# Fixed-mobile convergence — specifications

> Technical specifications: One network for desk and mobile; Mobile lines for a virtual PBX; An enterprise mobile operator for a large group; Industrial FMC…

Source: https://www.siltatel.net/fmc/specs/ · Service page: https://www.siltatel.net/fmc/

One business number on desk phone, softphone and mobile — calls follow the person, not the device.

- Virtual PBX with mobile lines (MVNO)
- One numbering plan, one external number
- Private LTE, IMS and MCPTT for industry
- eCall and NG-eCall for operators


### One network for desk and mobile

*FMC · concept*

Fixed-mobile convergence joins office telephony and mobile service into one network: one customer, one management view and one numbering plan for desk phones, softphones and mobiles.

Figure: FIG. 1 — Integrated fixed and mobile service for one customer. Fixed-mobile convergence: an IP or virtual PBX and an MVNO core share one numbering plan for a closed user group of desk phones, softphones and mobiles, with one external number and one customer portal

1. One customer: a single management view and one approach to fixed and mobile services for the whole company.
2. One numbering plan for a closed user group: desk phones, softphones and mobiles call each other by short numbers.
3. Data and SMS on the mobile lines, and one external number for the group.
4. A customer portal to manage users, numbers and services.
5. Calls follow the person, not the device.

Standards and references:
- IETF RFC 3261 — SIP: Session Initiation Protocol (https://www.rfc-editor.org/rfc/rfc3261)
- 3GPP TS 23.228 — IP Multimedia Subsystem (IMS); Stage 2 (https://www.3gpp.org/DynaReport/23228.htm)

### Mobile lines for a virtual PBX

*Project example · cloud telephony*

A provider of virtual PBX service adds mobile services through an MVNO, so every business customer of the PBX can get mobile numbers, data and SMS in the same service.

Figure: FIG. 2 — Who gains from adding mobile to a virtual PBX. Value of mobile services for a virtual PBX: for the operator lower acquisition cost, MVNO base growth, higher ARPU and market share; for partners mobility, more services and growth without extra cost; for the enterprise mobile staff, flexible working day, simple onboarding and one provider

1. Task: give the subscribers of a virtual PBX mobile service without a separate mobile contract.
2. Solution: virtual PBX and MVNO mobile lines as one integrated product — one numbering field for the closed group, data and SMS, one external number, one customer portal.
3. For the operator: lower cost of acquiring customers for an existing product, a growing MVNO base, higher ARPU of the business service and a larger share of convergent offers.
4. For partners — fixed-line operators and CRM systems: mobility added to fixed customers, a wider range of services, growth of the customer base without extra cost.
5. For the enterprise: mobile employees, a flexible working day, customers served from anywhere, simple onboarding of new staff and an extended set of services.
6. Diversification into mobile makes the operator's business more resilient.

### An enterprise mobile operator for a large group

*Project example · MVNO for FMC*

A fixed-line operator that serves a large enterprise group launches an MVNO on a host mobile network. Tens of thousands of employees move internal fixed telephony to mobile while keeping the existing numbering pool.

Figure: FIG. 3 — Enterprise MVNO for FMC: core, host networks and subscriber groups. Enterprise MVNO for FMC: the enterprise PBX numbering is kept, a full MVNO core runs services and tariffs and connects to one or more host mobile networks over standard roaming and interconnect interfaces; subscriber groups are FMC voice, data devices and MCPTT as a next stage

1. Task: turn the group's operational telephony from fixed to mobile, on the numbering pool already in use.
2. Subscriber groups: FMC voice users who had desk phones (model usage about 334 minutes and 9.7 GB per month), data devices (about 10 MB) and, as a next stage, MCPTT users.
3. Technical solution: a full core network, so services and tariffs are defined by the MVNO itself; one or more host networks connected over standard interfaces used for roaming and interconnect; own radio access can be added later with minimal changes.
4. For the host MNO: new revenue without sales, operation or customer-care costs; new subscribers through a separate brand without moving its existing base; traffic of the whole group at a fixed price for the life of the service; new services delivered together with the MVNO.
5. Economics: costs are allocated in MNO–MVNO settlements; in the model about 58% of the service cost is on the MVNO side and 42% on the host network.
6. Where regulation requires spectrum rights, the launch goes in stages: cooperation agreement, spectrum-sharing agreement with the host operator under a technical roaming scheme (no own base stations), licence, commercial launch.

### Industrial FMC with private LTE and push-to-talk

*Project example · industry*

An industrial group with open-pit mines, plants and offices needs one communication system: IP telephony, private LTE with mission-critical push-to-talk, the existing digital PBXs and professional radio — with one short numbering plan.

