knf-kongress 2022 slides
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OCTOI - Osmocom Community TDM over IP
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=====================================
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:author: Harald Welte <laforge@osmocom.org>
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:copyright: 2022 by Harald Welte (License: CC-BY-SA)
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:backend: slidy
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:max-width: 45em
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== Overview
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* WTF? Why?
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* History: Telephony / TDM networks
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* existing TDMoIP technology
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* OCTOI Protocol
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* OCTOI Software
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* Current OCTOI Network
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* WIP / Future Plans
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== Introduction
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Some people collect + operate old computers (_retrocomputing_)
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...
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But what's a 1980s or 1990s computer without it's contemporary networking technology?
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== Zyxel V.32bis Modem
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image::zyxel.jpg[width=1000,align="center"]
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== ELSA MicroLink ISDN TA
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image::ELSA_MicroLink_ISDN_2ab_front.jpg[width=800,align="center"]
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== TELES S0/16.3 passiver ISDN-Adapter
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image::teles_s0_16_3.jpg[width=1000,align="center"]
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== T-DisplayTel ISDN-BTX-Telefon
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image::displaytel.jpg[width=1000,align="center"]
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== T-View 100 ISDN-Videotelefon
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image::tview100.jpg[width=800,align="center"]
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== WTF is this all about?
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* enable people to run legacy WAN equipment
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** Modems
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** ISDN-Adapters
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** Phones, PBXs
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** Telefax
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** Frame Relay / HDLC / X.25 / routers
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* in a distributed fashion, over the internet
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* allow to run retronetworking tech from mid-1980s to about 2010 at a time where the related transport
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services are no longer available from public telephone operators / carriers
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== Migration paths for ISDN equipment
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* SIP ATA
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** provides analog phone jacks on phone side, speaks SIP to operator
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** works fine for voice telephony
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** can occasionally work for Fax
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** doesn't work well for Modems
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== Migration paths for ISDN equipment
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* Fritzbox with ISDN BRI (S0) port
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** terminates Q.921/Q.931 ISDN protocol stack internally
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** speaks SIP to operator
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** works fine for voice telephony
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** can work for Fax
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** doesn't work well for Modems
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** doesn't work at all for X.25/X.31
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== Migration paths for ISDN equipment
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* _enterprise grade_ SIP/ISDN gateways
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** available for BRI (S0) and PRI (E1)
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** typically to help companies avoid replacing their ISDN PBX
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** terminates Q.921/Q.931 ISDN protocol stack internally
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** speaks SIP to operator
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** works fine for voice telephony
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** can work for Fax
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** doesn't work well for Modems
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** doesn't work at all for X.25/X.31
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== VoIP: Why does only voice work well
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* well, it's called _voice_ over IP, not _modem_ over ip ;)
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* one problem is audio codecs
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** most VoIP uses lossy compression (think of MP3)
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** lossy codecs work for voice, but nothing else
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** can only be solved if end-to-end VoIP path can be forced to G711 or CLEARMODE
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** depending on situation (involved SIP operators, ...) this may or may not be possible
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* other problem is clocking
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** impossible to solve / work around
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== Clocking in synchronous networks vs VoIP
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* classic analog networks had analog connection end-to-end. There's constant phase / delay
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* ISDN networks used PDH and later SDH for transmission
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** tight synchronization between the clocks of all central offices
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** clocks means both the sample clock of ADCs/DACs as well as bit clock of ISDN PRI/BRI
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* In VoIP networks everyone uses their own clock source
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** typically a normal XTAL in your ATA / FritzBox with as much as 20 ppm tolerance
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* if clocks between two partners drift, there will be underruns or overruns
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** if this happens, you drop samples or insert samples
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** this creates phase discontinuity
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** modem standards were *not* designed for this
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== Modem/ISDN in the VoIP world
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* VoIP really is designed for voice only
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** codec issue can be worked around if you can control codecs end-to-end
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** clock issue requires hardware modding your ATA/FritzBox/Gateway
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* you still have no transparency
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** what about ISDN signaling subtleties like HLC/LLC in SETUP?
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** what about X.25 over ISDN D-Channel (X.31)
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What you really want a *transparent* way of transporting ISDN/PSTN over IP, not some gateway that's way too high up the protocol stack.
