Efficient Elevator Mode Protocol to Recover Active calls from Transient Network Outages

Voice over 5G New Radio (VoNR) and Voice over Long Term Evolution (VoLTE) service enables wireless operators to use the data network to provide voice. LTE and NR harness true power of IP Multimedia Subsystem (IMS). The IMS uses Real Time Protocol (RTP) to carry multimedia (e.g., audio, and video). Failing to transmit RTP packets to intended destination within configured time leads to RTP timeouts, eventually dropping voice call session. Reasons for such timeouts can be transient in nature, due to lack of network coverage occurring inside an elevator tunnel or basement areas eventually leading to call drop. In such cases, user initiates new call and re-establishes new session. This kind of call drop brings inconvenience to users. This paper presents a novel idea to mitigate such network coverage transient dropouts and defines new call flow to inform other party involved about expected drop in signal conditions in advance. The proposed idea is easy to deploy as they make use of defined options within existing protocol message exchange.