# M2PA and SUA adaptation layers

> M2PA (RFC 4165) and SUA (RFC 3868) are SIGTRAN adaptation layers for different migration points. M2PA replaces MTP2, giving an IP link on which full MTP3 runs — used to build IP-based STP links. SUA replaces SCCP entirely, carrying SCCP-users such as TCAP/MAP directly over SCTP without MTP3 or M3UA.

- Canonical URL: https://www.broadnet.me/reference/m2pa-and-sua
- Language: en
- Last updated: 2026-07-18
- Publisher: BroadNet (https://www.broadnet.me)

Two more SIGTRAN adaptation layers: M2PA (RFC 4165) replaces MTP2 to build IP-based STP links running full MTP3, and SUA (RFC 3868) carries SCCP-users (TCAP/MAP) directly over SCTP, bypassing MTP3.

## M2PA: MTP2 over IP

M2PA (MTP2 Peer-to-Peer Adaptation, RFC 4165) presents an MTP2-equivalent link over SCTP. Because it replaces only MTP2, the endpoints still run a full MTP3 above it — they behave like ordinary SS7 signalling points with point codes, performing MTP3 routing and network management. M2PA is therefore used to build IP-based signalling links between STPs (or between an STP and a signalling point), effectively an all-IP replacement for a TDM A/B/C/D-link rather than a gateway-to-application-server topology.

## M2PA vs M2UA

M2PA and M2UA both sit at the MTP2 level but do very different jobs. M2PA is peer-to-peer: both ends run MTP3 and the link is a true SS7 signalling link over IP. M2UA is backhaul: it carries MTP2 from a signalling gateway up to a separately located Media Gateway Controller that holds the MTP3 and above, using a Nodal Interworking Function. Confusing the two is a common source of design errors.

*M2PA vs M2UA*

| Aspect | M2PA (RFC 4165) | M2UA (RFC 3331) |
|---|---|---|
| Model | Peer-to-peer | Backhaul (SG ↔ MGC) |
| MTP3 location | On both endpoints | On the remote controller only |
| Point codes | Both ends have one | Gateway relays to controller |
| Typical use | IP-based STP links | Distributed gateway/controller split |

## SUA: SCCP-user adaptation

SUA (SCCP-User Adaptation, RFC 3868) carries SCCP-users — principally TCAP and therefore MAP — directly over SCTP, replacing SCCP itself. An SUA node addresses its peers using SCCP-style addressing (global titles, SSNs) but needs neither MTP3 nor M3UA beneath it. This is efficient when the endpoints are IP-native SCCP users, such as an IP-based HLR/HSS or SMSC talking to a signalling gateway that performs global-title translation on their behalf.

## SUA and connection modes

SUA supports both SCCP service types. Connectionless service (SCCP classes 0/1) carries the vast majority of MAP/TCAP traffic — SMS routing, roaming — as self-contained messages. Connection-oriented service (SCCP classes 2/3) is available for the applications that need a signalling connection. SUA can interwork with SCCP at a gateway: an IP SUA node on one side and a TDM SCCP peer on the other exchange the same TCAP/MAP application messages transparently.

*Where each adaptation layer cuts the stack*

| Layer replaced | Adaptation | Stack above it |
|---|---|---|
| MTP2 | M2PA | Full MTP3 + SCCP + TCAP |
| MTP3 | M3UA | SCCP + TCAP |
| SCCP | SUA | TCAP / MAP directly |

## Frequently asked questions

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

M2PA replaces MTP2, so both endpoints still run full MTP3 and act as ordinary signalling points — it builds IP-based STP links. M3UA replaces MTP3, connecting application servers to a signalling gateway. M2PA cuts the stack one layer lower than M3UA.

### When would I use SUA instead of M3UA?

Use SUA when your IP endpoints are SCCP-users (TCAP/MAP) that do not need MTP3 — for example an IP-native HLR or SMSC. SUA carries the SCCP-user directly over SCTP and skips MTP3/M3UA. Use M3UA when you need to preserve MTP3 service for SCCP and ISUP.

### What is the difference between M2PA and M2UA?

M2PA is peer-to-peer: both ends run MTP3 over an IP signalling link. M2UA is backhaul: a signalling gateway carries MTP2 up to a remote Media Gateway Controller that holds MTP3. M2PA builds SS7 links; M2UA splits a gateway from its controller.

### Does SUA use global titles?

Yes. SUA preserves SCCP-style addressing — global titles and subsystem numbers — so applications address peers the same way they would over SCCP. A gateway can perform global-title translation and interwork SUA with classic SCCP transparently.

### Is M2PA a replacement for TDM SS7 links?

Effectively yes. Because M2PA presents an MTP2-equivalent link with full MTP3 above it, an M2PA link over IP can replace a TDM A/B/C/D-link between signalling points, letting operators build all-IP STP interconnects while keeping standard MTP3 routing.

## Sources

- [IETF RFC 4165 — MTP2 Peer-to-Peer Adaptation (M2PA)](https://datatracker.ietf.org/doc/html/rfc4165)
- [IETF RFC 3868 — SCCP-User Adaptation (SUA)](https://datatracker.ietf.org/doc/html/rfc3868)

## Related

- [M3UA: MTP3-User Adaptation](https://www.broadnet.me/reference/m3ua-mtp3-user-adaptation)
- [SCTP: Stream Control Transmission Protocol](https://www.broadnet.me/reference/sctp-stream-control-transmission-protocol)
- [SIGTRAN deployment architecture](https://www.broadnet.me/reference/sigtran-deployment-architecture)
- [SCCP and global title translation](https://www.broadnet.me/reference/sccp-and-global-title)
- [SIGTRAN overview](https://www.broadnet.me/reference/sigtran-overview)