* Many factors contribute to Vo-Fi quality
Keeping straight all the factors that play a role in voice-over-Wi-Fi QoS is getting tough. First, there’s the notoriously long-in-coming IEEE 802.11e standard for packet prioritization and scheduled access, or call admission control. The prioritization component has been stable for about a year; the full suite of 802.11e is expected to be approved next month and published as a standard by the IEEE in October.
But once 802.11e is here in its entirety and is implemented in purchasable products, it probably still won’t be enough to ensure the quality and reliability of Vo-Fi calls in a large enterprise environment, depending on how large your installation is and on your Wi-Fi system vendor’s architecture.
For one thing, 802.11e will likely rely on a few other 802.11 extensions to perform at its best. These other extensions relate to speeding up roaming times among wireless basic service sets (BSS) so that sessions aren’t interrupted, packets aren’t dropped, and quality doesn’t degrade:
* 802.11r – This is the fast-roaming protocol in development to speed session handoff times as a client device moves from one access point (AP) to another while keeping the user’s authentication credentials and real-time session intact. The current working goal is to keep this handoff time under 50 milliseconds. Standard status: Expected to be stable by September 2006 and ratified in April 2007.
* 802.11k – 802.11r actually relies on this, the Radio Resource Management protocol, currently in development to hasten a client’s roaming decisions by pre-discovering all neighboring APs, the distances to them and their available call capacity. Standard status: Expected to be stable by June 2006 and ratified in January 2007.
* 802.11i – The pre-authentication component of the security standard reduces roaming time by enabling the client to authenticate with neighboring APs before roaming. Standard status: Complete.
Next time: Beyond standards.
