TELECOM Digest OnLine - Sorted: Re: Using Two ADSL Internet Connections Simultaneously

Re: Using Two ADSL Internet Connections Simultaneously

Robert Bonomi (bonomi@host122.r-bonomni.com)
Tue, 06 Dec 2005 00:50:05 -0000

In article <telecom24.550.3@telecom-digest.org>, <jonfklein@gmail.com> wrote:

> Here is the problem,

> I have two telephone lines. I want to make both of these lines ADSL
> connections to the internet and use these connections to provide
> internet access to several wireless laptop computers. A maximum of
> about 20 laptops would be connected to the system at once. I would
> like the laptops to be able to use both lines simultaneously so that I
> don't have one line overloaded and one underloaded (ie: I want to
> balance the traffic on the lines at any given time).

Without assistance from the 'other end' of the DSL lines, you cannot
reliably accomplish load balancing.

Absent some 'special' arrangements, each DSL line will have it's own
address space. When a laptop connects to the wireless LAN, you can
assign it an address from one space or the other, and _attempt_ to
balance things by using addressing from the 'least busy' (at that
time) circuit. *BUT* the traffic loads can change _while_ that address
is assigned to that laptop.

Now, if you're using NAT/PAT on a per-connection-to-the-outside-world
basis, the *same* problem can occur -- the "window of vulnerability"
is merely "somewhat" narrower.

'Flipping' a laptop from one address-space to the other one is fraught
with peril -- even if it occurs 'between' connections to the outside
world, there may be a 'logical session' involved that spans those
connections. Having the IP address of the machine change _during_
the "session" MAY fatally confuse the machine on the other end.

Now, *IF* there are ways to control the type of traffic to/from those
laptops, then with _sufficient_knowledge_ of what they are doing, you
can come somewhat closer to being able to do 'dynamic' balancing of
your circuit utilization.

It's *really* easy, if you have 'co-operating' smarts on the far end
of the lines -- postulating that both lines go to the _same_ place,
that is. :)

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