we used to say TCP/IP but now only IP. what's wrong with TCP?
first, TCP has a curve to climb before it can explore and get right
the available bandwidth, and this process is slow (10 secs?). it's
not the width of the channel but the stability of RTT that keeps
the TCP climbing towards the maximum speed.
in a wireless network there are many reasons that the transfer may
suddenly pause for a while, or RTT changes radically, etc., when
S/N gets low, when the traffic is high, when the base station has
to switch the MS to another channel/sector, or during handoff to
another base station or MSC, ...
DoCoMo's TCP version, TLP, performs maybe only 1/3 as the WAP stack
in the worst case but on average maybe they can do 80%, because
i-mode is mostly used "in a sofa-bed at home". there are too many
70-80%s, all add cost to the DoCoMo's network which everyone have
to pay eventually.
also, even in the fixed network, TCP has a lot of problems for
streaming and signaling etc., and we know most of them many years
before UP and i-mode. but there is still no universal solution
yet to replace TCP, a not-so-good but great design.
interestingly, NEC used to use UDP in many of their products
because the TCP stacks they have were/are very badly implemented
and we didn't have as powerful boxes as today. during the design
of i-mode DoCoMo/NEC were convinced that they better to move to
TCP. one of the reasons they didn't like the UDP based WAP.
Japan's biggest telecom operator and manufacturer had no basic
understanding of Internet and i-mode was born.
cheers,
Ken
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Received on Thu Jun 27 10:53:46 2002