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// ***********************************************************************
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// History: TDM networks
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// ***********************************************************************
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== History: Analog Telephony Networks
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* analog telephony exited (in Germany) since 1877
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* analog electrical circuit from end to end
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* switching initially manually
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* automatic (electromechanical) switching introduced 1908-1966
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== History: Digitization inside the network
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* analog pairs of copper lines
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* carrier frequency systems (TF-Systeme) over coaxial wire
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* first digital PCM (pulse code modulation) links between exchanges
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* digital switching with analog switch matrix (EWS)
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* digital switching with digital switch matrix (EWSD, S12)
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* 1979: decision to migrate entire German PSTN to digital switching
|
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** estimated completion date in 2018
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** actual completion of all 6200 exchanges in 1997
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== History: TDM networks
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* at some point (1970s?), digital PCM technology was introduced between exchanges
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** initially PDH, later SDH (which can transport PDH)
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** see https://media.ccc.de/v/osmodevcall-20211112-laforge-tdm[OsmoDevCall on TDM/PDH/SDH]
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* external interfaces, particularly to subscriber, still analog until mid-1980s
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* ISDN changed that: Introduced digital subscriber lines
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** Basic Rate ISDN (BRI): 2x B, 1x D-Channel
|
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*** German: Basisanschluss (Anlagenanschluss, Mehrgeraeteanschluss)
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** Primary Rate ISDN (PRI): 30x B, 1x D-Channel
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*** German: Primaermultiplexer / S2M
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== Present: TDM networks mostly dead
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* Telcos have meanwhile mostly migrated to All-IP telephony
|
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* PDH/SDH networks mostly shut down, occasionally still in operation for legacy customers or some internal
|
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legacy services. Not actively sold anymore.
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* You cannot get a real PRI line anymore to connect your ISDN PBX or your Cisco router
|
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* Idea: Create community network of people who want to play with ISDN / TDM stuff
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* Naive approach: Use existing, off-the-shelf TDMoIP devices
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== Wanted: TDMoIP network
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[graphviz]
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----
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graph G {
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hub [shape=box, label="TDMoIP hub\ncross-connect\nin public internet"];
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subgraph cluster_1 {
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label="Hobbyist A";
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ad1 [label="Access Device\n"];
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pbx1 [label="PBX"];
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phone1a [label="Phone"];
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modem1b [label="Modem"];
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ta1c [label="ISDN TA"];
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pbx1 -- ad1 [label="E1"];
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phone1a -- pbx1 [label="POTS"];
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modem1b -- pbx1 [label="POTS"];
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ta1c -- pbx1 [label="ISDN-BRI"];
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}
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subgraph cluster_2 {
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label="Hobbyist B";
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ad2 [label="Access Device\n"];
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pbx2 [label="PBX"];
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phone2a [label="Phone"];
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modem2b [label="Modem"];
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ta2c [label="ISDN TA"];
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pbx2 -- ad2 [label="E1"];
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phone2a -- pbx2 [label="POTS"];
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modem2b -- pbx2 [label="POTS"];
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ta2c -- pbx2 [label="ISDN-BRI"];
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}
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subgraph cluster_3 {
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label="Hobbyist C";
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ad3 [label="Access Device\n"];
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pbx3 [label="PBX"];
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phone3a [label="Phone"];
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modem3b [label="Modem"];
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ta3c [label="ISDN TA"];
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pbx3 -- ad3 [label="E1"];
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phone3a -- pbx3 [label="POTS"];
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modem3b -- pbx3 [label="POTS"];
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ta3c -- pbx3 [label="ISDN-BRI"];
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}
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ad1 -- hub [label="TDMoIP\nInternet"];
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ad2 -- hub [label="TDMoIP\nInternet"];
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ad3 -- hub [label="TDMoIP\nInternet"];
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}
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----
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// ***********************************************************************
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// Existing TDMoIP technology
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// ***********************************************************************
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== Existing TDMoIP: SAToP / CESoPSN
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So we just get some of these and all is good?
