wireless ad hoc networking

MultiChannel MAC Protocols for Mobile Ad Hoc Networks 315
Low preference (LOW): This channel is already taken by at least
one of the host’s immediate neighbors.
Here we briefly illustrate the operations of hosts while negotiating the data
transmitted channel during ATIM windows. If a source node (say A) wants
to send a data package to a destination (say B), it will notify B by sending an
ATIM packet including its PCL. Upon receiving the ATIM packet, B selects
one channel based on its own and on A’s PCLs. After that, B will reply an
ATIM-ACK packet embedding the selected channel. The selection rules will
be described later. On receiving the ATIM-ACK, A will comprehend which
channel it should switch to at the end of ATIM window to compete for the
medium to communicate with B and then it will broadcast an ATIM-RES
packet to notify its neighboring nodes.
In this paragraph, we illustrate the state transitions of channels in PCL
and the channel selection rules of MMAC. When the node is powered up,
all the channels in the PCL are reset to MID state at the start of each beacon
interval. A channel will be changed to HIGH state in the PCLs of both the
source and the destination after they have finished their negotiation and
agree upon that one for data transmission. If a node obtains the selected
channel by overhearing ATIM-ACK or ATIM-RES packets, the state transition
of this channel can have three possibilities: First, the channel which was
previously in HIGH state stays in the high state, second, the channel which
was previously in the MID state changes to LOW and the associated counter
is set to 1, Last and third, the channel which was already in the LOW state,
would have its associated counter incremented by 1.
If there is a HIGH state channel in the receiver’s PCL, this channel
is selected.
Or else, if there is a HIGH state channel in the sender’s PCL, this
channel is selected.
Or else, if there is a channel which is in the MID state at both the
sender and the receiver nodes, it is selected. If there are more than
one, one of them is randomly selected.
Or else, if there is a channel which is in the MID state at only
one end, it is selected. If there are more than one, one of them is
randomly selected.
If all of the channels are in the LOW state, sum up the sender’s
and the receiver’s associated counters and select the one with the
least load.
Figure 11.8 is a simple example of MMAC, assuming that nodes B and C
have data packages to send to A and D separately. During ATIM window,
all nodes should negotiate in a common channel (e.g., channel 1 in this
example). At first, B sends an ATIM packet including its own PCL in which