The RRZ provides various courses for beginners: e.g. introduction to the various computer operating systems, and the use of the Internet.
The Communication Protocol is Point-to-Point (PPP).
A TAE-6NFN telephone socket is required to connect to the telephone network. Telekom AG installs a TAE-6NF/N three-way socket as standard when installing new lines. The socket connects a telephone and two attachments (e.g. answerphone, modem, or Fax). When only a one-way TAE-6F is installed an adaptor may be used to convert it into a three-way socket.
There are different types of modem:
· table machines with their own power supply.
· socket cards to build into the PC.
· PCMCIA cards to build into Laptops.
· socket cards to build into modem racks.
We recommend the use of external modems i.e. table machines. The advantages of such machines
is that they give better means of adjustment through loudspeaker and LED (light-emitting diode)
readings. Hearing whether the machine is dialling or transmitting data simplifies the situation
when problems arise. They place less strain on the PC network adaptor, have better conduction, and
suffer less from interrupts.
Modems are available from all computer shops or from Telekom.
Modern modems allow a transmission rate of up to 28800 bps (bits per second) with an interface rate of up to 115200 bps, and cost between DM 100,- and DM 1,500,-. The charges for data transmission via the telephone network are the same as for telephone calls.
| Modem | Protocol |
|---|---|
| V.21 | 300 bps duplex manual dialup |
| V.22 | 1200 bps duplex |
| V.22bis | 2400 bps duplex compatible with V.22 |
| V.23 | 600/1200 bps half-duplex with help canal, Btx 1200/75 bps duplex |
| V.24 | Serial interface with 25- or 9-poligem port |
| V.25 | |
| V.25bis | automatic dialing and/or answering device using V.24 for serial automatic dialup. |
| V.32 | 9600 bps duplex dialup 4800 or 2400 bps |
| V.32bis | 14400 bps duplex |
| PEP | 19200 bps duplex Telebit multi-carrier protocol |
| V.34 | 28800 bps duplex dialup 28800 bps and less |
| V.fast | 28000 bps duplex forerunner of V.34 (Industry standard only) |
| V.FC |
Some standards specify the form of error management, data transfer, and data security through protocol.
| Modem | Protocol |
|---|---|
| MNP4 | Error correction technique |
| MNP5 | Data compression |
| V.42 | Error correction technique (LAPM) (includes MNP4) |
| V.42bis | Data compression (includes MNP5) |
| V.100 | V.100 Adaptive transfer adjustment |
| V.110 | Connection of V.24 terminals via ISDN |
Including baud rate adjustment:
| Modem | Protocol |
|---|---|
| PEP | Data protection and compression |
| V.terbo | AT&T transmission method (19200 bps) |
| HDLC | Data Security Protocol (level 2) |
| PPP | Point to Point Protocol (see 3.1) |
| X.75 | Level 2/3 Protocol, similar to HDLC, for data protection (ISDN) |
| T.70 | Level-4-Protokoll (above X.75), used with VTX T.70NL and file transfer (ISDN and EuroISDN). |
The most important commands are:
| Command | Meaning |
|---|---|
| AT | Attention |
| A/ | Repeat the last command line. |
| Dn | Instructs the modem to go on-line in originate mode. If followed by a telephone number your modem dials the number and waits for an answer tone from the remote modem. |
| ',': | Pause delimiter. S8 (S register) dial pause time: (range 1-10, default 2). |
| 'W': | Wait for dial tone. |
| 's=n': | Dial a stored phone number. When S proceeds the D command (i.e. ATDS=1) |
| '@': | Wait for silence. |
| 'P': | Dial modifier for Pulse or Rotary phone types. |
| 'T': | Dial modifier for Touch Tone phone systems. |
| '!': | Dial modifier for hook flash. |
| 'R': | Reverse mode. To dial an originate only modem. |
| E0 | Echo off. |
| E1 | Echo enabled. The modem echoes back commands sent from the DTE. |
| H | Puts the modem on hook and consequently terminates the call. |
| H1 | Takes the modem off hook in command mode. |
| I | Identity (Range 0-6). |
| Q | Quiet modus |
| S | Status register |
| X0 | (blind dialling) The modem attempts to dial regardless of the presence or absence of a dial tone after the period specified by register S6. After dialling, the modem: (1) returns a CONNECT message having established a connection; or (2) returns the NO CARRIER message if the connection could not be made. |
| X1 | Same facility as X0, but additionally, the CONNECT message is enhanced with the connection speed. |
| X2 | Behaves as for X1 but only dials when a tone is detected. If dial tone is not detected within five seconds the NO DIALTONE message is returned. Engaged signals are not recognised. |
| X3 | Behaves as for X1 but detects engaged or number unobtainable signals and returns the BUSY message. |
| X4 | Enables all messages and provides both dial tone and engaged signal detection. |
| Z | Reset modem to User profile. |
Important "extended command set" commands:
| Command | Meaning |
|---|---|
| &Fn | Restore factory defaults (n=0,1) |
| &Vn | Displays the modem's current configuration, user profiles 0 and 1, and the first four stored telephone numbers. |
| or | or; |
| I4 | Returns the modem's identification followed by its version number. |
| &Wn | Writes the current S register and AT command settings to the non-volatile memory of the modem as User profile defaults (n=0,1). |
Example:
atz (software reset to User profile 0)
ats7=90s=0 (S-Register 7: wait 90 seconds after dialling for a remote carrier signal, S-Register
0: disable the automatic answer facility).