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image::RAD_IPmux-1_front.jpg[width=1000,align="center"]
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== Existing TDMoIP: SAToP / CESoPSN
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Examples for _transparent_ TDMoIP technologies
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||||
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* SAToP (Structure Agnostic TDM over IP)
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||||
** RFC 4553
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||||
* CESoPSN (Circuit Emulation Service over Packet Switched Network)
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** RFC 5086
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* transport of raw E1 frames over MPLS or UDP
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* designed for use in LAN or carrier backbone networks
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* waste a lot of bandwidth, even if TDM circuits are completely idle
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** > 2Mbps plus header/packet overhead, bi-directional
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* typically no support for dynamic IP addresses
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== Existing TDMoIP: SIGTRAN IUA, EL2TPD
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||||
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||||
Examples for _non-transparent_ TDMoIP technologies
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||||
|
||||
* SIGTRAN IUA (ISDN User Adaptation)
|
||||
** RFC 3057
|
||||
** works only for ISDN BRI/PRI with Q.921 as Layer 2 on signaling channel
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||||
** uses SCTP as transport (might not pass all middleboxes in public internet)
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** no specification how the B-channels are handled, pure signaling solution
|
||||
* Ericsson L2TP / PacketAbis over IP
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||||
** proprietary, but FOSS implementation in @osmo-el2tpd@
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** makes specific assumption of use of E1 as Ericsson Abis (GSM BTS back-haul)
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||||
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// ***********************************************************************
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// OCTOI TDMoIP protocol
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||||
// ***********************************************************************
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||||
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== The case for a new TDMoIP protocol
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||||
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There's room for a new protocol based on the following goals:
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||||
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||||
* *transparent*. Should work for ISDN and other use cases (Frame Relay, Abis, SS7, ATM, ...)
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* *efficient*. Should not waste a lot of bandwidth on an otherwise idle/unused link
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* *dynamic IP*. End-user internet access normally has dynamic IP addresses
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* *nat friendly*. Should work through any number of NATs and CG-NAT without special ALG/helper
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* *IPv6 support*. Should support IPv6 just like IPv4
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* *authentication*. Should have built-in mutual authentication
|
||||
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== OCTOI Protocol: Bandwidth
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|
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* Timeslot Suppression
|
||||
** Transmitter has history of 1 TDM frame
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||||
** Before Tx, to-be-transmitted frame is compared with last frame
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** only those timeslots with value != that of last frame are transmitted
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* Batching
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** Batch 32 (up to 40) E1 frames per UDP packet
|
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*** 8000 frames/s / 32 => 250 packets/s
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Result: About 70 kbit/s internet bandwidth use (including UDP + IPv4 overhead) for an idle E1 link
