Information Technology Reference
In-Depth Information
Figure 3. H-MAC slot structure
Let H be a pseudo-random hash function. S
max
:
number of slots, V
2
: two-hop neighbors, α: a node
and List
α
is a list of slots.
After the initialization phase, all nodes switch
to the control channel CC at slot start, and they
must be ready to run the transmission control. In
H-MAC, a node can be in one of two modes: low
contention level (LCL) or high contention level
(HCL). A node is in HCL only when it receives
an explicit contention notification (ECN) mes-
sage from a two-hop neighbor within the last
frame t
ECN
. Otherwise, the node is in LCL. A slot
is divided into:
SBSA algorithm (α, List
α
);
{ List
α
= Ø; j=0;
repeat
{ i=1; found = false;
repeat
{
for
(k
∈
V
2
∪
{α}) H
k
= H(k
⊕
S
i
⊕
C
j
)
⊕
k;
if
(
∀
k
∈
V
2
, H
α
> H
k
)
then
found = true; List
α
= List
α
∪
S
ij
; break;
else
i++;
}
while
(i< S
max
);
if
(found == false)
then
i = arg max H
α
; List
α
=
List
α
∪
S
ij
;
j++;
}
while
(j< C
max
);
}
Broadcast List
α
to 2-hop neighbors.
•
Control period
: to negotiate the slot
i
on
different channels using RTS/CTS with
priority (QoS), and the first which succeed
its CTS
jn
(j: channel j, n: destination node)
wins slot S
ij
.
•
Transmission period
: the winners and their
destination nodes switch to the appropriate
channel to exchange unicast packets (Figure
3
)
.
a. The LCL mode
In LCL, any node can compete to transmit in any
slot. The control phase is divided into 3 periods
in this mode:
THE COMMUNICATION PHASE
•
High priority T
HP
: it is reserved to owners or
to high priority packets (real time traffic).
•
Medium priority T
MP
: it is reserved to one-
hop neighbors or to medium priority packets
(audio, video).
In H-MAC, a slot 0 of each local frame is re-
served to broadcast packet transmission (access
by CSMA). The channel negotiation is done in a
dedicated
Control Channel
(CC); this channel can
be used for transmission after the control period.
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