Thursday, 31 March 2011

What 21CN really means?

"Putting all your eggs in one basket" is a phrase that comes to mind, or so it seems.

The way networks used to be run is that different services used different infrastructure and worked in different ways. Indeed, many services would inherently allow re-routing around problems either automatically or manually. If one service failed another continued as it did not use the same infrastructure.

Apparently, 21st Century Networks are different. It seems that with 21CN you can have lots of single points of failure, like a router in Slough perhaps, that can simultaneously take out lots of services and somehow not allow them to be re-routed! You can have Ethernet links and broadband services go down at the same time even though they are not actually in that area, just because they are routed via Slough.

Of course, in the good old days, a failure would mean using spare equipment or mending a fibre, and it would be done within a 4 hour window at most. But no, with 21CN you can have huge routers that don't apparently have hot, or even vaguely warm, spares, and so the idea of things fixed in 4 hours is out of the window.

Yes, this is a lot of guess work about the network of a major UK telco, but it is guess work based on the fact that 10% of our broadband and Ethernet lines have been down for NINE HOURS so far, and all that has happened during that time is some more lines going off in another area...

I guess we now know what 21CN means though. Thanks for showing us the way.


  1. I yearn for 21CN to get here... What's most annoying is that the equipment in the exchange is ADSL2+ capable (I know this because FaveTelco™ managed to misconfigure my port on the MSAN and I was getting ADSL2+ sync speeds) but they still won't use it.

    By the time the rest of the country is using FTTP, we might see ADSL2+

  2. It would have been nice if they'd actually been sending out updates like they're supposed to. (I received mails about the relatively minor London Faraday outage, but not about Slough/Reading for some reason!)

  3. They do seem to have carefully built 21CN to have as many single points of failure as possible. Do they not have *any* network engineers working for them any more?

  4. It was the same on 20cn - if a RAS went dowwn somewhere you couldn't re-route to get round the problem, just had to wait for it to get fixed.

    I was hoping the lessons learned from 20cn would have been used in 21cn, but it never came to pass. Single points of failure are still part of teh design :(

  5. So BT haven't learned since they last time you named and shamed based on their complete lack of resilience.

    Of course, with Ofcom forcing Bt Wholesale to cut prices I don't see things getting better. First thing to go is the 'hot standby' as it looks like a waste of money to the bean counters.

  6. I guess we'll have to wait for 22CN then? :)

  7. If marketing departments get involved, we can expect 22CN next year I would think.