final version of CSD slides

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Harald Welte 2023-03-15 19:54:28 +01:00
parent 7f68ce18c6
commit 4d1f688ac0
4 changed files with 26 additions and 11 deletions

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\begin{frame}{CSD Users}
\begin{itemize}
\item Early Machine-to-Machine (M2M) communication; most well-known user is data connection between
train engines and controllers in GSM-R
\item End-to-end encrypted telephones (like older/original GSMK Cryptophone)
\item At least in theory, there's also a spec for Teletex over GSM
\begin{itemize}
\item unclear if it was ever deployed
\item Teletex used 2400 bps synchronous X.21 CSPDN in Germany; see related RetroNetCall talks
\end{itemize}
\item Early Machine-to-Machine (M2M) communication; most well-known user is data connection between
train engines and controllers in GSM-R
\end{itemize}
\end{frame}
@ -202,9 +202,8 @@
}
\end{frame}
\begin{frame}{CSD Services}
CSD comes im many different flavours:
\begin{itemize}
\item both synchronous and asynchronous services
\item both transparent and non-transparent services
@ -236,14 +235,15 @@
\begin{frame}{Transparent (T) vs. Non-Transparent (NT)}
\begin{itemize}
\item Transparent
\item Transparent CSD:
\begin{itemize}
\item bit stream passed transparently end-to-end
\item air interface FEC, but no reliable (re)transmission in case of loss
\item defined latency, but possible loss
\item available for sync and async services
\item explicit relation / correspondence to ISDN V.110
\end{itemize}
\item Non-Transparent
\item Non-Transparent CSD:
\begin{itemize}
\item works only for async services
\item characters sent via RLP (Radio Link Protocol)
@ -251,6 +251,7 @@
\item RLP is a HLDC-style protocol with ABM
\item frames are re-transmitted as needed
\item indeterminate latency, but guaranteed delivery (or disconnect)
\item conceptual relation to ISDN V.120 or X.75
\end{itemize}
\end{itemize}
\end{frame}
@ -264,25 +265,30 @@
\end{frame}
\begin{frame}{CSD signaling in Layer 3 Call Control}
\parbox{.65\textwidth}{
\begin{itemize}
\item Normal Q.931-derived GSM Layer 3 Call Control with SETUP / CONNECT / etc.
\item Normal Q.931-derived GSM Layer 3 Call Control with SETUP / ALERTING / CONNECT / etc.
\item Only difference: Bearer Capabilities IE
\end{itemize}
}\hfill\parbox{.35\textwidth}{
\includegraphics[width=60mm]{mo_call_isdn.png}
}
\end{frame}
\begin{frame}{CSD on the Um (MS-BTS) interface}
\begin{itemize}
\item A variety of new convolutional coding/interleaving schemes
\item TCH/F9.6, TCH/F4.8, TCH/H4.8, TCH/H2.4, TCH/F14.4
FIXME: TABLE
\end{itemize}
\includegraphics[width=150mm]{csd_tch.png}
\end{frame}
\begin{frame}{CSD on the Abis (BTS-BSC) interface}
\begin{itemize}
\item Classic GSM uses TRAU frames over E1 timeslots/sub-slots
\item Special TRAU frame formats specifically for CSD
FIXME
\item Modern GSM implementations don't have no (channelized) E1 anymore
\item various proprietary, vendor-specific formats instead of TRAU frames :/
\end{itemize}
\end{frame}
@ -290,7 +296,6 @@
\begin{itemize}
\item Voice calls in the GSM core network are just ISDN calls (64k PCM timeslots)
\item CSD calls in the GSM core network are just ISDN data calls (64k V.110 timeslots)
FIXME: something about V.110 from the RetroNetCall
\item for more details about V.110, see the 12/2022 RetroNetCall about ISDN B-Channel protocols at
\url[https://media.ccc.de/v/retronetcall-20221207-laforge-isdn-b-channel-protocols]
\end{itemize}
@ -325,7 +330,11 @@
\begin{frame}{Interworking with POTS Telefax}
\begin{itemize}
\item
\item transparent, synchronous CSD bearer
\item FA protocol frames (64bits) transmitted over that bearer
\item IWF terminates the FA protocol; implements V-series modem (V.21, V.27ter, V.29, V.17) towards PSTN side
\item higher layer Fax protocol (T.30) transported end-to-end
\item only Group 3 Fax is supported, not older 1/2 or Group 4 (ISDN)
\end{itemize}
\end{frame}
@ -386,9 +395,15 @@
\end{itemize}
\item RFC4040 complaint RTP CLEARMODE in osmo-mgw
\item osmo-bsc handling on Abis and A interface; MGCP towards osmo-mgw
\item osmo-bts work for CSD TCH (in L1/scheduler) has started
\end{itemize}
\end{frame}
\begin{frame}{Omsocom CSD TODO}
\begin{itemize}
\item Lots :)
\end{itemize}
\end{frame}
\begin{frame}{The End}
EOF

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