From: Kevin Wampler (wampler@cs.washington.edu)
Date: Wed Oct 06 2004 - 03:36:19 PDT
In this paper Cerf and Kahn sketch out the ideas for the transmission
protocol TCP. They describe both the technical details of this protocol
and the motivations for its features.
The protocol described shows great deal of though in its design. many
properties that a protocol might have are considered, and are accepted or
rejected on well thought-out bases. Early on the need of a standardized
protocol (as opposed to translations between different protocols at
gateways), but some flexibility is built into TCP to accommodate different
networks. Similarly a protocol requiring packets to be of uniform size
between networks is rejected, but the use of a sequencing number based on
bytes rather than packet count easily allows the message to be
reconstructed if a packet is fragmented. Perhaps most elegant is TCP's
use of the sliding window and acknowledgment schemes to support segment
sequencing, dropped packets, and flow regulation.
As far as the limitations of the described protocol are concerned, there
are the issues with the insufficiency of a 32-bit sequence number and a
16-bit window size which are discussed in the book. It is also clear that
TCP is intended only for applications where a reliable byte stream is
needed. I would imagine that across noisy networks the overhead and
delays incurred for retransmission of lost packets and acknowledgments may
be significant, particularly in applications such as voice over IP where
data loss during transmission is not as critical an issue as timely
delivery.
This paper clearly remains relevant, as TCP is still a widely used
protocol. Since networks continue to evolve, future work will no doubt be
of many different varieties. The textbook mentions some simple extensions
which solve some of the problems arising from the limited size of some of
the fields in the protocol. Given that multimedia over the Internet seems
to be an increasingly important capability, I might also imagine work
being done on more advanced flow regulation control, such as the ability
to specify the allowed data loss that might be tolerated for the sake of
improved speed of transmission.
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