRS during the retransmission. Ensure that flow control is enabled on the LRS before enabling error correction.

To configure flow control, see Flow Control.

Figure 9-11: Enabling Error Correction

Local>> DEFINE PORT 2 MODEM ERRORCORRECTION ENABLED

When error correction is enabled on a port, the LRS will send a string to the modem to instruct it to enable error correction. When error correction should be disabled, a disable string may be sent. The default enable and disable strings vary, dependent upon the modem profile used. To display the default strings for a particular modem profile, use the List Modem command:

Figure 9-12: Displaying a Modem Profile's Strings

Local>> LIST MODEM 11

To modify these strings, use the Define Port Modem Errorcorrection command. The first string specified is the disable string; the second is the enable string.

Figure 9-13: Changing the Disable and Enable Strings

Local>> DEFINE PORT 2 ERROR CORRECTION "&q5" "q0"

9.3.7 Security

• If a remote user hangs up without logging out, the modem will sense the loss of carrier, and deassert the DCD signal. The server will then log the port out.

• If the remote user logs out, the server will force the modem to hang up immediately and reset.

Dialback security, discussed below, can be used in conjunction with these techniques on modem ports for an additional layer of security.

The Ports and Security chapters cover security features in detail. The best tools for securing modem ports are username and password pairs, server passwords, and idle timeouts.

9.3.8 Autostart

For information on Autostart or the DCD/DSR signals, see Chapter 8 - Ports

9.3.9 Dialback

For a complete discussion of dialback, see Dialback.

9.4 Wiring

If you're using an LRS16, you'll need to wire the DB25 adapter from the LRS16 DSR/DCD pin to the DCD pin on the modem. See the Pinouts appendix of the LRS16 Installation Guide for complete wiring information.

For a description of the serial signals, see Serial Signals.

9.5 Examples

9.5.1 Typical Modem Configuration

Figure 9-14: Typical Modem Configuration

Local>> LIST MODEM Local>> DEFINE PORT 2 MODEM ENABLED Local>> DEFINE PORT 2 MODEM TYPE 4 Local>> DEFINE PORT 2 MODEM SPEAKER DISABLED Local>> LOGOUT PORT 2

9.5.2 Modem Configuration Using Generic Profile

Port 2's speed must be set properly for the modem. To determine the appropriate port speed, examine the following table:

Table 9-2: Maximum Baud Rates

Modem	Typical Maximum Baud Rate
V.32	19200
V.32bis	57600
V.fast	115200
V.34	115200

To determine the maximum baud rate supported by the modem, the port speed must be set and tested. Modem handling must be disabled on the port; if it is enabled, the LRS will attempt to initialize the modem when the port is logged out.

Figure 9-15: Configuring Port Speed

Local>> DEFINE PORT 2 MODEM DISABLED Local>> DEFINE PORT 2 SPEED 115200

The port speed is tested by logging into the port and sending an attention ("at") command. The modem should respond with "OK". If it does not send "OK", the port speed should be set to a lower baud rate (see Table 9-2 above).

Figure 9-16: Testing the Port Speed

Local>> SET PORT 2 LOCAL SWITCH ^\ Local>> CONNECT LOCAL PORT_2 Local protocol emulation V2.2 at OK   Local>>

After the appropriate port speed is determined, the port must be configured using the generic modem profile. In addition, modem operation must be enabled.

To determine which profile number is the generic profile (the number will change as new profiles are added), the List Modem command is used:

Figure 9-17: Displaying Modem Profiles

Local>> LIST MODEM 1- Modem 1 2- Modem 2 3- Modem 3 4- Generic Local>> DEFINE PORT 2 MODEM ENABLED Local>> DEFINE PORT 2 MODEM TYPE 4 %Info: Port speed changed to 57600. %Info: Port flow control changed to CTS.

The generic modem profile made a series of configurations to port 2. To determine port 2's current configuration, the List Port and List Port Modem commands are used.

Figure 9-18: Current Port Configuration

Local>> list port 2 Port 2 : Username: Physical Port 2 (Idle) Char Size/Stop Bits: 8/1 Input Speed: 57600 Flow Ctrl: Cts/Rts Output Speed: 57600 Parity: None Modem Control: Disabled   Access: Local Local Switch: None Backward: None Port Name: Port_2 Break Ctrl: Local Session Limit: 4 Forward: None Terminal Type: Soft() Preferred Services: (Telnet) Characteristics: Broadcast Loss Notify Telnet Pad Verify

Port 2's speed is now 57600. This speed must be set to the appropriate speed (determined earlier by setting and testing the speed), 115200.

