Reliable and efficient transmission of emergency calls during a massive network failure
is both an indispensable and challenging task. In this paper, we propose a novel fully 3GPP and
5G compatible emergency call protocol named 5G StandalOne Service (5G-SOS). A 5G-SOS-enabled
emergency service provides potential out-of-coverage victims’ devices with a way to contact the
4G/5G core network through D2D multi-hop relaying protocol. The objective of 5G-SOS is to maintain
this connection even when a large fraction of the network infrastructure is destroyed. 5G-SOS is a fully
distributed protocol designed to generate zero additional control traffic and to adapt its parameters
based on the local emergency call congestion. Therefore, devices behave as an ad-hoc network with
the common purpose to ensure the best chances for emergency call transfer within a reasonable delay.
A densely populated Traverse city of Michigan, USA, with a 15,000 population, is used to evaluate
5G-SOS under extreme emergency scenarios. The performance of 5G-SOS is shown to be significant
when compared with existing protocols, namely, M-HELP and FINDER, in terms of transmission
success rate, end-to-end latency, network traffic control, and energy management. 5G-SOS provides
satisfactory performance (success rate of 50%) even when the number of simultaneous emergency
calls is very high (5000 calls over 10 min). On average, 5G-SOS performs 24.9% better than M-HELP
and 73.9% than FINDER in terms of success rate. Additionally, 5G-SOS reduces the average end-end
latency of the emergency calls transfer by 20.8% compared to M-HELP and 61.7% compared to
FINDER.