Subject: Re: Open Issue in GLP: Scope

From: Scott Petrack <[email-masked]>
Date: Thu, 1 Jul 1999 08:26:42 -0400 (EDT)

I need a bit more explanation for your case 1 please:

On Wed, 30 Jun 1999, Jonathan Rosenberg wrote:

> 
> 1. For 800 numbers, or other numbers which have global signficance
> (i.e., you can call them from anywhere), but are not unique, 

Please explain. As far as I know, 800 numbers do not have global
significance. I cannot call an 800 number from anywhere. I can only call
North American 800 numbers from North America. 1-800-3456789 is a 
valid freephone number in North America and also in Israel, but they are
two completely separate phones.

> the scope
> is an attribute which almost extends the original number to make it
> unique. 

What do you mean "almost extends". Sorry if I'm being thick.

> This scope could be a unique ID which has no real signficance
> other than being unique. But, in this case, if an LS receives two
> routes, both to the same numbers but with different scopes, which one
> should it use for routing calls? Perhaps some kind of semantic is
> required for the scope beyond uniqueness?

Do you just mean that the pair (scope, number) is globally unique,
so in my example above, the scope would have the semantics of "the number
is in the North American Dialing plan" or "the number is in the Israeli
Dialing plan". If this is correct, I'd like to repeat what I said at the
last IETF: PINT had a similar problem, and defined an attribute called
"phone-context" to solve it. Perhaps you might consider it -- there were
two kinds of values allowed for the "phone-context":

a) An international network prefix -- this is basically a plus sign, then
country code, then perhaps more digits, which must completely disambiguate
the number. Examples might be +1 or +972 for the example above. Another
example (with extra digits) is the (context, number) pair (+97252, *123).
This would be the "phone number" *123 within a particular Israeli
Cellphone network (this happens to be the number of customer service
within that cellphone network).

b) A domain name -- this must completely disambiguate the number within
that domain. This was how we covered the case of private networks and
numbering plans: we said that you can't use this kind of scope unless you
own the domain, and then it's up to you what it means. Note that our
problem here was not the "scope of the advertisement", as in your second
case below. It was just a way of saying that the number in question 
belonged to some private numbering plan. I would suggest that GLP might
have this problem too -- there may be applications where it is desired
to advertise routes to some telephones within a private numbering plan 
over the wide area (this would be necessary for certain kinds of IP-based
wide area centrex).

As an experimental kludge, because we need some implementation experience,
we also allowed special X-domain.name scopes.

Very possibly I don't understand the problem, but it does seem to me that 
these two kinds of "context" give you what you need.

> 
> 2. There is an enterprise customer with several locations. They use a
> private numbering plan, with some numbers in each location, and gateways
> in each location to reach those numbers. The enterprise customer would
> like to purchase IP telephony VPN service from a provider, so that the
> provider can route calls between the customers' locations. So, for this
> to work, the customer has an LS in each location which advertises the
> private prefixes in that location. These are then propagated through the
> provider's LS's (the provider itself may be a collection of ITAD's that
> have formed some kind of federation or something). So, this introduces a
> need for a scope to indicate that these private numbers are not callable
> from everywhere, but just from within the domains of the customer. The
> scope would also indicate that an LS in the provider domains should not
> advertise these prefixes into other customer domains. In this case,
> having the scope be some kind of customer identifier seems appropriate.
>

We did not have this problem of limiting the scope of an advertisement. I
would like to suggest that this is a different problem from the 
disambiguation problem above, and that you need two different fields. 

> So, the questions are:
> 
> 1. do we see a need for cases 1 and/or 2?

1, definitely -- 1 800 3456789 is not a global international E.164 number,
but I certainly hope that it will be possible to use GLP to advertise
routes to it.

2, there must be a way to limit the scope of advertisements, no?

> 2. If so, what should be the semantics of the scope in each case?

I would suggest calling the first one "phone-context" and the second one
"scope."

Again, apologies if I am misunderstanding everything. Please try to
explain if I am.

Scott

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 01 Jul 1999 10:35:42 -0400

> two completely separate phones.

I guess global significance is the wrong term. What I mean is, it can be
dialed from any phone, and it is a valid number at any phone, but it is
not unique - depending on where you dial from (i.e., which gateway
actually dials the number) you get a different result. Basically, what
you describe.

> What do you mean "almost extends". Sorry if I'm being thick.

No, its just my poor explanation. Remove the word "also". The idea is
that the scope would be an extension of the original number to make it
unique.

> Dialing plan".

Thats one possible semantic, but the general idea is what you first
describe; (scope, number) is globally unique.

 If this is correct, I'd like to repeat what I said at the
> within that cellphone network).

Well, I would expect that when advertising an 800 number, you would
usually include the country code as part of the number anyway. I guess
this approach is useful when the country code is not enough. For
example:

(+1 732, +1 800 123-4567) and
(+1 908, +1 800 123-4567)

would be the same 800 number in the US, but the scope indicates one is
unique within the 732 area code, and the other within the 908 area code.
Is this what you are suggesting?

> over the wide area (this would be necessary for certain kinds of IP-based

Right; case #2 below really includes this issue as well as scope of
advertisement.

> these two kinds of "context" give you what you need.

No, I think perhaps you understand it better than I do :)

> disambiguation problem above, and that you need two different fields.

This is a good point. I guess case 1 uses scope as a number
disambiguation, and case 2 as BOTH a disambiguation AND limitation on
advertisement. Perhaps it might make sense to define two attributes
according to Scott's breakdown:

1. a disambiguation attribute, which is either a domain or prefix as in
pint, or perhaps also an ITAD number?
2. a scope limitation attribute - not sure what this would look like.
Perhaps an ITAD number also?

> but I certainly hope that it will be possible to use GLP to advertise

I think the conclusion of past discussions is that ideally, GLP would
not advertise things like 800 numbers. Rather, these would be translated
first to real routing numbers, and so GLP would advertise those. It
avoids all kind of horrible triangle routing that might otherwise
happen. But, since we can't prevent people from advertising the 800
numbers, and since there isn't any other way for now, we would support
it.

> 2, there must be a way to limit the scope of advertisements, no?

Its purely a matter of policy. An LS can drop an advertisement based on
any criteria it wants. I think our scope limitation attribute might need
to be some kind of identifier that can help an LS make this decision.

> I would suggest calling the first one "phone-context" and the second one

Well, I'd rather avoid the word scope all together, but a name is just a
name after all.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX:   (732) 834-5379                       Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

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