Μελέτη πρωτοκόλλων μεταφοράς σε δορυφορικά περιβάλλοντα
Date Issued
September 21, 2021
Type
Μεταπτυχιακή Διπλωματική Εργασία
Abstract
Satellite communications have had an enormous rise in the last century. This can
be mainly attributed to their ability to cover large areas of ground where communication
cannot be otherwise achieved, due to the lack of alternative infrastructures.
Satellite networks can provide a large enough ground coverage and therefore allow
continents, or even the majority of the planet to connect to the Internet. These
networks present various intricate properties, which can be attributed to the physical
channel for data transmission, the magnitute of the distances between the Earth
and its satellites, and consequently the high probability of errors during transimissions.
All of the described properties lengthen the transmission times and cause high
bandwith-delay product. For all these reasons, transport protocols play a critical
role in the performance and success of the satellite networks.
This thesis studies and implements three different Transmission Control Protocols
(TCP): New Reno, Westwood and Hybla, and their behaviour is compared
to the underlying theoretic modelling and the findings of the litarature. To make
this experimental comparison possible, a highly realistic environment is used, that
is based on the OMNeT++ network simulator and the INET framework.
The evaluation of these three TCP protocols focuses on metrics such as throughput,
the number of acknowledgements (ACKs) received in a given time interval,
etc. The experimentation takes place under different parameters, such as different
number of nodes, volume of information to be transmitted and nodes’ links.
The acquired results are generally in agreement with the theoretical findings of
the litarature. In more detail, Hybla protocol achieves the highest throughput, which
can be attributed to the more abrupt increase of the congestion window, a fact that
also makes it suitable for satellite environments, where the high bandwidth-delay
product can be exploited. At the same time, Westwood protocol performs better
than New Reno, due to its ability to adapt to the environmental changes using its bandwidth estimation mechanism.
Due to the restrictions of the simulation environment, different ideas for future
improvements are discussed that focus on further extending the experimental evaluation
of the protocols under more diverse conditions. A highly promising framework
that focuses on satellite environments is ESTNeT, which could be used to achieve
more realistic conditions, while other protocols like CoAP and MQTT could also be
taken into account.
Subjects