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ABSTRACT Most of the data transfer applications like FTP, web transactions use TCP/IP, the internet end-to-end
transfer protocol. TCP has been tuned for traditional networks comprising wired
links and stationary hosts. It assumes congestion in the network to be the primary
cause for packet losses and unusual delays, and adapts to it. The TCP receiver sends cumulative acknowledgments (ACKs) for successfully
received segments, which the sender uses to determine which segments have been
successfully received. The sender identifies the loss of a packet either by the
arrival of several duplicate cumulative ACKs, triggering a fast retransmission,
or by the absence of an ACK for a timeout interval equal to the sum of the
smoothed round-trip delay and four times its mean deviation. TCP reacts to
packet losses by retransmitting missing data, and simultaneously invoking
congestion control by reducing its transmission (congestion) window size and
backing off its retransmission timer. These measures reduce the level of
congestion on the intermediate links. Unfortunately, when packets are lost for reasons other than congestion,
these measures result in an unnecessary reduction in end-to-end throughput and
hence, in sub-optimal performance. Communication over wireless links is often
characterized by high bit-error rates due to channel fading, noise or
interference, and intermittent connectivity due to handoffs. TCP performance in
such networks suffers from significant throughput degradation and very high
interactive delays because the sender misinterprets corruption for
congestion
Many schemes have been proposed to alleviate this problem. The aim of
this paper is to analyze these various schemes and propose newer ones which
might help to circumvent this problem. Section 1 begins with an introduction to TCP. It discusses the various
features of TCP, and then goes on to discuss the various congestion control
schemes. The discussion is complimented with time-line diagrams which give a
pictorial view of the various scenarios considered. Section 2 tries to find out
an answer to whether TCP is really required for the mobile clients and discusses
the various wireless models like the wireless LAN and the cellular network. It
then discusses the various problems that are associated with using TCP over the
wireless links like the BER, Handoff?s due to user roaming into a new cell etc
and goes on to describe the various proposed schemes. |
Attachment:
The Transmission Control Protocol.doc
Description: MS-Word document