at&w (write the current configuration to User profile 0)
| Modem | Baud Rate |
|---|---|
| V.22bis | 9600 bps |
| V.32 | 38400/57600 bps |
| V.34 | 57600/115200 bps |
High Speed Modems:
| Modem | Facility |
|---|---|
| V.32bis/V.42/MNP4 | Error Correction |
| V.42bis/MNP5 | Data Compression |
Computer Settings:
| Modem | Baud Rate |
|---|---|
| High Speed: | 28800 |
| Otherwise, as appropriate: | 19200, 9600, or 2400 |
|
8 Data bits 1 Stop bit no parity |
| | | |
8 N 1 |
|
When the modem has a baud rate capacity of 14400 or more:
Set both the baud rate on the modem (usually AT&B1) and the Hardware Flow Control.
Save these settings either in the Terminal Programme or in the modem (AT&W).
With most current modems a specific Initstring is not required.
One can use at&f or atz as standardised settings. With high screen modems one
may try the following Initstring:
atq0v1e0l1m1%c1\c0\j0\n6s7=120
With Creatix SG144 modem they advise S48=0.
The settings S48=7 or S48=128 are also possible.
For a USRobotics V.34 modem they advise
Initialisation: ats54=32
For Motorola: at&r0%r2*th1*ft1*td15\v4
Further information about other types of modem is found under Modem FAQ's (Frequently Asked Questions).
Flow Control RTS/CTS
Set the speed as specified on the modem;
with modems with data compression (V.42bis, MNP5), when possible set them
to the highest possible value.
| Modem | Baud Rate |
|---|---|
| V.22bis | 9600 bps |
| V.32bis | 38400/57600 bps |
| V.34 | 57600/115200 bps |
| RRZ Gateway IP Address: | 134.100.41.253 |
| Netmask Number: | 255.255.255.0 |
| Domain Number: | public.uni-hamburg.de |
| Mameserver Address: | 134.100.33.240 |
| Backup Nameserver: | 134.100.9.61 |
The Link Speed should, when possible, be set to variable with automatic Fallback. This is
normally preset on all modems. When connection is not achieved one should initially try setting
"no data compression" (MNP, V.42bis disabled) and then set the Link Speed. One can then try
increasing the Carrier waiting time to 90 seconds (usually ats7=90). Sometimes a better
connection is attained when the Hamburg Area Code 040 is dialled, when dialling from within
Hamburg.
Higher charges are not accrued.
Some modems are interrupted by a meter pulse.
Some other machines achieve connection when "Result Code Options" are set.
Tips when buying a modem:
Our experience is that cheap (no name) modems generally create more problems than brand
name machines (e.g. Zyxel, USRobotics, Elsa, Multilink).
Modems costing under DM 300,- very often fail to connect or break down during connection,
or non-completion of connection.
NO DIALTONE
Wrong connection lead, faulty or damaged.
Wrong telephone socket installed, or faulty.
With a multiple socket the telephone must be connected!
With PABX: dialling tone is not recognised, set atx0
NO CARRIER
Pulse or Rotary dialing rather than Touch Tone dialling!
Waiting period for carrier signal is too short (set ats7=90)
All RRZ lines are busy.
Abort of the H i g h s p e e d - connection.
Frequent cause: 14400/V.42bis/MNP5 setting unsuccessful.
Login not possible
Wrong parity set (data format 8N1)
Password incorrect(N.B. upper and lower case letters)
Characters are lost
Set flow control to RTS/CTS
PC interface too slow: download Drivers / TSRs, exit Windows
Reduce interface speed (19200)
Connection broken
Telephone charge counter impulse? (every 6 minutes)
Lengthy period without either input/output (Timeout)
Telephone line interference