Configuring DCMs for dialup access

This “how-to” will help you set up an installation as shown in the diagram below, with a Güralp sensor and DCM connected to a PC over a standard modem link. This link is carried over telephone lines, possibly via satellite.

With this setup, you can connect to the DCM at will in two ways:

• You can use minicom or hypertrm to dial in to the DCM and get access to the login: prompt and shell.

• You can set up a PPP connection to the DCM in your computer's dial-up networking settings, and access the DCM over the network.

Setting up the instrument

This document assumes you have already installed and configured the instrument and DCM to record or transmit data, and are ready to connect them to your local network.

Connecting the modem

You will need a suitable cable to connect a modem (with a 25-pin D-type connector) to either the PORT A or B, or the DATA OUT connector of a surface DCM unit.

The cable layout for connecting to PORT A or B is:

If you want to connect your modem to the DATA OUT port, remember that the transmit and receive pins (J and K) are reversed, so the cable should be made up as follows:

Suitable cables can be obtained by request from Güralp Systems.

Setting up modem links using the Web interface

Once the modem is connected, you will need to configure the DCM to listen for remote logins.

1. On the Serial Port Configuration page for the port connected to the modem, set serial.x.service to mgetty. mgetty is the program that configures the modem and provides access to the login: prompt.

   If you only want to connect directly to the DCM, without using PPP, finish here.

2. Under Network Configuration → PPP, edit the options file to read

   defaultroute
   crtscts
   lcp-echo-interval 5
   lcp-echo-failure 3
   asyncmap 0
   name your-dcm-name

3. Edit the chap-secrets file to read

   # Secrets for authentication using CHAP
   # client             server         secret    IP addresses
   connecting-username your-dcm-name password  *

4. Under Network Configuration → mgetty, edit the login.config file to include the line

   /AutoPPP/ - a_ppp  /usr/sbin/pppd auth debug dcm-ip-address:pc-ip-address

   This line instructs mgetty to spot incoming PPP connections and automatically pass them on to pppd. The two IP addresses refer to the two ends of the PPP connection only. You should choose local network addresses (beginning 10., 192.168., etc.) which neither the DCM nor your computer is already using.

Setting up modem links using the console

If you prefer, you can perform the same configuration with console commands. First set the service with

gcfgdbset serial.x.service mgetty

Now edit the files /etc/ppp/options, /etc/ppp/chap-secrets and /etc/mgetty+sendfax/login.config as described above.

Setting up the modem

US Robotics Courier modems

Güralp Systems recommend this model of modem, because you can completely configure its behaviour using dip switches on the underside of the case. Using other modem types, you may have to set the modem link up using AT commands before you will be able to communicate with the digitizer.

To communicate with the DCM, you should set the dip switches to their initial positions, which are:

OFF	OFF		OFF		OFF	OFF		OFF	OFF
		ON		ON			ON
1	2	3	4	5	6	7	8	9	10
DTR normal	Verbal Result Codes	Display Result Codes	Echo offline commands	Suppress Auto Answer	Normal CD	Display all result codes	Enable AT Commands	Disconnect with +++	Load NVRAM settings

If you have previously used the modem to communicate with a DM24 digitizer, you will need to set the switches back to this position.

You may also need to reset the modem's internal memory. To do this, open a serial connection to the modem. When it replies, enter

at&F1&W
ath

This command copies the ROM template for hardware flow control into the internal memory, overwriting any custom settings you may have made.

Other modem types

To communicate with the DCM, you should configure the modem to use the following settings:

• Baud rate at least 57600 (depending on capabilities)
• 8 data bits, no parity bit, 1 stop bit
• Hardware flow control enabled
• Software flow control disabled

Also configure the modem so that asserting DTR returns to command mode or hangs up.

You will probably want to save these settings for general use. Consult the documentation for your modem to find out how to do this.

Logging in with minicom

minicom is the standard Linux modem program. To use it:

1. If you are using a second DCM to contact your installation, first free the serial port you are going to use with

   gcfgdbset serial.x.service none

   replacing x with the correct port number.

2. Run minicom -s.

3. Use the cursor keys to highlight Serial port setup, and press ENTER.

4. Use the key choices to set up the serial port as above.

5. When you have finished, select Exit from the menu. The computer will connect to your modem.

6. If necessary, reset your modem to its default settings as detailed above.

7. Enter

   atdtyour-DCM-phone-number

   and press ENTER.

8. If the connection is successful, the modem will reply with a line like

   CONNECT 57600 V42
   BIS

   You are now connected to the DCM, and will shortly see a login prompt.

9. Log in as normal.

10. At the end of your session, press <Ctrl>-A then Q. minicom will automatically reset the modem.

    Alternatively, if you want to dial a second installation, type +++ to close the connection and return to the modem command line. Continue from step 7.

Logging in with hypertrm

To log in directly over the modem link:

1. Run hypertrm, and choose a name for the new connection.

   

2. Click OK.

   

3. Enter the telephone number and click OK.

   

4. Check your location and modify it if necessary. Click Dial.

5. Once you are connected, the DCM should respond with a login: prompt. Log in with your username and password to obtain a command shell.

This connection is not encrypted and may be intercepted in transit. If you want to connect to the DCM securely, you should use PPP as described below.

Configuring Windows dial-up networking

To configure Microsoft Windows XP to communicate with the DCM using PPP:

1. Open the Control Panel, and choose Network Connections.

   

2. Click Create a new connection.

   

3. Follow the wizard through, selecting Connect to the Internet, Set up my connection manually and Connect using a dial-up modem. Enter a name to represent the connection and the DCM's telephone number. If the Use this user name and password... and Make this the default Internet connection boxes are checked, uncheck them.

4. When the wizard is finished, it will pop up a window allowing you to dial up straight away.

   

   You can access this window at any time by double-clicking on the DCM's icon in the Network Connections window.

   Check the settings and click Dial to set up the connection.

5. You should now be able to connect to the DCM's Web site at the address you configured above:

   https://dcm-ip-address/

6. If you have configured a Scream! server on the DCM, check that you can receive data in Scream! over the network.