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Figure 1. Throughput comparison between CSMA and TDMA
HYBRID MAC PROTOCOLS
similar approach like PTDMA, but is much sim-
pler.
Z-MAC (Rhee, Warrier, Aia and Min, 2005) is
also an hybrid scheme based on the same approach
as ADAPT. It has been optimized for multi-hop
scenario and adapted to perform in sensor net-
work. Z-MAC uses STDMA scheduling to reduce
collision probability of CSMA based scheme
(Gronkvist, 2004). Like ADAPT, by combining
CSMA and TDMA, Z-MAC delivers a robust
scheme which even in worst case, performs as
well as CSMA scheme.
Bandwidth Aware Hybrid MAC (Krishna Rana,
Hua Liu, Nyandoro and Jha, 2006) is another pro-
tocol similar to Z-MAC. It improves the hybrid
schemes of ADAPT and Z-MAC by proposing
an algorithm that allocates slots to the nodes in
proportion to their bandwidth requirements.
Based on the access strategy used, MAC protocols
can be sorted into three categories: random-access
or contention-based, schedule based and hybrid.
A random-access scheme like CSMA works
well with low contention and provides better
throughput. However, the data throughput de-
grades significantly when increasing the number
of contending nodes. A scheduled scheme like
TDMA does not provide good throughput with
low contention. But, the network throughput
progresses proportionally according to the number
of contending nodes (Krishna Rana, Hua Liu,
Nyandoro and Jha, 2006; Chlamtac, Farago, My-
ers, Syrotiuk and Zaruba, 2000; Henderson, Kotz
and Abyzov, 2004).
Some approaches combining the strength of
random and schedule based schemes have been
developed. In the schema described in (Koubias
and Haralabidis, 1996), the default transmission
is random-based. However, when detecting a
collision, a round of token passing (contention-
free) transmission mode is initiated. Thus, when-
ever collision probability increases, the scheme
shifts to schedule-based contention-free transmis-
sion. PTDMA is a hybrid protocol presented by
Emphremides and Mowafi (Ephremides and
Mowafi, 1982). In this protocol the probability
of collision is controlled by programming nodes
to transmit with different probability. ADAPT
(Myers, 2002) is another protocol that employs
MULTI-CHANNEL MAC PROTOCOLS
A large number of multi-channel MAC protocols
and TDMA scheduling algorithms have been
proposed in the literature (Kyasanur, Jungmin,
Chereddi and Vaidya, 2006). Multi-channel MAC
protocols have extended the DCF (Distributed
Coordination Function) function of IEEE 802.11
protocol (IEEE 802.11 Working Group, 1997) and
use certain type of control messages for frequency
negotiation (So and Vaidya, 2004; Fitzek, Ange-
lini, Mazzini and Zorzi, 2003; Li, Haas, Sheng
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