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

Re: Using Two ADSL Internet Connections Simultaneously

Robert Bonomi (
Sun, 18 Dec 2005 00:12:01 -0000

In article <>, James Carlson
<> wrote:

> (Robert Bonomi) writes:

>>> - NAT in use, and load balancing on a per-connection basis. This
>>> automatically balances the return traffic as well, as everyone on
>>> the net thinks you're actually two separate independent IP nodes.

>> NO, it does _Not_. You cannot change the NAT translation _during_ a
>> 'session' (a single TCP connection). And if the 'incoming' data
>> characteristics change radically _during_ that session, the 'balance'
>> goes out the window.

> What part of "per-connection" was unclear?

Do you note that the above problem identification specifies a *single*
*connection*? What part of "single connection" is unclear to you?

Do you understand that 'per connection' balancing does not work when:
1) the characteristics of the traffic are _unknown_ at the time of
connection initiation, and
2) the characteristics of the traffic *change* _during_ that single

The rest of the problem description that you chose not to quote gave a
concrete example of the problem -- using a first user with a streaming
audio stream, and a bunch of other people then doing something as
simple as having multiple HTTP requests ("keepalive" protocol option)
over a *single* connection. If you don't like that, consider
'passive' FTP -- where where a number of users first pull a small
'readme' file, and then (still within the _same_ connection), a
multi-megabyte binary.

Without 'co-operation' from the other end of the links, the
'per-connection' approach _is_ the 'best' you can do. And in the
average case, it does work FAIRLY well. In pathological cases,
however, it can degrade to barely more than the capacity of -one-
circuit. Those pathological cases are relatively rare, but they
*do*exist*. And, when you get into one, performance gets =really=
poor, for comparatively _long_ times.

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