Subject: Comment on SIP

From: [email-masked]
Date: Mon, 16 Feb 98 19:22:43 +0900

Dear Authors of SIP,

I have worked for Iwatsu electric in Japan.
The company is a Japanese manufacture that produces
PBXs, test and measurement instruments and others.
I belong to CTI engineering department of the company,
and have developed CTI relational software.

I read your internet draft named "SIP:Session Initiation
Protocol" and I have some comments on that.

Q 1.
On page 49 and 50 there are some PSTN phone addresses that
I think they use a notation defined in a working phase draft 
called "URLs for telephony".
But the directive, "phone" is different from the draft and
they have additional descriptions such like "service=", 
"mobility="...
Do they use a different notation from the draft. If so, could
you name the specification(s).

Q 2.
If the answer of Q 1 is using a different or modified specification,
is it possible for you to add a new parameter to the specification ?

The parameter is "scope=" that specifies the valid scope of 
the phone number.

The following is the usage of this parameter.
If the scope is extension, the number can be reached from
a local PBX, i.e. the number is a PBX extension number.
If the scope is global or the parameter is omitted, the number can be
reached from any PSTN network, i.e. the number is an international number 
in ITU Recommendation E.123.

If the destination cannot be reached via computer network, dialing the
extension number is a good alternative method, if it can be used.

P.S.
Recently I have worked on a project that is something to do with
a telephone dialer.
The dialer can dial a telephone number which is in an attachment file
of a e-mail.
A way to call the sender of the e-mail is to simply double click the attachment
file, if the mailer is Microsoft Internet Mail and maybe other mailers require 
the same operation.
Our intention is that those attachment files use the SIP syntax.
This is very convenient for those who get a SIP OPTION response.
Because they use the same destination information for Internet phone and e-mail.
Our Idea is that the information can be at least converted automatically.

I asked the same question about the scope to Vaha-Sipila, but
I was replied that my asking is valid but the draft cannot be modified.
Please refer the following quotations.

Any comments on our idea are also solicited.

Best Regards,

+-----------------------------------------------+
 Hiroaki Takagi
 Iwatsu Electric Co., Ltd.
 CTI Engineering Dept.

 Address: 7-41, Kugayama 1-Chome Suginami-ku, 
          Tokyo, Japan
 Phone:  +81-3-5370-5239 FAX:+81-3-5370-5477
 Email:  [email-masked]
+-----------------------------------------------+

The following is an e-mail I sent to the author of 
"URLs for telephony".
-------------------QUOTE --------------------------
Dear Antti,

I have worked for Iwatsu electric in Japan.
The company is a Japanese manufacture that produces
PBXs, test and measurement instruments, and others.
I belong to CTI engineering department of the company,
and have developed CTI relational software.

I read your internet draft named URLs for telephony,
and have some comments on that.

local-phone-number on page 3, fax-local-phone on page 4 
and the relational example on page 7 have ambiguity.
Because the valid scope of this number is undefined.

Some can dial this number to reach the destination
successfully, but others cannot. It depends on their telephone
environment.

In order to let users or software know whether this local number
is valid for their environment or not, the number should have 
a valid scope range.

But I understand that defining the scope range is very difficult.
Because telephone networks are very complex and not systematically configured.
The definition might be just a clue that cannot completely specify the range.

Here are some local scopes.
(1) no country code.
(2) no country code nor area code(local phone call).
(3) a PBX extension number(includes VPN).

Here are possible solutions.
(1) use country name.
(2) use ,say city name or etc.
(3) use ,say company name.

I think this is still very difficult for a machine including software to 
correctly determine any time its environment is in the scope or not.
But chances that people can say it is very much.

So local-phone-number would be something like

local-phone-number = 1*(phonedigit... scope
scope = ";scope=" anychar
anychar = 1*(alphanumeric character)

An example of local-phone-number would be

telephone:1234;scope=ACME SOFTWARE
telephone:0353705239;scope=japan

I think this works better than old one.
Thank you for your consideration in advance.

