The Columbia University
High-Speed Dial-up Modem Pool

Last update: May 4, 1995


This document explains the configuration and use of Columbia University's high-speed dialin modem pool, installed and operated by Academic Information Systems. This document will change from time to time as modem pool is expanded and upgraded. This document does not discuss SLIP (Serial Line Internet Protocol) service, which is explained elsewhere.

Technical terms are explained in a companion document, Modem Protocols Explained.

The dialin modem pool consists of 122 US Robotics (USR) Courier V.32bis (14400 bps) plus 32 USR Courier V.34 (28800 bps) high-speed modems. You can reach the new modem pool by calling these numbers:

  212 854-9924  <-- V.32bis entry, hunts to V.34.
  212 853-9903  <-- V.34 entry, does not hunt.
The old low-speed ROLM-based modem pool remains available for fallback purposes, but at reduced capacity and support. The numbers are:
  212 854-1812  <-- ROLM entry, hunts to 854-9924
  212 854-1824  <-- ROLM entry, hunts to 854-9924
If you call any of these numbers and get a busy signal, it means all lines are busy. Peak usage hours are between about 10am and 2am.

The remainder of this document describes the high-speed modem pool. The low-speed, ROLM-connected modems are a holdover from earlier days, and are described elsewhere. The old pool is being deemphasized because it does not support high speeds, error correction, data compression, or flow control. However, the old pool is still our only dialout modem pool.

Overview of the High-Speed Modem Pool

The high-speed modems are all US Robotics Courier V.32bis 14400-bps or V.34 28800-bps modems supporting V.42 (LAPM) and MNP error correction, V.42bis and MNP data compression, hardware flow control, and high interface speeds. USR HST, Telebit PEP, and other proprietary protocols are not supported.

These modems are attached at 57600 bps to Cisco terminal servers that are connected directly to Columbia's TCP/IP campus network as well as to some Rolm data lines. This gives you terminal access to Columbia's TCP/IP-based hosts and services, to Rolm-connected computers, and it gives you IBM 3270 protocol conversion for connecting to Columbia's IBM mainframes. It also gives you SLIP and PPP access to the Internet, which is described in a separate document.

The US Robotics (USR) modems support the following types of connections:

  Modulation      Connection Speed    Fallback
   ITU-T V.34         28800 bps        26400 -> 24000 -> ... -> V.32bis
   ITU-T V.32bis      14400 bps        12000 -> 9600 -> 7200 bps -> V.32
   ITU-T V.32          9600 bps        4800 bps -> V.22bis
   ITU-T V.22bis       2400 bps        Bell 212A
   Bell 212A           1200 bps        Bell 103J
   Bell 103J            300 bps        110 bps
The interface speed on all the modem-pool modems is fixed at 57600 bps, but the interface speed of the modem you are calling from can be anything at all; the modems will provide any needed speed conversion. For best results, you should set your communication software to use the highest speed available to it, 57600 bps or lower (57600 bps, 38400 bps, 19200 bps, etc), that is also compatible with your modem and fix your modem's interface speed to the same value (see your modem manual), and set your modem and communication software for hardware (RTS/CTS) flow control.

Setting up Your Modem

We do not, at present, recommend or endorse any particular brand of modem for dialing in to the new modem pool. However:
  1. We do note that the modem pool has been used successfully in conjunction with the types of modems shown in Table 1. Some of entries are from our own tests (marked "*"), others from user reports. (NOTE: Telebit T2500 features depend on firmware version. Early versions support only MNP4, later ones MNP5, still later ones ITU-T error correction and compression.)

    Please send reports of success (or failure) for other types of modems to

  2. We recommend the following modem features: V.34 and lower modulations, V.42bis and/or MNP5 compression, V.42 or MNP4 error correction, interface speed 57600 bps, bidirectional hardware (RTS/CTS) flow control, and escape sequence guard time (as opposed to "TIES" = Time Independent Escape Sequence).

  3. We do NOT recommend "V.Terbo", "V.Fast", or "V.FC" modems. Similarly, we do not recommend modems that implement proprietary protocols like HST or PEP -- these are not supported by our modem pool, and will be of no use to you unless you are also calling other services outside Columbia that support these protocols. You should be able to call our modem pool from modems that do support these modulation techniques, if your modem properly falls back to V.32bis or lower.

  4. We do NOT recommend internal PC modems, particularly the new breed of low-cost, high-speed V-Dot-Everthing Data/Fax modems, which are almost always difficult to install and configure, and many of which are reportedly buggy. For best results, stick with external modems.

  5. We absolutely do NOT recommend or support RPI (Rockwell Protocol Interface) modems or the software that comes with them.

