Dataplane bug in L2NFAPI_NOS1

The noS1 mode of the L2NFAPI emulator has a bug that makes the dataplane traffic of all the emulated UEs to go through the interface of the first UE (oaitun_ue1).

To trigger the bug, you can run the eNB as follows:

sudo -E ./ran_build/build/lte-softmodem -O ../ci-scripts/conf_files/rcc.band7.tm1.nfapi.conf --noS1

and then 2 or more UEs in the following way:

sudo -E ./lte-uesoftmodem -O ../../../ci-scripts/conf_files/ue.nfapi.conf --L2-emul 3 --num-ues 16 --nums_ue_thread 1 --noS1 --nokrnmod 1

The UEs attach successfully and you can use ping (e.g. for UE 16):

ping 10.0.1.1 -I oaitun_ue16 -s 1000

However, all the dataplane traffic goes through oaitun_ue1. This behavior can be verified using network monitoring tools like nmon. The issue appears to be at the PDCP layer and in the way the forwarding of the packets is done.