Information Technology Reference
In-Depth Information
The Network Model
that support the QoS requirements (IEEE Std
802.11e, 2004).
H-MAC operates in two phases: initializa-
tion phase and communication phase. In the
initialization phase, the following operations
run in sequence: neighbor discovery, channel
assignment, slot assignment, and finally global
time synchronization. These operations run only
once during the setup phase and does not run again
until a significant change in the network topol-
ogy (such as HELLO joining, or QUIT message)
occurs. In the communication phase, each node
performs channel negotiation and runs the LCL
or HCL mode according to the contention level.
In our protocol, we assume that each node is
assigned a unique identifier. The network inter-
face is equipped with a single half duplex radio
transceiver. We also assume that the network
card is capable to send either unicast or broadcast
packets. The network topology is represented by
an undirected graph G = ( V;E ), where V is the
set of nodes, and E is the set of links between
nodes. The existence of a link ( u; v ) ∈ E implies
that ( v; u ) ∈ E , and that node u and v are within
the transmission range of each other. In this case,
u and v are called one-hop neighbors of each
other. The set of one-hop neighbors of a node if
is denoted by N if 1 . Two nodes are called two-hop
neighbors of each other if they are not adjacent,
but have at least one common one-hop neighbor.
The neighbor information of node if refers to the
union of the one-hop neighbors of if itself and
the one-hop neighbors of if i's one-hop neighbors,
which is equal to:
This set contains the entire one hop and two
hops neighbors of a node if .
THE INITIALIZATION PHASE
a. Neighbor Discovery
At the initialization, each node broadcasts its ID.
After that, it periodically broadcasts a ping mes-
sage to its one-hop neighbors to build its one-hop
neighbors list. A ping message contains the current
list of its one-hop neighbors N if 1 . This message
is sent at a random time in each second for 30
seconds. Through this process, each node gathers
the information received from the pings from its
one-hop neighbors which essentially constitutes
its two-hop neighbor information (See Figure 2).
PROTOCOL DESCRIPTION
H-MAC uses the two contention modes LCL and
HCL similar to that of Z-MAC. It also imple-
ments two allocation algorithms. The first one is
a Receiver Based Channel Assignment Algorithm
(RBCA ) . In this algorithm, each node is assigned
a unique channel in which it will receive all its
packets. The second is the Sender Based Slot
Assignment algorithm (SBSA) where each node
is assigned a set of slots of which it will become
the owner. These algorithms are an extension of
NCR (Neighbor-aware Contention Resolution) al-
gorithm defined in (Bao and Garcia-Luna-Aceves,
2003), which does not require any control message
exchange. H-MAC uses a medium access function
similar to the IEEE 802.11e EDCA techniques
b. Channel Allocation Algorithm
RBCA
The Receiver Based Channel Assignment (RBCA)
is an implicit Consensus algorithm. Each node is
assigned a unique channel in which it will receive
all its packets. This algorithm uses pseudo-random
generator similar to that used by the NCR algorithm
(Bao and Garcia-Luna-Aceves, 2003). It solves a
special election problem where an entity decide
its leadership among a known set of contenders in
any given contention context. Each node calculates
a hash using its ID as a seed, and if its hash is
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