Regards,

+-----------------------------------------------+
 Hiroaki Takagi
 Iwatsu Electric Co., Ltd.
 CTI Engineering Dept.

 Address: 7-41, Kugayama 1-Chome Suginami-ku, 
          Tokyo, Japan
 Phone:  +81-3-5370-5239 FAX:+81-3-5370-5477
 Email:  [email-masked]
+-----------------------------------------------+

---------------- UNQUOTE -----------------------

The following is the reply for my e-mail.

---------------- QUOTE -------------------------
Dear Hiroaki Takagi,

Thanks for your comments. Your comments are valid, and the scope of the
phone number is indeed ambiguous. However, this has been discussed
previously on some mailing lists (namely IETF-FAX, the mailing list of
Fax-over-Internet working group). The consensus was that if the phone
number is to be written in local notation, it is the URL writer's
responsibility to make sure that the nobody that does not know the scope
has access to that URL.

The draft exclipitly encourages the use of international notation.

The local phone number scheme was added later because the "phone numbers
in mail addresses" draft from IETF-FAX had it, and the notation I use is
similar to that. It is very probable that I cannot make any
modifications to my proposal any more as the fax addressing draft has
already been frozen, and my draft was supposed to mirror the fax
addressing proposal very closely.

As you pointed out, it is very hard for the computer to determine
whether it is in the correct scope or not. This is why I think that it
would be easier to include this information (if required) in
human-readable form somewhere close the URL, like this:

My phone number is <a href="telephone:0011223344">0011223344</a>, from
inside Foobar Industries, Inc.

Another problem with computer-readable scope information is that the
scope should eventually be some form of unambigous reference to the
company/country/etc., and assigning object identifiers to every living
and non-living entity has been proved to be very hard (I refer to X.500
directories).

But, thanks for your input. I think I will add a word of warning about
the use of local telephone numbers in the next version of the draft.

Best Regards,

Antti

---------------- UNQUOTE -----------------------

---

From: Henning Schulzrinne <[email-masked]>
Date: Mon, 16 Feb 1998 09:49:11 -0500

> they have additional descriptions such like "service=",

I looked at
ftp://ds.internic.net/internet-drafts/draft-antti-telephony-url-03.txt
and did not find any reference to "service" or "mobility". I assume you
are thus referring to the SIP draft. These modifiers are (now more
clearly...) *not* part of the URL, but part of the Location header and
described in the "Call Control" SIP extensions draft.

> you name the specification(s).

The intent is to align phone number notation as much as possible with
other ongoing IETF work; thanks for pointing out the discrepancy. 

Some of the things contained in the URL are part of the Location header
in the "Call Control" draft. Our intent was to keep the phone URL to
what's necessary to make a phone call, rather than describe the service
completely, that being the job of other protocols. (One reason not to
include this in the URL is that classifications such as business and
home are of interest for all kinds of URLs, including H.323, SIP,
possibly even email and web pages. This blurs the distinction between a
"locator" and descriptor (URC). Another reason is that it makes URLs too
long and it becomes unclear as to whether one has to specify all of it
to actually make the phone call.)

> extension number is a good alternative method, if it can be used.

One of the greatest weaknesses of the phone numbering system is that
phone numbers are not source-independent, i.e., depending on where I am,
I need to dial different numbers to reach a location or, conversely,
that a number which is valid from location X is not valid from location
Y. (Example: In Atlanta, you have to dial the area code for local
numbers, but you are not allowed to dial the 1. Try convincing the
Windows'95 dialer of that...)

I thus agree with Antti Vaha-Sipila's reasoning that including scoped
numbers is (a) a bad ideas, (b) if it has to be done, cannot be
automated in any meaningful way. "Local" has very little meaning on the
Internet, as it is quite likely that web pages, for example, don't have
the same locality as phone numbers.

Unless there is a strong reason not to do this, I would much rather
force all phone numbers in SIP to be global (that is, full E.164) and
let the PBX figure out that this is a local number (trivial, by
comparing the prefix) and strip any numbers not needed for dialing.

Henning