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== OCTOI Protocol: dynamic IP / NAT-friendly
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||||
|
||||
* Classic client/server approach
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* Server currently requires fixed IP (no STUN/ICE/...)
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* Clients can have dynamic IPs
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* All messages (control plane + TDM user plan) in one UDP flow
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// ***********************************************************************
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// OCTOI Software
|
||||
// ***********************************************************************
|
||||
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== First supported OCTOI hardware: icE1usb
|
||||
|
||||
* osmocom icE1usb is an open source hardware/gateware/firmware/driver E1 interface
|
||||
* originally developed for talking to GSM base stations
|
||||
* contains a GPS disciplined oscillator for high-precision bit clock timing
|
||||
* further reading
|
||||
** https://osmocom.org/projects/e1-t1-adapter/wiki/IcE1usb
|
||||
** https://media.ccc.de/v/osmodevcon2019-97-software-defined-e1
|
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||||
image::icE1usb-usb_side.jpg[width=550,align="center"]
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== E1oIP: osmo-e1d + icE1usb
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||||
* osmo-e1d was the first (libusb, userspace) driver for the icE1usb hardware
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* traditionally, it sits between icE1usb hardware and applications using E1 like osmo-bsc
|
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* instead of a local application, it can now interface icE1usb to OCTOI
|
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** `octoi-server` mode
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** `octoi-client` mode
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||||
First 5 OCTOI users were connected to the hub that way
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[graphviz]
|
||||
----
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graph {
|
||||
rankdir=LR;
|
||||
subgraph cluster_L {
|
||||
label="Site L";
|
||||
PBX_L [label="PBX"];
|
||||
icE1usb_L [label="icE1usb"];
|
||||
GW_L [label="GW L"];
|
||||
PBX_L -- icE1usb_L [label="E1"];
|
||||
icE1usb_L -- GW_L [label="USB"];
|
||||
}
|
||||
subgraph cluster_R {
|
||||
label="Site R";
|
||||
PBX_R [label="PBX"];
|
||||
icE1usb_R [label="icE1usb"];
|
||||
GW_R [label="GW R"];
|
||||
PBX_R -- icE1usb_R [label="E1"];
|
||||
icE1usb_R -- GW_R [label="USB"];
|
||||
}
|
||||
Internet;
|
||||
GW_L -- Internet [label="IP"];
|
||||
GW_R -- Internet [label="IP"];
|
||||
}
|
||||
----
|
||||
|
||||
== E1oIP: osmo-e1d + dahdi-trunkdev
|
||||
|
||||
* having one icE1usb per peer/user doesn't scale at the hub
|
||||
* this triggered the development of `dahdi-trunkdev`
|
||||
** virtual E1 _span_ for DAHDI without any real hardware
|
||||
** simply provides stream of E1 frames on a character-device
|
||||
** can be used to implement any virtual TDM interface/protocol
|
||||
* osmo-e1d was extended to open dahdi-trunkdev instead of icE1usb
|
||||
|
||||
This has become the only method of connecting to the OCTOI hub in September 2022
|
||||
|
||||
[graphviz]
|
||||
----
|
||||
graph {
|
||||
rankdir=LR;
|
||||
subgraph cluster_L {
|
||||
label="Site L";
|
||||
PBX_L [label="PBX"];
|
||||
icE1usb_L [label="icE1usb"];
|
||||
GW_L [label="GW L"];
|
||||
PBX_L -- icE1usb_L [label="E1"];
|
||||
icE1usb_L -- GW_L [label="USB"];
|
||||
}
|
||||
subgraph cluster_R {
|
||||
label="Site R";
|
||||
PBX_R [label="PBX\n(Virtual DAHDI)"];
|
||||
}
|
||||
Internet;
|
||||
GW_L -- Internet [label="IP"];
|
||||
PBX_R -- Internet [label="IP"];
|
||||
}
|
||||
----
|
||||
|
||||
// ***********************************************************************
|
||||
// Current OCTOI Network
|
||||
// ***********************************************************************
|
||||
|
||||
== Current OCTOI network hub
|
||||
|
||||
[graphviz]
|
||||
----
|
||||
graph G {
|
||||
subgraph cluster_colo {
|
||||
label = "Co-Located Hub";
|
||||
divf [label="DIVF\nCentral Switch",shape="house"];
|
||||
icE1usb;
|
||||
pm3 [label="Livingston Portmaster 3"];
|
||||
as54 [label="Cisco AS5400"];
|
||||
icE1usb -- divf [label="E1 (timing master)"];
|
||||
pm3 -- divf [label="E1"];
|
||||
as54 -- divf [label="7xE1"];
|
||||
}
|
||||
divf -- laforge [label="TDMoIP"];
|
||||
divf -- manawyrm [label="TDMoIP"];
