ed for time-bounded services such as real-time voice and/or video. Table 3.9 shows the evolution of traffic shaping protocols developed by the work group under the task name 802.11 e. The traditional bandwidth-allocation mechanisms used in 802.11 b (distributed coordination function and point coordination function using a point coordinator) are supplemented with two new protocols specified by the 802.11 e work groups based on traffic prioritisation (802.11 d). The new functions are EDCA - extended data channel access also known as the wireless media extension. This establishes four prioritisation levels, background, best effort (equivalent to existing DCF capabilities), video and voice. Video and voice data streams are given dedicated transmission opportunities known as TXOP. HCCA - hybrid controlled channel access, replaces or rather supplements the existing point coordination functions with the point coordinator replaced by a hybrid coordinator. The hybrid coordinator establishes eight queues in the access point ingress and egress ports, which can then treat individual data/traffic streams in accordance with their traffic specification (TSPEC). 3.5.2 802.11 f Handover 802.11 has always worked on the principle of 'break before make' rather than 'make before break'. Simply put, if acknowledgement packets stop coming back, the device will channel scan and look for another beacon. The time taken to do this is typically about 70 milliseconds. Making Telecoms Work If you were walking from access point to access point within an office using WiFi for voice this would be annoying. A fast-roaming study group is looking at reducing these roaming delays to less than 50 milliseconds. The question then arises as to the degree of mobility being supported and whether the base station/access point or the user's device should take the handover decision. Seamless 'make before break' handover protocols (used in cellular voice networks) imply substantial amounts of measurement reporting and a rework of the beacon structure (see 802