UTF-8

This document discusses subsets of the Unicode character repertoire for use in protocols and data formats and specifies three subsets recommended for use in IETF specifications.

This specification extends the Internet Message Access Protocol, specifically IMAP4rev1 (RFC 3501), to support UTF-8 encoded international characters in user names, mail addresses, and message headers. This specification replaces RFC 6855. This specification does not extend IMAP4rev2 (RFC 9051), since that protocol includes everything in this extension.

This specification extends the Post Office Protocol version 3 (POP3) to support international strings encoded in UTF-8 in usernames, passwords, mail addresses, message headers, and protocol-level text strings.

This memo splits message submission from message relay, allowing each service to operate according to its own rules (for security, policy, etc.), and specifies what actions are to be taken by a submission server.

Message relay is unaffected, and continues to use SMTP over port 25.

When conforming to this document, message submission uses the protocol specified here, normally over port 587.

This separation of function offers a number of benefits, including the ability to apply specific security or policy requirements. [STANDARDS-TRACK]

This document explores issues with Internationalized Domain Names (IDNs) that result from the use of various encoding schemes such as UTF-8 and the ASCII-Compatible Encoding produced by the Punycode algorithm. It focuses on the importance of agreeing on a single encoding and how complicated the state of affairs ends up being as a result of using different encodings today.

The Internet today is in need of a standardized form for the transmission of internationalized "text" information, paralleling the specifications for the use of ASCII that date from the early days of the ARPANET. This document specifies that format, using UTF-8 with normalization and specific line-ending sequences. [STANDARDS-TRACK]

There are a number of circumstances in which an escape mechanism is needed in conjunction with a protocol to encode characters that cannot be represented or transmitted directly. With ASCII coding, the traditional escape has been either the decimal or hexadecimal numeric value of the character, written in a variety of different ways. The move to Unicode, where characters occupy two or more octets and may be coded in several different forms, has further complicated the question of escapes. This document discusses some options now in use and discusses considerations for selecting one for use in new IETF protocols, and protocols that are now being internationalized. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

This document specifies an RTP payload format for the transmission of 3GPP (3rd Generation Partnership Project) timed text. 3GPP timed text is a time-lined, decorated text media format with defined storage in a 3GP file. Timed Text can be synchronized with audio/video contents and used in applications such as captioning, titling, and multimedia presentations. In the following sections, the problems of streaming timed text are addressed, and a payload format for streaming 3GPP timed text over RTP is specified. [STANDARDS-TRACK]

ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279.