SIP Call Control Reducing Transcoders in CDMA Voice Paths
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Solution Overview
Problem
CDMA circuit-switched networks require two transcoders for mobile-to-mobile calls, leading to voice quality degradation and increased time delays, and traditional ringback mechanisms in these networks are delayed, causing user discomfort.
Innovation Solution
Implementing SIP/SIP-T as the call control protocol in CDMA wireless networks to reduce or eliminate transcoders in the voice bearer path and enable early ringback for calling parties by transmitting additional bearer-related information, such as supported codecs, and triggering ringback from the originating MSCe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SS7 protocol is used for call control in CDMA circuit-switched networks, then call setup is supported, but two transcoders are required in the voice bearer path causing voice quality degradation and increased time delays
Solution Approach 1:
The patent changes the signaling protocol parameter from SS7 to SIP/SIP-T, which enables direct voice bearer path establishment between mobile stations with compatible codecs. This parameter change eliminates the requirement for transcoders, thereby removing the harmful effect of voice quality degradation while maintaining call setup functionality.
Solution Approach 2:
The patent extracts and removes the transcoder elements from the voice bearer path by using SIP-based call control. Instead of requiring transcoders at both ends as in SS7-based networks, the SIP protocol allows direct connection between compatible mobile stations, taking out the harmful transcoding components entirely.
2Reliability
If SS7 protocol is used for call control in CDMA circuit-switched networks, then call setup is supported, but time delays are increased due to multiple transcodings
Solution Approach 1:
By changing the call control protocol parameter from SS7 to SIP/SIP-T, the system eliminates the time-consuming transcoding operations. The SIP protocol enables direct voice bearer path establishment, removing the multiple transcoding steps that cause time delays while preserving call setup capability.
Solution Approach 2:
The patent extracts the transcoder elements from the call path, eliminating the time delays associated with multiple transcoding operations. The SIP-based approach establishes a direct voice bearer path without intermediate transcoding steps, thereby reducing loss of time.
3Ease of operation
If traditional ringback mechanism is used in CDMA networks, then ringback is provided to calling party, but timing is delayed causing user discomfort
Solution Approach 1:
The patent applies preliminary action by enabling the originating MSCe to generate and send ringback to the calling party immediately upon call initiation, before the voice bearer path is fully established. This early ringback eliminates the timing delay and user discomfort associated with traditional mechanisms, while still providing the necessary ringback function.
Solution Approach 2:
The patent uses the originating MSCe as an intermediary to provide early ringback. The MSCe generates ringback locally and sends it to the calling party before the called party's network establishes the voice bearer path, acting as a mediator to eliminate the timing delay without requiring changes to the called party's network.
Data Source
AI summary
A system and a method in a wireless network utilizing session initiation protocol (SIP) for call control. The SIP payload (SDP) contains a list of voice codecs to coordinate the selection of voice bearer resources (between a calling party and a called party) such that the number of transcoders in the voice bearer path is minimized. An additional aspect of the embodiment of the present invention includes a serving MSCe that is operable to determine whether to initiate or discontinue ringback to the calling party. If ring back is to be initiated, ringback can be initiated from a Serving MGW controlled by the serving MSCe. The call negotiation process according to the described embodiment of the invention eliminates the requirement for any transcoding in specific situations to result in the number of transcoders used in the voice bearer path to be reduced to 0 (TrFO, Transcoder Free Operation) or to 1 (RTO, remote transmitter operation).