Retronetworking » OCTOI - Osmocom Community TDM over IP

{{>toc}}

h1. Community TDM/ISDN/SS7 Network

This wiki page describes a _work in progress_ creating a community TDM/ISDN/SS7 network, enabling retronetworking enthusiasts around the world to interconnect their TDM equipment, such as PBXs, telephony switches, RAS servers, access multiplers, etc.

For classic analog telephones, there is the C*NET (https://www.ckts.info/).  This is basically the same idea but for one later generation of technology: Digital TDM/PDH/ISDN/SS7 networks.  And of course one can connect analog telephone/modem equipment via ISDN/SS7, if that is desired.

h2. Current Network

The network has a number of additional participants by now, but the general principle looks the same, updating the graph with every participant would make it rather complex without immediate gain:

{{graphviz_link()

graph G {

  newrank=true;

  divo [shape=house,label="Central Office\nyate + TE820"];

  subgraph cluster_1 {

    label="@laforge / Berlin";

    uei1a [label="ISDN Phone"];

    uea1a [label="Analog Phone"];

    ues1a [label="SIP Phone"];

    pbx1a [label="Auerswald COMmander\nBasic 2 PBX"];

    pm3a [label="Livingston\nPortmaster 3\nRAS Server"];

    ice1a [shape=box3d,label="icE1usb\nGPS-DO\nosmo-e1d"];

    uei1a -- pbx1a [label="ISDN\nBRI"];

    uea1a -- pbx1a [label="POTS"];

    pbx1a -- divo [label="ISDN\nPRI"];

    pm3a -- divo [label="ISDN\nPRI"];

    ice1a -- divo [label="ISDN\nPRI"];

    ues1a -- divo [label="SIP"];

  }

  subgraph cluster_2 {

    label="@manawyrm / Kiel";

    ue2a [label="ISDN Phone\n"];

    pbx2 [label="Auerswald COMmander\nBasic 2 PBX"];

    ice2 [shape=box3d,label="icE1usb\nGPS-DO\nosmo-e1d\n"];

    ue2a -- pbx2 [label="ISDN\nBRI"];

    pbx2 -- ice2 [label="ISDN\nPRI"];

  }

  subgraph cluster_3 {

    label="@roox / Franconia";

    pbx3 [label="Auerswald COMmander\nBasic 2 PBX"];

    ice3 [shape=box3d,label="icE1usb\nGPS-DO\nosmo-e1d\n"];

    ue3a -- pbx3 [label="ISDN\nBRI"];

    pbx3 -- ice3 [label="ISDN\nPRI"];

  }

  subgraph cluster_4 {

    label="@gruetzkopf";

    pbx4 [label="PBX"];

    ice4 [shape=box3d,label="icE1usb\nGPS-DO\nosmo-e1d\n"];

    ue4a -- pbx4 [label="ISDN\nBRI"];

    pbx4 -- ice4 [label="ISDN\nPRI"];

  }

  internet [shape=hexagon,label="Public Internet"];

  cnet [shape=hexagon,label="C*NET"];

  ice1a -- internet [label="OCTOI\nTDMoIP"];

  ice2 -- internet [label="OCTOI\nTDMoIP"];

  ice3 -- internet [label="OCTOI\nTDMoIP"];

  ice4 -- internet [label="OCTOI\nTDMoIP"];

  divo -- cnet [label="IAX2"];

}

}}

h2. How to contact us

h3. Mailing List

We now have a public "mailing list":https://lists.retronetworking.org/postorius/lists/octoi.lists.retronetworking.org/ for discussion among interested parties. The list has a public "archive":https://lists.retronetworking.org/hyperkitty/list/octoi@lists.retronetworking.org/

Don't be surprised by the lack of traffic on the ML, almost all communication happens on the IRC channel

h3. IRC Channel

A lot of us are hanging out on the @#retronetworking@ IRC channel on libera.chat. If you don't know much about "IRC":https://en.wikipedia.org/wiki/IRC, feel free to use the provided "webchat":https://web.libera.chat/ interface

h2. Underlying Protocol / Hardware

The underlying transport protocol is being designed around the wiki page [[e1-t1-adapter:Proposed_efficient_TDMoIP]].  The initial hardware implementation is an [[e1-t1-adapter:icE1usb]] attached to some kind of [embedded] Linux sytem like a Raspberry Pi.  The unique property about the icE1usb is that it contains a GPS-DO to ensure the same clock reference is used in all locations.

h2. Services

h3. ISDN PRI (available)

ISDN (Q.921/Q.931) permit to connect equipment like PBXs.   The hub offers the NT / central office function, while the client side implements the TE function.

A user connecting to the ISDN PRI service needs to be allocated telephone numbers in the dialling plan, see [[Phonebook]]..

On the hub side, the PRI lines and ISDN service are currently terminated in a yate instance.