Figure: FIG. 4 — Convergence of telephony, private LTE, MCPTT and radio. Industrial FMC: voice and conferences across digital PBX, IP telephony, private LTE, MCPTT and professional radio with one short numbering plan, video across IP telephony, private LTE and MCPTT; a central IP telephony core in two data centres with survivable local IP PBXs at the sites

1. Two delivery models were compared: the customer owns the system, or an operator provides it as a service.
2. IP telephony: a central core with 1+1 redundancy in two data centres and local IP PBXs with dual power supplies at the sites. When the core or the links fail, or link quality (RTT, packet loss, jitter) degrades, registration and call switching move to the local PBX automatically; manual switching is also possible.
3. Encrypted media (SRTP), lawful-interception interfaces where regulation requires them, central management, reporting and monitoring; desk phones, softphones and video terminals.
4. Private LTE: EPC with IMS and MCPTT (VoWiFi as an option), 1+1 high availability at every site, QoS classes and priorities with dedicated end-to-end channels for critical services, LTE security.
5. Radio planning: site surveys, mast positions, coverage and transmission calculations, design documentation and permits for spectrum and radio equipment.
6. Convergence: voice calls and conferences between digital PBX, IP telephony, private LTE, MCPTT and PMR; video between IP telephony, private LTE and MCPTT; calls on site, between sites and offices, and with external PSTN, mobile and IP users.
7. Data: on-board units of mining machines send data to the dispatch system over private LTE, with GPS tracking of machines within the site boundaries; integration with public-address systems.
8. Scale: a pilot site with about 1,000 telephony users and up to 2,000 mobile devices, about 100 MCPTT users; the system is sized for 20,000 users across several sites.

Standards and references:
- 3GPP TS 22.179 — Mission Critical Push To Talk (MCPTT); Stage 1 (https://www.3gpp.org/DynaReport/22179.htm)
- 3GPP TS 23.379 — Functional architecture and information flows to support MCPTT (https://www.3gpp.org/DynaReport/23379.htm)
- 3GPP TS 23.228 — IP Multimedia Subsystem (IMS); Stage 2 (https://www.3gpp.org/DynaReport/23228.htm)
- IETF RFC 3711 — The Secure Real-time Transport Protocol (SRTP) (https://www.rfc-editor.org/rfc/rfc3711)
- ETSI EN 300 392-2 — TETRA; Voice plus Data (V+D); Air Interface

### eCall and Next Generation eCall

*Vehicles · emergency calls*

eCall is the in-vehicle emergency call: after a serious accident the car calls 112 by itself and sends a minimum set of data (MSD) to the emergency centre. Next Generation eCall moves it from 2G/3G circuit switching to 4G/5G and IMS.

Figure: FIG. 5 — eCall over 2G/3G and NG-eCall over 4G/5G IMS. eCall: the in-vehicle system places a 112 emergency call with a minimum set of data; on 2G/3G the MSD is sent by an in-band modem in the voice channel, on 4G/5G (NG-eCall) inside the IMS SIP INVITE; calls go to the public safety answering point or a third-party service provider, satellite (NTN) access is next

1. Since 31 March 2018 every new car and light-van type approved in the EU carries an eCall in-vehicle system (IVS). The call is triggered automatically by crash sensors or manually by the occupants.
2. MSD: time of the incident, vehicle position and direction of travel from GNSS, vehicle identification, propulsion type, number of occupants and whether the vehicle rolled over.
3. Legacy eCall: an in-band modem sends the MSD inside the voice channel of a 2G/3G emergency call, then the line switches to voice with the emergency centre (PSAP).
4. NG-eCall: the MSD travels in the SIP INVITE of an IMS emergency session and is acknowledged in the answer; voice runs as VoLTE or VoNR. As operators switch off 2G and 3G, circuit-switched eCall loses its network.
5. Third-party eCall (TPSP): the call goes first to a service centre of the carmaker or a service provider, which passes the case to the PSAP.
6. Satellite (non-terrestrial network) access extends eCall to areas without terrestrial coverage; the technology is still being defined.
7. The mobile operator carries eCall traffic with emergency priority, keeps IMS emergency sessions and the eCall flag working end to end, and supplies connectivity for the IVS SIM or eSIM.

Standards and references:
- EU Regulation (EU) 2015/758 — Type-approval requirements for the deployment of the eCall in-vehicle system based on the 112 service (https://eur-lex.europa.eu/eli/reg/2015/758/oj)
- EU Regulation (EU) 2017/79 — Technical requirements and test procedures for EC type-approval of eCall in-vehicle systems (https://eur-lex.europa.eu/eli/reg_del/2017/79/oj)
- UNECE UN Regulation No. 144 — Accident Emergency Call Systems (AECS)
- CEN EN 15722 — eCall minimum set of data
- CEN EN 16062 · EN 16072 — eCall high-level application requirements over GSM/UMTS; pan-European eCall operating requirements
- CEN CEN/TS 17184 · 17240 — eCall over IMS packet-switched networks: application protocols and end-to-end conformance testing
- 3GPP TS 23.167 — IP Multimedia Subsystem (IMS) emergency sessions (https://www.3gpp.org/DynaReport/23167.htm)
- IETF RFC 8147 — Next-Generation Pan-European eCall (https://www.rfc-editor.org/rfc/rfc8147)
- IETF RFC 8148 — Next-Generation Vehicle-Initiated Emergency Calls (https://www.rfc-editor.org/rfc/rfc8148)

### eCall and NG-eCall service for a mobile operator

*Project example · operator*

A mobile operator prepares an eCall and NG-eCall offer for carmakers, importers and emergency services. The proposal covers service monitoring, eSIM connectivity for in-vehicle units and the operator's role on the emergency-centre side.

