Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

The IEEE approved 802.11f on June 12, 2003. 802.11f is not a specification, per se. Instead, it's a "recommended practice" document, meaning that vendor compliance is completely voluntary. The document was drafted with the goal of improving the handover mechanism in Wi-Fi networks, so that end-users can maintain a connection while roaming between two different switched segments (radio channels), or between access points attached to two different networks. This is vital if Wi-Fi networks are to offer the same mobility that cell phone users take for granted.

To reach the stated goal, the 802.11f Task Group found a method that will provide access point (AP) interoperability within a multivendor WLAN network. Thus the 802.11f document defines the registration of access points within a network and the interchange of information between APs when a user is handed over from one access point to another.

The original 802.11 Working Group specifically left out the definition for this element in order to provide flexibility in working with different distribution systems (i.e. wired backbones that interconnect access points). However, this omission has caused unforeseen problems. For instance, users roaming between APs may experience a loss of some data packets, especially when moving between APs manufactured by different vendors because many times they don't easily interoperate to support roaming.

802.11f serves to reduce vendor lock-in and allow multi-vendor infrastructures, and still provide the necessary information that access points need to support 802.11 distribution system functions, such as roaming.

In the absence of 802.11f, when installing a WLAN, you should employ the same vendor for access points to ensure interoperability for roaming users (although a mix of access point vendors might work correctly, especially if the APs are Wi-Fi-certified).

It remains to be seen, however, whether manufacturers will adopt 802.11e features. "Why do you need it," scoffed one Cisco wireless LAN marketing executive at a recent industry trade show.