{{graphviz_link()

graph G {

  hub [shape=box, label="TDMoIP hub\ncross-connect\nin public internet"];

  subgraph cluster_1 {

    label="Hobbyist A";

    ad1 [label="Access Device\n"];

    pbx1 [label="PBX"];

    phone1a [label="Phone"];

    modem1b [label="Modem"];

    ta1c [label="ISDN TA"];

    pbx1 -- ad1 [label="E1"];

    phone1a -- pbx1 [label="POTS"];

    modem1b -- pbx1 [label="POTS"];

    ta1c -- pbx1 [label="ISDN-BRI"];

  }

  subgraph cluster_2 {

    label="Hobbyist B";

    ad2 [label="Access Device\n"];

    pbx2 [label="PBX"];

    phone2a [label="Phone"];

    modem2b [label="Modem"];

    ta2c [label="ISDN TA"];

    pbx2 -- ad2 [label="E1"];

    phone2a -- pbx2 [label="POTS"];

    modem2b -- pbx2 [label="POTS"];

    ta2c -- pbx2 [label="ISDN-BRI"];

  }

  subgraph cluster_3 {

    label="Hobbyist C";

    ad3 [label="Access Device\n"];

    pbx3 [label="PBX"];

    phone3a [label="Phone"];

    modem3b [label="Modem"];

    ta3c [label="ISDN TA"];

    pbx3 -- ad3 [label="E1"];

    phone3a -- pbx3 [label="POTS"];

    modem3b -- pbx3 [label="POTS"];

    ta3c -- pbx3 [label="ISDN-BRI"];

  }

  ad1 -- hub [label="TDMoIP\nInternet"];

  ad2 -- hub [label="TDMoIP\nInternet"];

  ad3 -- hub [label="TDMoIP\nInternet"];

}

}}

h3. ISDN BRI

ISDN BRI service is expected to initially only be obtained indirectly: By connecting a ISDN PRI capable PBX to the hub, and then locally connecting to ISDN BRI ports of the PBX.

At a later point, one could consider implementing a ISDN BRI version of the TDMoIP protocol and some software implementation for ISDN BRI cards that support NT mode.  One notable topic is clocking:  The hardware would either need a GPS-DO (like [[e1-t1-adapter:icE1usb]] has for E1) or at the very least a VCTCXO that can be disciplined by software to match the timing recovered from the IP packet side.  See #5436 and #5417 

h3. TDM layer hub / cross-connect (future)

The TDM layer would allow to interconnect any E1 line (or even only some timeslots of a line) with any other E1 line.  It doesn't interpret the payload but just passes it around.

{{graphviz_link()

graph G {

  hub [shape=box, label="TDMoIP hub\ncross-connect\nin public internet"];

  subgraph cluster_1 {

    label="Hobbyist A";

    ad1 [label="Access Device\n"];

    pbx1 [label="PBX"];

    pbx1 -- ad1 [label="E1"];

  }

  subgraph cluster_2 {

    label="Hobbyist B";

    ad2 [label="Access Device\n"];

    frr [label="FrameRelay Device"];

    frr -- ad2 [label="E1"];

  }

  subgraph cluster_3 {

    label="Hobbyist C";

    ad3 [label="Access Device\n"];

    ras [label="RAS Server"];

    ras -- ad3 [label="E1"];

  }

  ad1 -- hub [label="TDMoIP\nInternet"];

  ad2 -- hub [label="TDMoIP\nInternet"];

  ad3 -- hub [label="TDMoIP\nInternet"];

}

}}

h3. Classic SS7

Classic SS7 (MTP2/MTP3 plus ISUP) permit us to connect STPs and SPCs, such as those of telephony exchanges / switches.

We currently have two such connections:

* An _international_ ISUP/SS7 connection to the EWSD of Jan Pesak in Brno/CZ (routing +4205....)

* A _national_ ISUP/SS7 connection to the EWSD of @jolly in Doerphof/DE (routing +494644....)

The TDMoIP protocol with osmo-e1d and icE1usb is identical to the more common ISDN PRI setup described above.  It's just the signaling protocols on top which are different (MTP2/MTP3/ISUP) insteadl Q.921/Q.931.

h4. SS7 Point Codes

We're using _ITU_ point codes with _international_ network indicator formatted in the 3-8-3 format.

|_.Point Code|_.System using it|_.Responsible|

|0-0-1|yate @divf.retronetworking.org@|@laforge|

|0-8-0|EWSD Doerphof/DE|@jolly|

|2-229-5|EWSD Brno/CZ|jpesak|

h3. SCCP/MAP/TCAP (future)

SCCP/MAP/TCAP on top of SS7 can be used to provide interworking between private cellular networks.

h3. Frame Relay (future)

A Frame Relay network could be implemented on top of the TDM hub.  In this case, framed E1 would be used with groups of 64k timeslots (typically all 31) building the underlying FR transport medium.

h3. POTS / analog telephony

There is no plan to directly support analog telephony.  Rather, analog ports for phones, modems, etc. can be provided by means of ISDN PBXs connecting via ISDN PRI  (and possibly later ISDN BRI)