Although the wireless technology nowadays provides satisfying bandwidth and higher speeds, it still lacks improvements with regard to handoff performance. Several studies have shown that the IEEE 802.11 scanning phase introduces most of the latency in pre-802.11i deployments. However, when IEEE 802.11i is used, link layer authentication based on the Extensible Authentication Protocol (EAP) can also introduce substantial delays.
There exist four main alternatives for reducing authentication delays during handoffs in IEEE 802.11 networks.
IEEE 802.1X pre-authentication
The IEEE 802.11i standard specifies how wireless stations can perform pre-authentication over the distribution system while still connected to their current access point. The idea is that if the station can perform authentication in advance, fewer exchanges will be needed during the handoff which reduces the handoff latency.
To initiate a pre-authentication, the station issues an IEEE 802.1X EAPOL-Start message destined to the target access point. This message is forwarded by the current access point to the target access point based on routing information embedded in the message. The target access point processes the EAPOl-Start message and initiates an IEEE 802.1X/EAP authentication. The result of a successful IEEE 802.1X/EAP pre-authentication is a security association shared between the station and the access point. When the station eventually decides to associate with the target access point the pre-established security association is used and the full EAP exchange is avoided.
Pairwise Master Key (PMK) caching
PMK caching is a basic handoff optimization technique that all IEEE 802.11i compliant wireless devices already support. Wireless stations and access points can store security credentials derived from a full EAP authentication. The stored security association can then be used later on if the wireless station comes back to the same location.
Opportunistic PMK pre-caching
The opportunistic PMK pre-caching technique works as follows: when a wireless station enters an access network, it uses IEEE 802.11i/EAP and establishes a fresh security association with the first access point it encounters. The controller of the local access network retrieves the security association from the first access point and forwards it to other access points in the access network. When the station moves to another access point, the pre-distributed security association is used to perform mutual authentication between the station and the access point without the need for using a full EAP exchange.
Fast BSS transitions : IEEE 802.11r
when an IEEE 802.11r compliant station enters an access network, it first performs authentication using EAP with the access network’s controller. The resulting keying materials are used by the station and the controller to derive a key called PMK-R0. PMK-R0 is then used to derive per-access-point keys. The name for such keys is PMK-R1. The controller finally sends the PMK-R1 keys to their corresponding access points. The controller that holds the PMK-R0 key is called ‘R0 Key Holder’ (R0KH), while the access points to which PMK-R1 keys are delivered are called ‘R1 Key Holders’(R1KH). After this initla key distribution phase, the wireless station is able to perform mutual authentication with any access point in the access network without the need for a full EAP exchange.
Be sure to check the latest information on wireless security and performance that will help you get more in depth in these topics.
By: Z. Saber
Posts Tagged ‘Wireless Technology’
The Functions of a WiFi Printer
March 29th, 2010
Wireless technology has quickly become an everyday part of modern business. The Internet has been at the forefront of this development, with networking available between numerous devices from just one hub. One such device to take advantage of this wireless freedom is the printer.
Wireless printers are much the same as their more regular cabled counterparts, although with one obvious exception. As the technology is still in its infancy, it does cost a little more than a conventional equivalent. Whilst the difference might only be fractional, this does mean that it is largely only adopted in laser and multifunction printers.
This probably doesn’t come as much surprise, particularly as inkjet printers tend to be more compact and cost less. In fact, they are more of a desktop printer for those looking to do shorter print runs. Anyway, laser printers and multifunction laser printers are the larger, high capacity devices you tend to find in offices of all size. They use a powdered ink, which is transferred quickly to the page after the image is magnetically plotted. It sounds complicated, but is a far speedier process than using liquid inks – like those found in inkjets.
The wireless functionality works in much the same way as a standard Internet modem router. It transmits a signal between the device (in this case the printer) and the sender (a computer or laptop) via a hub. So rather than connecting to the network through a conventional network cable, this is done with WiFi.
Of course the difference in performance is negligible. The task is the same, it’s just a slightly different way of transmitting the data. The one major advantage though is that you don’t have to have dozens of cables trailing across the office, connecting each individual terminal to the printer or network hub. Plus, if you are already working with WiFi Internet throughout your building, then this will slip in seamlessly and negate the need for any cabling.
A wireless laser printer, as previously alluded to, works in exactly the same way as the fully wired equivalent. More advanced models will include better features. This might include larger paper trays, duplex printing option (where the paper is printed on both sides) as well as improved printing speed, image quality and cost effectiveness. These printers rely on a powdered ink which is contained within a large toner cartridge – very different to the smaller ink cartridges for inkjets.
When it comes to a wireless multifunction laser printer, the options are far more diverse. Firstly, they all include additional features. These usually include a fax, copier and scanner functionality. Whilst even basic models tend to be of a reasonable specification, the more advanced you get, the better quality you can expect.
The scanner plays an integral part in the effectiveness and standard of copier prints and of course the scanned images themselves. Larger multifunction printers tend to resemble more traditional copiers, mostly due to the larger frame and the added paper capacity within. As a result of the various levels and standards of multifunction printers, the costs can be equally varied. You can spend as little as £100 and as much as £1,000 to get the perfect WiFi multifunction printer for your needs.
So to briefly surmise what you can expect to from a WiFi printer, they can:
Complete printing jobs wirelessly
Connect with your wider network
Multifunction devices can also be entirely controlled remotely
Basically they do everything that you would expect from a fully wired model, just without the hassle of having to run wires right throughout the building. Whilst they may not be in all offices just yet, the popularity of the WiFi technology and the need to remove the excess clutter that clogs up many modern offices could well see a much improved take up rate in future months and years. Wireless technology is developing all the time, as are printers. So to take advantage of both, you need to consider a WiFi printer.
By: Derek Rogers
