On Fri, 7 Sep 2001, Nik Frengle wrote:
> Hmm...I read this article, and said to myself 'I wonder how much data a user
> can transfer if they buy the Packet Pack 80. It turns out to about 48 mb/mo.
> for the initial 8000 yen. air H" on the other hand allows unlimited access
> for less.
It allows unlimited access to the packet network for 50,000 yen per month,
yes. But according to a friend who has it, this is considerably slower
than setting up a 64K circuit-switched connection. He says, in fact,
that it feels about like a 14.4K modem. (I'll probably be picking up my
own card next week, and if I ever get the darn cardbus working properly
on my L2 I can do some proper throughput tests.)
If we say for the moment you get a sustained throughput of 19.2 Kbps,
that 10 MB file you want to download takes 72 minutes (not including
packet overhead and whatnot). The less patient among us will set up a 64K
circuit-switched connection (JPY10/minute) and download it in 22 minutes,
at a cost of 220 yen. (When you buy DDI's 5000 yen/month flat rate plan,
you get along with it the ability to use the circuit-switched network
for an extra 10 yen per minute.)
Not that this is hard to live with, when you consider the FOMA
alternative. Sure, you download it in just over three and a half
minutes. But it costs you 1638 yen plus overhead!
And the overhead is going to be considerable. Just because I'm anal,
I'll calculate it. I think I'm being rather generous, but I'll guess
I'll guess that just under 10% of the 128-byte FOMA packet is overhead,
giving us a payload of 116 bytes. Let's say we've got some really optimal
conditions for the TCP link: path MTU discovery giving you 1500 byte MTU,
minimal header sizes, no retransmits, and so on. You're going to have 7184
IP packets sent down, corresponding to at least 93,392 FOMA packets. For
this, even with delayed ack, you're likely going to send at least 2398
acks. So given these optimal conditions, you're talking 1916 yen, a 17%
permium. (Given real-world conditions, it's likely to exceed 20%.)
(Of course, this leads us to the question, WTF would they be using a
128 byte packet size on a connection doing 64Kbps - 384Kbps? But I don't
know too much about the standards in this area.)
If we estimate the overhead for the 64K PHS connection to be about 20%
of connection time, and chuck on another 50 yen there, we're still
looking at FOMA being more than seven times as expensive as PHS. Ouch!
cjs
--
Curt Sampson <cjs_at_cynic.net> +81 3 5778 0123 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC
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Received on Fri Sep 7 09:29:25 2001