Text 9664, 61 rader
Skriven 2010-07-31 10:55:08 av Michiel van der Vlist (2:280/5555)
     Kommentar till en text av David Drummond (3:640/384)
Ärende: Cellphone woes
======================
Hello David,

On Saturday July 31 2010 07:24, you wrote to me:

 DD>>> I tested the student link at work today, 20.5 download and 1.5 up. I
 DD>>> was correct, the dual DSL2+ links multiplexed (or something) toge-
 DD>>> ther do not actually double the speed, just  the volume throughput.

 MvdV>> This I do not understand. If the volume transferred per unit of
 MvdV>> time doubles, that doubles the speed of transfer doesn't it?

 DD> The maximum speed of the DSL2+ link is 24mbps.

The DSL2+ specs provide for 24Mbps but here providers cap at 20 Mbps. The
reason is that a DSL line is usually combined with a voice line. This used to
be POTS or ISDN, but the telcos are phasing that out in favour of VOIP. So when
they now provide "internet + telephony", what you get is a box with among other
things, one or two sockets where one can connect an analog phone, but which
connect to the network via VOIP technoloy. They reserve 4 Mbps for VOIP, and
sell the internet connection at 20 Mbps max. The VOIP channel does not share
the bandwith with the internet part of the connection. So that when making a
phone call, it does not reduce the speed of the internet connection.

Having said that...

 DD> If one used one of those download accelerators that splits the
 DD> download into multiple streams I'm sure one would see the difference.
 DD> Obviously speedtest.net doesn't do that.

It seems to me that the two ADSL2+ lines are not multiplexed in the sense that
they act as one logical 48 Mbbps connection. They are just two connections.
It seems that an application requesting a stream is assigned one of the two
connections and so never gets more than 24 Mbps. The next application may get
the other connection and so also get 24 Mbps. So the students have 48 Mbps to
share between them, but speedtest never shows more than 24 Mbps.

Perhaps you can run a second incarnation of speedtest. Maybe it will show that
you can setup two connection that when added up, go above 24 Mbps.

 DD>>> I supposedly have DSL2+ at home too but I am almost 4km from the
 DD>>> telco exchange.

Too far to get full speed. To get the full speed, you must not be further away
than 400 meters from the DSLAM.

What does you telco claim you should have?

 DD>>> It slows down when it rains :(

 MvdV>> Overhead lines?

 DD> Actually underground. I suspect moisture leaks into a junction box
 DD> somewhere.

I'd say that is a reason to complain or negotiate a discount....


Cheers, Michiel

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