Ad Hoc Networks : Technologies and Protocols - University of ...

136 Transport Layer Protocols in Ad Hoc Networks
the section, we provide an overview of each of the above three approaches, and
in the ensuing sections we elaborate on the details of the approaches.
Figure 5.5. Classification of Approaches
A straight-forward and simplistic approach is to retain TCP as the transport
protocol, but make it mobility-aware by supplementing it with additional
mechanisms, along with simple support from the lower layers
to overcome the negative impacts of mobility. We refer to this approach
as the Modified TCP approach. While the transport layer does require
some changes in this approach, the level and complexity of changes can
be viewed as a trade-off with the performance improvements possible.
A key advantage of such an approach is that the general behavior of the
protocol is similar to that of TCP, and hence backward compatibility issues,
when mobile-hosts talk to static-hosts in the Internet, do not arise.
However, an obvious drawback is that the problems identified with the
design elements of TCP in Section 5.2 are still left un-addressed.
In the second approach, TCP is hidden from the underlying network characteristics
through appropriately designed lower layer protocols. Hence,
all the required mechanisms to mask out the negative effects of mobility
on TCP, are implemented at the MAC and routing layers. This requires
no changes to TCP’s operation. This approach is in fact more suitable
for addressing backward compatibility issues raised earlier. We refer to
this approach as TCP-aware Cross-layered Solutions. Note that unlike
in the first approach, where the underlying protocols are to a large extent
TCP unaware, this approach requires the lower layers to possess a
close awareness of TCP’s properties and behavior. Also, as in the first
approach, since the mechanisms are all implemented at the routing and