I might even add that a few companies have described themselves as
"tier 0", with the idea that they will dynamically select best routes
based on real-time measurements. I get nervous about that, as we have
enough instabilities caused by too-frequent change in the global
routing system.
Some of the larger carriers do publish their criteria for bilateral
peering. They aren't all the same, but they will give an idea what
one Tier 1 will consider another Tier 1 to be. Mind you, there have
been cases where the bilateral requirements were so stringent that a
given carrier wouldn't have been allowed to peer with itself.
Let me make an observation about a topic that comes up here quite a
bit. People used to enterprise routing always seem to be looking for
the "best route" through the Internet. Unless they contract (and pay)
for end-to-end managed QoS, they are apt to be frustrated. BGP is not
about route optimality, but about reachability and stability of the
global routing system. Intermediate providers with which you don't
have a business relationship simply don't care if you get optimal
routes, nor do they have any incentive to do so. That's one of the
reason the idea usually called the Destination Preference Attribute
keeps going nowhere--the idea is that the originator can state
preferred routes to them, but if the other players don't agree, the
originator has no power to enforce.
At 5:23 PM +0000 6/27/03, Priscilla Oppenheimer wrote:
>Thanks Howard. I had just been wondering about this very topic myself. You
>plugged one of your books, but I learned a lot about this same topic from
>another one of your books, which I will plug! :-)
>
>WAN Survival Guide
>
>That book is really helpful for people like myself who mainly work on the
>other side of the equation, as a customer of the ISPs at various tiers.
>Well, I do help (part-time) run a small ISP, but I think it would be Tier 5
>at best. :-)
>
>Priscilla
We should probably point to something about Chief Joseph and the
Trail of Tiers, eh?
Yep. WAN Survival Guide and Building Service Provider Networks really
were written to complement one another. Oh, there are user-side
concepts in BSPN that came to me with hindsight, but that's natural.
Ironically, my first two books, Building Addressing Architectures and
Building Routing and Switching Architectures, also were volumes I and
II to me.
For some reason, publishers absolutely hate the idea of mentioning
that books are really part of a series -- at least, that's what I got
from Macmillan and Wiley. To give Wiley some credit, they at least
have the Networking Council series that puts design books in context.
To varying extents, the Networking Council itself (Vint Cerf, Scott
Bradner, Lyman Chapin) do get involved in the project -- Scott was
very helpful for the WAN Surival Guide.
>
>Howard C. Berkowitz wrote:
>>
>> At 5:33 AM +0000 6/27/03, Mwalie W wrote:
>> >Hi All,
>> >
>> >This should be a simple one.
>> >
>> >I have heard that we have Tier 1, Tier 2, Tier 3 ISPs.I do
>> assume we only
>> >have Tier 1 and Tier 2 in the US, Europe and Asia (Japan,
>> China).
>> >
>> >In a third world country, can we have Tier 1 and Tier 2? Or we
>> just have
>> >Tier 3 ISPs which connect to Tier 1 and Tier 2 in the USA, etc?
>> >
>> >Okay, I ask this question because I was reading an article in
>> Kenya about a
>> >local ISP there called UUNET-Kenya (www.uunet.co.ke) and they
>> are saying
>> >that they are a Tier 1 ISP. I did not think that that Kenyan
>> ISP is Tier 1,
>> >but I do know that its parent company (Worldcom?) is Tier 1.
>> >
>> >Was it just marketing to the locals there??
>> >
>> >Thanks for your answers
>>
>> The tier concept is mostly marketing these days, although there
>> is
>> some technical basis.
>>
>> An essential part of the difference is the relationship of the
>> provider to other ISPs. Unfortunately, the terminology is
>> awkward
>> here, because there are two meanings of the word "peer". The
>> familiar
> > one is a BGP session, regardless of economics. The other
>> definition
>> is an economic one. A "peer relationship" means that the two
>> ISPs do
>> not charge one another for transit and send at least full
>> customer
>> routes to each other, on the basis they are both of about the
>> same
>> aize and it's to their mutual advantage to let their customers
>> have
>> access to each other, without worrying about the billing.
>>
>> The other relationship is a customer-provider one, where the
>> "less
>> valuable" provider buys transit from the "more valuable" one.
>> In
>> other words, if ISPs are peers, no money changes hands.
>>
>> A tier 1 provider never buys transit. It gets all its routes
>> from
>> bilateral peering arrangements. It will have a 24/7 network
>> operations center, and a national or intercontinental
>> transmission
>> network, either leased or physically operated, of at least DS-3
>> (more
>> likely OC-3 to OC-48 these days). Its non-provider customers,
>> if it
>> has them, will usually be large enterprises only -- it's really
>> a
>> wholesaler.
>>
>> A tier 2 provider is regional and gets all its regional routes
>> through peering arrangements. It does buy transit to go
>> outside its
>> region, although it's likely to have significant bulk
>> discounts. It
>> has 24/7 NOC and a broadband transmission network within its
>> region.
>>
>> A tier 3 provider buys transit from multiple upstreams and runs
>> a
>> default-free routing table. It may or may not operate a
>> significant
>> transmission network. Usually, if it doesn't have a full 24/7
>> NOC,
>> technical support remains available to other providers (not
>> necessarily customers) through pagers and the like.
>>
>> A tier 4 provider buys transit from one or more upstreams, with
>> connectivity to multiple POPs of the same provider if it only
>> uses
>> one upstream. It does run BGP with a substantial part of the
>> global
>> table.
>>
>> A tier 5 provider is a reseller, perhaps an Internet cafe. It
>> owns or
>> leases ("virtual POP") end user access and buys transit.
>>
>> There are lots of refinements and variations. As a shameless
>> plug,
>> I'll mention my own book, _Building Service Provider Networks_.
>> Geoff Huston's _ISP Survival Guide_ complements it, going
>> further
>> into the business model, as do the many papers on peering
>> economics
>> by Bill Norton of Equinix.
>>
>> Do I at least get a cup of Kenyan coffee for all this? I'm
>> trying to
>> remember some of the more solid dishes. For the people in the
>> US, if
>> you think "what's the best CCIE number" is bad, try a
>> discussion
>> among various African cultures as to who makes the best Joloff
>> rice!
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