The WLAN port MTU value is set to 1500 bytes and cannot be changed. Since cellular ports have a lower MTU with a maximum of 1486 bytes, and WLAN traffic from stations connected to the WLAN AP is carried over an IP/MPLS service that adds additional overhead to traffic traveling over cellular ports, the operator must understand the requirements of the MTU for their applications in order to successfully use the WLAN interface.
For example, when the WLAN interface AP is connected to the Nokia WLAN GW using an Epipe service, there is at most 1454 bytes available to carry a Layer 2 packet for the WLAN AP packet that includes a Layer 2 header of 14 bytes (see MTU considerations over a cellular port for information about the SAP MTU of an Epipe service over a cellular port). In order to successfully send these packets over a cellular port without further modification, the MTU of the IP payload in the WLAN AP Layer 2 packet must be restricted to 1440 bytes.
The MTU of the WLAN interface can be handled in one of two ways:
by modifying the MTU value on clients that are connecting to the WLAN AP such that they send traffic that conforms to the service MTU of the IP/MPLS transport service, minus the 14 byte Layer 2 overhead
by configuring GRE SDP fragmentation and reassembly on the node to allow packets that require an MTU greater than that available on the cellular interface to be fragmented and reassembled when carried over the cellular interface