Max Transmission Unit
The standard GTP header has a size of 36 bytes. Due to the low costs of Ethernet-based carrier-grade links, it is likely that many cell networks are already using IP over Ethernet on the internal backhaul between network nodes.
Ethernet traditionally has a 1500-byte MTU. 1500 - 36 = 1464 bytes. If carriers are subject to that limit, this means the user-side MTU may be 1464 bytes. IP/UDP overhead is 28 bytes so WAP payload limit may be 1436 bytes.
This means WML files should ideally not exceed 1420 bytes on the wire to avoid unusual network behavior or slowdowns.
Byte: a unit made of 8 bits, the bits inside can have any combination of 0s and 1s.
MTU: Maximum Transmission Unit. The maximum amount of data (including IP and TCP/UDP headers) one can transmit in a single packet.