<s>
Internet	B-Protocol
exchange	I-Protocol
points	I-Protocol
(	O
IXes	O
or	O
IXPs	B-Protocol
)	O
are	O
common	O
grounds	O
of	O
IP	B-Protocol
networking	O
,	O
allowing	O
participant	O
Internet	O
service	O
providers	O
(	O
ISPs	O
)	O
to	O
exchange	O
data	O
destined	O
for	O
their	O
respective	O
networks	O
.	O
</s>
<s>
IXPs	B-Protocol
are	O
generally	O
located	O
at	O
places	O
with	O
preexisting	O
connections	O
to	O
multiple	O
distinct	O
networks	O
,	O
i.e.	O
,	O
datacenters	B-Operating_System
,	O
and	O
operate	O
physical	O
infrastructure	O
(	O
switches	B-Protocol
)	O
to	O
connect	O
their	O
participants	O
.	O
</s>
<s>
Organizationally	O
,	O
most	O
IXPs	B-Protocol
are	O
each	O
independent	O
not-for-profit	O
associations	O
of	O
their	O
constituent	O
participating	O
networks	O
(	O
that	O
is	O
,	O
the	O
set	O
of	O
ISPs	O
which	O
participate	O
at	O
that	O
IXP	B-Protocol
)	O
.	O
</s>
<s>
The	O
primary	O
alternative	O
to	O
IXPs	B-Protocol
is	O
private	O
peering	B-Protocol
,	O
where	O
ISPs	O
directly	O
connect	O
their	O
networks	O
to	O
each	O
other	O
.	O
</s>
<s>
IXPs	B-Protocol
reduce	O
the	O
portion	O
of	O
an	O
ISP	O
's	O
traffic	O
that	O
must	O
be	O
delivered	O
via	O
their	O
upstream	O
transit	B-Application
providers	I-Application
,	O
thereby	O
reducing	O
the	O
average	O
per-bit	O
delivery	O
cost	O
of	O
their	O
service	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
increased	O
number	O
of	O
paths	O
available	O
through	O
the	O
IXP	B-Protocol
improves	O
routing	O
efficiency	O
(	O
by	O
allowing	O
routers	O
to	O
select	O
shorter	O
paths	O
)	O
and	O
fault-tolerance	B-General_Concept
.	O
</s>
<s>
IXPs	B-Protocol
exhibit	O
the	O
characteristics	O
of	O
the	O
network	O
effect	O
.	O
</s>
<s>
Internet	B-Protocol
exchange	I-Protocol
points	I-Protocol
began	O
as	O
Network	O
Access	O
Points	O
or	O
NAPs	O
,	O
a	O
key	O
component	O
of	O
Al	O
Gore	O
's	O
National	O
Information	O
Infrastructure	O
(	O
NII	O
)	O
plan	O
,	O
which	O
defined	O
the	O
transition	O
from	O
the	O
US	O
Government-paid-for	O
NSFNET	O
era	O
(	O
when	O
Internet	O
access	O
was	O
government	O
sponsored	O
and	O
commercial	O
traffic	O
was	O
prohibited	O
)	O
to	O
the	O
commercial	O
Internet	O
of	O
today	O
.	O
</s>
<s>
The	O
four	O
Network	O
Access	O
Points	O
(	O
NAPs	O
)	O
were	O
defined	O
as	O
transitional	O
data	O
communications	O
facilities	O
at	O
which	O
Network	O
Service	O
Providers	O
(	O
NSPs	O
)	O
would	O
exchange	O
traffic	O
,	O
in	O
replacement	O
of	O
the	O
publicly	O
financed	O
NSFNET	O
Internet	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
As	O
a	O
transitional	O
strategy	O
,	O
they	O
were	O
effective	O
,	O
providing	O
a	O
bridge	O
from	O
the	O
Internet	O
's	O
beginnings	O
as	O
a	O
government-funded	O
academic	O
experiment	O
,	O
to	O
the	O
modern	O
Internet	O
of	O
many	O
private-sector	O
competitors	O
collaborating	O
to	O
form	O
a	O
network-of-networks	O
,	O
transporting	O
Internet	O
bandwidth	O
from	O
its	O
points-of-production	O
at	O
Internet	B-Protocol
Exchange	I-Protocol
Points	I-Protocol
to	O
its	O
sites-of-consumption	O
at	O
users	O
 '	O
locations	O
.	O
</s>
<s>
