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Tom Nakase

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Basics of Asynchronous Connection-Less (ACL) Bluetooth Communication Protocol

Posted by Tom Nakase on 2016-12-07 04:44:32

Today, I will write about basics of Bluetooth Classic specification. We will find an answer to simple question from the specification that who or what decides Bluetooth (ACL) frame type. In this article, I will refer to original bluetooth specification document  like “Vol.2 Part.B …” from the Core Spec 4.2 unless noted otherwise.


ACL Frame Type

Bluetooth Classic defines ACL (Asynchronous Connection Less) for general data frame and SCO (Synchronous Connection Oriented) for synchronous audio frame. ACL has two frame types, DM (which provides Forward Error Correction:FEC) and DH (which doesn’t provide FEC). In addition to these, the number is appended to these frame types like “DM1” or “DH3” to indicate
how many 625 usec. “slot” will be occupied. In EDR (Enhanced Data Rate) introduced with Bluetooth 2.0, DH frame got double and triple the data rate mode denoted like “2-DH1” or “3-DH5”. All these ACL frame types defined in Vol.2 Part.B 6.5.4 are summarized in Table 1. 

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Tags: Bluetooth