On Wed, 5 Sep 2007, Thomas Bridge wrote:
> No I don't - you're either not understanding or I'm not making
> clear - there typically isn't an issue buying the international
> transit required to support a service.
Ok, then I don't understand. What was the issue with external links,
can you expand on that?
> You never had a problem when the packet was being wrapped up in a
> nice little ATM header all the way (or being ATM, split into about
> 40 different cells each with their own nice little ATM header).
I do actually.. ;)
The L2 stuff not so much (ok, it doesn't quite suit IP, but hey). All
the L3 stuff of ATM OTOH.
> It makes very little difference and is actually easier for the ISP
> and the telco to manage the L2TP way.
Sure. That doesn't make it good.
> I think you're getting so obsessed with network purity, you're
> bemoaning the fact that MPLS, L2TP and BGP are all protocols
> designed to deal with different administrative domains.
No I'm not. I'm bemoaning the fact we invented MPLS and L2TP -
because of shortcomings with IP, and (to a lesser extent) because of
how telecommunication networks had to deal with deregulation, across
> I don't regard it as particularly technically awful that my packet
> may hvae to travel 50 or even 100 miles around Ireland to get to
> another user on the same local exchange. This is a possibility
> even in the Telco world if I'm using one carrier to call another
It's a rare possibility, AIUI. Though, I'm not aware of how
number-portability is implemented and whether that depends on scenic
routing (but old POTS doesn't, for most normal numbers, imlu)...
> That's exactly where I have the issue - the existing model has
> evolved to fit the "business" requirements.
I'd disagree, the current model is one where telcos and others have
done all they could to avoid facing the premise of IP (simple) and
packet-switching generally (independent, but informed,
That's an anathema to telcos. To avoid it, they've helped develop
several circuit-switching transports, so they can continue to pretend
to customers their networks consist of independent circuits..
> Economies of scale. And it's the nature of many industries that
> they start off with lots of smaller companies and then finally
> consoldidate into many big ones.
Yes, economies of scale means consolidation. Note though that NOT A
SINGLE reseller of wholesale RADSL has survived (ie Netsource).
Though, there weren't many independent ISPs in Ireland to begin with.
There are a lot more in Britain, but there the market is biased by
the general aversion to end-user customer service of the incumbent
>> Anyway, no matter the business model: Scenic routing sucks..
>> It's the nature of the world we live in. Its the nature of networks
> that traffic doesn't always take the physically shortest path.
It's the nature of networks that they /should/ route traffic
according the shortest path in the topology, according to some
That ought to be stunningly obvious. At least, no one would /set out/
to design a networking system that did otherwise.
It's also obvious that todays consumer broadband networks fail (by
quite a margin) to do so. Unless of course you think "political
expediency" is something that ought to be factored into network
The problem with not taking the shortest-paths, instead ignoring them
in favour of routing via some small set of central points, is that
you get large loads at those central points, loads which NEED NOT be
there, if you used the network fully.
It's the exact same problem that STP has, but writ in the history of
deregulation and perversity of the telco world..
> At the risk of starting a whole new thread by it self - how is IPv6
> "less costly" than IPv4 to administer?
It's capable of auto-configuration.
> Hint: The issue isn't the allocation of IP addresses.
> But why? Other than aesthetics?
BTW: P2P app designers are working on how to distribute stuff inline
with IP topology....
As and when that becomes more prevalent, the ISPs who expose more of
their link topology to IP will have an efficiency advantage.
> My viewpoint is hardly unique - the entire point of an IP layer is
> that I route IP - I don't worry about what the guys at the lower
> layers do. In the broadband aggregation world for instance, I
> simply want a lot of point to point links to my client sites.
And why do you want that?
> In $LASTJOB, we had a clear and distinct management domains between
> the various layers of the network - we had the fibre guys, the SDH
> guys, and the IP guys. We didn't worry too much about what the
> other layers were doing.
Right, and you shouldn't.
Except you didn't have that nice layering. You had:
- the layer1 guys (wire pullers ;) )
- the layer2 guys
- the layer3 guys (ATM I guess?)
IP guys: <exact same stack pretty much>
There's a big overlap in L3, which is quite inefficient.
FWIW, there are ways to do multi-topology, shortest-path routing
correctly (ie efficiently).
> mind of the IP administrator from worrying about pernickity issues
> like SDH or ATM configuration.
I agree the IP guy shouldn't be worrying about that, problem is BOTH
the ATM and IP guys are worrying about routing!!!
> Assume that instead of L2TP and a BAS, $TELCO runs ATM direct to
> your ISPs BAS. That's still scenic routing. It does however remove
> the ugliness of tunnel protocol over tunnel protocol. Even two
> users connected to the same ISP will have to send their traffic to
> the central site to exchange.
We ought to be doing IP routing between them at either the exchange
(IP routing capable DSLAMs are available, even if most today are
not), or else at the BAS (which are IP routers).
> And when Magnet and BT unbundle the exchanges in Limerick, and stop
> using the BAS, the traffic will still travel all the way around
> Ireland so that they can cross over to Eircom at INEX.
Yes, this is known as a bad thing.
> No - ATM's bandwidth allocation is much nicer than IPs.
Then that's a problem with IP, which ought to be fixed. Or
alternatively, we should have switched the internet to native ATM..
> Yes - it's designed to ensure that instead of taking the
> technically best path, it takes the path most appropriate based on
> administrative domains, cost and politics.
Right, that's known as the 'best path'. The metric is set arbitrarily
at each node (AS) in the topology. However it's determined, if it can
be expressed in the policy of an ASes routers, then it's technically
You can not apply routing policy to links which do not exist.
I.e. if you conceal a sub-network and represent it as one link, you
can no longer apply routing policy within that sub-network.
You can always /reduce/ information (as we do within BGP, by
representing the networks of ISPs as a single node, an AS). You can
never extract information though, once removed.
So if you conceal topology at too low a level..
> If you can come with an easy, workable, cheaper solution that
> allows multiple ISPs (and therefore administrative domains) to send
> their traffic to other users in the same exchange, then I'm
> interested in hearing what it is.
> Of course, the fact remains that one of the reasons the ISPs aren't
> particularly interested in fixing that problem is that the amount
> of traffic that is exchanged between users within the same exchange
> is tiny.
Times a couple of hundreds and it all adds up.
Problem today is, to do it today would be a nightmare cause:
- hysterical reasons around evolution of telco deregulation
- one operator, but they can't switch traffic between
consumers because of competitive reasons
- To switch, with multiple organisations having a stake: IP
administration overheads spectacularly painful (configuration and
Paul Jakma paul at clubi.iepaul at jakma.org Key ID: 64A2FF6A
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