Posted at 2009-10-17 12:31 BST by RevK
Update #0: 2009-10-17 12:46 BST

Session steering is a system of ensuring connections from customers
over the broadband network reach the right equipment at our end.

At our end we have two LNS servers. These are what the connection
terminates on, before going in to our network. We have two of these for
obvious reasons, mainly in case one breaks. Also in case one of the two
links to BT breaks.

When a customer tries to connect to us, BT send a message to our RADIUS
server to say that they are connecting and we reply saying to which LNS
we want the traffic to go. For 21CN lines BT take notice of our reply
and connect to the specified LNS. For 20CN they do not, and connect to
one of the two LNSs at random. We automatically change the response in
the event of a problem so that the backup LNS gets the traffic instead.

We want all of the customers to connect to one LNS - the master LNS.
The other is the backup. We need this for several reasons.

  * Because multi-line bonding does not work well split between LNSs

  * Because we have to manage traffic to BT to avoid stupid 100th%
    burst charging

  * Because we upgrade software and so need everyone on the other LNS
    when we do that

Its not that unusual a requirement!

So, how can we do that. Well, like many ISPs with the same issues we
have, until now, allowed the connection to come in, worked out it is on
the wrong LNS and closed the connection. Then the customer router has
to try again. So 50% of the time the connection fails. This means it
can take several attempts to connect (on 20CN lines).

Could BT sort this? Of course they could. They even ran a trial for
session steering and dropped the idea. So it is possible.

Today we installed a new release of the FireBrick FB6202 router code
which has an update to handle this issue. It is just one of a series of
features to handle BT specific quirks. The update works by tracking the
platform RADIUS requests from BT and rejecting connections sooner if
they are on the wrong LNS. It means that the customer's router does not
have to re-try the connection any more. It should always get through
first time, even if BT has to send a few extra messages in the process
to get the connection to us on the right LNS.

By the end of this weekend we should have this fully deployed on both
LNSs and working. It should reduce hassle, delay and confusion
customers have had with this in the past.

It is also yet another way that a British designed router can cater for
specific issues UK ISPs have dealing with BT connections.[IMAGE]

URL: http://aaisp.blogspot.com/2009/10/tech-session-steering.html

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URL:http://aaisp.blogspot.com/