Today	O
,	O
the	O
phrase	O
"	O
Network	O
Access	O
Point	O
"	O
is	O
of	O
historical	O
interest	O
only	O
,	O
since	O
the	O
four	O
transitional	O
NAPs	O
disappeared	O
long	O
ago	O
,	O
replaced	O
by	O
hundreds	O
of	O
modern	O
Internet	B-Protocol
Exchange	I-Protocol
Points	I-Protocol
,	O
though	O
in	O
Spanish-speaking	O
Latin	O
America	O
,	O
the	O
phrase	O
lives	O
on	O
to	O
a	O
small	O
degree	O
,	O
among	O
those	O
who	O
conflate	O
the	O
NAPs	O
with	O
IXPs	B-Protocol
.	O
</s>
<s>
The	O
primary	O
purpose	O
of	O
an	O
IXP	B-Protocol
is	O
to	O
allow	O
networks	O
to	O
interconnect	O
directly	O
,	O
via	O
the	O
exchange	O
,	O
rather	O
than	O
going	O
through	O
one	O
or	O
more	O
third-party	O
networks	O
.	O
</s>
<s>
However	O
,	O
a	O
connection	O
to	O
a	O
local	O
IXP	B-Protocol
may	O
allow	O
them	O
to	O
transfer	O
data	O
without	O
limit	O
,	O
and	O
without	O
cost	O
,	O
vastly	O
improving	O
the	O
bandwidth	O
between	O
customers	O
of	O
such	O
adjacent	O
ISPs	O
.	O
</s>
<s>
A	O
typical	O
IXP	B-Protocol
consists	O
of	O
one	O
or	O
more	O
network	B-Protocol
switches	I-Protocol
,	O
to	O
which	O
each	O
of	O
the	O
participating	O
ISPs	O
connect	O
.	O
</s>
<s>
Prior	O
to	O
the	O
existence	O
of	O
switches	B-Protocol
,	O
IXPs	B-Protocol
typically	O
employed	O
fiber-optic	B-Architecture
inter-repeater	O
link	O
(	O
FOIRL	O
)	O
hubs	O
or	O
Fiber	B-Protocol
Distributed	I-Protocol
Data	I-Protocol
Interface	I-Protocol
(	O
FDDI	B-Protocol
)	O
rings	O
,	O
migrating	O
to	O
Ethernet	O
and	O
FDDI	B-Protocol
switches	B-Protocol
as	O
those	O
became	O
available	O
in	O
1993	O
and	O
1994	O
.	O
</s>
<s>
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
switches	B-Protocol
were	O
briefly	O
used	O
at	O
a	O
few	O
IXPs	B-Protocol
in	O
the	O
late	O
1990s	O
,	O
accounting	O
for	O
approximately	O
4%	O
of	O
the	O
market	O
at	O
their	O
peak	O
,	O
and	O
there	O
was	O
an	O
attempt	O
by	O
Stockholm-based	O
IXP	B-Protocol
NetNod	O
to	O
use	O
SRP/DPT	B-Protocol
,	O
but	O
Ethernet	O
has	O
prevailed	O
,	O
accounting	O
for	O
more	O
than	O
95%	O
of	O
all	O
existing	O
Internet	B-Protocol
exchange	I-Protocol
switch	B-Protocol
fabrics	O
.	O
</s>
<s>
All	O
Ethernet	O
port	O
speeds	O
are	O
to	O
be	O
found	O
at	O
modern	O
IXPs	B-Protocol
,	O
ranging	O
from	O
10	O
Mb/second	O
ports	O
in	O
use	O
in	O
small	O
developing-country	O
IXPs	B-Protocol
,	O
to	O
ganged	O
10	O
Gb/second	O
ports	O
in	O
major	O
centers	O
like	O
Seoul	O
,	O
New	O
York	O
,	O
London	O
,	O
Frankfurt	O
,	O
Amsterdam	O
,	O
and	O
Palo	O
Alto	O
.	O
</s>
<s>
The	O
principle	O
business	O
and	O
governance	O
models	O
for	O
IXPs	B-Protocol
include	O
:	O
</s>
<s>
The	O
technical	O
and	O
business	O
logistics	O
of	O
traffic	O
exchange	O
between	O
ISPs	O
is	O
governed	O
by	O
bilateral	O
or	O
multilateral	O
peering	B-Protocol
agreements	O
.	O
</s>
<s>
When	O
an	O
IXP	B-Protocol
incurs	O
operating	O
costs	O
,	O
they	O
are	O
typically	O
shared	O
among	O
all	O
of	O
its	O
participants	O
.	O
</s>
<s>
Some	O
exchanges	O
charge	O
a	O
setup	O
fee	O
to	O
offset	O
the	O
costs	O
of	O
the	O
switch	B-Protocol
port	I-Protocol
and	O
any	O
media	O
adaptors	O
