\section{OpenBSC}

\subsection{OpenBSC Introduction}

\begin{frame}{OpenBSC software}
OpenBSC is a Open Source implementation of (not only) the BSC features
of a GSM network.
\begin{itemize}
	\item Support A-bis interface over E1 and IP
	\item Support for BTS vendor/model is modular, currently Siemens BS-11 and ip.access nanoBTS
	\item Multiple BTS models/vendors can be mixed!
	\item Can work as a {\em pure BSC} or as a full {\em network in a box}
	\item Supports mobility management, authentication, intra-BSC hand-over, SMS, voice calls (FR/EFR/AMR)
	\item GPRS + EDGE support if combined with OsmoSGSN and OpenGGSN
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC}
\begin{itemize}
	\item Supports Siemens BS-11 BTS (E1) and ip.access nanoBTS (IP based)
	\item Has classic 2G signalling, voice and SMS support
	\item Implements various GSM protocols like
	\begin{itemize}
		\item A-bis RSL (TS 08.58) and OML (TS 12.21)
		\item TS 04.08 Radio Resource, Mobility Management, Call Control
		\item TS 04.11 Short Message Service
	\end{itemize}
	\item Telnet console with Cisco-style interface
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC software architecture}
\begin{itemize}
	\item Implemented in pure C, similarities to Linux kernel
	\begin{itemize}
		\item Linked List handling, Timer API, coding style
	\end{itemize}
	\item Single-threaded event-loop / state machine design
	\item Telnet based command line interface {\em Cisco-style}
	\item Input driver abstraction (mISDN, Abis-over-IP)
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC: GSM network protocols}{The A-bis interface}
  \begin{description}[Layer 4+]
    \item[Layer 1] Typically E1 line, TS 08.54
    \item[Layer 2] A variant of ISDN LAPD with fixed TEI's, TS 08.56
    \item[Layer 3] OML (Organization and Maintenance Layer, TS 12.21)
    \item[Layer 3] RSL (Radio Signalling Link, TS 08.58)
    \item[Layer 4+] transparent messages that are sent to the MS via Um
  \end{description}
\end{frame}

\begin{frame}{OpenBSC: How it all started}
\begin{itemize}
	\item In 2006, I bought a Siemens BS-11 microBTS on eBay
	\begin{itemize}
		\item This is GSM900 BTS with 2 TRX at 2W output power (each)
		\item A 48kg monster with attached antenna
		\item 200W power consumption, passive cooling
		\item E1 physical interface
	\end{itemize}
	\item I didn't have much time at the time (day job at Openmoko)
	\item Started to read up on GSM specs whenever I could
	\item Bought a HFC-E1 based PCI E1 controller, has mISDN kernel support
	\item Found somebody in the GSM industry who provided protocol traces
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC: Timeline}
\begin{itemize}
	\item November 2008: I started the development of OpenBSC
	\item December 2008: we did a first demo at 25C3
	\item January 2009: we had full voice call support
	\item Q1/2009: Add support for ip.access nanoBTS
	\item June 2009: I started with actual security related stuff
	\item August 2009: We had the first field test with 2BTS and > 860 phones
	\item Q1/2010: The first 25 OpenBSC instances running in a commercial network
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC: Field Test at HAR2009}
\begin{figure}[h]
\subfigure{\includegraphics[width=5cm]{bts_tree_full.jpg}}
\subfigure{\includegraphics[width=5cm]{openbsc_host.jpg}}
\end{figure}
\end{frame}