|
||||
divf -- gruetzkopf [label="TDMoIP"];
|
||||
divf -- roox [label="TDMoIP"];
|
||||
divf -- DrDeke [label="TDMoIP"];
|
||||
etc [label="other users..."];
|
||||
divf -- etc [label="TDMoIP"];
|
||||
}
|
||||
----
|
||||
|
||||
* DIVF: Debian 11 with `dahdi-trunkdev`, `osmo-e1d` and `yate`
|
||||
* 2x TE820 8-port E1 cards, attaching to
|
||||
** icE1usb (clock source)
|
||||
** Livingston PortMaster 3 RAS
|
||||
** Cisco AS5400 RAS
|
||||
|
||||
== Rack view
|
||||
|
||||
image::octoi_hub-colocated.jpg[width=900]
|
||||
|
||||
== 1U Enclosure with APU, icE1usb, OVP
|
||||
|
||||
image::octoi_hub-ice1usb.jpg[width=1100]
|
||||
|
||||
== GPS Antenna mounted on the roof
|
||||
|
||||
image::octoi_hub-gpsant.jpg[width=600]
|
||||
|
||||
this is an old antenna mount previously used for a satellite dish
|
||||
|
||||
== GPS Antenna mounted on the roof
|
||||
|
||||
image::octoi_hub-gps.jpg[width=1200]
|
||||
|
||||
|
||||
|
||||
== Current OCTOI participants
|
||||
|
||||
The hub currently has the following clients / participants:
|
||||
|
||||
* using icE1usb at hub side
|
||||
** laforge
|
||||
** manawyrm
|
||||
** gruetzkopf
|
||||
** roox
|
||||
** cquirin
|
||||
** drdeke
|
||||
** tmwawpl
|
||||
** tom/sirtux
|
||||
** tnt
|
||||
** marrold
|
||||
|
||||
== Current OCTOI services
|
||||
|
||||
* E1 / TDM as "transport" layer
|
||||
* ISDN network as "routing" layer
|
||||
** hub simulates the network / central office / switch side
|
||||
** client devices implement the "user" side, just like when attaching to ISDN/PSTN
|
||||
* Services on top of ISDN
|
||||
** Audio Telephony
|
||||
** Video Telephony (T-View 100 / H.320)
|
||||
** ISDN Data Calls
|
||||
** Analog Modem Calls
|
||||
** Telefax
|
||||
|
||||
== OCTOI ISDN / Modem calls
|
||||
|
||||
* hub currently has a https://osmocom.org/projects/retronetworking/wiki/Livingston_Portmaster_3[Livingston Portmaster 3] RAS
|
||||
** up to 30 ISDN data or analog modem calls (up to V.90)
|
||||
* services can be created in RADIUS, identified by Called Party Number
|
||||
** PPP dial-up locally terminated
|
||||
** PPP dial-up with forwarding of data via L2TP to remote LAC
|
||||
** telnet or TCP clear forwarding to remote BBSs
|
||||
* Cisco AS5400 with much higher capacity is waiting to be provisioned
|
||||
|
||||
== Challenges: Clocking
|
||||
|
||||
* TDM networks need a stable bitclock at all parts of the network
|
||||
* everyone must transmit and receive at the same rate of bits / frames
|
||||
* we use GPS disciplined oscillators (GPS-DO) to ensure same clock everywhere
|
||||
** this avoids overruns / underruns resulting in cycle slips that would create phase discontinuity for
|
||||
any modem signals carried over the network
|
||||
|
||||
== Challenges: Packet Re-ordering
|
||||
|
||||
* It seems like particularly on DOCSIS there is quite a bit of UDP packet re-ordering
|
||||
* Initially, osmo-e1d used a FIFO and dropped all out-of-order packets
|
||||
* later, we introduced a RIFO (Random In, First Out) to support re-ordering without loss
|
||||
|
||||
== Challenges: Packet Loss
|
||||
|
||||
* There is quite a bit of packet loss on the public internet
|
||||
* People probably don't generally notice much, as most services use TCP or retransmit UDP
|
||||
* Surprisingly, I couldn't find any comprehensive studies / research papers on packet loss behaviour of
|
||||
consumer internet that are less than 10 years old?
|
||||
* Right now we just accept it exists
|
||||
* Some early thoughts and experiments on FEC (Forward Error Correction)
|
||||
|
||||
== Challenges: Latency
|
||||
|
||||
* intercontinental public IP can easily reach >= 200ms RTT
|
||||
* ISDN timers in Q.921 and Q.931 are luckily working just fine over that kind of RTT
|
||||
* some suspicion that the high latency might have negative impact on Fax (T.30 timers) and modems (buffer
|
||||
sizes). I'm personally not yet convinced it is really an issue.
|
||||
|
||||
== Current Services on top of OCTOI ISDN
|
||||
|
||||
* Participants can call each other for any ISDN call/bearer type
|
||||
* Central hub provides
|
||||
** Dial-Up (Modem up to V.90 + ISDN V.120/X.75) access
|
||||
*** Tons of telnet-reachable BBSs all around the world
|
||||
*** BTX (an instance of Neu-Ulm courtesy of https://btx-museum.de/)
|
||||
**** unfortunately currently still crashes ISDN BTX Terminal T-DisplayTel
|
||||
*** Fax gateway (WIP)
|
||||
* Some other users provide
|
||||
** Video on demand for ISDN video telephony
|
||||
** Remote DOOM for ISDN video telephony
|
||||
** Chiptune audio on demand via voice calls
|
||||
|
||||
https://osmocom.org/projects/octoi/wiki/Phonebook
|
||||
|
||||
== What do I need to connect to the network?
