Osmocom Remote SIM Software Suite https://osmocom.org/projects/osmo-remsim
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arehbein 56ef474988 bankd: Use gsmtap_inst_fd2()
- Use gsmtap_inst_fd2() because gsmtap_inst_fd() is deprecated
 - Add TODO-RELEASE file

Related: OS#6213
Change-Id: I2a7736d6fba795b2c479b2a0bc371b90f838ed61
2023-10-30 12:13:10 +01:00
asn1 server: Detect duplicate client/bankd connection; drop new ones 2022-05-03 18:09:14 +02:00
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debian debian: set compat level to 10 2023-04-25 16:48:32 +02:00
doc bankd: Don't use as default IP address for the server 2023-07-21 11:10:15 +00:00
ffasn1c add ffasn1c example for RSPRO 2018-09-24 17:46:05 +02:00
include server: Detect duplicate client/bankd connection; drop new ones 2022-05-03 18:09:14 +02:00
src bankd: Use gsmtap_inst_fd2() 2023-10-30 12:13:10 +01:00
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README.md README.md: add 'osmo-' prefix to remsim-{server,bankd,client} 2019-04-03 17:24:42 +02:00
TODO-RELEASE bankd: Use gsmtap_inst_fd2() 2023-10-30 12:13:10 +01:00
configure.ac Depend on libosmo-simtrace >= 0.8.0 2021-12-09 08:18:46 +01:00
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libosmo-rspro.pc.in Add libosmo-rspro.pc.in for pkg-config integration 2019-04-03 09:35:48 +02:00
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osmo-remsim - Osmocom remote SIM software suite

This software suite is a work in progress.


The client interfaces with GSM phones / modems via dedicated "Card Emulation" devices such as the Osmocom SIMtrace2 or sysmocom sysmoQMOD board + firmware. This hardware implements the ISO7816-3 electrical interface and protocol handling and passes any TPDU headers received from the phone/modem to osmo-remsim-client for further processing of the TPDUs associated to the given APDU transfer.

osmo-remsim-client connects via a RSPRO control connection to osmo-remsim-server at startup and registers itself. It will receive configuration data such as the osmo-remsim-bankd IP+Port and the ClientId from osmo-remsim-server.

After receiving the configuration, osmo-remsim-client will establish a RSPRO data connection to the osmo-remsim-bankd IP:Port.

As the USB interface for remote SIM in simtrace2.git uses one interface per slot, we can implement the client in blocking mode, i.e. use blocking I/O on the TCP/RSPRO side. This simplifies the code compared to a more complex async implementation.


The osmo-remsim-bankd (SIM Bank Daemon) manages one given SIM bank. The initial implementation supports a PC/SC driver to expose any PC/SC compatible card readers as SIM bank.

osmo-remsim-bankd initially connects via a RSPRO control connection to osmo-remsim-server at startup, and will in turn receive a set of initial [client,slot]:[bankd,slot] mappings. These mappings determine which slot on the client (corresponding to a modem) is mapped to which slot on the SIM bank. Mappings can be updated by osmo-remsim-server at any given point in time.

osmo-remsim-bankd implements a RSPRO server, where it listens to connections from osmo-remsim-clients.

As PC/SC only offers a blocking API, there is one thread per PC/SC slot. This thread will perform blocking I/O on the socket towards the client, and blocking API calls on PC/SC.

In terms of thread handling, we do:

  • accept() handling in [spare] worker threads ** this means blocking I/O can be used, as each worker thread only has one TCP connection ** client identifies itself with client:slot ** lookup mapping based on client:slot (using mutex for protection) ** open the reader based on the lookup result

The worker threads initially don't have any mapping to a specific reader, and that mapping is only established at a later point after the client has identified itself. The advantage is that the entire bankd can live without any non-blocking I/O.

The main thread handles the connection to osmo-remsim-server, where it can also use non-blocking I/O. However, re-connection would be required, to avoid stalling all banks/cards in the event of a connection loss to the server.

worker threads have the following states:

  • INIT (just started)
  • ACCEPTING (they're blocking in the accept() call on the server socket fd)
  • CONNECTED_WAIT_ID (TCP established, but peer not yet identified itself)
  • CONNECTED_CLIENT (TCP established, client has identified itself, no mapping)
  • CONNECTED_CLIENT_MAPPED (TCP established, client has identified itself, mapping exists)
  • CONNECTED_CLIENT_MAPPED_CARD (TCP established, client identified, mapping exists, card opened)
  • CONNECTED_SERVER (TCP established, server has identified itself)

Once the client disconnects, or any other error occurs (such as card I/O errors), the worker thread either returns to INIT state (closing client socket and reader), or it terminates. Termination would mean that the main thread would have to do non-blocking join to detect client termination and then re-spawn clients, so the "return to INIT state" approach seems to make more sense.

Open topics:

  • detecting multiple connections from a server, logging this or even avoiding that situation