[ILUG] Free software for .pando files?
paul at clubi.ie
paul at clubi.ie
Fri Sep 7 00:24:53 IST 2007
On Wed, 5 Sep 2007, Thomas Bridge wrote:
> The entire thrust of my comments have been aimed at the position
> that as a cost of managing and routing P2P traffic, transit is not
> particularly high on the list. I've never suggested there were
> problems with using transit (by which I include peering with other
So there are no problems - at least, nothing mentioned by me or the
other two posters so far is a problem.
How about going into detail as to what (if any) problems P2P is
causing ISPs, with respect to load particularly. That'd be far more
productive application of your operational experience than this
>> Uh, ATM, MPLS, L2TP all:
>> - post-date IP!!!!
>> - are circuit-switched
> MPLS and L2TP are not circuit switched.
The packets forming an L2TP need not be circuit switched, no - but
it's used to create circuits and hide stuff from IP still.
MPLS most definitely /is/ circuit-switched, rather than
No packets for a given circuit (how packets are classified is network
specific) can flow until LDP sets up an end-end path (well, where
egress controls setup of label - which is the common case). All
packets of a given class follow the same circuit (an MPLS
label-switched path, i.e. circuit, might be renegotiated to a new
- path setup triggered by need
- network control messages converge on a path /before/ data flows
- path for some class of data is fixed
- does not rely on any fancy graph-theory, distributed algorithm for
- Control messages and circuit setup precedes data and they probe
the entire path, in both directions. So it's self-evident that
any circuit that gets setup is both viable and loop-free.
- Yes, MPLS still has TTLs, that's cause we've learned that
forwarding without TTLs is NOT robust (see ethernet).
- with distributed algorithms, the network /regularly/ will have
loops as and when things change. With LDP/MPLS, it shouldn't
happen normally, but it's still better to have TTLs to be
It's pretty much classic circuit-switching (though, a lot more
dynamic than older circuit-switching networks).
The last bullet point particularly is pretty indicative of
circuit-switching, versus networks which independently route each
packet, hop by hop.
Yes, some control information is now in-band (label header prependend
to data), and acted on per-packet, per-node - rather than out-of-band
(ie in the network, as with older circuit-switched networks), but
even POTS calls have long been digitised and prepended with headers
before being passed through a circuit switched network.
If you don't believe me, go read 3.21 of RFC3031, "MPLS
Route selection refers to the method used for selecting the LSP for a
particular FEC. The proposed MPLS protocol architecture supports two
options for Route Selection: (1) hop by hop routing, and (2) explicit
Hop by hop routing allows each node to independently choose the next
hop for each FEC. This is the usual mode today in existing IP
networks. A "hop by hop routed LSP" is an LSP whose route is
selected using hop by hop routing.
In an explicitly routed LSP, each LSR does not independently choose
the next hop; rather, a single LSR, generally the LSP ingress or the
LSP egress, specifies several (or all) of the LSRs in the LSP. If a
single LSR specifies the entire LSP, the LSP is "strictly" explicitly
routed. If a single LSR specifies only some of the LSP, the LSP is
"loosely" explicitly routed.
- "explicit routing" boils down to 'ordered distribution control'
mode of LDP - which is what I'm talking about above.
- The other possibility, independent per-hop-packet routing, (so not
circuit switching) is not, in my limited operational knowledge,
used much (e.g. JunOS doesn't support it in their LDP apparently.
And I'd imagine few people use OSPF or IS-IS to distribute labels).
It seems slightly pointless from a management POV (it exists purely for
> I'm thinking protocols like SDH, ISDN and ATM. And my point would
> have better made had I said "predate wide deployments of IP".
All of those post-date the wide deployment of IP. ATM was a reaction
by the telco world to the rise of packet switching - IP being the
predominant packet-switched technology, along with ISO.
> No - I said the costs of getting traffic from the customer site to
> the ISP's data centre were the biggest part of the cost involved in
> supplying a DSL service. For clarity, it's the cost of building
> and maintaining the DSL "circuit/link" in the first place - not
> just the cost of carrying traffic over the link.
The whole 'connect customers to ISPs' circuit-switching model also
has a lot over administrative overhead.
Intriguingly, this does NOT seem to be borne by the IP guys. All the
work of co-ordinating with Eircom to connect "DSL at line with number
Y" -> ISP X seems to get done by non-technical administrative staff.
