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MTU

The largest packet a link carries in one piece; BLE has its own, smaller one.

The maximum transmission unit caps the payload of one link-layer frame, 1,500 bytes of IP packet on Ethernet and Wi-Fi, so bigger messages are split. BLE's ATT MTU caps the payload of one attribute operation (23 bytes by default, negotiable upward), which together with the connection interval limits throughput.

Examples

  • Ethernet and Wi-Fi have an MTU of 1,500 bytes, so a 2,000-byte message crosses them as at least two packets.

  • With BLE's default MTU of 23 bytes, a notification carries at most 20 bytes of value.

  • Negotiating an MTU of 247 lets one notification carry 244 bytes, enough for 40 accelerometer samples.

See also

notification connection interval
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