U.S.B. speeds

[colin davidson]

Every communication protocol has protocol overhead. The more
connections deviate from a simple point-to-point communication between
two and only two devices, the heavier that overhead will tend to
become. As an example, the original ethernet had a physical transfer
rate of 10 million bits per second, but it was widely held that the
maximum useful data throughput was around 3 million bits per second.
Thus data transfer rates are almost always lower than the physical bit
rates (though in some cases data compression can give a higher data
transfer rate than physical bit rate, but only for data with fairly
high redundancy.

Protocol overhead isn't the only reason for poor performance, however.
It can also be the result of poor configuration (settings that don't
work well with the actual connection), poor topology, inteference,
signal loss and so on. These all apply to every form of communication,
though the causes and sources of the problems can vary massively
depending on the technology.

If your problems are caused by protocol overhead, there's nothing you
can do except change your connection technology. If you are
experiencing significant problems from other causes, however, there
will often be things you can do about it to gain significant
performance improvements.

There, that deals enough with the theoretical. Everyone else can deal
with the practical :-)

Cheers, Colin

On Wed, Jun 16, 2010 at 5:17 AM, Slack Rat <slacker-MOdoAOVCFFcswetKESUqMA at public.gmane.org> wrote:
> phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org a écrit profondement:
>
> | Because of handshaking and protocol overhead, the effective transfer rate
> | over USB is *much* less than the basic speed numbers would seem to
> | indicate.
> | It also depends on the type of transfer you are doing.
>>
> | I don't know exact figures, but I do remember that USB 1.0 was in effect
> | not all that much faster than a high baud rate serial connection, in the
> | order of 100k bytes per second. (I'm going from memory...)
>>
> Would this affect WiFi too?
>
> I have an Ad-Hoc net set up and the transfer is painfully slow
>
> I get  around 85Kb/s
>
> There is also a wired WAN on the server
>
> USB MSI Dongle in the server using ndiswrapper
> Bus 002 Device 002: ID 0db0:6861 Micro Star International MSI-6861 802.11g =
> WiFi adapter
> Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
>
> Built in Broadcom 43XX in a Lappy - again using ndiswrapper
>
> --
> Slackrat
> --
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