Yeah it is actually RTCP network round trip time propagation delay using the DSLR values.
Now, in general as I have explained and calculated by Wireshark, in one direction it seems good but in another direction the delay is very very low which is not practical.
Now, I have tried a tool called Hammer Call analyzer by Empirix (this tool also uses libpcap and calculate the various values as Wireshark do) with the same pcap, i have captured on a LTE network for VoIP calls, the values on both the directions are almost same but that is not the case with the Wireshark.
I have validated it with almost 10 captures I have taken so far. Also, i have seen the RFC 3550 and it seems like that the way WIreshark is calculated the values by referring that RFC only but in all of my captues i dont see any RR(Response Request) packet but only SR(Senders Request) packet but RFC explains calculation using RR packet only.
I can provide you a pcap, please see the attachment. ( i have made a rar as without rar size was more than 800KB which this list is not allowing)
Regards