Tesis y Tesistas 2020 - Postgrado - Fac. de Informática - UNLP

MAESTRÍA
redes de datos
Mg. Diego Rodríguez Heirlen
e-mail
diegorh@gmail.com
Advisors
Ing. Luis Armando Marrone
Ing. Carlos A. Talay
Thesis defense date
September 25, 2020
SEDICI
http://sedici.unlp.edu.ar/handle/10915/108216
TCP performance analysis
in wireless access networks
Keywords: TCP; Congestion Control; WLAN; Performance; Fairness
Motivation
Wireless networks have experimented a significant boom in
the last couple of years due to the appearance of devices based
on the 802.11x norm series. Easy to use and to access, they
offer flexibility and mobility to the user, without sacrificing the
Internet connection or the network at the workplace.
The “standard” congestion control is custom designed for
wired networks, where data usually arrives orderly and
practically without errors. However, wireless links present
significant challenges, due to its unpredictable nature.
In wired networks, packet rearrangement is infrequent
and losses aren’t caused by congestion. The opposite
happens on wireless links, where these events are common
occurrences: these have more losses due tothe signals
propagated suffering from attenuation, interference and
noise. Because of this, received packets can be damaged
and are discarded, causing packet losses in transit -on
the link layer, not network layer-, scenario for which most
congestion control techniques were thought. Due the the
high error rate in transmission and, in some cases, to the
wireless network mobility, packet rearrangement is more
frequent. Thus, congestion control faces new challenges in
wireless environments.
When a packet is loss, “standard” TCP assumes that it’s
caused by network congestion and triggers the congestion
control mechanism. However, in wireless environments this
loss can also be caused by packet reordering and losses
in transit. In this way, TCP tends to retransmit packets
unnecessarily and to reduce the packet rate of transmitted
data. In consequence, available network resources are
wasted and underutilized, reducing TCP performance.
TCP carries most of the Internet traffic, which is why the
performance of the latter depends in great measure upon
the way TCP works. The performance characteristics for
any particular version of TCP are defined by the congestion
control algorithm it implements. The problem regarding
congestion control is about the smart use of available
network resources. As a result, congestion control has been
one of the most studied topics in research regarding the
Internet over the last 20 years.
The increasing use of mobile equipment has generated
a lot of interest in research about performance and
possible improvements for TCP on wireless environments.
These improvements were distributed around different
kinds on approaches.
This thesis aimed to contribute to the knowledge, update
and advancement on the state of the art about solutions
to enhance TCP performance on networks with wireless
links, considering simple scenarios and simulating WLAN
access networks.
Even though there are multiple approaches to enhance TCP
performance in wireless networks, this study is focused
on solutions preserving the End-to-End spirit of TCP, which
characterizes the networks as a black box, meaning it
doesn’t provide any kind of explicit information about the
state of congestion or loss to any of the hosts involved. This
line of research attempts to manage losses to amend the
performance allowed by the TCP analysis of the proposed
upgrades for congestion control on the transport layer,
e.g, Fast Retransmission and Fast Recovery algorithms.
In general, their implementation requires changes in the
transmitter TCP, although in some cases it might also
require some modifications on the receiver as well.
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