Table 1 - Modems Reportedly Compatible with the Modem Pool

.........NEGOTIATED FEATURES.......... MODEL MODULATION ERROR-CONTROL COMPRESSION * AT&T Paradyne DataPort 14400 V.32bis V.42 V.42bis Bocamodem 14.4K V.32bis V.42 V.42bis Gateway Telepath External V.32bis V.42 V.42bis * Hayes 1200 V.22 none none * Hayes 2400 V.22bis none none * Hayes Ultra 144 V.32bis V.42 V.42bis Intel 14400 Fax/Modem V.32bis V.42 V.42bis Modular Circuit Tech MCT-144IF+ V.32bis V.42 V.42bis * Multitech MT1432 V.32bis V.42 V.42bis PowerPort Gold (in Mac PowerBook) V.32bis V.42 V.42bis Practical Peripherals SA9600 V.32 V.42 V.42bis * Practical Peripherals PM14400FXSA V.32bis V.42 V.42bis * Practical Peripherals PM14400FXMT V.32bis V.42 V.42bis * Racal-Vadic 9632VP (V.32/MNP) V.32 MNP4 MNP5 SupraFaxModem V.32bis V.32bis V.42 V.42bis * Telebit Qblazer V.32 V.42 V.42bis Telebit T1600 V.32 V.42 V.42bis * Telebit T2500 V.32 none none * Telebit T3000 V.32bis V.42 V.42bis * Telebit TrailBlazer V.22bis none none * US Robotics Courier V.32bis ASL V.32bis V.42 V.42bis * US Robotics Sportster 14400 FAX V.32bis V.42 V.42bis * US Robotics Sportster 28800 FAX V.34 V.42 V.42bis Worldport 2496 Fax/Data V.22bis none none

We do not know the details of operation of every kind of modem in the world. It might be necessary for you to consult your modem manual for details of operation of your modem.

Error Correction

A full selection of standard error correction techniques is available. This feature lets the modems correct transmission errors that occur in the telephone system, so even if you have a noisy connection, you won't see the noise (provided the connection between your PC and modem is also reliable). The new modems support ITU-T V.42 (LAPM) and MNP Level 4 (and below) error correction. Now you can (and should) enable all the corresponding error correction features of your own modem, rather than disabling them, as was necessary with the old modem pool. The modems will negotiate the highest level common to both of them: V.42 LAPM first, and the various MNP Levels in descending order (MNP 4, 3, 2, 1). Here are some sample modem commands for enabling error correction:
 MODEM                        COMMANDS                REMARKS
  AT&T DataPort 14400          \N7                     V.42 ->. MNP ->. buffered
  Digicom Connection 144+      \N5                     V.42 ->. MNP ->. buffered
  Hayes 2400, 1200                                     V.42 & MNP not available
  Hayes ULTRA 9600 or 144      &Q5 S36=7 S46=138 S48=7 V.42 ->. MNP ->. buffered
  Multitech MT1432             &E1 &E15 $BA0           V.42 ->. MNP ->. buffered
  Practical Peripherals 14400  &Q5 S36=7               V.42 ->. MNP ->. buffered
  Practical Peripherals 9600   &Q5 S36=7               V.42 ->. MNP ->. buffered
  Telebit T3000, T1600         S180=2 S181=1           V.42 ->. MNP ->. buffered
  Telebit WorldBlazer, QBlazer S180=2 S181=1           V.42 ->. MNP ->. buffered
  Telebit T2500                &Q5 S36=1               MNP ->. buffered
  Telebit TrailBlazer                                  V.42 & MNP not available
  USR Sportster                &M4                     V.42 ->. MNP ->. buffered
  Zoom 14400 V.32bis           &Q5S36=7                V.42 ->. MNP ->. buffered

Data Compression

Data compression makes a connection faster than its modulation speed by "shrinking" the data. The sending modem compresses, the receiving modem decompresses. Compression only makes sense if the interface speed of both modems is higher than the connection speed between them. Depending on the particular compression method and the nature of the data being transmitted, the speed improvement ranges from 0% to about 400%.

Compression can (and should) be used with the new modem pool (but need not be). Supported techniques are ITU-T V.42bis and MNP Level 5. Compression is possible only when error correction is also enabled. Here are some sample commands for enabling compression on various types of modems.

 MODEM                         COMMANDS                REMARKS
  AT&T DataPort 14400           %C1                     V.42bis ->. MNP 5
**Digicom Connection 144+       %C1                     V.42bis ->. MNP 5
  Hayes 2400, 1200              N/A                     Not available
  Hayes ULTRA 9600              &Q5 S36=7 S46=138 S48=7 V.42bis ->. MNP 5
  Multitech MT1432              &E1 &E15 $BA0           V.42bis ->. MNP 5
  Practical Peripherals 14400   S46=2                   V.42bis ->. MNP 5
  Practical Peripherals 9600    S46=2                   V.42bis ->. MNP 5
  Telebit T3000, T1600          S190=1                  V.42bis ->. MNP 5
  Telebit WorldBlazer, QBlazer  S190=1                  V.42bis ->. MNP 5
  Telebit T2500                 S95=2                   MNP ->. none
  USR Sportster                 &K1                     V.42bis ->. MNP 5
  Zoom 14400 V.32bis            &Q5S36=7                V.42bis ->. MNP 5
**Depends on what software is loaded in the modem.

To take full advantage of compression, you should set your modem and your communication software to use an interface speed that is higher (by at least a factor of 2, and preferably 4) than the connection speed. For example, if you make a V.32bis 14400 bit-per-second connection, and the modems are able to compress data by a factor of four, your interface speed should be set to 57600 bits per second.

In general, you should configure your modem to use the highest interface speed that it reliably supports, and to "lock" the interface speed; that is, not to change the interface speed based on the connection speed (as most modems do automatically based on their factory configurations). The method for setting and locking a high communication speed varies from modem to modem, and might involve more than one parameter. Please read your modem manual carefully.

And of course, you must also set your communication software to use the same speed as your modem's interface speed; for example, in MS-DOS Kermit, "SET SPEED 57600".

