SIP in higher education

[Ed Guy <>]

Sip.edu'ers

I really like John Todd's proposal of using the ITAD to indicate the 
"domain"
portion when mapping numbers to sip uri's however, everyone I talk to 
outside
of this group about using the '*' as a delimiter cringes.  While no one 
I've discussed
it with can say with full certainty that an asterisk in the middle of a 
dial string will
absolutely break some system,  they're willing to bet it will.  There's 
got to be a
better way to encode this info.   This email introduces another approach
after a bit of analysis.

For the sake of this discussion,  I'll work from the following 
requirements:
* The sip:user@domain  uri Shall be translated into two sets of digits 
that are combined
   into  a string composed of  common DTMF characters {0..9*#} suitable 
for dialing
   on a traditional phone.
* The "user" portion of the string Shall be determined by a policy local 
to the domain.
* The "domain" portion string Shall be common for all members of a given 
"domain"
* the non-numeric DTMF characters SHOULD be used in a manner consistent with
  known dialing limitations.
* The total length of the string SHALL NOT exceed 15 characters
* E.164 numbers in the NANP SHALL NOT be used as an identifier.

I'll further make these assumptions:
* ITAD numbers are the choice for domain numbering.
* collisions with other dialing patterns are not a concern because some 
local dialing
  prefix (e.g. 012, or 0110) will be used.
* partial dialing and dial patterns are not a major concern; there is no 
need to collect
  subsequent digits.

Therefore,  I'll go back to my short list of simple methods to 
accomplish this two
part encoding. 

* the two fields can be delimited by a known character:
* one of the fields can be fixed length
* or the length of the field can be determined from the number.

Using a known character as a delimiter is difficult because any numeric 
choice limits the
valid user and domain choices and '*' and '#' just might make dialing 
difficult.

The US Phone company made the 'carrier' field fixed length and kept 
having to extend
it.  10XX, 10XXX?, 101XXXX.  Any choice we make is likely to be wrong 
and wasteful
My number might be 33489-000258 or 000258-33489 

Country codes are of known length based on the first digit.  Assigning 
them this way would
be difficult and it changes the IANA assignment procedure.  BUT, we can 
use the IANA
assigned ITADs and run length encode them by prefixing  (or appending) 
the length of the
ITAD.  So, my number might be 3258-33489 for ITAD 258 or  41234-33489 
for ITAD 1234. 

So the proposed algorithm to encode sip.edu numbers  is
   sip.edu number = strlen(ITAD)+ITAD+USER
where '+' is the concatenation operator.

This technique is no longer than the delimited case, it is surely more 
compatible with
traditional phone systems, and it maps nicely into private ENUM and SRV 
records,
with out any changes. It can also use a table lookup if needed.

(By the way, another possibility is to put the ITAD and length at the 
end: making it
33489-2583. 
   sip.edu number =? USER+ITAD+LEN(ITAD)
while the Internet does least-to-most significant encoding,  the phone 
system does
most-to-least encoding and other than being in the same order as the 
email address, I
cant come up with any advantages of this over the prior method)


Comments??  Fire way!

/ed


--
======================================================================
Edward T. Guy, III, Ph.D. Chief Scientist, Pulver.com Enterprises 
Melville, NY 11747
sip:
mailto:
tel:+1.973.437-4519