[Sip] language info in SIP headers

[Shingo Fujimoto <shingo_fujimoto@jp.fujitsu.com>]

Hello. I would like to raise the new issue to solve.

SIP RFC specified UTF-8 friendly transport, but I think that did not
specified the way to use multi bytes characters in header part of
SIP messages.

If I use Japanese Kanji letters in From: header (as display name),
the receiver UA cannot determine which language of characters are
used in UTF-8 encoded text. Additionally, since UTF-8 CJK kanji
characters are overlapped between Chinese, Japanese, and Korean,
sometimes UA can not determine which font should be used to display
them.

MIME part 3 and updated RFC2231 introduced some solution for this
problem with combination of character set and language tag. However
RFC2231 always required escaping 8bit-flaged characters, there are
huge overhead to express multi byte characters.

As another option, recent Unicode 3.x specification includes
"language tag" characters to solve this problem, but it is not
common to support such new feature in the any UTF-8 handling
libraries. I guess that results corrupted display in UAs.

My suggestion about this, we should prepare supplemental document
for SIP which specify the way to express international characters
with language information in header part (modified RFC2231 or UTF-8
with "lang tag" support).

I would like to hear your opinion.

Thank you.
-- 
======================================
         SHINGO FUJIMOTO
    FUJITSU LABORATORIES LIMITED
E-mail: shingo_fujimoto@jp.fujitsu.com



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