Private peering makes sense when there
are very few equivalent players.
Connecting to one other ISP costs X.
Connecting to two other ISPs
cost two times X. Connecting
to three other ISPs cost three times X
and so on where X is usually half the
cost of infrastructure the circuit plus
a port cost the more private peers the
greater the cost and this doesn't scale
the costs go up as we add each private
peering link the internet exchange point
is a more scalable solution to this
problem connecting to an exchange point
means the ISP pays for one router port
on the local border router one circuit
to where the exchange point location is
and potentially one router to locate at
the exchange point some exchange points
will charge and your maintenance fees
this goes towards the cost of the
infrastructure the air conditioning the
remote hands and so forth the
maintenance fee actually has potential
to significantly influence the cost
balance for a service provider generally
connecting to an exchange point in
pealing there becomes cost effective
when there at least three other peers
but the real amount varies from region
to region from exchange point to
exchange part so who would peer at an
exchange points access providers would
go there because then they don't have to
pay the regional provider transit fees
for local traffic this keeps latency low
and it keeps the costs for local traffic
low as well and this basically unlimited
bandwidth through the exchange part
compared with costly and limited
bandwidth through the transit provider
regional providers would also peer at an
exchange part because they don't have to
pay the global provider transit fees for
local and regional traffic and likewise
it keeps latency for local and regional
traffic low and it keeps the costs for
local and regional traffic flow and
again thus unlimited
ban word through the exchange point at
least when compared with costly and
limited bandwidth through the global
provider we also find that content
providers and content distribution
services peer at exchange parts they
don't have to pay the regional provider
for transit fees for local traffic again
it helps latency and cost for local
traffic and again they see the unlimited
bandwidth through the exchange point
infrastructure for the same reason we
will find the root name server operators
country top-level domain operators and
the general top-level domain operators
this adds resiliency to the global DNS
system as well as keeping latency and
response time for local resolver traffic
very little this effectively speeds up
the DNS and gives the end users of the
impression that the internet is fast
continue the discussion about the
exchange points role we also find that
global providers will be located close
to the exchange points they can be
attracted by the potential transit
business available they won't peer at
the exchange part themselves but will be
located close by and this makes it
advantageous for the access and regional
providers they can pair with other
similar providers at the exchange point
and in the same facility they can pay
for transit to the regional or global
provider they don't take the transit
across the exchange point fabric most
exchange points don't allow this and
anyway it's not good practice they
generally provide a separate private
connection back to our P&I to connect to
the transit provider
now let's look at the connectivity
decisions for transit provider you need
that to reach the rest of the internet
so every ISP does need a transit
provider one provider is no redundancy
two providers is ideal for traffic
engineering as well as redundancy three
providers gives even better redundancy
but we have to work a little bit harder
with our traffic engineering more than
three provides diminishing returns
rapidly escalating costs and complexity
and is not recommended by most major
operators today peering means low or
zero cost access to another network and
peering can be private or public as
we've learned earlier the goals of an
operator are these to minimize the
number of transit providers but maintain
redundancy to is ideal for or more is
getting really hard also we want to
aggregate capacity to our transit
providers the more aggregated capacity
there is the better the value we see
because of the law cost per megabit per
second as the bandwidth capacity grows
for example for stm-1 or OC 3 links
which 155 megabits each to four
different ISPs will almost always cost
more than two stm-4 or OC 12 which is
622 megabits links to two different ISPs
yet the bandwidth of the latter 1.2
gigabits per second is greater than that
of the former 620 megabits per second is
much easier to configure as far as bgp
traffic engineering goes and is much
easier to operate in the medium to long
term so what do we do we obviously need
peering and we need transit how do we
choose though and it comes down to the
cost of going to an internet exchange
point
at an exchange point we will get free
peering and we could pay for transit
from an isp which is cool located in the
same facility or maybe close by it could
be in a neighboring building or in the
same city or we could just decide not to
go to an exchange point and pay for the
cost of transit directly to an upstream
provider there may be no exchange point
in the vicinity and so transit might be
the only option there's no right or
wrong answer to this
someone has to sit down and do the
arithmetic work out what the costs are
should we be doing private peering well
as we've learned there's a scaling issue
the more circuits we have two more
neighboring providers the greater the
cost will become one about public
peering well this will make sense when
more potential peers are located in the
same location and more is usually
greater than two and then there's a
question about which public peering
point we should go to well the local
internet exchange point is great for
local traffic and local peers and
there's almost no argument for not
turning up at one. Regional internet
exchange point is also interesting.
It's great for meeting peers outside
the locality and might be cheaper
than buying transit to reach
the same consumer base.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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