TROUBLESHOOT_COTS_UE_TRAFFIC.md

OpenAirInterface 5G Core Network : testing with Commercial UE traffic troubleshooting

COTS-UE means Commercial Off-The-Shelf UE.

Prior to 2022.w12 tag, if you were deploying a minimalist or basic OAI 5G CN, you would see the following issue:

• Ping operations from ext-dn to COTS-UE or from COTS-UE to ext-dn were OK
• TCP iperf traffic test was OK in Downlink and Uplink
• UDP iperf traffic test was OK in Uplink (ie from COTS-UE to ext-dn)
• But UDP Downlink iperf traffic test was not working.

The issue is the MTU value affected to the interface on the UE.

For example, we are using Quectel modules and it looks like this:

$ ifconfig wwan0
wwan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1356
        inet 12.1.1.129 netmask 255.255.255.0  broadcast 12.1.1.255

2 solutions:

• Either you force the MTU value (if possible):

$ sudo ip link set dev wwan0 mtu 1500

• The better one is to tell the SMF to use this 1500 value.

I made 2 examples in the docker-compose/docker-compose-basic-nrf.yaml and docker-compose/docker-compose-mini-nrf.yaml files:

$ git diff docker-compose/docker-compose-basic-nrf.yaml
diff --git a/docker-compose/docker-compose-basic-nrf.yaml b/docker-compose/docker-compose-basic-nrf.yaml
index 04aceae..fef0835 100644
--- a/docker-compose/docker-compose-basic-nrf.yaml
+++ b/docker-compose/docker-compose-basic-nrf.yaml
@@ -250,6 +250,7 @@ services:
             - DNN_RANGE1=12.1.1.2 - 12.1.1.128
             - DNN_RANGE0=12.2.1.2 - 12.2.1.128
             - DNN_NI1=default
+            - UE_MTU=1500
         depends_on:
             - oai-nrf
             - oai-amf
$ git diff docker-compose/docker-compose-mini-nrf.yaml
diff --git a/docker-compose/docker-compose-mini-nrf.yaml b/docker-compose/docker-compose-mini-nrf.yaml
index cd58557..35b3d3b 100644
--- a/docker-compose/docker-compose-mini-nrf.yaml
+++ b/docker-compose/docker-compose-mini-nrf.yaml
@@ -147,6 +147,7 @@ services:
             - DNN_RANGE1=12.1.1.2 - 12.1.1.128
             - DNN_RANGE0=12.2.1.2 - 12.2.1.128
             - DNN_NI1=default
+            - UE_MTU=1500
         depends_on:
             - oai-nrf
             - oai-amf

With this SMF setup:

$ ifconfig wwan0
wwan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 12.1.1.129 netmask 255.255.255.0  broadcast 12.1.1.255