Original: http://m.eepw.com.cn/article/201808/386024.html

Consumer electronics time: 2018-08-09 source: network

Establishment process of bluetooth is a complex process, even quite some work and use the experience of people, if not carefully to understand still don't understand all,

Usually we use bluetooth headset to listen to music, and different devices to share files, make a phone call, etc., there is a companion - connections - the process of data transmission,

The bluetooth pairing process, is actually a process of certification,

Why not matching cannot establish a connection?

Any wireless communication technology have been monitored and the possibility of cracking, bluetooth SIG in order to guarantee the security of bluetooth communication, interaction, using data authentication way to ensure ease of use at the same time, in the form of pairs to complete the first communication between two bluetooth devices certification, after matching, then the communication connection don't have to do every time, so the authentication codes have started with matching are matched, equipment to PIN agreed the link between the key used to generate the initial authentication codes, for later established connection,

So don't match, and the relationship between two devices cannot establish certification can not connect to and after the operation, so the match to a certain extent to ensure the safety of bluetooth communication, of course, the security guarantee mechanism is relatively easy to be cracked, because now a lot of personal equipment no human-machine interface, so the PIN is fixed and mostly set for gm, such as 0000 or 1234, so it is easy to guess and, in turn, matching and connections,

Bluetooth connection process

Now the bluetooth chip suppliers to provide strong technical support ability, has the complete hardware and software solutions, for the application, provide the firmware for the underlying protocol stack, provides a profile libraries and source code specifications for a variety of applications, the developers just focus on application development, for the bluetooth underlying some of the things is often unclear, I also like this before, recently doing the application of an automatic search in order to realize the automatic connection, found that still need to know some of the underlying mechanisms,

We can easily operate in a connection is established between mobile phones and hands-free devices, so how the connection is established?

First of all, the main equipment (master, that is, a connection device) pages (page) from a device (slave, receiving connection device), the master would have fh way paging slave, a slave to the fixed interval to scan (scan) external paging, namely page scan, when the scan to external page will response the response of the page, it will establish a link connection between two devices, namely the ACL link connection, when the ACL link after the connection is established, the main equipment will initiate the channel connection request, namely the L2CAP connections, establishment of L2CAP connection, main equipment use SDP to queries from a hands-free equipment service, get rfcomm channel number, and then the master will launch rfcomm connections of rfcomm connections, and then established the application connection,