Merge pull request #249122 from robswain/158607-mtu

ADO 158607 - configurable MTU

Author: prmerger-automator[bot]

articles/private-5g-core/modify-packet-core.md

@@ -46,6 +46,7 @@ The following changes will trigger the packet core to reinstall, during which yo
 - Detaching a data network from the packet core instance.
 - Changing the packet core instance's custom location.
 - Changing the N2, N3 or N6 interface configuration on an attached data network.
+- Changing the UE Maximum Transmission Unit (MTU).
 
 The following changes require you to manually perform a reinstall, during which your service will be unavailable for up to two hours, before they take effect:
 

articles/private-5g-core/private-mobile-network-design-requirements.md

@@ -118,9 +118,15 @@ To avoid transmission issues caused by IPv4 fragmentation, a 4G or 5G packet cor
 
 IP packets from UEs are tunneled through from the RAN, which adds overhead from encapsulation. The MTU value for the UE should therefore be smaller than the MTU value used between the RAN and the packet core to avoid transmission issues.
 
-RANs typically come pre-configured with an MTU of 1500. The packet core’s default UE MTU is 1300 bytes to allow for encapsulation overhead. These values maximize RAN interoperability, but risk that certain UEs will not observe the default MTU and will generate larger packets that require IPv4 fragmentation and that may be dropped by the network.
+RANs typically come pre-configured with an MTU of 1500. The packet core’s default UE MTU is 1440 bytes to allow for encapsulation overhead. These values maximize RAN interoperability, but risk that certain UEs will not observe the default MTU and will generate larger packets that require IPv4 fragmentation and that may be dropped by the network. If you are affected by this issue, it is strongly recommended to configure the RAN to use an MTU of 1560 or higher, which allows a sufficient overhead for the encapsulation and avoids fragmentation with a UE using a standard MTU of 1500.
 
-If you are affected by this issue, it is strongly recommended to configure the RAN to use an MTU of 1560 or higher, which allows a sufficient overhead for the encapsulation and avoids fragmentation with a UE using a standard MTU of 1500.
+You can also change the UE MTU signaled by the packet core. We recommend setting the MTU to a value within the range supported by your UEs and 60 bytes below the MTU signaled by the RAN. Note that:
+
+- The data network (N6) is automatically updated to match the UE MTU.
+- The access network (N3) is automatically updated to match the UE MTU plus 60.
+- You can configure a value between 1280 and 1930 bytes.
+
+To change the UE MTU signaled by the packet core, see [Modify a packet core instance](modify-packet-core.md).
 
 ### Signal coverage