Subject: RE: [Enum] non-E.164 Numbers in ENUM

From: "Yu, James" <[email-masked]>
Date: Wed, 15 Sep 2004 14:30:54 -0400

To add to the discussion, the ENUM registrars and Tier 1 Registry or
Registries can enforce that a registered phone number is indeed a valid
E.164 # per that country's or region's numbering plan.   An end user who is
assigned 1-571-434-1234 cannot register 1-571-434-1235 or 1-571-434-123.

There is no way to prevent the Tier 2 nameservers from having an entry on
1-571-434-1234-3 in addition to an entry on 1-571-434-1234 unless there is a
policy that the Tier 2 nameserver operators/providers must not include
entries for phone numbers (in ENUM domain name format) that do not appear at
the Tier 1 Registry and that policy can be enforced (e.g., end users cannot
operate the Tier 2 nameservers for their own #s).  But if the end users can
operate their own Tier 2 nameservers, it would be difficult to detect the
policy violation and enforce that policy, even if one exists.

ENUM resolver (one that generates the ENUM query for a phone number) can
only check if the phone number has more than 15 digits (a valid E.164# is up
to 15 digits long) because it is not likely to understand the numbering plan
in every country.   It won't be able to know if 1-571-434-1234-5 is a valid
E.164# if it does not understand the numbering plan for country code 1. 

So if someone tries to reach 1-571-434-1234-5 by following the advertised
phone number or by mistakenly entering one additional digit , the ENUM
resolver will generate an ENUM query on 5.4.3.2.1.4.3.4.1.7.5.1.e164.arpa.
If the end user has the NAPTR RRs for 5.4.3.2.1.4.3.4.1.7.5.1.e164.arpa. or
a wild card, the requester will get a response, whether there is a policy
violation or not.

Allowing the above would allow the caller to reach the called party based on
the # advertised in either the IP domain or the PSTN domain.

James

-----Original Message-----
From: Marian Durkovic [mailto:md at bts.sk]
Sent: Wednesday, September 15, 2004 1:23 PM
To: Mpierce1 at aol.com
Cc: enum at ietf.org
Subject: Re: [Enum] non-E.164 Numbers in ENUM

> For ENUM, there needs to be a clarification of what entries can be
supported 
> in ENUM. I believe it needs to be made very clear that it can not include 
> number combinations that exceed the E.164 defined numbers (as regulated by
various 
> countries). In the world zone 1, that is currently 10 digits.

I'm afraid this is not technically possible. Once you delegate a zone with 
NS record(s), the dalegated nameserver can put any number of subdomains
under the delegated domain or even a wildcard record to match anything
- this in fact drops all extra digits right away.

In some cases adding extra digits might even be useful - for example
to be able to directly reach PBX extensions on a PBX without DDI block.

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---

From: Jim Reid <[email-masked]>
Date: Wed, 15 Sep 2004 15:09:04 -0400

>>>>> "James" == Yu, James <james.yu at neustar.biz> writes:

    James> ENUM resolver (one that generates the ENUM query for a
    James> phone number) can only check if the phone number has more
    James> than 15 digits (a valid E.164# is up to 15 digits long)
    James> because it is not likely to understand the numbering plan
    James> in every country.  It won't be able to know if
    James> 1-571-434-1234-5 is a valid E.164# if it does not
    James> understand the numbering plan for country code 1.

Indeed. In fact it would be very foolish for anyone to put a priori
knowledge of a numbering plan into an ENUM resolver. Especially on an
embedded device like a handset. Numbering plans change. Pretty much
all an ENUM resolver could/should do is check that the input string
conforms to the length and legal character set defined in E.164.

---

From: [email-masked] (Claus Färber)
Date: Fri, 17 Sep 2004 07:22:56 -0400

Yu, James <james.yu at neustar.biz> schrieb/wrote:
> ENUM resolver (one that generates the ENUM query for a phone number)
> can only check if the phone number has more than 15 digits (a valid
> E.164# is up to 15 digits long) because it is not likely to understand
> the numbering plan in every country.

In Germany, for example, there is no numbering plan that indicates the
length of the numbers. For example, +49-9999-123 could be a complete
number while +49-9999-124 is not. With PBXes, this can even be the sole
decision of the PBX's operator.
It's even possible, although very rare, that both +49-9999-123 and
+49-9999-1234 co-exist.[1]

Further, while E.164 says that phone numbers can't be longer than 15
digits, some network or PBX operators hand out longer numbers for
"special" purposes. Those can't be reached from all around the world, of
course, but they still have their uses.

Claus

[1] In ENUM, it's possible to do that with CNAME:

$ORIGIN 3.2.1.9.9.9.9.9.4.e164.int.
@       CNAME   _
_       XXX     # entries for +49-999-123
1       XXX     # entries for +49-999-1231
2       XXX     # entries for +49-999-1232

Suddenly, you do need non-digits in the ENUM tree...
-- 
http://www.faerber.muc.de