# Global connectivity — specifications

> Technical specifications: Voice, SMS and signalling interconnect; Sponsored roaming.

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

Connectivity on our own MVNO and partner networks, for enterprises, providers and operators.

- Sponsored roaming
- Data, voice and SMS on our MVNO
- DID numbers worldwide
- Calls and SMS over SIP, SMPP, SS7, IPX/GRX


### Voice, SMS and signalling interconnect

*SIP · SMPP · SS7 · IPX/GRX*

SILTATEL exchanges calls, SMS and roaming traffic with carriers, aggregators and partner networks over standard interconnects — each partner connects over the interface it already runs.

Figure: FIG. 1 — Interconnects of the SILTATEL core. SILTATEL core interconnects: SIP to voice carriers, SMPP to SMS partners, SIGTRAN to SS7 networks, IPX/GRX to roaming partners

1. Voice: SIP (RFC 3261) with RTP media (RFC 3550); SIP-I (ITU-T Q.1912.5) where ISUP information must pass end to end.
2. SMS: SMPP v3.4 / v5.0 binds to aggregators and SMSCs; MAP MO/MT-ForwardSM on the SS7 side (3GPP TS 29.002).
3. SS7 over IP: SIGTRAN — M3UA (RFC 4666) over SCTP (RFC 9260); call control with ISUP (ITU-T Q.761–Q.764).
4. Data roaming: GTP (3GPP TS 29.274, 29.281) and Diameter S6a (3GPP TS 29.272) across IPX/GRX (GSMA IR.34); LTE roaming per GSMA IR.88.
5. Numbers: E.164 ranges, including DID numbers for inbound calls and SMS.

Standards and references:
- IETF RFC 3261 — SIP: Session Initiation Protocol (https://www.rfc-editor.org/rfc/rfc3261)
- IETF RFC 3550 — RTP (https://www.rfc-editor.org/rfc/rfc3550)
- ITU-T Q.1912.5 — Interworking SIP – BICC/ISUP (SIP-I) (https://www.itu.int/rec/T-REC-Q.1912.5)
- SMS Forum SMPP v3.4 / v5.0 — Short Message Peer-to-Peer protocol
- 3GPP TS 29.002 — Mobile Application Part (MAP) (https://www.3gpp.org/DynaReport/29002.htm)
- IETF RFC 4666 — SS7 MTP3 User Adaptation Layer (M3UA) (https://www.rfc-editor.org/rfc/rfc4666)
- IETF RFC 9260 — Stream Control Transmission Protocol (SCTP) (https://www.rfc-editor.org/rfc/rfc9260)
- ITU-T Q.761–Q.764 — ISDN User Part (ISUP) (https://www.itu.int/rec/T-REC-Q.761)
- 3GPP TS 29.272 — Diameter S6a/S6d (https://www.3gpp.org/DynaReport/29272.htm)
- 3GPP TS 29.274 · 29.281 — GTPv2-C · GTP-U (https://www.3gpp.org/DynaReport/29274.htm)
- GSMA IR.34 — Guidelines for IPX Provider networks
- GSMA IR.88 — LTE and EPC Roaming Guidelines
- GSMA IR.92 — IMS Profile for Voice and SMS (VoLTE)

### Sponsored roaming

*GSMA IR.21 · IR.73 · TD.57*

With sponsored roaming a subscription uses the roaming agreements of a sponsor network. The SIM carries the sponsor's IMSI, so visited networks treat the device as the sponsor's roamer — while service, tariffs and the customer relationship stay with SILTATEL.

Figure: FIG. 2 — Sponsored roaming: traffic, signalling and settlement. Sponsored roaming: the device attaches to a visited network as a roamer of the sponsor network, which provides wholesale service to SILTATEL

1. Network data of roaming partners is exchanged in GSMA IR.21 records; visited networks route signalling to the sponsor's HLR/HSS.
2. Steering of roaming (GSMA IR.73) lets the sponsor prefer selected networks in each country.
3. Visited networks charge the sponsor with TAP records (GSMA TD.57); the sponsor bills SILTATEL wholesale.
4. A multi-IMSI applet can switch between sponsors by region — managed over the air (see the eSIM sheets).

**Q: What is sponsored roaming?**

Access to networks abroad through another operator's (the sponsor's) roaming agreements: the device roams with the sponsor's IMSI, and the service provider buys that access wholesale.

**Q: Why not sign own roaming agreements?**

Bilateral agreements with every network take years to sign and test. A sponsor gives its whole footprint at once; own agreements can be added later where volumes justify them.

**Q: What is a DID number?**

Direct Inward Dialling: an E.164 number that routes calls or SMS straight to a customer's system — a PBX, contact centre or application — over SIP or SMPP.

**Q: How is an SMS delivered worldwide?**

Over SMPP to an aggregator or SMSC, or over SS7 MAP directly to the destination network; the route is chosen per destination for quality and cost.

Glossary:
- **HPMN / VPMN** — Home and visited public mobile networks.
- **IPX** — IP eXchange: the GSMA inter-operator IP backbone (IR.34).
- **GRX** — GPRS Roaming eXchange: the predecessor of IPX for data roaming.
- **TAP** — Transferred Account Procedure: roaming charging records.
- **SIGTRAN** — SS7 signalling carried over IP.
- **DID** — Direct Inward Dialling number.

Standards and references:
- GSMA IR.21 — Roaming Database, Structure and Updating Procedures
- GSMA IR.73 — Steering of Roaming Implementation Guidelines
- GSMA TD.57 — Transferred Account Procedure (TAP3)
- GSMA IR.34 — Guidelines for IPX Provider networks