Basic concepts of Android wlansubsystem Parsing

I write binder and WLAN related topics, which is easier for me. After all, this is what I do. The binder is probably the most complicated thing in Android. In this section, I will talk about some basic concepts first. To lay a foundation for the future. Start with the question.

WLAN includes the following basic concepts:

Wireless Network Protocol
WPA/wpa2
WLAN and WiFi

I personally think that before learning WLAN, you need to understand some basic wireless network protocols and the differences between different wireless protocols. It seems that HTC cares about this when recruiting WLAN driver engineers. He believes that this can examine a person's knowledge of basic knowledge. The concept of WPA and wpa2 must be mastered. Then there is the relationship between WLAN and WiFi. Many people think that WLAN and WiFi are the same concept. I think this is wrong. What are the differences between them? Later, I will come to the next article.

Wireless Network Protocol

The wireless network protocol generally includes the 802.11 series protocol, which includes the first (later mentioned, IEEE omitted), and 802.11a/B/E/g/h/I ..... and so on. I will focus on 802.11a/B/E/g/h/I.

802.11a
The High-Speed WLAN protocol uses the 5G Hz band. The maximum speed is 54 Mbps. The actual usage rate is about 22-26 Mbps. Strong anti-interference capability and fast transmission rate. Because of the high frequency, the transmission distance is greatly reduced. Being incompatible with 802.11b is the biggest drawback.

802.11b
Currently, the most popular WLAN protocol uses the 2.4g Hz band. The maximum speed is 11 Mbps. The actual usage rate is variable based on the distance and signal strength (1-2 Mbps within 150, 11 Mbps within 50 ). The low rate of 802.11b makes the cost of wireless data network affordable. In addition, the compatibility between 802.11b devices is guaranteed by the products of all manufacturers certified by a unified certification authority. Compatibility promotes competition and user acceptance. The disadvantage is that the trend cannot meet the needs of users.

802.11e
QoS Based on WLAN, through which 802.11a, B, and gcan be used for VoIP. That is to say, 802.11e is a protocol for implementing the voice call function through the wireless data network. This protocol will be a powerful weapon for wireless data networks to compete with traditional mobile communication networks.

802.11 GB
Because neither 802.11b nor 802.11a is satisfactory, IEEE has developed a new 802.11g standard. At present, the latest 802.11g technology has been put into application. Compared with 802.11a, the 802.11g provides the same 54 Mbps high speed and uses the same 2.4 GHz band as 802.11b, therefore, the compatibility problem after upgrade is solved. At the same time, 802.11g also inherits the advantage of wide coverage of 802.11b, and its price is relatively low. When you transition to G network, you only need to purchase the corresponding Wireless AP, and the original 802.11b wireless network card can continue to be used, the flexibility is much higher than 802.11a. The advantages of 802.11g can be summarized as follows: the speed of 802.11a is better than that of 802.11b, and it is also compatible with the latter. However, the problem is that 802.11g and 802.11b both use three channels, and the communication lines are too small, so the security is inferior to 802.11a.

802.11 H
802.11h is an extension of 802.11a to be compatible with other 5G Hz band standards, such as hyperlan2 used by the European Union.

802.11i
802.11i is a new wireless data network security protocol. The vulnerabilities in the popular WEP protocol will become a security risk for wireless data networks. 802.11i proposed a new TKIP protocol to solve this security problem.

Of course, there are other 802.11 series protocols, but here is just a simple description of common. However, there is a concept that has gained popularity. Some people will certainly ask what level these protocols are working on, or where they are in the OSI. In brief, the main standard categories of IEEE 802.11 are classified into the media layer (MAC) and the physical layer (PHY). The former is the media access control sub-layer in the data link layer of OSI, the latter directly corresponds to the OSI physical layer. The IEEE 802.11a/B/g, which we are familiar with, is distinguished by the differences in the PHY layer. Therefore, their differences are directly reflected in the operating frequency band, data transmission rate, and maximum transmission distance. The standard working on the media layer, IEEE 802.11e/f/I, is shared by the entire IEEE 802.11 family. Now we should be able to better understand it.

WPA/wpa2

WPA
WiFi protected access is a system that protects the security of wireless computer networks (Wi-Fi). WPA implements most of the IEEE802.11i standards, and is a transitional solution that replaces WEP before 802.11i is complete.
Wpa2
It is an IEEE802.11i standard certification that has been verified by the Wi-Fi Alliance.

WPA is a standard-based and interoperable WLAN Security Enhancement solution that greatly enhances the data protection and access control levels of existing and future wireless LAN systems. WPA is derived from the IEEE802.11i standard being developed and will maintain forward compatibility with it. If the deployment is appropriate, WPA ensures that the data of WLAN users is protected and only authorized network users can access the WLAN Network. As WEP has proved insecure, WPA was used to provide users with a temporary solution before the 802.11i protocol was improved. The standard data encryption uses the TKIP protocol (temporary Key Integrity Protocol). Two authentication modes are available, one is to use 802.1x protocol for authentication; one is pre-shared key PSK (pre-shared key) mode. Wpa2 encryption method CCMP. I have to talk about the two authentication modes of WPA/wpa2, which may be mentioned later. So I will mention it here first. Wpa2 has two styles: wpa2 Personal Edition and wpa2 Enterprise Edition. The wpa2 Personal Edition also refers to the pre-shared key (PSK) mode, which is designed for networks of families and small companies that cannot afford the cost and complexity of 802.1x verification servers, each user must enter a password to access the network. The password can contain 8 to 63 ASCII characters or 64 hexadecimal digits (256 bits ). Users can choose whether or not to store passwords on their computers to save the trouble of repeatedly typing. However, passwords must be stored in Wi-Fi access points. The Wi-Fi Alliance also announced the addition of EAP (Extensible Authentication Protocols) in WPA and wpa2 Enterprise Edition certification plans to ensure that products that have passed WPA Enterprise Edition certification can communicate with each other.

WLAN and WiFi

WLAN is the Wireless Local Area Network. Wireless LAN, which is an effective supplement to wired LAN. It usually works at 2.4 GHz and 5 GHz frequencies.
WiFi, wirelessfidelity. Wireless fidelity technology, like bluetooth technology, is a short-distance wireless technology used in offices and homes. This technology uses a 2-4 GHz band, which is currently not licensed as a wireless band. Currently, two standards are available: IEEE802.11a and IEEE802.11b. Wi-Fi is a technology used in WLAN implementation. Therefore, WLAN is not equal to wifi. The Wi-Fi Alliance is a non-commercial but strongly beneficial alliance. The reason for this alliance was that IEEE defined wireless communication protocol standards, but it did not guarantee compatibility between different wireless devices. The Wi-Fi Alliance is dedicated to managing compatibility.

WAPI is not wifi. Many people use WAPI as Wi-Fi. This is not the case. The WAPI standard is similar to 802.11b. It was launched by China for the international implementation of 802.11i. The country believes that 802.11i has obvious vulnerabilities and insecure factors. Therefore, we have developed our own WAPI and made it mandatory nationwide. And intends to promote international standards of conduct. In fact, this is related to national interests. First, China's key development strategy in the wireless communication field. If it is not your own standard, it will be subject to people. Second, the encryption method of wireless protocols seems to be State secrets. Therefore, WAPI implementation is of great significance. This is why mobile phones from mainland China have no wifi function in the past few years. Because WiFi that does not support WAPI is prohibited from entering the Chinese mainland.

Now, let's talk about the basic concepts first. The Wi-Fi system architecture in Android will be involved in the next section.