Answer:  Some networks will employ Encapsulated Security Protocol for the data packets that are used for voice call set up (SIP layer) , and packet transmission (RTP layer).  Link Master will attempt to decode these packets when the authentication key is available and it will show the "K" as "green"; but in the case when the key is not available, Link Master will provide a status alert to the user with the red "K" and the notification "No Key".   Without the ESP key Link Master will not be able to properly decode the SIP and RTP packets.  The SIP layer is important for call control messaging and if you are trying to set up a voice call using either ADB Command, or RMA Application, then the SIP layer is critical to the call process: without the SIP layer, LML will not know when the call is connected and moved into "conversation" mode.  The RTP layer is important for VoLTE and VoNR calls to extract the audio codec used and well as to calculate jitter and packet loss.

When you see the red "K", the best option is to put the phone into airplane mode ON/OFF while connected to LML.  This will force the registration of the device with the IMS and in this process LML will be able to capture the ESP key.