add osmodevcall on GSM-R

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+GSM-R and its difference to GSM
+===============================
+:author:	Harald Welte <laforge@osmocom.org>
+:copyright:	2021 by Harald Welte (License: CC-BY-SA)
+:backend:	slidy
+:max-width:	45em
+
+== Overview
+
+What this talk is about
+
+* GSM-R history, stakeholders
+* GSM-R technical introduction
+* assumes good understanding of GSM
+* focuses on differences between GSM-R and GSM
+
+== key GSM-R types of communication
+
+* 1:1 voice calls (normal CS calls)
+* 1:n voice calls (broadcast calls)
+* n:m voice calls (group calls)
+* transmission of data for train control
+** between RBC and train engine
+
+== GSM-R key acronyms before we start
+
+UIC:: International Union of Railways
+ERTMS:: European Rail Traffic Management System
+ETCS:: European Train Control System
+RBC:: Radio Block Centre
+Controller:: A person in a RBC in charge of controlling trains
+
+more acronyms to come, of course
+
+== GSM-R stakeholders / players
+
+UIC:: International Union of Railways
+* established in 1922 with 51 members from 29 countries
+* today 208 members from 5 continents
+EC:: European Commission
+GSM-R IG:: Industry Group
+* representatives from equipment suppliers
+CEPT:: Conférence Européenne des Administrations des Postes et des Télécommunications
+
+== GSM-R history
+
+* pre-1992: UIC requests allocation of frequencies from CEPT
+* question whether to use TETRA or GSM
+** GSM wins as it is already deployed in 1991/1992
+* 1992: EIRENE project started by UIC and EC
+** specify requirements of railways for mobile networks
+** first specs released 1995
+* 1995: MORANE project started by UIC
+** validate EIRENE functional specs
+** develop detailed technical specs [with ETSI, 3GPP]
+** steering group of French, Italian and German Railways
+** 3 trial deployments with all parts of the network
+* 1997: MoU in UIC to stop investing in analog sytems
+** later amended by AoI (Agreement of Implementation)
+* 2000: conclusion of EIRENE and MORANE
+
+
+== GSM-R related groups
+
+* ERTMS/GSM-R group
+** ERIG: European Railway Implementors Group
+*** those railways signing the MoU and AoI
+** FG: Functional Group
+*** maintains FRS (Functional Requirements Spec)
+** OG: Operators Group
+*** maintains SRS (System Requirements Spec)
+
+
+== GSM-R related specs
+
+* EIRENE (European Integrated Radio Enhanced NEtwork)
+** FRS (Functional Requirements Spec)
+** SRS (System Requirements Spec)
+** both are one document, versioned. current: FRS 8.0 and SRS 16.0
+* MORANE (MObile radio for RAilway Networks in Europe)
+** many specs, divide in three classes of spec documents
+*** FFFIS (Form Fit Function Interface Specification)
+*** FIS (Functional Interface Specification)
+*** FFFS (Form Fit Functional Specification)
+* ETCS specifications
+* plus of course the ETSI / 3GPP GSM specs (R99 or R4)
+
+
+== GSM-R mobile station types
+
+* Cab Radio
+** fixed installation in the engine cab, mainly for voice communication of driver
+* EDOR (ETCS Data Only Radio)
+** fixed installation in engine, exclusively for ETCS
+* GP (General Purpose) Radio
+** handheld for staff
+* Operational / Shunting Radio
+** handheld for staff in specific use cases
+
+== GSM-R frequencies
+
+* R-GSM band
+** 876-880 MHz UL / 921-925 MHz DL
+** mandatory in EU
+* ER-GSM band
+** 873-876 MHz UL / 918-921 MHz DL
+** optional, used in Germany
+* other countries use GSM-R in normal bands
+** China: E-GSM, India: P-GSM, Australia: DCS 1800
+
+
+== GSM-R teleservices
+
+* mandatory
+** classic GSM voice calls
+** CSD (circuit switched data)
+** Supplementary Services (SS) like UUS1
+** USSD
+* optional
+** GPRS/EGPRS
+** SMS
+
+
+== ASCI - Advanced Speech Call Items
+
+VBS:: Voice Broadcast System
+* 1:n voice calls using shared radio resources
+VGCS:: Voice Group Call System
+* n:m voice calls using shared radio resources
+UUS:: User-to-User Signaling
+* ability to send information along call signaling (CC)
+eMLPP:: Enhanced Multi-Level Precedence and Pre-emption
