wireless ad hoc networking

Communication Protocols 45
hop. The neighborhood receiver decides to forward it if and only if
the sum of consumed cost (contained in packet) and the cost of the
node (stored in node) matches the cost of source node (contained in
packet). That is, Cost source = Cost consumed + Cost current_node , implying
that the current node is on the optimal path. In the example
shown in Figure 2.13, the hop number is employed as the cost
field. The main contribution of MCFN is that it presents a scheme
to avoid the excessive advertisement packets that may overwhelm
the network when establishing the cost field. It makes sure that
every node only advertises its cost field once with the correct value.
GRAB 20 (Figure 2.14) is a mesh version of MFCN to increase the
transmission reliability. In GRAB, rather than using the single optimal
path, a mesh between the source and the sink is formed, and
all the nodes in that mesh are involved. The width of the mesh
is proportional to the distance to the sink. To build the mesh, the
concept of extra credit is introduced as the budget that packets
could consume. GRAB greatly increases the reliability of MCFN
without introducing too much overhead—only the packet header
is a little longer. In practice, both hop counts and energy can be
used as the cost field. We should note that MCFN and GRAB both
need symmetric links so that the established cost field is valid when
transmitting.
ARRIVE 28 applies the hop number as the gradient. Apart from GRAB,
nodes in ARRIVE explicitly maintain the list of directed neighbors
and assign the next hop. The main contribution of ARRIVE is the
4
3
1
4
3
2
1
0
4
3
2
1
1
Hop distance
Data path
Figure 2.13
An example of transmission route in MCFN.