|
||||
|
||||
* Currently, we only offer PRI (E1) service, so you need
|
||||
** an icE1usb plus some Linux USB host (Raspi, beaglebone, ...)
|
||||
** some equipment that talks E1, like an _enterprise_ PBX
|
||||
*** Auerswald COMmander2 Basic with S2M is a popular and widely available choice
|
||||
*** this PBX then offers analog and BRI ports for your phones / modems / TAs
|
||||
|
||||
== The setup used to connect KNF-Kongress
|
||||
|
||||
* 19" Version of Auerswald COMmander2 Basic PBX
|
||||
* sufficient space internally to put Beaglebone + icE1usb inside
|
||||
|
||||
image::octoi-event-pbx.jpg[width=1100]
|
||||
|
||||
|
||||
== What will I need to connect to the network?
|
||||
|
||||
* We're working on a small, low-power fully integrated device
|
||||
* Ethernet/IP connection towards Internet / OCTOI hub
|
||||
* 2x S0 (BRI) ports for your ISDN equipment, or analog phones via a/b TA
|
||||
* First prototype looks promising. Main work pending is the uC software.
|
||||
|
||||
image::osmo-xhfc2su-breakout.jpg[width=1100]
|
||||
|
||||
// ***********************************************************************
|
||||
// Future Plans
|
||||
// ***********************************************************************
|
||||
|
||||
== Future Plans
|
||||
|
||||
* ISDN BRI (S/T) access to OCTOI network
|
||||
** more end-user friendly; many people have S0 equipment and no E1/S2M PBX at home
|
||||
* Frame Relay switch / hub
|
||||
** second, additional service, completely independent of the current ISDN service
|
||||
** initial testing has confirmed HDLC / FR over OCTOI works without problems
|
||||
* X.25 network support
|
||||
** X.25 access via ISDN D-Channel (X.31)
|
||||
* exhibits at hacker and vintage computing events (like VCFB!)
|
||||
|
||||
== ISDN BRI (S/T) access to OCTOI
|
||||
|
||||
* BRI (ISDN basic rate aka "S/T" aka "S0") support in OCTOI protocol
|
||||
* BRI hardware with 2x S/T interface and GPS-DO
|
||||
** unlike icE1usb: Ethernet/IP support, not USB
|
||||
** complete _appliance_ for OCTOI client mode: no need for computer
|
||||
** Status: design of first break-out / evaluation board for ISDN BRI side complete
|
||||
** Software not even started yet. Idea is to use Nuttx on Atmel SAMV71
|
||||
|
||||
== Longer-Term Future Plans
|
||||
|
||||
* improve FOSS soft-modem situation (linmodem, spandsp)
|
||||
* investigate somewhat limited V.90 performance so far
|
||||
* support for other Q.931 dialects than DSS1 (like 1TR6 or even NI1)
|
||||
* dive into H.320 / H.221 to have software endpoint for ISDN video phones
|
||||
|
||||
|
||||
== Thanks
|
||||
|
||||
Thanks to
|
||||
|
||||
* Sylvain "tnt" Munaut for icE1usb and all his help
|
||||
* All of the early OCTOI network participants manawyrm, gruetzkopf, roox, DrDeke, tmwawpl, cquirin
|
||||
* noris.net for sponsoring the co-location of the OCTOI hub
|
||||
|
||||
== Further Reading
|
||||
|
||||
* https://osmocom.org/projects/octoi/wiki[OCTOI Project Homepage/Wiki]
|
||||
* https://osmocom.org/projects/octoi/wiki/Proposed_efficient_TDMoIP[OCTOI Protocol Description]
|
||||
* https://osmocom.org/projects/retronetworking/wiki[Retronetworking Wiki]
|
||||
* https://osmocom.org/projects/osmo-e1d/wiki/Wiki[osmo-e1d software]
|
||||
* https://osmocom.org/projects/octoi/wiki/Proposed_efficient_TDMoIP[icE1usb hardware]
|
||||
|
||||
|
||||
== Grafana / Stats
|
||||
|
||||
Let's have a look at the statistics...
|
||||
|
||||
|
||||
== Modem call
|
||||
|
||||
Let's demo a modem call
|
||||
|
||||
== EOF
|
||||
|
||||
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