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SERVICE INTEROPERABILITY
For inter-service provider aspects, GSMA PRD IR.92, IR.94 and RCC.07 refer to GSMA PRD IR.88, IR.65,
IR.90 and RCC.54. These specifications document IMS-NNI-specific details associated with the IMS-based
services:
• GSMA PRD IR.88 defines LTE and Evolved Packet Core (EPC) roaming guidelines required
for interworking and definition of mobile network capabilities when customers roam.
Consequently, IR.88 provides technical roaming guidelines for VoLTE using the local breakout
(LBO) and S8HR options in the LTE roaming architecture. In the LBO roaming scenario, IMS
traffic is broken out from the packet data network gateway (P-GW) in the visited network
traversing the IMS-NNI to the functions in the home network and taking advantage of optimized
media routing methods defined in 3GPP standards. In the S8HR roaming architecture, the IMS
PDN is anchored on the P-GW in the HPMN with the IMS traffic traversing the S8 interface
between the VPMN and HPMN (hence the name). Since all the IMS network elements reside
in the HPMN, an IMS-NNI may not be needed with the current solution being developed by
3GPP for handling emergency calls and Lawful Intercept (LI) for roaming situations. GSMA
PRD IR.88 also covers relocation to CS voice and SMS services using CSFB as defined in
3GPP TS 23.272 when VoLTE or SMSoIP is not available. Furthermore, GSMA PRD IR.88
specifies capabilities to facilitate roaming for IMS-based services, such as VoLTE, and is based
on the IMS Access Point Name (APN).
• GSMA PRD IR.65, or IMS Roaming and Interworking Guidelines, expands on details related
to network-level roaming and interworking between two IMS networks and use of the IMS NNI
as defined in 3GPP TS 29.165. PRD IR.65 also specifies operational requirements for
VoLTE/ViLTE and RCS associated with routing of signaling and media over IMS, considering
that it should be as optimal as done for CS communications. VoLTE roaming guidelines are
specified for both roaming models (LBO and S8HR)
• GSMA PRD IR.90 defines interworking guidelines for RCS. GSMA PRD IR. 90 helps service
providers select the optimal solution for service interconnection at the IMS NNI based on the
possible service alternatives associated with RCS. This further provides general service
interoperability aspects related to RCS as input to GSMA PRD IR.65. PRD IR.90 also defines
the interworking that service providers could use for setting up mutual agreement for IMSbased
service interconnection.
• GSMA PRD RCC.54 defines guidelines for interconnection between service providers for the
purposes of interchanging VoLTE, ViLTE and RCS Messaging inter-service-provider traffic.
The current version of the PRD is based on a set of features or profile defined for North
American deployments. Interconnection aspects for other regional RCS profiles will be
captured in future versions. The document supports interconnection via direct bilateral
connectivity and connectivity via internetwork packet exchange (IPX). However, the current
scope addresses guidelines only for service providers rather than IPX providers. GSMA PRD
IR.34 facilitates guidance on procedures for IPX providers associated with the inter-serviceprovider
IP backbone.
In addition to the specifications mentioned above, other GSMA interworking guidelines – such as PRDs
IR.67 and IR.77 – are used to address issues related to addressing, quality of service (QoS) and security,
all of which rely on 3GPP standards.
The verification of the inter-service-provider aspects is documented in GSMA PRD RCC.51, which defines
end-to-end testing of VoLTE, ViLTE and RCS Messaging over IMS. It also covers testing of NNI based on
The Evolution of 3GPP Communications Services – 5G Americas – July 2016
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