+* different priorities of users / calls
+
+== VBS/VGCS on Um interface
+
+* uni-directional activation of TCH
+** listeners are using DL-only TCH
+** all MS in one cell assigned to same TCH/timeslot
+** each BTS with at least one participant transmits same DL data
+* talker (VGCS only) requests access via RACH in UL
+* one talker at a time gets allocated the uplink TCH
+* signaling via a new NCH (steals one SDCCH/8 like CBCH)
+** NCH notification acts like a "shared assignment"
+** group call reference + channel description
+
+== VBS/VGCS extensions in BTS
+
+* uni-directional TCH
+* talker detection
+* listener detection
+* NCH support in downlink
+* handle RSL notification procedure
+
+== VBS/VGCS extensions in BSC
+
+* definition of BS areas in BSC
+* generation of RSL NOTIFICATION
+* parsing VBS ASSIGNMENT REQ
+* generating VBS ASSIGNMENT RESULT
+* generationg VBS ASSIGNMENT STATUS
+
+== VBS/VGCS extensions in MGW, MSC
+
+* in MGW
+** AoIP circuit sharing [one RTP in, many out]
+* in MSC
+** A/BSSMAP procedures
+** BCC (Broadcast Call Control) protocol support
+** GCC (Group Call Control) protocol support
+
+
+== eMLPP
+
+* priorities A, B, 0, 1, 2, 3, 4
+** A+B not used in GSM-R
+** 0 used for railway emergency calls
+** 4 used for classic 1:1 / ptp calls
+* BSC will pre-empt (kill) lower priority calls if higher priority calls come up
+
+
+== ETCS / Euroradio
+
+* ETCS signaling between RBC and train engine
+** exchanges information on position of train, permission to enter section of track, ...
+* typically uses an EDOR installed in the engine
+** at least two GSM-R MS inside, for redundant connection
+* traditionally uses GSM CSD calls with transparent, async teleservice
+** network required to support 2.4, 4.8 and 9.6 kbps
+* EURORADIO layer inside the CSD call
+* most recently also possible via TCP over GPRS
+
+
+== ETCS extensions per network element
+
+* libosmocoding
+** CSD convoluitional coding
+* osmo-bts
+** CSD de-interleaving
+** RSL channel mode parsing
+** CSD RTP encapsulation/decapsulation
+* osmo-bsc
+** RSL channel mode encoding
+* osmo-mgw / libosmo-mgcp-client
+** CSD in SDP
+* osmo-msc
+** CSD in L3 CC / MNCC
+
+
+== Functional + Location Dependent Addressing
+
+* in classic GSM, addresses (MSISDN) identify a subscriber
+* in railway networks, you often want to address users
+** by their function (conductor, catering, driver, ...)
+*** dialling plan encodes train number + function
+** by their location (manager of _this_ train)
+* USSD is used to register/deregister as a function
+* HLR stores related functional addresses
+
+== GSM-R numbering plan
+
+The following prefixes define the GSM-R numbering plan:
+
+[cols="1,9"]
+|===
+|1|Reserved for short codes 
+|2|Train Function Number
+|3|Engine Function Number
+|4|Coach Number
+|50|Group calls
+|51|Broadcast calls
+|6|Maintenance and shunting team members
+|7|Train controllers
+|8|Mobile Subscriber Number
+|===
+
+
+
+== GSM-R SIM cards
+
+* specified in MORANE FFFIS for GSM-R SIM cards
+* normal GSM SIM card with DF_GSM and DF_TELECOM
+* additional files in DF_GSM related to
+** eMLPP
+** VGCS
+** VBS
+* additional files in [additional] DF_EIRENE, related to
+** functional numbers
+** shunting, call confirmation for emergency calls
+** GSM-R network selection
+** international code, network name
+
+
+== GSM-R RAN / CN feature requirements
+
+* RANflex / MSC pooling required for redundancy
+* ISUP + MAP for roaming between networks
+* if GPRS (optional) is supported:
+** NACC (network assisted cell change) mandatory
+** inter-PCU LLC forwarding mandatory
+* connection of controller equipment via ISDN or SIP
+** DTMF is used to end/mute calls
+
+
+== Roaming
+
+* international roaming between railway companies
+** trains crossing borders is normal in Europe
+* national roaming from GSM-R to public GSM
+** in case of coverage gaps
+** for fail-over
+
+
+== EIRENE / MORANE specs
+
+can be found and downloaded at https://uic.org/rail-system/gsm-r/
+
+== EOF
+
+End of File