Classic Bluetooth connection process

Classic Bluetooth connection process

Want to know the connection process of Bluetooth , You have to understand 3 A concept ：
1, link Link： Physical link , It is a concept in baseband Protocol , Include ACL Links and SCO There are two kinds of links , The former is mainly used to transmit data , The latter transmits voice . A pair of Bluetooth devices , There is only one ACL link , Allow to exist 3 strip SCO link

2, channel channel: This is a L2DAP Concepts in the agreement , It's a logical channel , The endpoint of the channel is marked with a channel identifier CID Express , In two bytes , So at most 65536 Channels . That's one ACL Links can exist up to 65536 Channels . Channels include signaling channels and data channels , Establish data channel through signaling channel , Then the data is transmitted by the data channel . Signaling channel CID by 0x0001

3, Connect connection： Apply the concept of Profile , With this profile connection, Only in this way can the service and application of this profile be carried out .

among link establishment Partly from LMP Realization ,channel establishment Partly from L2CAP Realization ,connection establishment By the specific application profile （profile） To implement the .

We use the connection between mobile phones and Bluetooth headsets commonly used in life to analyze the connection process of Bluetooth in detail ：

First , Main equipment （master, That is, the device that initiates the connection , Here's the cell phone ） Can page （page） Slave device （slave, Receive connected devices , This refers to Bluetooth headset ）,master Will have hopped the way to page slave,slave Will scan at regular intervals （scan） External paging , namely page scan, When scan To the outside page Will respond response The page, In this way, a link The connection of , namely ACL Link connection . When ACL After the link connection is established , The master device will initiate channel Connection request for , namely L2CAP The connection of , establish L2CAP After connecting , The main equipment adopts SDP Go to inquire about the hands-free service of the slave device , Get from it rfcomm Your channel number , Then the master device will initiate rfcomm Connection request establishment rfcomm The connection of . Then the connection of the application is established .

namely link establish->channel establish->rfcomm establish->connection

from : http://blog.sina.com.cn/s/blog_4b475f4b0101iwua.html