Subject: Re: GLP, number portability and wireless subscribers

From: Matt Squire <[email-masked]>
Date: Wed, 10 Mar 1999 08:29:04 -0500

At 06:56 PM 3/9/99 -0500, Jonathan Rosenberg wrote:
>David R. Oran wrote:
>> 
>> Then scopes are identical to a deeper hierarchy and splitting them out
>> is simply a syntactical, not a semantic distinction, right?
>
>My understanding is that it is semantic. By "splitting them out", I
>presume you mean having them be separate from the address itself. The
>prefix represents information on "where you're calling to", and the
>scope information on "where you are calling from". So, a prefix Y with
>scope X means you can call Y from X. I think we need explicit scopes if
>there are cases where route attributes for a prefix only apply when
>calling from numbers outside of the prefix (and apply only when calling
>from somewhere defined by the scope).

I don't see how we can guarantee any determination of 'where you are
calling from.'  What does my pc call from?  Where is an LS?  A gateway
might be considered to have a 'location', where the location is given by
the area code of its PSTN connectivity, but other devices without PSTN
connectivity aren't tied to a PSTN location.

It seems like any definition of scope along these lines requires alot of
administrative help, ie where LSs are tied/located with certain geographic
areas.  Would not a TTL-like attribute provide similar functionality (again
based on geographic ties/connectetions in LSs)?  A number could be
advertised with a certain TTL that prevents it from being advertised after
too many hops.  If your connections are geography-based, then this gives
you geographic scoping.  We make an additional statement that given
multiple potential routes to a destination, the one with the higher/lower
TTL is preferred (because its 'closer').  

>
>> 
>> Do you think we would need hierarchical scopes? If so, do you see
>> aggregation of hierarchical scopes? How would this differ from
>> hierarchical aggregation of addresses? Are scopes always more global
>> than addresses?
>
>We could potentially define hierarchical scopes (if they are also
>represented as prefixes, they are hierarchical). The rules for
>aggregation would presumably be the same. But, adding another
>aggregatable entity in a route advertisement seems like it will make
>route aggregation overall more complex, so I'd rather avoid this. Are
>scopes global? I think they need to be. The whole idea is that a prefix
>advertised in one place is only useful somewhere else. 
>

Unless someone says something to convice me otherwise, I'd vote against
this concept of scoping.  

- Matt

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From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 10 Mar 1999 10:15:37 -0500

Phew. Lots of mail flying around here. let me take a moment to summarize
what I think I've heard so far on scopes. Several definitions have been
explicitly or implicitly used. These include:

1. Scope is a way to disambiguate prefixes which are not globally
unique. For example, a particular 800 number might exist in NY, and
another in CA, and they are the same number, but who you get connected
to is different in NY and in CA. The scope would be used as an extra
identifier to make prefix+scope (or vpn-id as Matt calls it in this
email) globally unique. 

2. Scope is a way to disambiguate prefixes which are not globally
unique, but the scope further defines the places where the prefix is
valid. Ideally, this would mean "this prefix is only valid in NY" or
something like that. These scopes might be registered as tags with IANA,
or defines as prefixes themselves. For example, a prefix of Y with scope
X means that entities within scope X can call the prefix Y.

3. Scope is a way to define how far a prefix is propagated. If LS's were
organized hierarchically, the scope would indicate the level in the
hierarchy. Boundary LS's wouldn't propagate prefixes with a scope
corresponding to their level outside their level. Matt has also
mentioned a TTL for this purpose.

Functions (1) and (2) are similar, (3) is different. The question is:
(1) do we need all three functions, and (2) can a single identifier
serve both purposes? We might be able to get a grip on this by first
figuring the first one out - what is it we wish to accomplish with
scopes, and then we can decide how many attributes we are talking about.

-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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