GSM-R and its difference to GSM =============================== :author: Harald Welte :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