OsmocomBB

h1. CSD (Circuit Switched Data)

{{>toc}}

This page documents Circuit Switched Data support in the [[mobile]] application (see #4396).

h2. L1 PHY support

At the time of writing this wiki page, CSD support is implemented for the following L1 PHYs:

* [[Layer1bin]] firmware for [[Phones#TI-Calypso-based|Calypso based phones]]

* SDR PHY ([[osmotrx:|osmo-trx-ms]]) + [[TRX_Interface#The-trxcon-application|trxcon]] application

* SDR PHY ([[osmocom-bb-sdr-phy:|grgsm_trx]]) + [[TRX_Interface#The-trxcon-application|trxcon]] application

* [[FakeTRX]] (virtual Um) + [[TRX_Interface#The-trxcon-application|trxcon]] application

h2. L23 support state

* async (soft-UART) transparent V.110 calls

* [not tested] sync transparent V.110 calls

** [not tested] including fax calls

* TCH/F9.4, TCH/F4.8, TCH/F2.4 (only @ 2400 bps)

* [not tested] TCH/H4.8, TCH/H2.4 (only @ 2400 bps)

h3. TODO/limitations

* non-transparent calls (V.110 RLP, V.120)

* TCH/F14.4 (see #6346 and #6167)

* TCH/F2.4 and TCH/H2.4 @ 300 bps, 1200/75 bps (see #6347)

* ECSD (multi-TCH support)

* "CUSE (Character devices in user space)":https://lwn.net/Articles/308445/

h2. VTY configuration

Below is an example configuration snippet (only relevant params):

<pre>

ms 1

 support

  no full-data-14400

  full-data-9600

  full-data-4800

  half-data-4800

  full-data-2400

  half-data-2400

 tch-data

  io-handler unix-sock

! 'ti' is valid for Calypso PHY, change to 'osmo' for trxcon

  io-tch-format ti

  unix-socket /tmp/ms_data

  call-params type-rate 71

  call-params ce transparent

  call-params async

  call-params async nr-stop-bits 1

  call-params async nr-data-bits 8

  call-params async parity none

</pre>

(you can use @osmo-config-merge@ from [[libosmocore]] to merge this snippet into your mobile.cfg)

h3. Call parameters

You can configure data call parameters either using @call MS_NAME params@ command:

<pre>

OsmocomBB(mobile)> enable

OsmocomBB(mobile)# call 1 params ?

  data  Parameters for data calls

OsmocomBB(mobile)# call 1 params data ?

  type-rate  Type and rate (values like in AT+CBST; see 3GPP TS 27.007, section 6.7)

  ce         Connection element (does not apply to FAX calls)

  sync       Synchronous connection (always used for FAX calls)

  async      Asynchronous connection (does not apply to FAX calls)

</pre>

... or by entering the configuration node:

<pre>

OsmocomBB(mobile)> enable 

OsmocomBB(mobile)# configure terminal 

OsmocomBB(mobile)(config)# ms 1

OsmocomBB(mobile)(ms)# tch-data 

OsmocomBB(mobile)(tch-data)# list

...

  io-handler (none|unix-sock|loopback)

  no io-handler

  io-tch-format (osmo|ti)

  unix-socket PATH

  call-params type-rate (4|5|6|7|68|70|71)

  call-params ce (transparent|non-transparent) [prefer]

  call-params (sync|async)

  call-params async nr-stop-bits <1-2>

  call-params async nr-data-bits <7-8>

  call-params async parity (none|even|odd|mark|space)

</pre>

Below is the list of supported bearer type/rate combinations:

<pre>

OsmocomBB(mobile)# call 1 params data type-rate?

  type-rate  Type and rate (values like in AT+CBST; see 3GPP TS 27.007, section 6.7)

OsmocomBB(mobile)# call 1 params data type-rate ?

  4   2400 bps (V.22bis)

  5   2400 bps (V.26ter)

  6   4800 bps (V.32)

  7   9600 bps (V.32)

  68  2400 bps (V.110 or X.31 flag stuffing)

  70  4800 bps (V.110 or X.31 flag stuffing)

  71  9600 bps (V.110 or X.31 flag stuffing)

</pre>

This list may be extended in the future, e.g. after adding support for TCH/[FH]2.4 @ 300 bps, 1200/75 bps.

h2. Making calls

Making a data call is as easy as making a regular voice call:

<pre>

OsmocomBB(mobile)# call 1 MSISDN ?

  [voice]  Initiate a regular voice call (default)

  [data]   Initiate a data call (UDI or 3.1 kHz audio)

  [fax]    Initiate a data call (Facsimile group 3)

</pre>

An incoming data call is answered just like a voice call:

<pre>

OsmocomBB(mobile)# call 1 answer

</pre>

After the call is connected (i.e. answered either locally or remotely), you can connect to the UNIX socket.

An ongoing call can be terminated just like a regular voice call:

<pre>

OsmocomBB(mobile)# call 1 hangup

</pre>

An incoming call can also be rejected using this command.

h3. Example: sending text using @socat@

<pre><code class="shell">

socat UNIX-CONNECT:/tmp/ms_data STDIO,echo=0,icanon=0

</code></pre>

h3. Example: sending files using @socat@ and @[xyz]modem@

On the receiving side:

<pre><code class="shell">

socat UNIX-CONNECT:/tmp/ms_data EXEC:"lrzsz-rz -v"

</code></pre>

On the sending side:

<pre><code class="shell">

socat UNIX-CONNECT:/tmp/ms_data EXEC:"lrzsz-sz -v /usr/share/licenses/spdx/GPL-2.0-or-later.txt"

</code></pre>