TUN interface is created in the UE, and not in the gNB

[endrigoshi]

Hello all,

As I was playing around with UERANSIM and free5gc, I tried out a setup where the UEs are running in a separate PC from the gNB. The deployment works fine and I can communicate with other nodes in the network.

However, what caught my attention was the creation of the uesimtun interface. From my understating of the 5G U-Plane, the gtp tunnel runs between gNB and UPF. Meaning that packets are sent from UE to gNB, and then in gNB they are tunneled to the UPF. In the case of UERANSIM, the TUN interfaces are created in the PC where the UE is running, and thus the packets do not flow at all towards the gNB before reaching UPF.

Is this behavior intended by the developer, or is it an issue inside the code?

Thanks!

[CharlaftisBill]

We have noticed the same behavior.

@endrigoshi Have you found any answer to this question?

[aligungr]

Hello,

Yes, this is intended behavior. uesimtun is not a GTP tunnel. GTP protocol is actually a simple UDP based protocol between gNB and UPF. There is no need to create a network interface for that purpose. GTP is just an (almost) pure UDP.

uesimtun is, on the other hand, utilized to simulate passing packets from UE to gNB in a Linux environment.

Best Regards.