That's essentially a human form of LDP ;). But it's a cost you, in
your network-ops capacity, don't fully see. (I imagine you're aware
of it though).
If everything ran in a single network, with the /ability/ to
short-circuit ISP traffic at exchanges and/or BAS (if the ISPs
involved deemed that to be 'shortest'), you might save some of those
human overheads. Hence the 'build' cost might be slightly lower..
> As an ISP would typically deliver several thousand customers over
> the same STM-1 circuit, there is an additional cost for carrying
> the traffic, as the value of "several" depends on the average
> amount of traffic that each customer is carrying.
The average amount is going to tend towards "the link capacity". The
masses *will* one day be watching corry via IP.. And P2P is the new
Cable ISPs will be able to take advantage (some already do TVoIP from
headends to STBs), simply by letting customers see each other. ISPs
tied to the state-telco-wholesaler model are going to have to bear
the extra costs of shipping a *lot* of quite redundant bits.
That surely will hurt those ISPs..
> I would say that the proportion of traffic travelling from house to
> house within the same street is typically less than 0.1% of the
> average DSL users traffic.
>From your view of a DSL network operatio. Agreed. Because it's
impossible at present for people to do so.
The P2P applications at present have no incentive to look locally
first (as discussed) + the masses aren't yet watching Corrie online
(but ITV do now have it online..).
There are IPTV apps which try to be topology aware.. It is the
I bet the picture is different with cable networks where customers
can see each other..
> In other words, you're fussing about a very small amount of data
> that is taking a sub optimal route.
> No my problem with "native" IP networks is that it's impossible for
> more than one ISP to run a service into the exchange.
> The fact you can't have multiple providers using the same exchange
But all the Irish ISPs seem to be doing their best to have the 'share
the equipment' scenario be their /last resort/. So the few remaining
Irish ISPs are doing their best to try avoid it.
Layers of crap and scenic routing are quite a price to pay to allow
multiple ISPs to share access to the copper.
We could have invented ways to distribute IP configuration
information from ISPs to wholesaler, rather than have invented ways
to fake-up L2 links between customer and ISP (e.g. PPPoE, L2TP -
> MT routing?
Multi-Topology. E.g. doing one kind of routing (e.g. IP topology)
then another (e.g. an MPLS-like one) over another, etc...
So you can have a single, unobscured link topology, but apply an
ordered set of routing mechanisms to it.
> It's worth noting at this point that at the time Tinet was launched
> - there were already several ISPs offering dial up IP services -
> IEunet, Ireland On Line, Indigo, Connect and Club Internet all come
> to mind.
> If we'd left it to incumbent telco to run the country's ISP
> infrastructure, we'd all still be using 33.6K modems at an average
> cost of about 40 a month.
>> It is. Though not in the sense you mean here - BGP links are
>> between ASes. For eBGP sessions, links often do correspond to IP
>> links (some crazy people run multihop eBGP, to a central router,
>> for various reasons to do with lack of resources ;) ).
> Thats not what a link aware protocol is. BGP significantly abstracts
> the topology - and when calculating the forwarding table from it's
> database, isn't remotely interested in the status of a given link.
Again, you're using "link" solely in the sense of "layer-2 link". You
need to reread what I wrote. ;)
> With the state of IP as it stands, you can't have more than one
> ISP. The entire network would have to be under a single
> administrative domain for it to work.
Yes you could: Distribute control information, not L2 data..
I.e. instead of having invented PPPoE, L2TP, MPLS, etc.. If we'd
dealt with the fundamental management problems instead (that retail
ISPs didn't have a way to exchange IP configuration information with
wholesale ISPs, and have wholesale ISPs apply that information) then
we'd today have much more efficient broadband networking.
Inventing one wouldn't have taken any extra thought over the other,
except that telco people seem wedded to thinking of networking as
circuits - so to solve problems they create things to make circuits..
You can continue to think these networks of circuits of networks of
circuits of neto.... are a good thing, the reality is they're a
kludge. It's provably inefficient, and it needn't have been so.
We might not be able to change it today, but we should try learn from
Paul Jakma paul at clubi.ie paul at jakma.org Key ID: 64A2FF6A
Age and treachery will always overcome youth and skill.
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