Hello Experts…
My friend was asked an interesting question in an interview at VVDN:
If two people are standing at the same distance from the same cell tower and both initiate a call at the exact same instant to their mutual friend, who is located in a different hexagonal cell, whose call will the receiver get first?
What factors determine the order of call arrival in this scenario?
Interesting. We need to consider factors that could prioritize one call over the other, assuming all parameters are identical.
It likely depends on which user the eNB schedules first and whose request gets processed by the core network first.
Between two users with equal priority and equal resource allocation, the determining factor would be the scheduler.
If you are referring to IMS-based calls (VoLTE or VoNR), the ultimate deciding factor is the INVITE message - whichever UE’s INVITE reaches first, the call will be received from that UE.
Other factors such as RAN scheduling, IMS processing delay, and transport network issues can also influence the outcome.
If two people are standing at the same distance from the same serving tower, the one who receives the call first will be the one with fewer obstacles along the signal path.
Obstacles can introduce delays by causing signal attenuation and propagation delays.
This is not entirely accurate, as many other factors can influence the outcome.
I agree… the decision is made at the gNB.
Yes, the decision is made at the gNB, but it depends on obstacles that introduce signal errors, causing delays in transmitting bits from the gNB to the UE.
It’s not just the gNB - many other factors come into play, from the MO UE to the MT UE, including gNBs, backhaul, transport network, and the MT UE’s RAN, all of which can impact call setup timing.
UE model?
Are both High-Speed (HS) capabilities the same?
Yes, of course, the UE also plays a role.
The receiver will get the call first from the person whose call encounters the least network delay. This depends on factors such as channel allocation timing, base station processing, and routing delays through the network to the receiver’s tower. While the signal propagation to the tower may be identical, backend processing and overall network conditions ultimately determine which call is received first.
I think this question is quite complex, as there are many factors and variables to consider. RTTs in signaling, processing delays, prioritization mechanisms, and other network conditions all play a role, making it difficult to determine a straightforward answer.
In my opinion, if the technological conditions are exactly the same, the outcome will depend on external factors that may impact the signal between the cellphone and the tower, influencing the amount of delay that accumulates. However, there are numerous factors to consider, making it a complex analysis.
Great question – excellent for an interview.
Without QoS, it will be a matter of milliseconds.
Obstacles may delay the access procedure on the air interface, but other factors will also have an impact.
Yes i agree, obstacles and radio factors play the role within the originating cell, backhauling capacity factors playing the role in transmitting part and obstacles and radio factors play role within the terminating cell