NOTE: Interface speeds in excess of 57600 bps are not presently recommended, as they are not reliably and consistently implemented in many types of computers and modems, and because 57600 is the modem pool speed, so higher speeds on the calling end buy you nothing.

Flow Control

An effective method of flow control is absolutely necessary when error correction or compression are being done by the modems. This is because the local interface speed is not going to be the same as the communication speed between the two modems. If your PC is sending data to your modem faster than your modem can send it to the other modem, your modem needs to be able to tell your PC to stop sending while it catches up. Similarly, if your modem is sending data to your PC faster than your PC can process it, your PC must be able to control the flow of data from your modem.

Here is just one example: the telephone connection is very noisy, so there must be frequent retransmissions between the two modems. While the modems are busy retransmitting, you can't keep sending more data into them indefinitely. Eventually their buffers will fill up, and they must have the ability to stop the flow of data. Otherwise data will be lost.

The most effective form of flow control is hardware flow control, which uses special wires, separate from the data wires, to signal stop and start requests. The most common form of hardware flow control is called RTS/CTS (Request to Send / Clear to Send), and should be supported by any modem that also supports error correction and compression. For RTS/CTS flow control to be effective, the cable that connects the modem to your PC (see below about Macintoshes) must include wires for these signals.

A second method of flow control is called "software flow control". It is accomplished by embedding special characters in the data stream. These characters are called XOFF (Control-S) and XON (Control-Q). XOFF means "stop sending" and XON means "resume sending". Software flow control is inferior to hardware flow control for several reasons:

Therefore, use XON/XOFF flow control only if hardware flow control is unavailable to you.

Note that flow control should be enabled in both directions (PC-to-modem and modem-to-PC); some modems require you to enable flow control in each direction separately.

You must enable flow control in your modem AND in your communication software so the PC and the modem agree about how flow control will be done. Here is how to enable hardware flow control in several types of modems:

 MODEM                            INPUT   OUTPUT
  AT&T DataPort 14400             \Q3     \Q3
  Digicom Connection 144+         &K3     &K3
  Hayes 2400, 1200                Hardware Flow Control Not Available
  Hayes ULTRA 9600                &K1     &K3
  Hayes ULTRA 144                 &K3     &K3
  Multitech MT1432                &E4     &E4
  Practical Peripherals 14400     &K3     &K3
  Practical Peripherals 9600      &K3     &K3
  Telebit T3000 or T1600          S58=2   S68=2
  Telebit WorldBlazer or QBlazer  S58=2   S68=2
  Telebit T2500                   S58=2   S68=2
  Telebit TrailBlazer             S58=2   S58=2 (same register governs both)
  USR Sportster                   &R2     &H1
  Zoom 14400 V.32bis              &K3     &K3
(See below for the corresponding Kermit software commands.)

As noted above, our present terminal servers support hardware flow control in only one direction: the modem can stop data from the terminal server, but the terminal server cannot stop data from the modem because its interface lacks the RTS wire. Problems can occur when you are pushing voluminous amounts of data at high speeds into the terminal server, for example when uploading a file to a host computer from your PC using a streaming protocol (like Kermit with sliding windows, or Zmodem). Data loss can occur because the terminal server is overloaded, the network behind the terminal server is overloaded, or the destination host computer is overloaded. Without an RTS signal, the terminal server has no way to pass the "back pressure" on to the modem.

If you experience problems uploading files through the new modem pool, try using shorter packets or a smaller window size (assuming you are using Kermit). Here is a sample configuration for C-Kermit on the UNIX hosts for receiving files that you are uploading:

  set window 2                     ; (or 1)
  set receive packet-length 700    ; (or lower)
Eventually, the modems will be attached to a terminal server that offers hardware flow control in both directions, and uploading problems (if you are having them) should vanish.

Modem Settings Summaries

MS-DOS Kermit scripts are available on the MS-DOS Kermit diskette for each of these modems. Read the MODEMS\READ.ME file for further information.

AT&T Paradyne DataPort 14400 (NOT DataPort Express):
Connect at 57600 bps and give the following AT commands:

  ATX6       Extended result codes when dialing
  AT%B14400  14400 bps connection speed
  ATS41=1    V.32bis modulation
  ATS78=0    Fallback enabled
  AT\Q3      RTS/CTS hardware flow control
  AT\N7      Error correction enabled, negotiated
  AT%C1      Compression enabled, negotiated
  AT\K5      Nondestructive, nonexpedited BREAK handling

Digicom Connection 144+ or 96+
Connect at 57600 bps and give the following AT commands:

  ATX4       Extended result codes when dialing
  AT&K3      RTS/CTS hardware flow control
  AT\N5      Error correction enabled, negotiated
  AT%C1      Compression enabled, negotiated

Hayes ULTRA 144:
Connect at 38400 bps and give these AT commands:

  ATX4W1     Extended result and progress codes when dialing
  ATS87=28   Fix interface speed
  ATS37=11   Begin modulation negotiation at V.32bis, 14400 bps
  ATN1       Allow modulation fallback
  AT&K1      Input flow control = RTS
  AT&K3      Transmit flow control = CTS
  AT&Q5      Error correction enabled
  ATS36=7    Enable error correction fallback
  ATS46=2    Compression enabled
  ATS48=7    Enable compression and error correction negotiation
  ATS82=128  Nondestructive, nonexpedited BREAK handling

