Android WiFi Communication--Introduction to WiFi and WiFi Direct

About WiFi

Wi-Fi can be divided into five dynasties: first generation 802.11, developed in 1997, operates only in 2.4GHz, the fastest 2mbit/s

• Second generation 802.11b, only run at 2.4GHz, the fastest 11mbit/s, is gradually eliminated

• Third generation 802.11g/a, running at 2.4GHz and 5GHz respectively, the fastest 54mbit/s

• Fourth generation 802.11n, operating at 2.4GHz or 5ghz,20 and 40MHz bandwidth up to 72 and 150mbit/s

• Fifth generation 802.11ac, only running at 5GHz

because the 2.4GHz bands in the ISM band are widely used, such as microwaves, Bluetooth, which interfere with WiFi, slow down, and have less 5GHz interference. Dual-band routers can operate at both 2.4GHz and 5GHz, while devices can use only one band.

WiFi Network connection function:

Establish an access point to build a wireless mesh network;

Set up a small wireless router, a total of peripheral devices connected to the Internet: to provide public access to the hotspot or create their own Wi-Fi hotspots;

Use Ad-hoc mode to connect a Wi-Fi device to a client to a client without a router.

Operating principle:

Wi-Fi settings require at least one access point (AP) and one or more client (HI). APS per 100ms willSsid(Service Set Identifier) broadcast through Beacons (signal station) packet once, beacons packet transfer rate is 1 Mbit/s, and the length is quite short, so this broadcast action has little effect on network performance. Because Wi-Fi provides a minimum transfer rate of 1 Mbit/s, make sure that all Wi-Fi client terminals receive thisSsidbroadcast packets, the client can decide whether toSsidAP Connection. The user can set which one to connect toSsid. Wi-Fi systems always open their connection standards to clients and support roaming, which is the benefit of Wi-Fi. But it also means that one wireless adapter might outperform the other adapters in performance.

wi-fi Direct : Formerly known as Wi-Fi point-to-point (Wi-Fi peer-to-peer), is a software protocol that allows WiFi devices to connect directly to another WiFi device without having to use the wireless network Base station (access point) for high-speed data transfer. In short, WiFi Direct is based on the Wi-Fi technology, so that WiFi devices can connect to point-to-point (peer) wirelessly without routers or hotspots. this Agreement show, support and certification, certified products will be able to obtain Wi-Fi certified Wi-Fi Direct logo.

Wi-Fi Direct architecture in the original802.11a,802.11g,802.11nabove, does not support802.11b. than the existingAd-hocmode is faster and supports the WPA2 encryption mechanism. The maximum transmission distance is 300 meters, the maximum transmission speed is 250Mbps, using the 2.4GHz and 5GHz bands. It supports one-to-one and one-to-many modes.

Advantages of WiFi Direct:

Mobility and portability: Wi-Fi Direct devices can connect to each other anytime, anywhere. Because a Wi-Fi router or access point is not required, Wi-Fi devices can be connected anywhere.

Instant Availability: Users will be able to establish a direct connection using the first Wi-Fi direct authentication device that brings home. For example, a newly purchased Wi-Fi direct notebook can create a direct connection to a traditional Wi-Fi device that the user already has.

Ease of Use : Wi-Fi Direct device Discovery (device Discovery) and service Discovery (Discovery) feature help users determine which devices and services are available and then establish a connection.

Simple and secure connection : The Wi-Fi direct device uses Wi-Fi Protected Setup to obtain the certificate and verifies that the wifi direct is being searched.

Device Discovery:

Using scanning technology to discover and identify other Wi-Fi direct devices, users can choose which devices have been found to connect, and if the target has not yet joined the team, a new team will be formed, and if the target has joined the team, the Wi-fi direct device being searched will attempt to join the existing group.

Service discovery:

Optional feature that enables you to communicate to other WiFi direct devices the services supported by your high-level apps, and you can implement service discovery capabilities (including before creating a connection) to other discovered Wi-Fi direct devices at any time. The vendor decides whether to implement the service discovery function.

To create a group:

A group can be created by a Wi-Fi direct device, a group can be created automatically between two devices, the device will be negotiated to determine which device is responsible for the management team, and the equipment responsible for the management team will determine whether the team is a temporary (single instance) or a permanent (repeated) group.

Energy Management:

Wife Direct employs the p2p-ps and p2p-vmmpowersave mechanisms, and the peer specification introduces two energy-saving mechanisms for energy saving (opportunistic Power Save) and Absence notifications (Notice of absence).

WiFi Direct V.s Bluetooth

Both are unlimited network connectivity standards, Bluetooth is mainly used for unlimited personal area network (WPAN), the most suitable for the connection between personal devices; WiFi is mainly used to provide wireless area network (WLAN), also used to connect between devices, WiFi Direct enters bluetooth existing domain But Wifidirect uses WiFi technology, transmission distance and speed better than Bluetooth, Bluetooth advantage is low power consumption.

This article is from "Whispering Autumn Wind" blog, please be sure to keep this source http://xjhznick.blog.51cto.com/3608584/1555042

Android WiFi Communication--Introduction to WiFi and WiFi Direct