自组网（Adhoc）和基础网（Infra）

自组网（Adhoc）和基础网（Infra）， 要说明无线网络的拓扑形式，首先要了解两个基本概念： 1：STA站点，每一个连接到无线网络中的终端（如笔记本电脑、PDA 及其它可以联网的用户设备）都可称为一个站点。2： AP，也就是无线接入点，是一个无线网络的创建者，是网络的中心节点。一般家庭或办公室使用的无线路由器就一个 AP。

 

基于自组网的无线网络（Adhoc：也称Peer toPeer），是仅由两个及以上 STA 自己组成，网络中不存在 AP，这种类型的网络是一种松散的结构，网络中所有的 STA 都可以直接通信。

AP 组建的基础无线网络（Infra）：Infra：也称为基础网，是由 AP 创建，众多 STA 加入所组成的无线网络，这种类型的网 络的特点是 AP 是整个网络的中心，网络中所有的通信都通过 AP 来转发完成.

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HTGExplains: What’s the Difference Between Ad-Hoc and Infrastructure Mode?

Not all Wi-Fi networks are created equal. Wi-Fi accesspoints can function in either “ad-hoc” or “infrastructure” mode, and manyWI-Fi-enabled devices can only connect to infrastructure-mode networks, notad-hoc ones.

Wi-Fi networks in infrastructure mode are generallycreated by Wi-Fi routers, while ad-hoc networks are usually short-livednetworks created by a laptop or other device. But it isn’t always so simple.

Infrastructureand Ad-Hoc Modes Explained

Most Wi-Fi networks function in infrastructure mode.Devices on the network all communicate through a single access point, which isgenerally the wireless router. For example, let’s say you have two laptopssitting next to each other, each connected to the same wireless network. Evenwhen sitting right next to each other, they’re not communicating directly.Instead, they’re communicating indirectly through the wireless access point.They send packets to the access point — probably a wireless router — and itsends the packets back to the other laptop. Infrastructure mode requires acentral access point that all devices connect to.

Ad-hoc mode is also known as “peer-to-peer” mode. Ad-hocnetworks don’t require a centralized access point. Instead, devices on thewireless network connect directly to each other. If you set up the two laptopsin ad-hoc wireless mode, they’d connect directly to each other without the needfor a centralized access point.

Advantagesand Disadvantages

Ad-hoc mode can be easier to set up if you just want toconnect two devices to each other without requiring a centralized access point.For example, let’s say you have two laptops and you’re sitting in a hotel roomwithout Wi-Fi. You can connect them directly with ad-hoc mode to form atemporary Wi-Fi network without needing a router. The new Wi-Fi Direct standard also builds on ad-hoc mode, allowing devices tocommunicate directly over Wi-Fi signals.

Infrastructure mode is ideal if you’re setting up a morepermanent network. Wireless routers that function as access points generallyhave higher-power wireless radios and antennas so they can cover a wider area.If you’re using a laptop to set up a wireless network, you’ll be limited by thepower of the laptop’s wireless radio, which won’t be as strong as a router’s.

Ad-hoc mode also has other disadvantages. It requiresmore system resources as the physical network layout will change as devicesmove around, while an access point in infrastructure mode generally remainsstationary. If many devices are connected to the ad-hoc network, there will bemore wireless interference — each computer has to establish a direct connectionto each other computer rather than going through a single access point. If adevice is out of range of another device it wants to connect to, it will passthe data through other devices on the way. Passing the data through severalcomputers is just slower than passing it through a single access point. Ad-hocnetworks don’t scale well.

 

Whento Use Each

Deciding when to use each type of network is actuallypretty simple. If you’re setting up a wireless router to function as an accesspoint, you’ll want to leave it in infrastructure mode. If you’re setting up atemporary wireless network between a handful of devices, ad-hoc mode isprobably fine.

There’s one other big catch here. Many devices don’tsupport ad-hoc mode because of its limitations. Android devices, wireless printers, Google’s Chromecast,and a wide variety of other Wi-Fi-enabled devices don’t want to deal with theproblems of ad-hoc networks and will refuse to connect to them, only connectingto networks in infrastructure mode. There’s not much you can do about this; youjust have to use a network in infrastructure mode rather than ad-hoc mode.

CreatingInfrastructure Mode Access Points on Your Laptop

You can easily create a local area Wi-Fi network on yourlaptop, whether you’re using Windows, Mac OS X, or Linux. Unfortunately, mostoperating systems will create an ad-hoc network by default. For example, youcan create an ad-hoc network fromthe Control Panel in Windows orcreate an ad-hoc network onyour Ubuntu Linux machine. This is fine if you want to connect twolaptops, but it’s very inconvenient if you need to connect a device that onlysupports networks in infrastructure mode.

If you’re using Windows 7 or 8, you can turn your Windows laptop intoan infrastructure-mode wireless access point using a few Command Prompt commands. Connectify makes this easier byproviding a nice graphical user interface, but it’s actually justusing the hidden feature built into Windows 7 and above.

If you need to create an infrastructure-mode access pointon Linux, look into the AP-Hotspottool. On aMac, enabling the Internet Sharing feature will create a network in infrastructuremode, not ad-hoc mode.