final version of CSD slides
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@ -177,14 +177,14 @@
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\begin{frame}{CSD Users}
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\begin{itemize}
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\item Early Machine-to-Machine (M2M) communication; most well-known user is data connection between
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train engines and controllers in GSM-R
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\item End-to-end encrypted telephones (like older/original GSMK Cryptophone)
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\item At least in theory, there's also a spec for Teletex over GSM
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\begin{itemize}
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\item unclear if it was ever deployed
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\item Teletex used 2400 bps synchronous X.21 CSPDN in Germany; see related RetroNetCall talks
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\end{itemize}
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\item Early Machine-to-Machine (M2M) communication; most well-known user is data connection between
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train engines and controllers in GSM-R
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\end{itemize}
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\end{frame}
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@ -202,9 +202,8 @@
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}
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\end{frame}
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\begin{frame}{CSD Services}
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CSD comes im many different flavours:
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\begin{itemize}
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\item both synchronous and asynchronous services
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\item both transparent and non-transparent services
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@ -236,14 +235,15 @@
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\begin{frame}{Transparent (T) vs. Non-Transparent (NT)}
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\begin{itemize}
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\item Transparent
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\item Transparent CSD:
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\begin{itemize}
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\item bit stream passed transparently end-to-end
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\item air interface FEC, but no reliable (re)transmission in case of loss
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\item defined latency, but possible loss
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\item available for sync and async services
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\item explicit relation / correspondence to ISDN V.110
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\end{itemize}
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\item Non-Transparent
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\item Non-Transparent CSD:
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\begin{itemize}
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\item works only for async services
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\item characters sent via RLP (Radio Link Protocol)
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\item RLP is a HLDC-style protocol with ABM
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\item frames are re-transmitted as needed
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\item indeterminate latency, but guaranteed delivery (or disconnect)
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\item conceptual relation to ISDN V.120 or X.75
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\end{itemize}
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\end{itemize}
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\end{frame}
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\end{frame}
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\begin{frame}{CSD signaling in Layer 3 Call Control}
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\parbox{.65\textwidth}{
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\begin{itemize}
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\item Normal Q.931-derived GSM Layer 3 Call Control with SETUP / CONNECT / etc.
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\item Normal Q.931-derived GSM Layer 3 Call Control with SETUP / ALERTING / CONNECT / etc.
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\item Only difference: Bearer Capabilities IE
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\end{itemize}
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}\hfill\parbox{.35\textwidth}{
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\includegraphics[width=60mm]{mo_call_isdn.png}
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}
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\end{frame}
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\begin{frame}{CSD on the Um (MS-BTS) interface}
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\begin{itemize}
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\item A variety of new convolutional coding/interleaving schemes
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\item TCH/F9.6, TCH/F4.8, TCH/H4.8, TCH/H2.4, TCH/F14.4
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FIXME: TABLE
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\end{itemize}
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\includegraphics[width=150mm]{csd_tch.png}
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\end{frame}
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\begin{frame}{CSD on the Abis (BTS-BSC) interface}
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\begin{itemize}
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\item Classic GSM uses TRAU frames over E1 timeslots/sub-slots
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\item Special TRAU frame formats specifically for CSD
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FIXME
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\item Modern GSM implementations don't have no (channelized) E1 anymore
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\item various proprietary, vendor-specific formats instead of TRAU frames :/
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\end{itemize}
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\end{frame}
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\begin{itemize}
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\item Voice calls in the GSM core network are just ISDN calls (64k PCM timeslots)
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\item CSD calls in the GSM core network are just ISDN data calls (64k V.110 timeslots)
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FIXME: something about V.110 from the RetroNetCall
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\item for more details about V.110, see the 12/2022 RetroNetCall about ISDN B-Channel protocols at
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\url[https://media.ccc.de/v/retronetcall-20221207-laforge-isdn-b-channel-protocols]
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\end{itemize}
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\begin{frame}{Interworking with POTS Telefax}
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\begin{itemize}
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\item
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\item transparent, synchronous CSD bearer
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\item FA protocol frames (64bits) transmitted over that bearer
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\item IWF terminates the FA protocol; implements V-series modem (V.21, V.27ter, V.29, V.17) towards PSTN side
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\item higher layer Fax protocol (T.30) transported end-to-end
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\item only Group 3 Fax is supported, not older 1/2 or Group 4 (ISDN)
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\end{itemize}
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\end{frame}
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\end{itemize}
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\item RFC4040 complaint RTP CLEARMODE in osmo-mgw
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\item osmo-bsc handling on Abis and A interface; MGCP towards osmo-mgw
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\item osmo-bts work for CSD TCH (in L1/scheduler) has started
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\end{itemize}
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\end{frame}
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\begin{frame}{Omsocom CSD TODO}
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\begin{itemize}
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\item Lots :)
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\end{itemize}
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\end{frame}
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\begin{frame}{The End}
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EOF
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