About the IP Short Message Gateway
The IP Short Message Gateway (IP-SM-GW) implements transport layer interworking for SMS over IP. It is based on 3GPP TS 24.341, and implements suitable SMS interworking as part of GSMA IR.92 version 9.0
This document includes the following topics:
How the IP-SM-GW fits into a network
Illustrative flows for key behaviour
Major functional components
Versions of GSM/3GPP MAP in the IP-SM-GW
The TCAP Leg Manager subsystem of the Sentinel IP-SM-GW service
Sentinel IP-SM-GW in an LTE network
The IP-SM-GW interfaces to several network elements.
Once a UE is IMS registered, and indicates support for receipt of SMS over IP, it may send and receive SMS through the IP-SM-GW. That is, the UE may use SMS over IP when registered via PS access networks, not only when registered via LTE. The IP-SM-GW also supports mobile-initiated USSD reports over IMS.
The IP-SM-GW performs a similar role to the VMSC, but for IMS registered UEs, rather than CS registered.
In order to aid understanding of the role of the IP-SM-GW, refer to Key Flows.
The diagram below shows the major components for the Sentinel IP-SM-GW.
The Sentinel Registrar, Sentinel USSI and Sentinel IP-SM-GW are services running on the Rhino TAS platform, written using the Sentinel Framework. Third Party Registration support is provided by the Sentinel Registrar service. USSD over IMS is provided by the Sentinel USSI service. The core SMS flows of the IP-SM-GW are provided by the Sentinel IP-SM-GW service. The Cassandra DB appears in the diagram for each role it fulfills in the architecture (routing correlation, registration ownership tracking, and registrar data storage).
to correlate the IMSI and Circuit Switched Routing Information,
to track the most recent site a subscriber registered at in a multi-site geo-redundant setup, and
to store Third Party Registration information. For more information refer to Sentinel Registrar Overview and Concepts
IMSI and Circuit Switched Routing Information correlation
The Sentinel IP-SM-GW uses a Cassandra Database to store and retrieve CS Routing Information.
This means that any IP-SM-GW cluster member can process the
MT Forward Short Message request regardless of the cluster member that processed the Routing Information for SM query.
This ensures that a deployment is simple from an SS7 addressing perspective, as only a single GT address is required.
Third Party Registration ownership tracking
The Sentinel IP-SM-GW uses a Cassandra Database to store and retrieve registration ownership information. This means that if IP-SM-GW is running in a multi-site geo-redundant setup, the site at which the subscriber most recently registered is tracked across all the sites. This ensures that subscribers can register at one site and re-register at a different site, with network-initiated de-registrations at sites previously registered at suppressing the AMT de-registration.
USSD over IMS
The Sentinel USSI service provides USSD capabilities over IMS by acting as a gateway between the IMS network and the HLR over MAP. It is able to process an INVITE, extract the USSD content from the message body and encode this as a MAP request towards the HLR. It will then translate the response from the HLR into a SIP message back towards the UE completing the USSD query.
Support for GSM MAP
The Sentinel IP-SM-GW supports GSM/3GPP MAP Phases 1, 2 and 2+ for MT SMS. It uses MAP Phase 2 for Mobile Originated SMS submission into the SMSC.
Protocol support is provided through the use of OpenCloud CGIN and OCSS7 stacks. For protocol compliance statements refer to CGIN Protocol Compliance and OCSS7 Compliance Matrix.