(	O
gigabit	B-Protocol
interface	I-Protocol
converters	I-Protocol
,	O
small	B-Protocol
form-factor	I-Protocol
pluggable	I-Protocol
transceivers	I-Protocol
,	O
XFP	B-Protocol
transceivers	I-Protocol
,	O
XENPAKs	B-Protocol
,	O
etc	O
.	O
)	O
</s>
<s>
Internet	O
traffic	O
exchange	O
between	O
two	O
participants	O
on	O
an	O
IXP	B-Protocol
is	O
facilitated	O
by	O
Border	B-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
(	O
BGP	B-Protocol
)	O
routing	O
configurations	O
between	O
them	O
.	O
</s>
<s>
They	O
choose	O
to	O
announce	O
routes	O
via	O
the	O
peering	B-Protocol
relationship	O
–	O
either	O
routes	O
to	O
their	O
own	O
addresses	O
or	O
routes	O
to	O
addresses	O
of	O
other	O
ISPs	O
that	O
they	O
connect	O
to	O
,	O
possibly	O
via	O
other	O
mechanisms	O
.	O
</s>
<s>
The	O
other	O
party	O
to	O
the	O
peering	B-Protocol
can	O
then	O
apply	O
route	O
filtering	O
,	O
where	O
it	O
chooses	O
to	O
accept	O
those	O
routes	O
,	O
and	O
route	O
traffic	O
accordingly	O
,	O
or	O
to	O
ignore	O
those	O
routes	O
,	O
and	O
use	O
other	O
routes	O
to	O
reach	O
those	O
addresses	O
.	O
</s>
<s>
In	O
many	O
cases	O
,	O
an	O
ISP	O
will	O
have	O
both	O
a	O
direct	O
link	O
to	O
another	O
ISP	O
and	O
accept	O
a	O
route	O
(	O
normally	O
ignored	O
)	O
to	O
the	O
other	O
ISP	O
through	O
the	O
IXP	B-Protocol
;	O
if	O
the	O
direct	O
link	O
fails	O
,	O
traffic	O
will	O
then	O
start	O
flowing	O
over	O
the	O
IXP	B-Protocol
.	O
</s>
<s>
In	O
this	O
way	O
,	O
the	O
IXP	B-Protocol
acts	O
as	O
a	O
backup	O
link	O
.	O
</s>
<s>
When	O
these	O
conditions	O
are	O
met	O
,	O
and	O
a	O
contractual	O
structure	O
exists	O
to	O
create	O
a	O
market	O
to	O
purchase	O
network	O
services	O
,	O
the	O
IXP	B-Protocol
is	O
sometimes	O
called	O
a	O
"	O
transit	B-Application
exchange	O
"	O
.	O
</s>
<s>
The	O
Vancouver	O
Transit	B-Application
Exchange	O
,	O
for	O
example	O
,	O
is	O
described	O
as	O
a	O
"	O
shopping	O
mall	O
"	O
of	O
service	O
providers	O
at	O
one	O
central	O
location	O
,	O
making	O
it	O
easy	O
to	O
switch	B-Protocol
providers	O
,	O
"	O
as	O
simple	O
as	O
getting	O
a	O
VLAN	B-General_Concept
to	O
a	O
new	O
provider	O
"	O
.	O
</s>
<s>
Advocates	O
of	O
green	O
broadband	O
schemes	O
and	O
more	O
competitive	O
telecommunications	O
services	O
often	O
advocate	O
aggressive	O
expansion	O
of	O
transit	B-Application
exchanges	O
into	O
every	O
municipal	O
area	O
network	O
so	O
that	O
competing	O
service	O
providers	O
can	O
place	O
such	O
equipment	O
as	O
video	B-Application
on	I-Application
demand	I-Application
hosts	O
and	O
PSTN	O
switches	B-Protocol
to	O
serve	O
existing	O
phone	O
equipment	O
,	O
without	O
being	O
answerable	O
to	O
any	O
monopoly	O
incumbent	O
.	O
</s>
<s>
Since	O
the	O
dissolution	O
of	O
the	O
Internet	B-General_Concept
backbone	I-General_Concept
and	O
transition	O
to	O
the	O
IXP	B-Protocol
system	O
in	O
1992	O
,	O
the	O
measurement	O
of	O
Internet	O
traffic	O
exchanged	O
at	O
IXPs	B-Protocol
has	O
been	O
the	O
primary	O
source	O
of	O
data	O
about	O
Internet	O
bandwidth	O
production	O
:	O
how	O
it	O
grows	O
over	O
time	O
and	O
where	O
it	O
is	O
produced	O
.	O
</s>
