# SIGTRAN overview: SS7 signalling over IP

> SIGTRAN is the IETF family of protocols (framework RFC 2719) for transporting SS7 signalling over IP. It uses SCTP as a reliable transport and adaptation layers — M3UA, SUA, M2PA — that present the same service MTP3 or SCCP provided, so the SS7 application layer (TCAP, MAP, ISUP) runs unchanged over a packet network.

- Canonical URL: https://www.broadnet.me/reference/sigtran-overview
- Language: en
- Last updated: 2026-07-18
- Publisher: BroadNet (https://www.broadnet.me)

What SIGTRAN is: the IETF framework (RFC 2719) for carrying SS7 signalling over IP, using SCTP transport and adaptation layers (M3UA, SUA, M2PA) that preserve the MTP3/SCCP/TCAP/MAP application stack.

## What SIGTRAN is

SIGTRAN (Signalling Transport) is the set of protocols the IETF standardised, starting with the RFC 2719 framework, to carry telephony signalling over IP. Its purpose is narrow and important: move existing SS7 (and ISDN) signalling across IP networks without changing the signalling applications. An operator keeps MAP, ISUP, TCAP and SCCP exactly as they are, and replaces only the lower transport — the TDM MTP1/MTP2 links — with SCTP over IP plus an adaptation layer.

## Why signalling moved to IP

TDM signalling links are fixed 64 kbit/s channels: expensive, capacity-limited and tied to circuit infrastructure. Carrying signalling over IP lets operators converge onto commodity packet networks, scale well beyond a single timeslot, and interwork with IP-native cores and application servers. SCTP was designed specifically to give this transport the properties SS7 depends on — reliable in-sequence delivery and fast failover — that plain TCP or UDP could not provide adequately.

## The SIGTRAN stack

SIGTRAN is layered. At the bottom is IP. Above it, SCTP (RFC 4960) provides a reliable, message-oriented, multi-homed association between two endpoints. On top of SCTP sits an adaptation layer chosen to match the classic layer being replaced: M3UA presents MTP3 service, SUA presents SCCP service, and M2PA presents an MTP2-like link so full MTP3 can run over IP. The SS7 user parts — TCAP/MAP, ISUP — ride on top exactly as before.

*The SIGTRAN protocol stack*

| Layer | Protocol | Role |
|---|---|---|
| Application | MAP / ISUP / CAP / TCAP | SS7 services — unchanged |
| Adaptation | M3UA / SUA / M2PA / M2UA | Presents MTP3 or SCCP (or MTP2) service |
| Transport | SCTP (RFC 4960) | Reliable, multi-homed, message-oriented association |
| Network | IP | Packet transport |

## Choosing an adaptation layer

Which adaptation layer an operator uses depends on where they cut over from TDM to IP. M3UA is the most common: it replaces MTP3 and connects IP application servers to a signalling gateway, carrying SCCP and ISUP users. SUA replaces SCCP itself and carries TCAP/MAP users directly, skipping MTP3. M2PA replaces MTP2 and is used to build IP-based STP links where the endpoints still run full MTP3. The right choice preserves the interfaces the surrounding nodes already expect.

*SIGTRAN adaptation layers at a glance*

| Layer | RFC | Replaces | Carries |
|---|---|---|---|
| M3UA | RFC 4666 | MTP3 | SCCP / ISUP users over IP |
| SUA | RFC 3868 | SCCP | TCAP / MAP users directly |
| M2PA | RFC 4165 | MTP2 | Full MTP3 over IP (STP links) |
| M2UA | RFC 3331 | MTP2 (backhaul) | MTP2 from gateway to controller |

## Frequently asked questions

### What does SIGTRAN stand for?

SIGTRAN is short for Signalling Transport — the IETF working group and protocol family for carrying SS7 and ISDN signalling reliably over IP networks, defined by the RFC 2719 framework and the SCTP, M3UA, SUA and related RFCs.

### Is SIGTRAN the same as SS7?

SIGTRAN carries SS7. The SS7 application layer — MAP, TCAP, SCCP, ISUP — is unchanged; SIGTRAN replaces only the TDM transport beneath it with SCTP over IP plus an adaptation layer. So SIGTRAN traffic is SS7 signalling, just transported over IP.

### What transport protocol does SIGTRAN use?

SCTP (Stream Control Transmission Protocol, RFC 4960). SIGTRAN uses SCTP rather than TCP or UDP because SCTP provides reliable, in-sequence, message-oriented delivery plus multi-homing for path redundancy — properties SS7 signalling requires.

### What is the difference between M3UA and M2PA?

M3UA replaces MTP3 and connects application servers to a signalling gateway, so SCCP/ISUP users run over IP. M2PA replaces MTP2, presenting an IP link on which full MTP3 runs — used to build IP-based STP links rather than gateway/application-server topologies.

### Does SIGTRAN make SS7 secure?

No. SIGTRAN changes the transport, not the application, so SS7's lack of message authentication remains — FS.11 signalling firewalling is still required. SIGTRAN does add IP-layer considerations, so the SCTP associations and peers must also be secured.

## Sources

- [IETF RFC 2719 — Framework Architecture for Signalling Transport](https://datatracker.ietf.org/doc/html/rfc2719)
- [IETF RFC 4960 — Stream Control Transmission Protocol](https://datatracker.ietf.org/doc/html/rfc4960)

## Related

- [SCTP: Stream Control Transmission Protocol](https://www.broadnet.me/reference/sctp-stream-control-transmission-protocol)
- [M3UA: MTP3-User Adaptation](https://www.broadnet.me/reference/m3ua-mtp3-user-adaptation)
- [SIGTRAN deployment architecture](https://www.broadnet.me/reference/sigtran-deployment-architecture)
- [SS7 vs SIGTRAN](https://www.broadnet.me/reference/ss7-vs-sigtran)
- [SIGTRAN explained](https://www.broadnet.me/answers/sigtran-explained)