SIP Endpoint Line Appearance Reservation via Early INVITE
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Solution Overview
Problem
SIP endpoints face challenges in providing timely line appearance updates and bridging functionality due to their inability to send off-hook signals to switches, leading to delays and line appearance collisions during call setup.
Innovation Solution
Implementing a method where a communication device detects an off-hook state and selects a line appearance, then sends a call setup message to a third-party call controller to reserve the line appearance and provide off-hook notifications, allowing the switch to manage resource allocation and prevent collisions by acknowledging the line appearance status before dialing is complete.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a SIP endpoint waits to receive all dialed digits before forwarding an INVITE to the switch, then the endpoint can provide complete call information, but the switch remains unaware of the endpoint's changed status and cannot update bridged line appearances or busy indicators timely
Solution Approach 1:
The patent applies preliminary action by sending an early INVITE message to the switch before the user completes dialing. This early INVITE includes the endpoint's off-hook status and selected line appearance, allowing the switch to update status information proactively. The endpoint then sends a subsequent INVITE with the complete dialed digits, ensuring both timely status updates and complete call information are provided.
2Reliability
If a SIP endpoint sends an INVITE message with complete dialed digits, then the switch receives accurate call information, but a race condition occurs when both the endpoint user and switch select the same line appearance for incoming and outgoing calls
Solution Approach 1:
The patent segments the call setup process into two distinct phases: first, an early INVITE message establishes the endpoint's off-hook status and reserves the selected line appearance; second, a subsequent INVITE message transmits the complete dialed digits. This segmentation allows the switch to acknowledge and reserve the line appearance before the user finishes dialing, preventing race conditions while ensuring accurate call information is ultimately provided.
3Manufacturing precision
If the switch waits for complete digit collection from the SIP endpoint, then accurate call routing is ensured, but resource allocation delays occur and line appearance collisions cannot be prevented
Solution Approach 1:
The switch performs preliminary resource allocation by receiving and processing an early INVITE message that contains the endpoint's off-hook status and selected line appearance. The switch can acknowledge this early INVITE to reserve the line appearance and update status information before the user completes dialing. This preliminary action enables faster call setup and prevents line appearance collisions while maintaining accurate call routing through the subsequent INVITE message with complete digits.
Data Source
AI summary
In one embodiment, a communication device includes an outgoing call alerting agent 196 that (i) detects that a communication device has entered an off-hook state and that a first line appearance has been selected by a user for an outgoing call, (ii) forwards a first call setup message to a third party call controller, the call setup message including a request to reserve the first line appearance for the outgoing call, and (iii) thereafter collects a set of digits dialed by the user for the outgoing call and provides the collected set of digits to the third party call controller.