Multitech MT1432 Series
Connect at 57600 bps and give these AT commands:

  AT&Q1X4    Extended result codes when dialing
  AT$SB57600 Lock interface speed at 57600
  AT$MB14400 Start modulation negotiation at 14400
  AT$BA0     Speed buffering
  AT&E4      RTS/CTS hardware flow control
  AT&E1&E15  Error correction & compression enabled, negotiated
  AT%E1      Nondestructive, nonexpedited BREAK handling

Practical Peripherals 14400FXMT or 14400FXSA
Connect at 57600 bps and give these AT commands:

  ATX4S95=47 Extended result codes when dialing
  ATN1S37=11 Modulation fallback enabled, begin at V.32bis
  AT&K3      RTS/CTS hardware flow control
  AT&Q5S36=7 Error correction enabled, negotiated
  ATS46=2    Compression enabled, negotiated
  ATS82=128  Nondestructive, nonexpedited BREAK handling

Practical Peripherals 9600, 9600SA, 9600FXMT
Connect at 38400 bps and give these AT commands:

  ATX4S95=47 Extended result codes when dialing
  ATN1S37=9  Modulation fallback enabled, begin at V.32
  AT&K3      RTS/CTS hardware flow control
  AT&Q5S36=7 Error correction enabled, negotiated
  ATS46=2    Compression enabled, negotiated
  ATS82=128  Nondestructive, nonexpedited BREAK handling
Telebit T3000, T1600, WorldBlazer, or QBlazer:
NOTE: Obtaining a high interface speed is a bit tricky; start at 19200, get OK response to AT command, then set S51 to desired speed.
  ATX12      Extended result codes when dialing
  ATS59=15   Show connection speed and interface speed separately
  ATS51=7    Fix interface speed at 57600 (or highest speed allowed)
  ATS50=0    Automatic determination of connection speed
  ATS94=1    Allow full modulation fallback
  ATS58=2    RTS/CTS output flow control
  ATS68=255  Input flow control same as output flow control
  ATS61=0    BREAK signal handled as specified in S63
  ATS63=0    Send BREAK in sequence with data
  ATS180=2   Enable V.42 EC with fallback to MNP4
  ATS181=1   If error control not negotiated, connect anyway
  ATS190=1   V.42bis compression enabled in both directions, fall back to MNP5

US Robotics Sportster or Courier:
Connect at 57600 bps and give these AT commands:

  ATX4&A3    Extended result codes when dialing
  AT&B1      Fix interface speed
  AT&N0      Modulation fallback enabled
  AT&H1      Transmit flow control = CTS  
  AT&R2      Input flow control = RTS
  AT&M4      Error correction enabled, negotiated
  AT&K1      Compression enabled, negotiated
  AT&Y3      Nondestructive, nonexpedited BREAK handling

Zoom 14400 V.32bis (not verified):
Connect at 57600 bps and give these AT commands:

  ATX4S95=47 Extended result codes when dialing
  ATN1S37=11 Modulation fallback enabled
  AT&K3      RTS/CTS hardware flow control
  AT&Q5S36=7 Error correction enabled, negotiated
  ATS46=138  Compression enabled, negotiated
  ATS82=128  Nondestructive, nonexpedited BREAK handling

Recommended Software and Settings

The recommended communications software for terminal emulation and file transfer is Kermit.

When connecting to Columbia's central services (UNIX systems or IBM mainframes), the recommended settings for DOWNLOADING are:

  C-Kermit (UNIX, VMS):     Kermit-CMS (VM/CMS):

    SET WINDOW 5              (Use all defaults)

For UPLOADING, the recommended settings are:

  C-Kermit (UNIX, VMS):     Kermit-CMS (VM/CMS):    

    SET WINDOW 2    

MS-DOS Kermit

The recommended communication software for PCs with DOS or Windows is MS-DOS Kermit version 3.14. MS-DOS Kermit offers high-speed, reliable communication, faithful VT320, Tektronix, and other terminal emulations, RTS/CTS hardware flow control, and is fully supported by our technical staff. MS-DOS Kermit also offers TCP/IP and other types of network communications, important as we expand our campus network. Recommended MS-DOS Kermit settings for dialing into the new modem pool are:
  SET PORT 1          ; Or whichever serial port your modem is connected to.
  SET SPEED 57600     ; Or 38400 or 19200 if your modem doesn't support 57600.
  SET FLOW RTS/CTS    ; Set this on your modem too!
  SET WINDOW 3        ; For fast file transfer...
MS-DOS Kermit 3.14 comes with dialing scripts for many of today's popular high-speed modems, including AT&T Paradyne, Hayes Ultra, Practical Peripherals, Multitech, Telebit, US Robotics, Zoom, etc. These scripts automatically set up both Kermit and your modem appropriately for dialing up our new modem pool. For further information about MS-DOS Kermit dialing scripts, see the file ~kermit/a/msmaaa.hlp on any of the CUNIX systems. This is also found in the MODEMS subdirectory of the MS-DOS 3.14 diskette as READ.ME.

