How is my data traffic counted towards my bill?

Mobile data is charged starting from the IP header, e.g. if you have a TCP/IP connection the packets needed to establish and shut down the connection are also taken into account.

Example:  if you send a single byte, the size of the TCP data-gram alone is effectively 41 bytes.

Size of IPv4 Header (without any options) = 20 bytes

Size of TCP Header (without any options) = 20 bytes

This will result in the following packet flow:

3-way TCP handshake

• SYN 40 bytes
• SYN/ACK 44 bytes
• ACK 40 bytes

1 byte is sent in both directions, ACK combined with PSH

• PSH/ACK 41 bytes
• PSH/ACK 41 bytes

TCP connection shutdown

• FIN/ACK 40 bytes
• FIN/ACK 40 bytes
• ACK 40 bytes
• ACK 40 bytes

= 9 packets / 366 bytes total