Master glossary
- 2G/3G/4G/5G — mobile generations; radio access differs, core logic is similar.
- A2P / P2P — application-to-person (business bulk) / person-to-person.
- ACM — ISUP Address Complete Message ("ringing").
- AIT — Artificially Inflated Traffic; fake traffic to earn per-message fees.
- ANM — ISUP Answer Message ("answered"); billing starts here.
- ATI — anyTimeInterrogation (MAP); location/status on demand.
- AuC — Authentication Centre; holds SIM keys.
- CAP / CAMEL — Customised Applications for Mobile network Enhanced Logic; prepaid control.
- CDR — Call/Charging Detail Record.
- CIC — Circuit Identification Code (one per ISUP circuit).
- DCS — Data Coding Scheme (encoding of an SMS).
- Diameter — the 4G signalling protocol (replaces SS7's role).
- DLR / deliver_sm — delivery receipt in SMPP.
- DPC / OPC — Destination / Originating Point Code (MTP3 routing label).
- E.164 / E.212 — numbering plans for MSISDN / IMSI.
- ESME — External Short Message Entity; the application sending over SMPP.
- FISU / LSSU / MSU — MTP2 signal units: fill-in / link status / message.
- FSN / BSN — Forward / Backward Sequence Number (MTP2).
- GT (Global Title) — an SS7 node's logical address; routed by STPs via GTT.
- GTT — Global Title Translation (GT → point code + SSN).
- HLR / HSS / UDM — subscriber database in 2G-3G / 4G / 5G.
- HTTP/2 — the 5G service-based signalling transport.
- IAM — ISUP Initial Address Message (starts a call).
- IMEI — device identity.
- IMSI — SIM identity (MCC + MNC + MSIN).
- IPX — private IP network between operators.
- ISUP — ISDN User Part; voice call control.
- LAI / LAC — Location Area Identity / Code.
- MAP — Mobile Application Part; mobility + SMS operations.
- MCC / MNC — Mobile Country / Network Code.
- MME / AMF — 4G / 5G control-plane core nodes.
- MNP-SRF — Mobile Number Portability Signalling Relay Function.
- MO / MT — Mobile-Originated / Mobile-Terminated.
- MSC / VLR — Mobile Switching Centre / Visitor Location Register.
- MSISDN — the dialled phone number.
- MSRN — Mobile Station Roaming Number (temporary number to route a call).
- MTP1 / MTP2 / MTP3 — Message Transfer Part layers 1–3.
- mTAN — mobile transaction authentication number (SMS banking code).
- OTP — one-time password.
- PC (Point Code) — a node's local SS7 address.
- REL / RLC — ISUP Release / Release Complete.
- SCCP — Signalling Connection Control Part (GT routing + subsystems).
- SCP — Service Control Point (prepaid/service database).
- SCTP — Stream Control Transmission Protocol (SIGTRAN transport).
- SEPP — Security Edge Protection Proxy (5G border security).
- SIGTRAN — SS7 over IP (M2PA/M2UA/M3UA/SUA over SCTP).
- SLS — Signalling Link Selection (MTP3).
- SMPP — Short Message Peer-to-Peer; the A2P submission protocol.
- SMSC / SMS-GMSC / SMS-IWMSC — SMS centre / gateway for MT / interworking for MO.
- SRI / SRI-SM — Send Routing Info (for a call / for an SMS).
- SS7 — Signalling System No. 7.
- SSN — Subsystem Number (6 HLR, 7 VLR, 8 MSC/SMSC).
- SSP / STP — Service Switching Point / Signal Transfer Point (the SS7 router).
- TCAP — Transaction Capabilities Application Part (RPC for MAP/CAP).
- TMSI — Temporary Mobile Subscriber Identity (privacy over the air).
- TPDU — Transfer Protocol Data Unit (SMS message type).
- UDH — User Data Header (concatenation, etc.).
- UDT / XUDT — SCCP Unitdata / Extended Unitdata.
- USSD — Unstructured Supplementary Service Data (e.g. *100#).
The MT-SMS journey on one page
| # | From → To | Message | Protocol |
|---|---|---|---|
| 1 | Sender phone → MSC | SMS-SUBMIT | Radio / NAS |
| 2 | MSC → SMS-IWMSC | MO-ForwardSM | SS7 MAP |
| 3 | SMS-GMSC → HLR | SendRoutingInfoForSM | SS7 MAP |
| 4 | HLR → SMS-GMSC | IMSI + MSC address | SS7 MAP |
| 5 | SMS-GMSC → serving MSC | MT-ForwardSM | SS7 MAP |
| 6 | MSC → recipient phone | Paging + SMS-DELIVER | Radio / NAS |
| 7 | Phone → MSC → SMSC | Deliver report + MAP ack | NAS / SS7 MAP |
A2P replaces step 1 with SMPP: bind_transceiver (open an authenticated session) → submit_sm / _resp (message_id = accepted, not delivered) → deliver_sm (carries the DLR). Steps 2–7 are the same.
Reading an SMPP delivery receipt (v3.4)
id:4F2A91 sub:001 dlvrd:001 submit date:2611050841 done date:2611050841 stat:DELIVRD err:000 text:Your code is…
| stat | Meaning |
|---|---|
| DELIVRD | reached the handset |
| UNDELIV | permanent failure (e.g. unknown subscriber) |
| EXPIRED | validity ran out while retrying |
| REJECTD | refused — often by policy or an SMS firewall |
| ACCEPTD · UNKNOWN · DELETED | intermediate/indeterminate |
Encoding cheat-sheet
- GSM-7: 160 / 153 (single / part) · UCS-2: 70 / 67 · 8-bit: 140 / 134 bytes.
- One non-GSM char or emoji → whole message becomes UCS-2.
Q.850 cause codes (ISUP)
16 normal · 17 busy · 18 no answer · 34 no circuit · 38 network out of order.
MAP error quick list
1 unknownSubscriber · 6 absentSubscriberSM · 11 teleserviceNotProvisioned · 13 callBarred · 34 systemFailure.