OS/2 C-Kermit

For PCs with OS/2, the recommended software is C-Kermit 5A(191) for OS/2, which offers reliable high-speed communication, VT220 terminal emulation, hardware flow control, and is supported by our technical staff. Recommended OS/2 C-Kermit settings:
  SET MODEM name      ; Name of your modem (HAYES, TELEBIT, etc)
  SET DIAL SPEED-MATCHING OFF ; Keep interface speed constant.
  SET PORT 1          ; Or whichever serial port your modem is connected to.
  SET SPEED 57600     ; Or 38400 or 19200 if your modem doesn't support 54600.
  SET FLOW RTS/CTS    ; Set this on your modem too!
  SET WINDOW 3        ; For file transfer...

C-Kermit for UNIX and VMS Workstations

For UNIX or VMS workstations or servers, the recommended software is also C-Kermit 5A(190). On our central UNIX systems, just type "kermit" to start this program. Recommended UNIX C-Kermit settings (for file transfer only; dialout service is not yet available from our central hosts and servers):

Macintosh Kermit

For Macintoshes, the recommended software is Mac Kermit. Mac Kermit is currently under development, but in its present form -- version 0.991(190) at this writing -- supports high-speed connections and, when properly configured and equipped with a special cable -- supports hardware flow control. See the file ~kermit/f/ckmker.bwr on any of our central UNIX systems for further information about Mac Kermit.
  Communication Port:    MODEM or PRINTER, depending on your Mac model.
  Speed:                 57600
  Flow Control:          DTR and CTS (see below)
  Window size:           3
  Receive Packet-Length: 1000
To use the internal modem ("PowerPort") on the Powerbook, use the Portable or PowerBook control panel (depending on whether you're using System 7.0 or 7.1) to switch between the internal modem and the external modem serial port. One user recommended the following PowerPort modem settings:
  &F0   Initialize to factory settings
  V1    Full-word result codes
  \Q3   Bidirectional hardware flow control
  \J0   Fixed interface speed
  \N7   V.42 error correction with fallback to MNP
  %C1   Enable V.42bis data compression with fallback to MNP
but these have not been verified.

The Macintosh serial port is not an RS-232 device and does not support the full repertoire of modem signals needed for normal operation with modems. Communication with modems is accomplished using various "fakeouts", each of which sacrifices some feature in order to accomplish some other feature, since the Mac has only one modem signal to send to the modem, and reads only one modem signal from the modem. Thus, for example, the Mac can't hang up the phone by dropping DTR and use hardware flow control at the same time.

To have the ability to hang up the phone by dropping DTR, you need a regular Macintosh modem cable that connects the Mac's "Handshake Out" signal (Mini-Din-8 Pin 1) to the modem's DTR signal (DB25 pin 20), and the modem should be configured to hang up when DTR goes down. In Mac Kermit, you should NOT check "DTR input flow control" or "CTS output flow control".

To use hardware flow control with high-speed modems, you need:

  1. A special Macintosh hardware-flow-control-modem cable that connects the modem's CTS signal (DB25 pin 5) to the Macintosh's "Handshake In" signal (Mini-Din-8 Pin 2) and the Mac's "Handshake Out" signal (Mini-Din-8 Pin 1) to the modem's RTS signal (DB25 pin 4). This cable *might be* available from stores or suppliers as a "Macintosh Hardware Handshake Modem Cable" (buy at your own risk).

  2. You MUST configure your modem to ignore DTR ("&D0" on most Hayes and compatible modems) and to use RTS/CTS flow control. NOTE: This means you can't hang up the phone by "dropping DTR". Normally, it will hang up automatically when you log out from the remote computer or service. If it doesn't, use the escape sequence (such as +++) to get back to the modem's command processor, and then type the modem command for hanging up (usually ATH0).

  3. In Mac Kermit's Communications Settings menu, uncheck Xon/Xoff flow control, and check DTR input flow control and CTS output flow control.

Other File Transfer Protocols and Software

XMODEM, YMODEM, and ZMODEM file transfers are not recommended or supported. Kermit software transfers files more reliably and, when configured as described above, usually also faster than any of the X-Y-Z-MODEM protocols, generally 1600-5000 characters per second on a V.32bis modem connection, depending on the nature of the data (see Kermit News #5 for details).

Similarly, commercial and shareware communication software is not supported, even when it implements the Kermit protocol. Use it at your own risk, and obtain support from whoever you got it from.

How to Call the High-Speed Modem Pool

The telephone numbers are:
  212 854-9924   <--  V.32bis entry, hunts to 853-9903.
  212 853-9903   <--  V.34 entry, does not hunt.
For planning purposes, note that the dialin modem pool is most heavily used between the hours of 10:00am and 2:00am, and least heavily used between 3:00am and 10:am, and is used less heavily on weekends than on weekdays. Please don't use the modem pool for long periods of time unnecessarily, especially during peak hours. Note that there is a one-hour "idle timeout" -- your connection will be dropped automatically if an hour passes with no activity.

Watts: The Watson Laboratory Terminal Servers

All of our high-speed modems are connected Cisco ASM3 communications servers, also known as terminal servers. At present there are three terminal servers, known as watts, watts2, and watts3 (watts = WATson laboratory Terminal Server) (Watson Laboratory is the name of the building where the terminal servers are located, which is, by the way, the original IBM Thomas J. Watson Laboratory from the 1940s and 50s).

The configuration is:

  Watts   62 USR V.32bis
  Watts2  60 USR V.32bis
  Watts3  32 USR V.34
When the modem answers, you will see the "watts>", "watts2>", or "watts3>" prompt. The "watts>" or "watts2>" prompt means you are connected to a V.32bis modem; the "watts3" prompt means you are connected to a V.34 modem.

