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