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Making the Switch

Now that the LAN access point has told the device everything that it needs to know about timing, the LAN access point's Link Manager can send an LMP_switch_req. The Link Manager on the connecting device accepts the request, and the two devices swap time slots. The LAN access point takes over the even (master) slots, and the connecting device gets the odd (slave) slots.

Next the LAN access point sends an FHS packet. The header of the packet must have an active member address (AM_ADDR) identifying the device that should receive the packet. Now we're in an odd situation here: The LAN access point is starting the transmission as if it were the master, but the connecting device hasn't been allocated an active member address yet—how can it know what address to look for? The answer is quite simple: Just for this one packet, the LAN access point lends the connecting device its own AM_ADDR and uses that in the packet header. The connecting device knows to expect this, so it knows which AM_ADDR to look for in the packet header.

The loan of the LAN access point's AM_ADDR is just for this one packet. Inside the FHS packet is a parameter that allows the LAN access point to allocate a new AM_ADDR for the connecting device. From now on, that's the AM_ADDR that the connecting device will use.

The connecting device gets one more piece of information from the FHS packet: the value that the LAN access point's clock had at the moment it sent the FHS packet. Remember that the connecting device needs this clock value to work out where in its frequency-hopping sequence the LAN access point will be when it is a master. It already has the detailed subslot timing from the slot offset message, so by combining that with the clock value in the FHS packet, it now has everything that it needs to know about timing.

The connecting device just needs to acknowledge the FHS packet by returning an ID packet, and both devices can go ahead to the final stage of the switch: jumping onto the timing and hopping sequence of a piconet where the LAN access point is master.

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