Operator SMSC: SS7, SIGTRAN, SMPP & IMS

What is an operator SMSC?

An operator SMSC (short message service centre) is the core network element that receives SMS, stores them and delivers them to subscribers. It looks up where a subscriber is through the HLR with a MAP SendRoutingInfoForSM query, forwards the message with MT-ForwardSM, and keeps undelivered messages until the subscriber is reachable again. Modern SMSCs also deliver SMS over IMS and accept traffic from applications over SMPP and HTTP.

Who it is for

Mobile network operatorsReplacing or adding SMSC capacity, or consolidating MAP, SMPP and IMS messaging on one platform.
MVNOs and MVNEsRunning their own messaging services over SIGTRAN links with a host network.
IoT providersDevice messaging submitted over HTTP or SMPP and delivered over MAP.
Private LTE and 5G networksSMS for IMS subscribers alongside data services.

Messaging it handles

Mobile-originated (MO) and mobile-terminated (MT) SMS.
Application-to-person (A2P), person-to-application (P2A) and person-to-person (P2P) traffic.
Flash SMS and message classes 0 to 3, binary SMS, UCS2 and multilingual text.
Concatenated (multipart) messages and WAP Push.

Supported protocols and interfaces

Protocol or interface	Used for	Availability
MAP v1, v2, v3 over SS7	Operator signaling for SMS	Core
SIGTRAN (SCTP, M3UA, SCCP)	SS7 over IP	Core
SMPP v3.4	Application and aggregator binds	Core
SMPP over TLS	Encrypted binds	Core
SIP / IMS	SMS over IMS	Core
HTTP / REST	Application submission and provisioning	Core
HLR integration	Subscriber lookup	Core
SMPP v5.0	Enhanced ESME binds	Per deployment
Diameter SGd	SMS over Diameter in LTE	Per deployment

MAP operations handled include MO-ForwardSM, MT-ForwardSM, SendRoutingInfoForSM, AlertServiceCentre and ReportSM-DeliveryStatus.

Architecture

The SMSC is built as four layers that scale independently:

Signaling: SS7/MAP over SIGTRAN, and SIP for IMS delivery.
Processing: Message store, queues, retry scheduler, routing engine and CDR writer.
Gateway: SMPP and HTTP/REST access for applications and aggregators.
Management: Web interface, provisioning API, monitoring and reporting.

All protocol stacks run at the same time, so one platform serves 2G/3G subscribers over MAP, IMS subscribers over SIP and applications over SMPP.

Store-and-retry delivery

Receive. A message arrives over MAP, SIP, SMPP or HTTP and is written to the persistent message store.
Locate. The SMSC queries the HLR with SRI-for-SM, taking number portability and SMS home routing into account.
Deliver. The message is sent with MT-ForwardSM, or over IMS for IMS subscribers.
Wait if needed. If the subscriber is unreachable, the SMSC registers message-waiting data with the HLR and keeps the message within its validity period.
Retry. When the HLR sends AlertServiceCentre, or the retry schedule fires, delivery is attempted again.
Record. A delivery receipt is returned where requested and a billing-grade CDR is written.

Routing and subscriber resolution

HLR lookup through MAP SRI-for-SM, with alternative lookup over SMPP where needed.
SMS home routing and mobile number portability awareness.
Routing by country, operator, prefix, sender, customer, service and traffic type.
Cost-, quality- and load-based routing with automatic failover, priority queues and fallback routes.
Retry profiles per route and message class, with configurable validity periods.

Applications and enterprise access

Applications and aggregators bind over SMPP v3.4 (bind_transceiver, submit_sm, deliver_sm), with SMPP over TLS for encrypted sessions, or submit over HTTP/REST. Throughput and policy are set per client. For many business customers with their own routing and reseller structure, put the Enterprise SMPP Gateway in front of the SMSC.

Billing, monitoring and management

A billing-grade CDR for every message, exported in agreed formats for BSS and revenue assurance.
Real-time throughput, queue depth and delivery status, per route and per account.
SNMP traps, syslog and REST metrics for the NOC.
Web interface and REST provisioning for routes, accounts, retry profiles and message classes, with message tracing and bulk provisioning.

Security controls

SMPP over TLS for application binds.
Source-IP restrictions and credential policies per SMPP account.
Role-based access to the web interface and API, with audit and configuration-change logs.
Optional inline inspection by our SMS firewall.

High availability and scaling

Nodes run in active pairs with automatic failover; the persistent message store keeps messages safe across a failover. SIGTRAN associations and SMPP binds are redundant. Capacity grows by adding processing nodes, and the signaling, processing and gateway layers scale independently. Geographic redundancy is confirmed per deployment.

Deployment

Software-only on Linux, on bare metal or virtual machines, in your data centre, in colocation, or in a private or public cloud. It runs standalone or with our security products, and throughput and latency targets are set in a written sizing document for each deployment.

Use cases

MVNO messaging independence: the MVNO runs its own SMSC over SIGTRAN links with the host network.
Legacy SMSC replacement: MAP, SMPP and IMS messaging consolidated onto one software platform.
IoT messaging: devices and platforms submit over HTTP or SMPP; messages are delivered over MAP.
Private LTE/5G: SMS for IMS subscribers on a private network.

What it does not include

SMS firewall functions are a separate product. Multi-tenant management of many SMPP customers, resellers and supplier routes is the job of the Enterprise SMPP Gateway.

Frequently asked questions

Can an MVNO run its own SMSC?

Yes. A full or thick MVNO can run the Operator SMSC on SIGTRAN links agreed with its host network, which gives it control over its own messaging services, routing, billing records and A2P products.

Does the SMSC include an SMS firewall?

No. Firewall functions are a separate product, so operators can protect any SMSC, including ours. The SMSC can run with our SMS firewall inline when both are deployed.

Which protocol features depend on the deployment?

MAP over SIGTRAN, SMPP v3.4, SMPP over TLS, SIP/IMS and HTTP are core capabilities. SMS over Diameter SGd, SMPP v5.0 and geographic redundancy are confirmed per deployment.

What hardware does it need?

Standard Linux servers or virtual machines, on-premise, in colocation or in a private or public cloud. No proprietary signaling hardware is required.