Linux Unwired [Electronic resources] نسخه متنی

9.6 Acceleration

Although GPRS
and CDMA are pretty slow, some providers have put compression servers
on their network to compress documents before they make it to your
computer.

Verizon
Wireless uses a two-tier proxy server called
Venturi (http://www.venturiwireless.com/productsl).
One tier of the proxy server sits on the cellular
carrier's network and compresses documents before
they come down to your machine. The other tier is a local proxy
server that runs on your machine and decompresses the content on the
fly before presenting it to your web browser or any other
application. (Venturi can compress data sent over a number of
protocols including SMTP and POP3.) AT&T Wireless uses something
similar, but we do not know what it is. At the time of this writing,
there isn't a Linux client for either Venturi (or
whatever it is that AT&T Wireless uses). But that
shouldn't stop you from asking customer support
about it, because it may have changed (at the very least, you should
let them know the demand exists).

Sprint and
T-Mobile have transparent acceleration on
their networks. The nice thing about this approach is that it should,
in theory, obey web standards without requiring any fiddling on the
client side; so it doesn't matter what operating
system you're on. To compress HTML, the compression
server can use gzip compression; to compress images, it can reduce
the image quality. Figure 9-6 shows the T-Mobile
Internet Accelerator configuration page (http://getmorespeed.t-mobile.com). You will
not be able to reach this page unless you are connected to the
internet2.voicestream.com or
internet3.voicestream.com APNs on
T-Mobile's GPRS network.

Figure 9-6. Configuring the T-Mobile Internet Accelerator

Figure 9-7 shows detail from an image that was sent
across T-Mobile's network with compression disabled.
Figure 9-8 shows that same detail with maximum
compression. Although some artifacts appear in the image, the
differences should not annoy most users. This 799 x 599
pixel image started out at 96 KB; compression reduced it to 48 KB.

Figure 9-7. Photograph with no compression

Figure 9-8. Photograph with maximum compression

Your mileage will vary using acceleration; in theory, it should speed
things up. We've found this to be the case most of
the time.

However, we've also found cases where the
compression server was having a bad day, and the amount of time it
took to do its thing exceeded the acceleration we received from the
compression. Try it out and see how it works, and disable it if
it's a problem. Contact your cellular carrier for
instructions on turning compression on and off.