"Turn" Bluetooth Protocol Analysis (1) _ Basic Concepts

Original URL: http://www.wowotech.net/bluetooth/bt_overview.html

1. Preface

Since 1994 by Ericsson launched, Bluetooth technology has gone through 20 years. From the initial Bluetooth V1.0, to the Bluetooth V4.0 (the latest release for the end of v4.1,2013), has undergone nearly 9 revisions, evolving into the current situation.

To tell the truth, today's Bluetooth 4.1, is a hodgepodge: Br/edr follow the old Bluetooth specification, le plagiarism 802.15.4;amp directly use 802.11. And all of this is based on compatibility and ease of use, a dilemma between power consumption and transmission rate. This is not an elegant design, the snail thinks.

But it doesn't matter, the existence is reasonable. So the snail has opened such a topic, hope to be able to put the knowledge of Bluetooth technology up and down, in order to deepen their understanding of Bluetooth technology at the same time, to engage in Bluetooth-related work of the reader a little inspiration.

This article is the first article of this topic, mainly based on the Bluetooth 4.1 specification (core_v4.1.pdf), describes the basic concepts of Bluetooth technology.

2. Overview of Bluetooth Technology 2.1 Two types of Bluetooth technology: Basic rate (BR) and low energy (LE)

The Bluetooth protocol consists of two technologies: Basic rate (BR) and low energy (LE). Both of these technologies include search (discovery) management, connectivity (connection) management mechanisms, but they are not interoperable ! This is also one of the reasons why the snail is complaining about the elegance of the Bluetooth protocol.

A vendor can either implement one of these two technologies, and it is only interoperable with devices that realize the same technology, but not with devices that implement another technology. If manufacturers want to make sure that they can communicate with all Bluetooth devices, then only two technologies can be implemented at the same time, regardless of whether the need is really needed, so that you can meet someone to say what the words!

2.1.1 Basic rate (BR)

Basic rate is an authentic Bluetooth technology that can include optional (optional) EDR (Enhanced Data rate) technology, as well as alternately used (Alternate) mac (Media Access Control layer and PHY layer extensions (for short, AMP). It's a mouthful, but through the application scenario behind it, it's good to understand:

Bluetooth at the beginning of the birth, using the BR technology, at this time the theoretical transmission rate of Bluetooth, can only reach 721.2Kbps. In that era, 56Kbps of the modem is tall, this speed can be said to be a surprise for heaven Ah! But technology has changed so fast that BR technology is out of date. What about that? Mend, increase the speed, enhanced Data rate appeared.

Using EDR technology Bluetooth, the theoretical rate can reach 2.1Mbps. This time the upgrade, is still elegant, because there is no change in the hardware architecture, software architecture and use of changes in the way.

Perhaps you guessed, EDR again outdated, see people WiFi (WLAN), dozens of Mbps, hundreds Mbps, we are 2.1Mbps, too shabby! What about that? Bluetooth organization thought of a bad idea: Hey, wifi!. Lend me your physical layer and MAC layer! This is the amp (Alternate MAC and PHY layer extension). Emma, finally relieved, we can reach 24Mbps.

However, due to the difference between the physical layer and AMP technology of Bluetooth itself is too obvious, this extension can only be used interchangeably (Alternate), that is, I (BR/EDR) Without You (AMP). Well! Not elegant!

Buried a problem: can only be used interchangeably, then how do they switch? The snail will discuss the problem in the following content, according to the solution of the mainstream Bluetooth chip.

Note 1: Attentive readers may notice that the two words of optional and alternate are highlighted here, which is the exact word of Bluetooth spec. It means that BR and EDR can exist simultaneously, but Br/edr and amp can only be selected in two. 】

2.1.2 Low Energy (LE)

The evolution of the BR technology described above is the acceleration, acceleration and acceleration of the transmission rate. But the energy is conserved, and you want to pass it faster, at the cost of more energy. There are many applications that do not care about the transmission rate, but rather are concerned about power consumption. This is the background that Bluetooth LE (known as Bluetooth low power) produces.

Le technology compared to BR technology, the difference is very large, or two different technologies, coincidentally added a "bluetooth" prefix. We will explain in detail the differences and the behavior characteristics of Le in the following.

