Introduction 
One of the two basic operating modes used by
802.11 networks. When activated, wireless devices communicate directly with one another allowing networks to be created when out in the field. As no
access points are required for these setups, users do not need access to any external resources.
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Creating an Ad-Hoc Network
When a device 'connects' to an Ad-Hoc network it, in effect, creates the network. Any other devices connecting to an ad-hoc network with the same
SSID will then be able to communicate with each other. Note that as no
DHCP server is present on these networks, you may have to manually specify
TCP/IP settings for some tasks.
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OS X 10.4 
Figure 1 - Creating a new ad-hoc network in OS X 10.4.7
To create an ad-hoc network in OS X 10.4, select
Create Network from the Airport menu. In the resulting window (
fig. 1) enter a name (
SSID) and
channel then click the OK button. Once complete the computer will be connected to the new network.
Other computers or devices can then connect to this network and will be able to communicate with your Macintosh.
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Windows XP SP2 
Figure 2 - Creating a new ad-hoc network in Windows XP SP2
To create an ad-hoc network in Windows XP, right-click on the tray icon for the wireless network adapter and select
View Available Wireless Networks. In the resulting window, select
Changed advanced settings in the left hand column. Next, select the
Wireless Networks tab and click the
Add... button.
In the
wireless network properties dialog (
fig 2) enter an
SSID and check the
this is a computer-to-computer (ad hoc) network; wireless access points are not used checkbox. Click the OK button and the network will be created.
Note that if an
infrastructure network on your preferred list is in range, Windows will connect to it rather than the ad-hoc network. To work around this, you must click on the
advanced button in the
wireless network connection properties dialog and select
computer-to-computer (ad hoc) networks only. This will force Windows to connect to the ad-hoc network. Note that this setting must be reversed to use those networks again.
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Limitations
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802.11g Adapters
The
802.11g standard does not require devices to operate at speeds beyond those provided by the
802.11b standard. As such, when used in ad-hoc mode most
WiFi devices will revert to the slower 11mbps data rate. This results in a 4x reduction in throughput, so this can be a significant hiderance when used for high-bandwidth tasks.
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See Also - WiFi - A set of wireless networking standards providing electronic devices with high-speed communication.
- Infrastructure - A WiFi networking mode that uses centralized access points to coordinate the network.
Linear Mode
