1. Mobius SS7 Overview

Signaling System No. 7 (SS7) is a globally standardized protocol suite used by telecommunications networks to exchange control and service information between network nodes. SS7 was designed as common-channel signaling (CCS): signaling for many calls and services is multiplexed over dedicated signaling links rather than being carried in the same channel as the user’s voice or data.
SS7 is the network’s control plane for legacy circuit networks and many mobile “service-plane” functions: it carries messages that set up and clear calls, route signaling, manage congestion/failover, and perform database-style service queries.

SS7 supports several broad categories of functions:

• Call control (circuit-switched telephony): establishing, supervising, and releasing calls between exchanges (typically via ISUP).
• Signaling transport and routing: reliable delivery, routing, and network management within the signaling network (via MTP in TDM networks, or SIGTRAN adaptations in IP networks).
• Database-style service signaling: transaction-oriented queries/responses for mobility and value-added services (via SCCP + TCAP and an application part such as MAP/CAP/INAP).
• Interconnect between operators: standard signaling semantics across national and international networks, enabling consistent routing and service behavior.

Earlier telephone systems used in-band or channel-associated signaling (CAS), where control signals were tied to bearer circuits (tones, robbed-bit, etc.). That model was limited: it consumed bearer resources, was slow for large-scale automation, and constrained advanced services.

SS7 introduced a separate signaling channel (logically out-of-band) that can carry signaling for many bearers at once. This architecture enables:

• Faster call setup and higher signaling throughput
• Scalability through multiplexing and message routing
• Resilience with standardized rerouting and congestion mechanisms
• Service evolution (roaming, number translation, prepaid control, SMS-era routing, etc.) through transaction-based signaling

1.1 Where SS7 is used

SS7 remains widely deployed in two main places:
Legacy PSTN / circuit-switched interconnect: Many operators still use SS7/ISUP and SS7 routing cores for interconnect with legacy exchanges and gateways.

Mobile networks (especially 2G/3G and interworking edges): In GSM/UMTS networks, SS7 (notably SCCP/TCAP/MAP and CAP) supports subscriber/mobility services such as location procedures, subscriber data handling, and service control.

In LTE/5G cores, most “native” control signaling moved to Diameter and then HTTP/2-based service architectures, but SS7 commonly remains at the boundaries for:

• interworking with legacy 2G/3G roaming partners
• interconnect/translation with circuit-switched domains
• service gateways that still speak SS7 toward legacy nodes

1.2 SS7 over IP (SIGTRAN)

Modern deployments commonly carry SS7 signaling over IP networks using SIGTRAN. In this model:

• SCTP provides the transport association (robust, multi-homing capable).
• M3UA (or other adaptation layers) carries SS7 user signaling over SCTP.
• MTP3 routing concepts still apply (e.g., point codes, network indicator, routing labels), even though the physical link is IP rather than TDM.

Mobius SS7 configuration in this documentation focuses on exactly that practical reality: SS7 over IP using SCTP and M3UA, with SCCP/TCAP for transaction services and application parts such as MAP/CAP/INAP/ISUP depending on the product role.

1.3 References

This section lists the normative standards and specifications referenced throughout the Mobius SS7 documentation (concepts, protocol behavior, message formats, and SIGTRAN transport).

IETF RFCs (SIGTRAN / IP Transport)

RFC 4166 — Signaling Transport (SIGTRAN) Architecture

RFC 4666 — Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) – User Adaptation Layer (M3UA)

RFC 4960 — Stream Control Transmission Protocol (SCTP)

RFC 793 — Transmission Control Protocol (TCP)

ITU-T Recommendations (SS7 Core Network and SCCP/TCAP)

SS7 framework / MTP

ITU-T Q.700 — Introduction to CCITT Signalling System No. 7

ITU-T Q.701 — Functional description of the Message Transfer Part (MTP)

ITU-T Q.703 — Signalling Link (MTP Level 2)

ITU-T Q.704 — Signalling Network Functions and Messages (MTP Level 3)

ITU-T Q.705 — Signalling Link Set / Route Management (MTP Level 3 procedures)

ITU-T Q.708 — Numbering of International Signalling Points (International Signalling Point Code – ISPC)

SCCP

ITU-T Q.711 — Signalling Connection Control Part (SCCP) – Functional description

ITU-T Q.713 — SCCP formats and codes

ITU-T Q.714 — SCCP procedures

TCAP

ITU-T Q.771 — TCAP Functional description

ITU-T Q.773 — TCAP Protocol specification (transaction/dialogue/component encoding)

ITU-T Q.774 — TCAP Test specification

ISUP / IN

ITU-T Q.761 — ISDN User Part (ISUP) – Functional description

ITU-T Q.1200-series — Intelligent Network (IN) Recommendations (includes INAP-related specifications in ITU-T IN framework)

3GPP Specifications

3GPP TS 29.002 — Mobile Application Part (MAP) specification

3GPP TS 29.078 — CAMEL Application Part (CAP) specification

3GPP TS 33.200 — 3G security; network domain security (NDS/IP) (references SS7 as telecom signaling context)

3GPP TS 29.202 — SS7 over IP interworking/transport aspects (SIGTRAN-related context and mapping used in mobile networks)

ANSI / ATIS (North American SS7 variants)

ANSI/ATIS T1.111 — MTP Level 3 (ANSI SS7)

ANSI/ATIS T1.112 — SCCP (ANSI SS7)

ANSI/ATIS T1.114 — TCAP (ANSI SS7)