Dual Mode Myth # 4
Macro-Handoff is WiFi to GSM (or CDMA) handoff, while micro-handoff is all about WiFi access point to WiFi access point.
Myth # 4 – Micro-handoff can only be done in the network.
A WiFi device goes through a process of broadcast scanning to discover, then associating and authenticating with an appropriate access point that classically consumes as much as 350 milliseconds to accomplish. Generally, as a user moves from the effective range of one access point into the field of another, a ‘micro-handoff’ process must occur. Unlike the process used in cellular networks, the IEEE 802.11 protocol family that is responsible for WiFi standardization is silent in defining this process. The closest mechanism is 802.11r, which deals only with authentication handoffs.
Some believe that the wireless switch or WiFi access point controller, is the place for managing the micro-handoff, namely the transfer of an endpoint from one access point to another. With this expensive device handoffs in the range of 100 milliseconds are possible, however experience may be longer under typical load conditions.
This myth is false. Not only can the micro-handoff process be accomplished in the client, but it should be accomplished in the client. That’s because the client software is the most scalable solution. It can work equally well with one device and two access points as it can with a million devices and a million access points. The client does not require any degree of network uniformity of vendor or operations engineering. The client can more rapidly detect the least disruptive moment to execute the handoff.
For example, SIPquest has developed a patent-pending algorithm to allow the client to make the handoff in under 10 milliseconds. This amazing engineering feat is possible because people are territorial and smart network engineers will be clever if given the chance. A cache, selective channel scans and then finally standard-scans are the fastest, nearly-as-fast and never-as-fast steps in the algorithm.
The client is the best place for managing this kind of transition because it can also use this technology to improve battery life and audio quality.
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