2.2 Components of the Bluetooth system

The composition of Bluetooth system, related to Bluetooth application, Bluetooth Core, Bluetooth Host, Bluetooth controller and other words, do not know is because of the ambiguity of English understanding, Or because of the definition of the Bluetooth specification itself ambiguity, the scroll to understand these words feel a bit awkward. In this section, therefore, the relevant concepts and the meanings behind them are explained.

Describes the composition of the Bluetooth system, we need to pay attention to the following features:

1) The components of the Bluetooth system described in the figure, such as Bluetooth core and Bluetooth application, such as host and Controller, refer to the logical entity ". The so-called "logical entities" need to be separated from the "physical entity" areas of everyday life. As in the circuit design, a Bluetooth chip, a master CPU, refers to the physical entity. These "logical entities" described in the Bluetooth protocol do not necessarily correspond to physical entity one by one, as in real-world applications, host and Bluetooth application may be in the same physical entity (Master CPU). The controller is located in another physical entity (the Bluetooth chip) alone.

2) The Bluetooth protocol specifies two levels of protocol, namely Bluetooth core protocol (bluetooth® cores) and Bluetooth Application layer protocol (Bluetooth application). Bluetooth core protocol focuses on the description and specification of Bluetooth core technology, it only provides the basic mechanism, does not care how to use these mechanisms; Bluetooth application layer protocol is based on the Bluetooth core protocol, according to the specific application needs, blossom, define a variety of strategies, such as FTP, file transfer, LAN and so on.

3) Bluetooth core consists of two parts, host and controller. These two parts in different Bluetooth technology (BR/EDR, AMP, LE), assume a slightly different role, but the general function is the same. The controller is responsible for defining the specifications of the RF, baseband, and other hardware, and abstracting the logical link used for communication (Logical link), and the host is responsible for a more friendly encapsulation on the basis of the logical link, so that the details of the Bluetooth technology can be masked. make Bluetooth application more convenient to use.

4) in one system, the host has only one, but the controller can be one, or there can be multiple. such as: a separate Le controller; a separate br/edr controller; a separate le+br/edr controller; On the basis of a separate BR/EDR controller or LE+BR/EDR controller, Add one or more additional amp controllers.

"Note 2: For a detailed description of Bluetooth core, the scroll will be described in the next article, this article will not be introduced in depth. The

3. Br/edr vs LE vs AMP

Let's take a closer look at the Br/edr, AMP, and ble three technologies from the image below (click here to see the enlarged originals):

The picture is a overview of Bluetooth core, from the RF physical Channel, to baseband's physical link, Logical link, LMP, l2cap and other concepts, have some rough introduction. As can be seen from the picture, Br/edr, AMP, ble and other technologies have the following features:

1) Br/edr technology, which focuses too much on "point-to-point" communication, even though the concept of multicast (unidirectional) and broadcast (broadcast) is mentioned at the bottom of the protocol (e.g. logical Link), but in the upper-level scenario, There are almost no (and cannot exist) corresponding applications.

2) But with the development of the Internet of things, the industry's need for simple, non-connected multicast or broadcast communications is becoming more and more urgent, so BLE technology has been modified in the RF and baseband protocols to accommodate the need to modify the existing 79 channel frequency hopping method, Reduced the number of channel numbers to 40 and retained a fixed channel of not less than 3 for broadcast communications. To jump only on the remaining 37 data channel.

3) As a result of this change, the original search/connect/pairing concept, on the BLE no longer exist, replaced by Advertisor, Initialor and other concepts. But at the next level of data communication, try to keep it consistent.

4) for AMP, it is the BR/EDR controller, after the usual point-to-point connection, two Bluetooth devices negotiate whether the subsequent data traffic needs to be transferred to the AMP controller. This is the AMP technology introduced by Bluetooth 3.0.

We temporarily in this article on the Bluetooth technology to do a perceptual knowledge, in the subsequent article, will be based on the various levels of agreement, step by step, to promote, to be able to put Bluetooth technology analysis thoroughly.

Original articles, forwarded please indicate the source. Snail Nest technology, www.wowotech.net.

"Turn" Bluetooth Protocol Analysis (1) _ Basic Concepts