Networking Reference
In-Depth Information
Table 3.1
(continued)
Metric
Measures and selection
Sample protocol
Bottleneck link
capacity (BLC)
Indicates the residual capacity of the
bottleneck link of a routing path
Capacity-aware routing
(CAR) [ 56 ]
Based on the expected busy time (EBT)
of transmitting a packet over a link
EBT can be measured based on the packet
loss rate and transmission mechanism in
the MAC layer
The residual capacity of a link is defined
as the ratio between the idle time and
EBT
Selection of the path with the largest BLC
- The Resilient Opportunistic Mesh Routing (ROMER) protocol [ 60 ] also
follows the opportunistic routing approach. In ROMER, each packet carries a
cost that is set by the source node and decremented with each hop according
to the WMR cost. Duplicates of the packet may be sent through the network if
the packet has enough credit at many forwarders.
Some protocols apply network coding for their routing functions to reduce the
transmissions and utilize the bandwidth efficiently. In network coding, each
transmission carries the information of multiple packets coded all together and
decoded at the destination. It can be either applied to packets belonging to the
same data flow (intra-flow network coding) or packets belonging to different data
flows (inter-flow network coding) [ 57 ]. An example of the intra-flow network
coding routing protocols is the MAC-independent Opportunistic Routing and
Encoding (MORE) protocol [ 61 ] and an example of the inter-flow ones is the
Distributed Coding-Aware Routing (DCAR) protocol [ 62 ].
Vehicular Ad-Hoc Networks
The most important challenge for designing a VANET routing protocol is main-
taining connectivity while nodes—vehicles—are moving at high speeds causing
frequent topology changes. For that reason, route maintenance is required to be
included in all VANET routing protocols and the route maintenance component
will be activated and considered a core component in VANETs. By the inclusion
of the route maintenance component as a core one, the core routing components
for VANET routing protocols are the route discovery, route selection, route rep-
resentation and data forwarding, and route maintenance components.
Following is a discussion of the common functionalities for each component
and some examples of routing protocols that utilize these functionalities. In our
discussion, the focus is on the position-based functionalities and protocols as these
are the dominating ones in VANETs.
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