If you are having problems with your connection, type "sys" at the "watts>" (or "watts2>" or "watts3>") prompt, and take note of your "tty" number (yours is the one with an asterisk next to it). Include the prompt and the tty number when reporting problems, so we know which server and which line (and therefore which modem) is involved.

At the "watts>" or "watts2>" or "watts3>" prompt, you can type the name of any Columbia host computer or service that is reachable on our campus network, including departmental computers. Examples:

  watts> columbianet
  watts> cunix
  watts> ctr
  watts> nn
The terminal servers have an escape character, Ctrl-^ (Control-Caret, normally typed as Ctrl-Shift-6). If you need to send this character through the terminal server, you must type it twice. If you need to upload data containing this character through the terminal server, it must be doubled or otherwise quoted or escaped; Kermit file transfers take care of this automatically UNLESS you have told the sending Kermit to SET CONTROL UNPREFIX 30 (30 is the ASCII code for Ctrl-^), or SET CONTROL UNPREFIX ALL. When uploading files to C-Kermit through the Watts terminal server, you must PREFIX at least 0, 3, 30, 131, and 158.

If you want to escape back to the Watts terminal server without breaking your connection, type Ctrl-^ followed by the letter x. Type "help" at the "watts>" prompt to learn about the commands and services available at the terminal server (but not all of them are necessarily enabled).

When you log out from the remote host or service, you will see the "watts>" or "watts2>" or "watts3>" prompt again. If you wish to connect to another host or service, type its name (as above). If you wish to terminate your dialup session, respond with "exit":

  watts> exit
This should cause the modem connection to hang up.

Cisco Terminal Server Commands

The Cisco terminal servers allow commands to be issued at the Watts> (or Watts2>, etc) prompt. You can get a listing of the available command by typing a question mark (?).

One command is of special interest if you are having trouble transferring files through the Cisco:

This command disables the escape character, disables Xon/Xoff flow control, turns off all types of padding, and selects 8 data bits, no parity, and binary transmission mode, meaning all valid 8-bit characters are passed through transparently. In "download" mode, however, the Cisco is still sensitive to the BREAK signal, which gets you back to the Cisco prompt.

Connections to Columbia University TCP/IP Hosts and Services

At the "watts>" (or "watts2>", etc) prompt, just type the name of the host or service you wish to connect to, for example "cunix", "columbianet" (or "cn" or "cnet" for short), a departmental host name, etc. You can type any IP host name or IP numeric address that is in the Columbia University domain unless access is explicitly restricted.

When you access a UNIX system ("cunix"), it will think that your terminal speed is 38400, no matter what your true connection speed is. If you are dialing in from a slow modem, say 1200 or 2400 bps, this can affect the operation of time-sensitive applications like EMACS, rn, and Kermit. So if you are dialing in at 1200 or 2400 bps, then as soon as you log in, you should give an "stty" command to let UNIX know what your true communication speed is, for example:

  stty 1200

Connections to Columbia University Rolm-Based Hosts

If you need to access a host or PC or other computer that is on the Rolm system but that is not a TCP/IP host, type "rolm". A short message will appear instructing you to press the Enter or Return key several times to get the Rolm "CALL, DISPLAY OR MODIFY?" prompt. Do this, and then type the word "call" followed by a space and the name of the Rolm data group you wish to contact, for example "call help".

The connection from Watts, through the Rolm, to a Rolm-based host or service is at 19200 bps with no flow control (since the Rolm does not have any flow control capabilities).

Connections to Columbia University IBM Mainframes

You can access Columbia's IBM mainframes via the terminal servers' 3270 terminal emulation feature. NOTE: This is not the only way to access Columbia's IBM Mainframes. You can also access them -- subject to policies & procedures -- through ColumbiaNet, or via tn3270 on any of the CUNIX hosts, and you can also make a Rolm connection to SIMB or SIMC. All of these methods provide 3270 emulation for full-screen access to IBM mainframe-based applications and services.

To access an IBM mainframe such as CUVMB or CUVMC in fullscreen mode from the Watts terminal server, follow these steps:

  1. Make sure you are using a VT100 or higher, or VT52, or Heath-19 terminal or emulator (such as MS-DOS Kermit, OS/2 C-Kermit, or Mac Kermit).

  2. The default terminal emulation is vt100 (DEC VT100 or higher, which applies to the VT100, VT101, VT102, VT220, and VT320). Watts also supports 3270 emulation for Heath-19 or Zenith-19 terminals or emulators (which are, in turn, upwards compatible with the DEC VT52 terminal). If you wish to use Heath/Zenith-19 emulation rather than VT100 emulation, give the following command at the Watts prompt:
       term term h19
  3. Type the "tn3270" command with the name of the host, such as "cuvmb" or "cuvmc" ("simb" and "simc" are aliases for CUVMB and CUVMC, for compatibility with Rolm data group names, but, unlike the corresponding Rolm names, "simb" and "simc" on Watts connect you directly to the IBM mainframe hosts, rather than the SIMB and SIMC devices, which are IBM 7171 3270-emulation front ends). Examples (the two are equivalent):
       tn3270 simb
       tn3270 cuvmb

The 3270 keyboard mappings should be the same as when you "call simb" or "call simc" from the Rolm modem pool or a Rolmphone. The mappings are listed in Appendix I at the end of this document.

