Tethering is the act of sharing a data connection in a mobile phone with other computers. The sharing is typically done over WiFi or USB. This is done to provide Internet access to the other computers.
Tethering refers to connecting one device to another. In the context of mobile phones or Internet tablets, tethering allows sharing the Internet connection of the phone or tablet with other devices such as laptops. Connection of the phone or tablet with other devices can be done over wireless LAN (Wi-Fi), over Bluetooth or by physical connection using a cable for example, through USB.
If tethering is done over Wi-Fi, the feature may be branded as a Mobile Hotspot. The Internet-connected mobile device can thus act as a portable wireless access point and router for devices connected to it.
Many mobile phones are equipped with software to offer tethered Internet access. Windows Mobile 6.5, Windows Phone 7, Android (starting from version 2.2), and iOS 3.0 (or later) offer tethering over a Bluetooth PAN or a USB connection. Tethering over Wi-Fi, also known as Personal Hotspot, is available on iOS starting with iOS 4.2.5 (or later) on iPhone 4, 4S, 5, iPad (3rd generation), certain Windows Mobile 6.5 devices like the HTC HD2, Windows Phone 7 devices (varies by manufacturer and model), and certain Android phones (varies widely depending on carrier, manufacturer, and software version).
For IPv4 networks, the tethering normally works via NAT on the handset's existing data connection, so from the network point-of-view, there is just one device with a single IPv4 network address, though it is technically possible to attempt to identify multiple machines. On some networks, this feature is only contractually available by paying to add a tethering package to a data plan or choosing a data plan that includes tethering. This is done primarily because with a computer sharing the network connection, there may well be a substantial increase in the customer's mobile data use, for which the network may not have budgeted in their network design and pricing structures.
Some network-provided handsets have carrier-specific software that may deny the inbuilt tethering ability normally available on the handset, or only enable it if the subscriber pays an additional fee. Some operators have asked Google or any mobile producer using Android to completely remove tethering support from the operating system on certain handsets. Handsets purchased SIM-free, without a network provider subsidy are often unhindered with regards to tethering.
There are, however, several ways to enable tethering on affected devices without paying for it, including rooting Android devices or jailbreaking iOS devices and installing a tethering application on the device. Tethering is also available as a downloadable third-party application on most Symbian mobile phones as well as on the MeeGo platform and on WebOS mobiles phones.
