On Feb 14, 2008, at 3:44 PM, Andy Davidson wrote:
On 14 Feb 2008, at 17:02, Kai Chen wrote:
A typical Internet Exchange Point (IXP) consists of one or more
network switches, to which each of the participating ISPs connect.
We call it the exchange-based topology. My question is if some
current IXPs use directly-connected topology, in which ISPs just
connect to each other by direct link, not through a network
switch?? If so, what's the percentage of this directly-connected
case?
ISPs use a "direct link" (PNI) all the time to peer, and they don't
need to be a member/customer of an internet exchange point to do
so. In fact, the network you want to peer with might not be
available at your local IXP even though they're in your local
carrier hotel - then it becomes pretty much the only way to peer.
In London, the LINX offer switched *and* unswitched connectivity
between members - you can rent fibers from them in order to perform
PNI with other members. That the exchange offer this is unusual,
and it's offered as an additional service, in order to smooth the
process of organising interconnection between member organisations. [www.linx.net
]
LINX doesn't rent fibers. It's a one-time (NRC) fee for 8 pairs,
which are patched to any other member on the service for free for
life. (Although I don't know if they promise to keep it free forever,
but it's been free for many years with no mention of it changing.)
We (LONAP) don't offer PNI services, and only offer the conventional
switch ports, which members normally want so that they can get
access to our peering lan and swap some traffic. [www.lonap.net]
All exchanges offer this connectivity model. We offer private CUG
and member-to-member private VLANs, which is similar, but still
passes through the switch fabric.
I believe Exchange Point offers a PNI-like service over their network.
But in general, an "Internet eXchange Provider" offers a shared
switch. Anything else is really just a meet-me room. For instance, I
wouldn't call Suite 1515 (formerly NYCC) an "IXP".
--
TTFN,
patrick