\subsection{OpenBSC Network In The Box}

\begin{frame}{OpenBSC in NITB mode}{Network In a Box Mode}
The {\tt osmo-nitb} program
\begin{itemize}
	\item implements the A-bis interface towards any number of BTS
	\item provides most typical features of a GSM network in one software
	\item no need for MSC, AuC, HLR, VLR, EIR, ...
	\begin{itemize}
		\item HLR/VLR as SQLite3 table
		\item Authentication + Ciphering support
		\item GSM voice calls, MO/MT SMS
		\item Hand-over between all BTS
		\item Multiple Location Areas within one BSC
	\end{itemize}
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC NITB features}
OpenBSC NITB features
\begin{itemize}
	\item Run a small GSM network with 1-n BTS and OpenBSC
	\item No need for MSC/HLR/AUC/...
	\item No need for your own SIM cards (unless crypto/auth rqd)
	\item Establish signalling and voice channels 
	\item Make incoming and outgoing voice calls between phones
	\item Send/receive SMS between phones
	\item Connect to ISDN PBX or public ISDN via Linux Call Router
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC in NITB mode}{Network In a Box Mode}
The {\tt osmo-nitb} program
\begin{itemize}
	\item does not implement any other GSM interfaces apart from A-bis
	\item no SS7 / TCAP / MAP based protocols
	\item no integration (roaming) with existing traditional GSM networks
	\item wired telephony interfacing with ISDN PBX {\tt lcr} (Linux Call Router)
	\item Has been tested with up to 800 subscribers on 5 BTS
	\item Intended for R\&D use or private PBX systems
\end{itemize}
\end{frame}

\begin{frame}{OpenBSC LCR integration}{Interfacing with wired telephony}
OpenBSC (NITB mode) can be linked into Linux Call Router ({\tt lcr})
\begin{itemize}
	\item OpenBSC is compiled as libbsc.a
	\item libbsc.a includes full OpenBSC NITB mod code
	\item linking the library into {\tt lcr} results in GSM {\em line interfaces} to become available inside {\tt lcr}
	\item OpenBSC no longer takes care of call control, but simply hands everything off to {\tt lcr}
	\item Dialling plan, etc. is now configure in {\tt lcr} like for any other wired phones
\end{itemize}
\end{frame}

\subsection{OpenBSC BSC-only mode}

\begin{frame}{OpenBSC in BSC-only mode}
The {\tt osmo-bsc} program
\begin{itemize}
	\item behaves like a classic GSM BSC
	\item uses SCCP-Lite (ip.access multipex) to any SoftMSC like ADC
	\item used in production/commercial deployments (~ 75 BSCs)
	\item mainly intended to replace proprietary BSC in traditional GSM networks
\end{itemize}
\end{frame}

%\begin{frame}<handout:0>{OpenBSC}
%        Demonstration
%\end{frame}

\subsection{OpenBSC GPRS support}

\begin{frame}{GPRS and OpenBSC}
\begin{itemize}
	\item The BSC doesn't really do anything related to GPRS
	\item GPRS implemented in separate SGSN and GGSN nodes
	\item GPRS uses its own Gb interface to RAN, independent of A-bis
	\item OpenBSC can configure the nanoBTS for GPRS+EDGE support via OML
	\item Actual SGSN and GGSN implemented as OsmoSGSN and OpenGGSN programs
\end{itemize}
\end{frame}

\begin{frame}{OsmoSGSN}
The Osmocom SGSN program implements
\begin{itemize}
	\item basic/minimal SGSN functionality
	\item the Gb interface (NS/BSSGP/LLC/SNDCP)
	\item mobility management, session management
\end{itemize}
It's a work in progress, many missing features
\begin{itemize}
	\item no HLR integration yet
	\item no paging coordination with MSC/BSC
	\item no encryption support yet
\end{itemize}
\end{frame}

\begin{frame}{OpenGGSN}
\begin{itemize}
	\item GPL licensed Linux program implementing GGSN node
	\item Implements GTP-U protocol between SGSN and GGSN
	\item User-configurable range/pool of IPv4 addresses for MS
	\item Uses {\tt tun} device for terminating IP tunnel from MS
	\item provides GTP implementation as libgtp
	\item Experimental patches for IPv6 support
\end{itemize}
\end{frame}

%\begin{frame}<handout:0>{OpenBSC + OpenGGSN + OsmoSGSN}
%        Demonstration
%\end{frame}

\begin{frame}{OpenBSC and OsmoSGSN based network}
\begin{figure}[h]
\includegraphics[width=10cm]{osmosgsn.png}
\end{figure}
\end{frame}

% FIXME: include slide showing full OpenBSC+OsmoSGSN+OpenGGSN network