» cFos/Professional, Making outgoing and incoming connections


Connecting Actively

Use the "ATD" command to connect actively!

Besides telephone numbers, various ISDN parameters can be adjusted to select services and transfer protocols. By default, cFos is set to transmit data with X.75 as level 2 protocol and transparent (i.e., no) level 3 protocol. Parameters can be set manually by so-called 'modem registers' (please refer to modem.txt for more details).
To make choosing among the most important data transfer protocols as simple as possible, cFos allows you to set the following by AT commands:

Data transfer with X.75 and transparent B3 protocol, though in contrast to the CAPI default, X.75 window size and frame length are set to the values used during cFos startup (options -w and -b ). The Additional Service Indicator is set to 0.
Note: This is a particularly popular, wide-spread standard.
Data transfer with V.110 and transparent B2/B3 protocol, 38400, 8, n, 1, asynchronous. The Additional Service Indicator is set to 64 (40 hex).
Attention: Protocol signaling will only function in 'homogenous' ISDN networks (i.e., from 1.TR.6 to 1.TR.6 or from DSS1 to DSS1).
Data transfer with V.110 and transparent B2/B3 protocol, 19200, 8, n, 1, asynchronous. The Additional Service Indicator is set to 199 (C7 hex).
As " ATB0 " but with Teles Channel Bundling (128 kbps). This command supports only TELES Channel Bundling, not cFos Channel Bundling which is activated by " AT&Bn ." " ATB3 " is only available if the BUNDLE module has been loaded.
ELINK Mode – data transfer with X.75 and transparent B3 protocol. In contrast to the CAPI default, X.75 window size is set to 7 and frame length to 256 Bytes, if cFos has been loaded with at least -b256 . Otherwise, " ATB4 " will return " ERROR ." The Additional Service Indicator is set to 146.
Attention: Protocol signaling will only function in 'homogenous' ISDN networks (i.e., from 1.TR.6 to 1.TR.6 or from DSS1 to DSS1).
BTX Mode – BTX is a variant of the X.75 protocol with window size 7, which means cFos should be loaded with -w7 .
Like " ATB5 ," but a sequence is transmitted immediately after connection that has transfer switch from BTX to VT-100 mode.
Maximum-speed analog modem (if supported by your ISDN card).
Internet, synchronous PPP mode according to RFC 1662. HDLC is used as B2 protocol. Maximum MRU should be set to 1500 bytes.
Please note that when using a ZyXEL 2864I modem, ATB8 is identical to ATB40 .
CompuServe via BTX.
V.110 asynchronous, 9600 bps, 8, n, 1. This can be used for connecting to mobile modems or Datex-P Gateways.
V.110 asynchronous, 9600 bps, 7, n, 1. This is sometimes used by Datex-P Gateways as well.
V.120 (often used in the USA).
X.31 (more information can be found here).
Call to configure a remote. [PRO]
X.31. Synchronous PPP over X.31 with more-data bit support.

We strongly recommend you use these AT commands for connecting. But you can also configure how a connection is established by setting different 'registers' for special applications.
Here are some examples:

Setting service detection. For CAPI 2.0 this generates signaling values for BC, LLC, and HLC. For example, " S16=7 S17=0 " denotes data transfer with X.75 or HDLC. " S16=1 S17=1 " indicates telephony.
(CAPI 2.0) Employed B protocols (cf. modem.txt ).
Parameters for B protocols.
Controller number. This allows selection of which ISDN board(s) to use for making a call.
Analog call mode: 0=Voice, 1=Modem, 2=Fax.
S103-S106, S111-S113:
Further CAPI 2.0 protocol parameters.
CAPI 2.0 signaling elements. These can be set according to ETS 300 102. However, usually generates these itself using registers S16/S17.

We urge you to take a close look at the modem.txt file, which lists more than 100 registers that allow you to fine-tune your connections and configure special features.


For CAPI 2.0, you have to configure MSNs and subaddresses (cf. subadd.htm ). This is explained in more detail under " Connecting Passively " below.

Connecting Passively

During passive connection, cFos is waiting for a call on one or several predefined MSNs or EAZs with certain service signatures (data service, telephony, etc.). You need to inform CAPI to which ISDN service signatures it should respond by setting the "CIP Mask" with registers S107/S108 (CAPI 2.0).
Service features can, for instance, be set by " ATS107=<bit pattern> ."
For example, bit 2 activates incoming calls with a "data transfer" service signature, while bits 1 and 4 activate calls for "telephone service."
Both services can also be set with " AT&I... ", where " A " stands for analog while " D " represents data transfer. Thus, entering " AT&IAD " would have cFos "listen" to both.
By default, cFos is set respond to "data transfer."

For more on MSN settings, refer to /cfos-professional/subadd.htm . As some phone switches will allow a connection only when calling with the correct MSN, you should always use " AT&A0=<msn> " to enter at least one MSN (without area code).

On incoming calls with a "telephony" service signature, cFos will select "bit-transparent" as B2 and "transparent" as B3 protocol. This lets you receive a data stream of 8000 cps with digitized analog samples. But keep in mind that only "data transfer" is activated as default service.

On incoming calls with a "data transfer" service signature, cFos is (due to CAPI design restrictions) limited to choosing from transfer protocols depending on what BC, LLC and HLC signaling elements are being transmitted (for CAPI 2.0). Thereafter, an automatic change of protocol is not possible. This is why – in contrast to conventional modems – protocols cannot be negotiated once a connection has been established. To be on the safe side, enter " ATS76=1 " so that cFos will also use the protocols set for outgoing calls to accept incoming calls that transmit no signaling elements. With AT S76=2 these protocols are used, even if there are signaling elements.

Please note there are no officially accepted signaling elements for V.110, 38400 bps, asynchronous. However, cFos comes with substitute values for CAPI 2.0 that can often be used for detection and are usually transmitted by most networks. Failing that, " ATB1 S76=1 " can be used to force this choice of protocol.

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