To check your Watts/Watts2/etc terminal settings -- which only matter if you are making tn3270 connections -- use the "show terminal", "show tty", and "show keymap" commands.

For file transfer during 3270 emulation, use Kermit with small packet sizes. Large packet sizes don't work due to a bug in Cisco's 3270 emulator; the bug has been reported to Cisco and will be fixed in a future release (10.3.2) of the terminal server software. Until the bug is fixed, you must use a packet size of 72 or less for downloading, 107 or less for uploading. To set the packet length, give the following command to Kermit-CMS prior to uploading:

and give the following command to your local Kermit program prior to downloading:
(If that doesn't work, use an even lower number, like 40; the number seems to vary with the time of day, how busy the terminal server is, etc.)

Also, for tn3270 connections, tell your local Kermit program to:

If you have a frequent need to transfer files with the IBM mainframe, then it is probably better for you to access the mainframe via ColumbiaNet instead of through the Watts 3270 emulator, until such time as the Cisco bugs are fixed. In other words, at the Watts prompt, type "cnet" instead of "tn3270 simb". Then, in the ColumbiaNet menu, select "AcIS", and then "Connect to..." and then "CUVMB".

Known Bugs, Problems, Limitations, Restrictions

  1. When you type +++ to escape back to your local modem, the +++ is also transmitted to the remote host, which in turn echoes it back to the remote modem, but this does not break the connection.

  2. When you log out from a remote host or service that you have accessed via the USR pool, it will take about 15 seconds for the connection to hang up.

  3. If you dial the USR pool from a Telebit T3000 modem using an interface speed of 19200 or 38400 (instead of the recommended 57600), downloads might be slower than you expect.

  4. As noted earlier, uploads can suffer from lack of flow control from the terminal server to the pool modems. Be sure to use an error-correcting protocol like Kermit. At high speeds, using large packets and/or sliding windows, there will be occasional retransmissions.

  5. There is, as yet, no way to dial out from the new modem pool. For now, please continue to use the old Rolm dialout pool.

  6. Kermit file transfers through tn3270 connections only works with short packets, and require SET PARITY SPACE (hopefully this will be fixed soon).

  7. Heath-19 emulation on a tn3270 connection does not change the cursor size when you toggle insert/replace mode, like it does on the 7171s. This is because the tn3270 program on Watts does not include that feature.

  8. Pausing or interruption of host processes via control characters like Ctrl-S or Ctrl-C might take a long time. This is because of the disparity in transmission speeds between the modem side of the connection (57600 bps or less) and the network side (10,000,000 bps) -- by the time your pause or interrupt character arrives at the host process, it is already very far ahead of where it appeared to be, possibly with massive amounts of data already sent out and queued for display on your screen. To alleviate problems caused by delays in Ctrl-S "pause" commands:
    1. use "more" rather than "cat" to display files on the CUNIX systems.

    2. use the screen rollback features of your Kermit software to view text that has already scrolled off the screen.

  9. The modem pool is spread over several different terminal servers. Calls are assigned to terminal servers and ports on a rotary basis; thus you can not predict whether the terminal server prompt will be "watts>", "watts2>", or "watts3>"; the terminal server does not provide a method of customizing the prompt. When writing scripts to dial the new modem pool, you should allow for the different prompts. For example, a Kermit script might use a two-step method:
        INPUT 10 \13\10watts             ; Look for "Watts" on the left margin.
        IF FAIL STOP 1 No watts prompt
        INPUT 1 >                        ; Look for ">".
        IF FAIL STOP 1 No watts prompt
    This will match either "watts>", "watts2>", "watts3>, etc. See
    Using MS-DOS Kermit or Using C-Kermit to learn about Kermit script programming.

Please report any other problems to

More Information

  1. Modem Protocols Explained
  2. AcIS Dial-Up Network Service (SLIP/PPP)
  3. Your modem manual.
  4. Using MS-DOS Kermit and Using C-Kermit (available in Barnes & Noble and Papyrus bookstores). For Macintosh Kermit, see the files /pub/ftp/kermit/f/ckmker.bwr and /pub/ftp/kermit/f/ckmker.doc on any of the CUNIX systems.
  5. For details on nonstandard PC communications port and internal modem configurations, read the Kermit News #5, July 1993, for a discussion of file transfer performance.
  6. On the Web, URL for more information about Kermit software. In particular, see the Kermit FAQ (Frequently Asked Questions).
  7. The International Telecommunications Union, for the official V series of standards (V.32bis, V.34, V.42, V.42bis, etc). It is not obvious that these are ZIP'd PostScript files, so you must transfer them, Unzip them, and then look at them with a PostScript viewer or printer. E(nglish), F(rench), or S(panish), your choice.

The following sources of information may or may not be useful. Since they are outside Columbia University, we have no control over their content (accuracy, timeliness, maturity, political correctness). Use at your own risk.

  1. A V.34 Modems FAQ, primarily Microsoft Windows oriented, with links to many modem vendors.
  2. The comp.dcom.modems newsgroup.

If You Have Questions or Problems

Call the Academic Help Desk at 854-4854 or send e-mail to consultant.