Figure 9-19: Configuring Port Speed

Local>> DEFINE PORT 2 SPEED 115200

Port 2 will be used for incoming and outgoing connections, therefore, the access must be set to Dynamic.

Figure 9-20: Configuring Local Switch and Port Access

Local>> DEFINE PORT 2 ACCESS DYNAMIC Local>> LOGOUT PORT 2

The final command, Logout Port, ensures that the changes made will be in effect for the next login to port 2.

9.5.3 Editing Modem Strings

Figure 9-21: Changing Init String

Local>> DEFINE PORT 3 MODEM INIT "&fw1&c1&d2s2=128s38=0"

9.6 Troubleshooting

• Install a breakout box between the modem and the LRS. Set all modem switches to the "normal" position, and remove all jumpers. When the modem and LRS are powered on, the box's LEDs will display the state of the signals, enabling you to more easily diagnose the problem.

• Enable logging for modems. (See Set/Define Logging).

• Use the List Port Modem command to ensure that modem control is enabled on the port. All of the port's characteristics will be displayed; if modem control is enabled, Modem will be listed as a characteristic for the port.

• Ensure that all modems have been reset by rebooting the LRS.

Table 9-3: Modem Troubleshooting

Problem	Possible Cause(s)	Remedy
The modem won't answer the phone.	Modem isn't configured to answer the phone.	Enable answering with the Define Port Modem Answer command.
	The DTR signal isn't attached.	Verify the wiring. Ensure that the ground pins on the RJ45 ports are wired together.
	The LRS isn't asserting the DTR signal.	Ensure that the Dtrwait characteristic is disabled on the LRS port used.
	The modem has hung.	Cycle power on the modem.
The modem doesn't respond to the LRS' configuration requests.	The modem's flow control isn't set properly, or the modem's autobaud isn't functioning properly.	Reset the modem's NVR to the factory default state (the at&f string is commonly used). For instructions, refer to your modem's documentation.
	The modem isn't wired correctly.	Verify the wiring. Ensure that the ground pins on RJ45 ports are wired together.
The modem answers, but can't log into the LRS.	The Access characteristic on the LRS port used is set to None or Remote.	Set Access to Local or Dynamic.
	The modem's serial speed does not match the serial speed on the LRS port used.	Ensure that the modem and LRS port have matching serial speeds.
	A network user is connected to the modem.	Use the Show Ports command to verify that the LRS port is idle. If it is not idle, log out the port using the Logout Port command.
	The modem has hung.	Cycle power on the modem.
	The LRS cannot detect the DCD signal.	Verify the wiring. Ensure that the ground pins on the RJ45 ports are wired together.
All data is corrupted.	The ground pins aren't wired correctly.	Verify the wiring. Ensure that the ground pins on the RJ45 ports are wired together.
	The modem's serial speed does not match the serial speed on the LRS port used.	Ensure that the modem and LRS port have matching serial speeds.
	Flow control isn't working properly.	Ensure that the modem and LRS port are configured to use the same flow control method.
	The modem is set to the wrong baud rate.	Cycle power on the modem.
The first few lines of data are transmitted properly, but the subsequent data is corrupted.	Flow control isn't working properly.	Ensure that the modem and LRS port are configured to use the same flow control method. Flow control is discussed in detail in Flow Control.
	The ground pins aren't wired correctly.	Verify the wiring. On RJ45 ports, ensure that the ground pins are wired together.
When the port is logged out, the modem doesn't hang up the phone line.	Modem Control isn't enabled on the LRS port used.	Ensure that Modem Control is enabled. See Define Port Modem Control for details.
	The DTR signal isn't attached.	Verify the wiring. Ensure that the ground pins on RJ45 ports are wired together.
	The modem isn't configured to reset when the DTR signal is dropped.	Check the modem's configuration.
When the phone is hung up, the LRS doesn't log out the port.	Modem Control isn't enabled on the LRS port used.	Ensure that Modem Control is enabled. See Define Port Modem Control for details.
	The DCD signal isn't attached.	Verify the wiring. Ensure that the ground pins on RJ45 ports are wired together.
	The modem isn't configured to deassert DCD upon loss of carrier.	Check the modem's configuration.
The modem answers, but won't connect to the remote modem.	One or both modems are configured not to connect unless some feature is enabled (for example, error correction).	Check the documentation for both modems; verify their configuration.
	The two modems cannot be connected. (Some modems are incompatible with one another).	Replace one or both of the modems. Verify that the modem is using the correct and current version of its software.

9.7 Quick Reference

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