IMS MT Call Recovery via HSS P-CSCF Storage
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Solution Overview
Problem
In IP multimedia subsystem (IMS) networks, mobile-terminated calls are dropped when the serving Call Session Control Function (S-CSCF) is unavailable due to loss of Proxy Call Session Control Function (P-CSCF) information, as this information is only cached locally and not stored in the Home Subscriber Database (HSS).
Innovation Solution
The IMS registration process is modified to store P-CSCF information in both the S-CSCF's memory and the HSS, allowing the HSS to provide the necessary information for routing mobile-terminated calls even if the S-CSCF is unavailable. This involves encrypting and decrypting the P-CSCF's IP address using attribute value pairs (AVPs) during registration and using this information to pre-register and restore call sessions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If P-CSCF information is cached only in S-CSCF memory, then the system structure is simple, but MT calls are dropped when S-CSCF is unavailable
Solution Approach 1:
The patent applies preliminary action by storing P-CSCF information in the HSS database during the initial registration process, before any potential S-CSCF failure occurs. This advance preparation ensures that when an S-CSCF becomes unavailable, the P-CSCF information can be quickly retrieved from HSS without requiring complex real-time discovery mechanisms, thus maintaining call delivery reliability while avoiding overly complex system architecture.
2Reliability
If P-CSCF information is stored in HSS, then MT calls can be recovered when S-CSCF is down, but the registration process becomes more complex
Solution Approach 1:
The patent merges the P-CSCF information storage function into the existing HSS database, which already stores subscriber profile information. By combining these storage functions in a single centralized database, the patent avoids creating separate complex storage systems while ensuring P-CSCF information is preserved for call recovery purposes. The registration process incorporates additional encryption steps using AVPs, but leverages existing HSS infrastructure to minimize overall system complexity.
3Reliability
If P-CSCF IP address is transmitted in clear text, then the transmission process is simple, but security is compromised
Solution Approach 1:
The patent applies parameter changes by transforming the P-CSCF IP address from clear text to encrypted form using Attribute Value Pairs (AVPs) during transmission. This encryption process changes the state of the data parameter, ensuring security while maintaining the ability to decrypt and use the information when needed. The AVP encapsulation adds a layer of protection without fundamentally altering the transmission protocol structure.
Data Source
AI summary
Methods and systems for MT (mobile terminated) call recovery in an IP multimedia system (IMS) network are discussed herein. A method according to an implementation comprises receiving, via a network, a request to establish a call session with a user equipment (UE); sending, to a first serving call session control function (S-CSCF), a first invite associated with the request; determining that no response is received from the first S-CSCF after a pre-set time period; sending, to a second S-CSCF, a second invite associated with the request, causing the second S-CSCF to perform actions including: obtaining an authentication to establish the call session; and sending, to a proxy call session control function (P-CSCF) of the UE, a third invite associated with the request; and receiving, via the network, a confirmation that the call session with the UE is established.