APPENDIX I: Cisco Terminal Server 3270 Key Mappings

These are effective during tn3270 connections. They are similar to EMACS commands, and should be compatible with the key mappings used by Columbia's IBM 7171 front ends and by ColumbiaNet.

First the arrow or cursor-movement keys. These have a number of synonyms: EMACS-like control characters, plus the escape sequences sent by DEC or Heath terminal arrow keypads in various modes. In the following table, "VT100" means VT100 or higher (VT102, VT220, VT320, etc); "App" means Application Mode, "Cursor" means Cursor Mode, and "VT52/Heath" denotes DEC VT52 or Heath/Zenith-19 terminals. In other words, to produce the effect noted on the left, type any of the characters or sequences shown on the right, and if you have a DEC VT or Heath-19 or Zenith-19 terminal or emulator, you can also use the arrow keys (as noted below, the "Kermit Notation" is for use with Kermit's SET KEY command, and applies to the Control Character column -- MS-DOS Kermit also has "keyboard verbs" for the arrow keys: \Klfarr, \Krtarr, \Kuparr, and \Kdnarr, which take on the correct values automatically for each type of terminal in each mode):

               Control      Kermit     Arrow-Key Escape Sequences.........
               Character    Notation   VT100 App  VT100 Cursor  VT52/Heath 

Cursor Left     Ctrl-B        \2       ESC O D      ESC [ D      ESC D 
                Ctrl-H        \8 
                Backspace     \8 
                Delete        \127
                Rubout        \127 
Cursor Right    Ctrl-F        \6       ESC O C      ESC [ C      ESC C
Cursor Up       Ctrl-P        \16      ESC O A      ESC [ A      ESC A
Cursor Down     Ctrl-N        \14      ESC O B      ESC [ B      ESC B 

The remaining 3270 keyboard functions are entered using regular ASCII characters or sequences that are independent of your terminal type. You can type them as shown, or, if you have a PC, you can use MS-DOS Kermit's SET KEY command to map them to the desired function or other keys. For example, to assign the "Cursor Home" function to the PC's grey-keypad Home key, use "set key \4423 \22" (\4423 is the scan code of the Home key, \22 is the ASCII value of Ctrl-V).

Function                   Characters                Kermit Notation

Cursor Home                 Ctrl-V                    \22
Horizontal Tab              Ctrl-I (Tab)              \9
Back Tab                    ESC Ctrl-I                \27\9
Clear Screen                Ctrl-L                    \12
Erase current line          Ctrl-U or ESC Ctrl-K      \21 or \27\11
Erase to end of line        Ctrl-K                    \11
Erase All                   ESC Ctrl-U                \27\21
Toggle Insert/Replace Mode  Ctrl-X                    \24
Delete Character Forward    Ctrl-D                    \4
Enter                       Ctrl-M, Return, Enter     \13
Reset                       Ctrl-R                    \18
Redisplay Screen            Ctrl-T                    \20
Sync                        Ctrl-G                    \7
Newline                     Ctrl-A or Ctrl-J          \1 or \10

PA Key 1                    Ctrl-C                    \3
PA Key 2                    Ctrl-W                    \23
PA Key 3                    Ctrl-O                    \15

PF Key 1                    ESC 1                     \{27}1
PF Key 2                    ESC 2                     \{27}2
PF Key 3                    ESC 3                     \{27}3
PF Key 4                    ESC 4                     \{27}4
PF Key 5                    ESC 5                     \{27}5
PF Key 6                    ESC 6                     \{27}6
PF Key 7                    ESC 7                     \{27}7
PF Key 8                    ESC 8                     \{27}8
PF Key 9                    ESC 9                     \{27}9
PF Key 10                   ESC 0                     \{27}0
PF Key 11                   ESC - or ESC q            \27\45 or \27q
PF Key 12                   ESC = or ESC w            \27=   or \27w
PF Key 13                   ESC ! or ESC e            \27!   or \27e
PF Key 14                   ESC @ or ESC r            \27@   or \27r
PF Key 15                   ESC # or ESC t            \27#   or \27t
PF Key 16                   ESC $ or ESC y            \27$   or \27y
PF Key 17                   ESC % or ESC u            \27%   or \27u
PF Key 18                   ESC ^ or ESC i            \27^   or \27i
PF Key 19                   ESC & or ESC o            \27&   or \27o
PF Key 20                   ESC * or ESC p            \27*   or \27p
PF Key 21                   ESC ( or ESC a            \27(   or \27a
PF Key 22                   ESC ) or ESC s            \27)   or \27s
PF Key 23                   ESC _ or ESC d            \27_   or \27d
PF Key 24                   ESC + or ESC f            \27+   or \27f

APPENDIX II: Chronology

May  1, 1993: 10 Telebit T3000 V.32bis modems installed for evaluation.
May  5, 1993: 8 US Robotics Courier V.32bis modems added, 18 modems total.
Sep 11, 1993: Telebit modems retired, USR pool increased to 26 total.
Oct  4, 1993: USR pool increased to 61 and 854-1896 connected to USR pool.
Dec 15, 1993: USR pool increased to 82.
Jan 21, 1994: USR pool reorganized, size remains at 82.
Feb 11, 1994: USR pool expanded to 90.
Nov 11, 1994: USR pool expanded to 122.
Apr 17, 1995: 32 USR V.34 modems added at 853-9903 for a total of 154 modems.

Columbia University Academic Information Systems
Telephone: Help line +1 212 854-4854