Hosted ISSI Function for Inter-RF Subsystem Call Routing
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Solution Overview
Problem
Existing wireless communication networks face challenges with end-user configuration complexity, security, scalability, and interoperability policy enforcement, particularly in inter-radio frequency subsystem interface (ISSI) connections between P25 and TETRA systems.
Innovation Solution
The implementation of a Hosted Inter-RF Subsystem Interface (ISSI) Function (HIF) that enables unit-to-unit calls by processing invite messages, tracking mobility, and proxying SIP signaling across RFSSs, centralizing call management, and logically connecting multiple RFSSs through a single ISSI link, thereby reducing processing load and enhancing security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple SIP proxy architecture is used to route data packets between RFSSs, then device complexity is reduced, but calling capacity and network connectivity are limited
Solution Approach 1:
The patent merges the SIP proxy functionality with an RFSS (Radio Frequency Subsystem) by implementing the HIF (Hosted Inter-RF Subsystem Interface) function within the RFSS architecture. This integration allows the RFSS to simultaneously serve as both a communication endpoint and a signaling proxy, enabling multiple calling capacity while maintaining manageable system complexity through unified functional design
2Adaptability or versatility
If multiple IP networks are used to interconnect RFSSs, then connectivity and routing flexibility are improved, but security risks increase
Solution Approach 1:
The patent introduces a centralized HIF (Hosted Inter-RF Subsystem Interface) function as an intermediary between multiple RFSSs. This HIF acts as a security gateway that manages all ISSI connections through a single trusted interface, allowing network connectivity across multiple RFSSs while consolidating security control to reduce exposure to harmful factors
3Productivity
If a hosted ISSI function is implemented to centralize call management, then calling capacity and security are improved, but device complexity increases
Solution Approach 1:
The patent implements the HIF (Hosted Inter-RF Subsystem Interface) function within the RFSS architecture, enabling the RFSS to perform multiple functions: serving as a communication endpoint for units, acting as a SIP proxy for signaling, and managing ISSI connections. This multi-functionality approach increases calling capacity while managing complexity through functional integration rather than separate dedicated components
4Reliability
If multiple explicit messages are sent to target multiple RFSSs, then message delivery reliability is improved, but configuration complexity and processing load increase
Solution Approach 1:
The patent implements a subscription-based feedback mechanism where RFSSs subscribe to broadcast messages from the HIF. Instead of requiring explicit point-to-point configuration for each RFSS, the system publishes messages once and receives automatic feedback/acknowledgments from subscribed RFSSs. This maintains reliable message delivery while dramatically reducing configuration complexity through automatic distribution
Data Source
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AI summary
A method and device enable establishing an inter-radio frequency subsystem interface (ISSI) unit-to-unit call between a calling unit of a calling home radio frequency subsystem (RFSS), and a called unit of a called home RFSS, through a hosted ISSI function (HIF). The method includes processing, at the HIF, a first invite message received from the calling home RFSS, wherein the first invite message includes a first request uniform resource identifier (URI) that designates an alias system unit identification (SU-ID). In response to the first invite message, transmitting, from the HIF to the called home RFSS, a second invite message, including a second request URI that designates a real SU-ID, wherein the HIF acts as the calling home RFSS. The unit-to-unit call is thus established between the calling unit and the called unit through the calling home RFSS, the HIF, and the called home RFSS.