Editing Bluetooth (section)

==Limits==
===Protocol===
Bluetooth keyboards and mice typically use the higher levels of the HID protocol borrowed from the [[USB]] standard.
Classic Bluetooth have a packet size of 8 bytes, which in effect limits keyboards to an 8-byte protocol with 6-key [[rollover]].

Bluetooth 4.0/BLE supports up to 22 byte packages, and Bluetooth 4.2/BLE up to 244 with a Data Length Extension.

===Pairing and Connection===
In theory, up to seven devices can be ''connected'' to a host-side receiver at once, but in practice only three to four active devices are considered usable at once because of them sharing bandwidth. There are many other devices and protocols on the 2.4 GHz band, and interference from those could lower the practical use even more.<ref name="applebtfaq">Apple—[https://support.apple.com/en-gb/HT201171 Using a Bluetooth mouse, keyboard, or trackpad with your Mac]. Dated 2018-11-26. Retrieved 2019-01-13.</ref>

Hosts may also limit the number of simultaneous connected devices with the same profile: for instance allow only one headset at once but allow multiple keyboards.

The Bluetooth standard allows a host receiver to ''pair'' up to 255 devices, but the actual limit may be smaller depending on the receiver.
If the peripheral supports it, it could be ''paired'' to up to five hosts but be ''connected'' to only one at a time, unless it has "multipoint functionality".

===Speed===
Both classic Bluetooth and BLE have a packet sent at periodic intervals, which impacts latency.
Also, wireless protocols are susceptible to interference and if a packet gets lost then it will not be re-transmitted until the next time slot.

The scheduling, including the "connection interval" between each report is controlled by the host ("central") and varies depending on the operating system and network conditions.

The minimum connection interval allowed by the BLE spec is 7.5 ms, but operating systems could impose a larger minimum. For instance, some version of Apple iOS have 11.25 ms minimum for BLE-HID (input devices), but 30 ms for other types of connections.<ref name="PunchThroughMaximizingBLEThroughput">Punch Through—[https://punchthrough.com/maximizing-ble-throughput-on-ios-and-android/ BLE Maximizing BLE Throughput on iOS and Android]. Dated 2016-04-03. Retrieved 2020-04-02</ref> The minimum connection interval could be larger if a device asks for a larger interval. Also if a host has many connected devices, it would choose a larger connection interval to be able to schedule time slots for all connections.
The maximum connection interval allowed by the BLE-HID specification is 50 ms.

The data transfer speed is rated at between 1 and 3 megabit/second, but that is only during a time-slot when actually transmitting.
Starting with BLE in Bluetooth 5, a packet could be sent either at double the speed (which saves battery) or at ½ or ⅛ the speed with more resilience against transmission errors.
(The lower speed modes are actually intended to increase the range without increasing signal strength)