Figure: FIG. 6 — Operator-side eCall service: eSIM, monitoring, routing. Operator eCall service: IVS with eSIM connects through the operator RAN, IMS and core to emergency centres; the operator adds eSIM lifecycle management (SM-DP+), an eCall and NG-eCall monitoring platform with KPIs and reports, and optionally PSAP-side routing

1. Operator role is agreed first: transport of eCall and NG-eCall traffic only, or also a platform that receives, reads and routes eCall events to the competent emergency centres with service-level guarantees.
2. In-vehicle units: the operator either supplies IVS/TCU to carmakers and importers or acts as the connectivity and platform provider for units from several vendors.
3. Service monitoring, deployable on the operator side in a short time: end-to-end view of every eCall and NG-eCall session — call setup, MSD transmission, routing, failures.
4. Quality KPIs over time: success rate, setup time, MSD delivery, network conditions; troubleshooting of problem calls down to signalling messages.
5. Dashboards and reports for the operator and for external parties — emergency-centre operators, carmakers and IVS vendors. The operator can resell monitoring as a value-added service.
6. eSIM lifecycle for in-vehicle units: sUICC chips for IVS/TCU, an SM-DP+ platform as a fully managed service, or software for the operator's own GSMA SAS-SM certified site; remote provisioning and multi-operator scenarios.
7. Next steps in the proposal: an architecture for eCall and NG-eCall focused on operator-side monitoring and analytics, and integration options with the IMS core, emergency-centre partners and IVS vendors.

Standards and references:
- 3GPP TS 24.229 — IP multimedia call control protocol based on SIP and SDP (https://www.3gpp.org/DynaReport/24229.htm)
- IETF RFC 7852 — Additional Data Related to an Emergency Call (https://www.rfc-editor.org/rfc/rfc7852)
- CEN CEN/TS 17313 — Interoperability and user choice in eCall aftermarket and third-party eCall services
- GSMA SGP.22 — RSP Technical Specification (consumer eSIM)
- GSMA FS.08 — SAS-SM: Security Accreditation Scheme for Subscription Management

### FMC in questions and answers

*Questions · glossary*

**Q: What is fixed-mobile convergence?**

One network for office and mobile telephony: one numbering plan, one management view and the same services on desk phones, softphones and mobiles.

**Q: Can we keep our existing numbers?**

Yes. The existing numbering pool stays; mobile lines join the same numbering plan.

**Q: What happens if the central core is unreachable?**

Local IP PBXs at the sites take over registration and call switching automatically when the core or link quality fails, and can also be switched manually.

**Q: Can radios, mobiles and desk phones talk to each other?**

Yes — through MCPTT and integration with professional radio, voice and conferences work across all systems with one short numbering plan.

**Q: Own system or a service?**

Both models are possible: the customer owns the system, or an operator provides it as a service.

**Q: Why would a host mobile operator take part?**

It gets new revenue and the traffic of a whole enterprise group without sales or operation costs, while the MVNO runs the service and the customer relationship.

**Q: What is NG-eCall?**

eCall over 4G/5G: the minimum set of data is carried in the IMS emergency call setup instead of an in-band modem in a 2G/3G voice channel.

**Q: What does a mobile operator need for eCall?**

Emergency priority and IMS emergency sessions end to end, SIM or eSIM connectivity for in-vehicle units, and monitoring of call setup and MSD delivery.

Glossary:
- **FMC** — Fixed-mobile convergence.
- **IP PBX** — Private branch exchange on IP (SIP).
- **IMS** — IP Multimedia Subsystem: the 3GPP service platform for voice and video over IP.
- **MCPTT** — Mission Critical Push To Talk over LTE/5G (3GPP).
- **PMR** — Professional mobile radio, for example TETRA.
- **VoWiFi** — Voice over Wi-Fi.
- **Closed user group** — Users who call each other by short numbers under one plan.
- **Technical roaming** — Use of a host operator's radio network by another operator's subscribers.
- **MOU** — Minutes of use per subscriber per month.
- **eCall** — In-vehicle emergency call to 112 with a minimum set of data.
- **MSD** — Minimum set of data: time, position, direction, vehicle, occupants.
- **IVS** — In-vehicle system that places the eCall.
- **PSAP** — Public safety answering point, the emergency centre.
- **TPSP** — Third-party service provider for eCall.