ISDN (and POTS) at CCC Camp 2023

jolly and laforge are planning to operate an experimental ISDN and analog telephony network at the CCC Camp 2023

The subscriber lines will be terminated using de-commissioned V5_Access_Multiplexers that were donated by telecom operators together with the osmo-v5 protocol stack and osmo-cc

This network will be provided for people to re-enact the good old telephony days, using anything as old as rotary dial phones, up to the 1990s ISDN experience.

So if you still have your old wired telephones or ISDN equipment in a basement, feel free to bring it along and hook it up.

How to connect to the network?

Types of interfaces

We can offer
  • analog POTS ports, expsed as classic 2-wire "ab" interface according to German standards.
  • ISDN BRI (basic rate interface) ports using Uk0 interface, using 4B3T according to German standards. The signalling is EDSS1 (Euro-ISDN). The configuration is PTMP (German: Mehrgeraeteanschluss), which was the default for most private ISDN lines in Germany.

What Equipment do I need to bring

For analog lines, you can connect any analog phone, answering machine, fax, modem, etc. Even rotary phones from Sweden and New Zealand (with their special pulse sequences) will work.

For ISDN lines, you should bring your NTBA/NT1 (to convert Uk0 to S0) and then any ISDN equipment like phones, ISDN adapters, PBXs, ...

If you only have ISDN equipment for S0-bus but no NTBA, we have a few NTBA around that we can lend you, as needed, on a firs-come-first-serve basis.

In addition, it is wise to bring sufficient length of telephony wires so you can connect to the closest "Point of Presence".

Where can I connect to the network

You would need to run some telephony wire (or CAT5, if that's all you have) to one of our "points of presence", where we will put V5_Access_Multiplexers.

We are planning to deploy those at only a few (3-4) "Datenklo" (or other applicable location) around the camp site. One of them will be in the vicinity of the PoC tent, the other locations are yet to be determined and will be published here after they are deployed. Please record yourself in the etherpad (see below) so we can optimize the locations based on demand.

20230814_133737.jpg 20230814_133732.jpg

Etherpad of people interested in getting connected


What kind of services do you offer?

Our experimental analog + ISDN network will be interconnected with the PoC/eventphone so you should be able to connect not only with other users of the analog/ISDN network, but also the PoC DECT subsribers, as well as the c3gsm GSM subscribers.

There might also be connectivity with the OCTOI network, but we are uncertain if we can achieve that.

How to contact you

You can reach us on the #retronetworking IRC channel on

The network is operated/configured from the Osmocom-Analog village located behind the POC and GSM tents.

On-site electronic contact details on how to reach us will be provided ahead of the camp.

How is this implemented?

We are using de-commissioned V5_Access_Multiplexers (V5 AN) that were donated by telecom operators together with the osmo-v5 protocol stack and osmo-cc. Those V5 AN were used until recently to provide public telephony service (analog and ISDN) to subscribers.

All-in-all the setup looks like this:

  • Access Network side
    • your POTS/ab or ISDN/Uk0 line is terminated in a subscriber line card of the V5 AN
    • the V5 AN implements the ETSI V5 protocol over an E1 primary rate interface (30 B-channels, 1 signalling slot)
    • that E1 circuit is physically terminated by an Osmocom_icE1usb USB - E1 adapter
    • the icE1usb connects via USB to a nanopi R5S embedded Linux board
    • the osmo-e1d software is used in OCTOI client role to implement a TDMoIP protocol towards a central server (same principle as in our OCTOI network)
  • Core Network side
    • the TDMoIP streams are received by an osmo-e1d in OCTOI server role and handed into DAHDI trunkdev, creating one virtual DAHDI span for each E1 line (each corresponding to one V5 AN)
    • the osmo-v5 software implements the V5 protocol stack and its various protocols and state machines
    • the osmo-cc-pstn-endpoint is used for each POTS port
    • the osmo-cc-misdn-endpoint is used for each ISDN BRI port
    • the osmo-cc-sip-endpoint is used to expose the calls via SIP to eventphone/POC

If time permits, we are considering to give an ad-hoc talk/workshop/demo at the camp, probably on one of the later days.

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Files (2)
20230814_133732.jpg View 20230814_133732.jpg 2.42 MB EKSOS N20 in Datenklo (closeup) laforge, 08/27/2023 11:22 AM
20230814_133737.jpg View 20230814_133737.jpg 2.81 MB EKSOS N20 in Datenklo laforge, 08/27/2023 11:23 AM

Updated by laforge 6 months ago · 15 revisions

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