Voice Profile for Internet Mail (VPIM)

Voice Profile for Internet Mail (VPIM) is a specification for the exchange of voice and fax messages between messaging servers over an IP network. As such, it characterizes (similarly to SMTP and MIME) another essential component of unified messaging. VPIM defines the format of the messages as well as the way to transport the messages across the network. In particular, VPIM specifies a restricted profile of MIME and ESMTP (RFC 1869) (see the preceding sections.) The basis of the major Internet messaging standards explains why the various versions of VPIM have also been submitted to and reviewed by the IETF, even though they were originally developed by the Electronic Messaging Association (EMA) (www.ema.org). The IETF has approved VPIM Version 2 as a Proposed Standard (RFC 2421).

Add a Note HereVPIM enables Internet mail systems to be used to transport voice and fax messages, even though these messages may have originated or terminated in the PSTN. In addition, the user can be given access to voice and fax messages from an Internet mail application. The rest of this section summarizes key components of VPIM V2, including addressing scheme, message body format, and message transport.

Add a Note HereThe VPIM addressing scheme provides for the unique identification of the sender (or recipient) of a VPIM message, whose access device may be a simple telephone. It is composed of two parts: the host part for server identification and the local part for user or mailbox identifier. Specifically, the host part is based on the domain name system (DNS) (RFC1035) and the local part on ITU-T Recommendation E.164. The purpose of restriction to a numerical local part is to maintain compatibility with traditional messaging servers tailored to a single type of access device—telephones. An example of a VPIM address is +17329490321@lucent.com.
Add a Note HereRegarding the format of the message body, VPIM supports a profile of MIME. Using the extension mechanism of MIME, VPIM adds a new content type—multipart/voice-message. In most cases, this content type is declared in the top-level header of a VPIM message, which is typically composed of multiple parts containing content such as the spoken name, spoken subject, voice message (or fax message), and electronic business card of the originator. Each of the multiple parts also carries a content type. VPIM V2 only supports certain content types. In particular, Audio/32KADPCM is the content type that must be used for parts carrying voice information; 32KADPCM denotes the 32-kbps ADPCM voice encoding standard (as defined in the IUT-T Recommendation G.726) according to which the voice must be encoded. Image/Tiff, on the other hand, is the content type that must be used for parts carrying fax messages. Moreover, the F profile of Tag Image File Format (RFC 2306) must be used for fax encoding.

Add a Note HereVPIM V2 also specifies how the entire message should be encoded for transporting. If binary transport is available, voice and fax parts are to be sent in binary format (RFC 2045). Otherwise, they are to be encoded in base64. In order to meet MIME requirements and to preserve interoperability with the fullest range of possible devices, the detection and decoding of Quoted-Printable, 7bit, and 8bit is also mandatory in VPIM V2.

Add a Note HereAnother key issue addressed by VPIM V2 is how messages should be transported between messaging systems. ESMTP (RFC 1869) is the mechanism selected for message transporting.

Add a Note HereVPIM V2 does not interfere with desktop delivery protocols [such as Internet Message Access Protocol (IMAP) (RFC 2060) or Post Office Protocol Version 3 (POP3) (RFC 1939)]. The user can employ IMAP (or POP) to retrieve VPIM messages from a remote mailbox just like regular text e-mail messages.
Add a Note HerePOP3 is a simple protocol used for fetching e-mail from a remote mailbox and storing it on the user’s local machine to be read later. It has commands for the user to log in, log out, fetch messages, and delete messages. Encoded as U.S. ASCII text, it has some flavor of SMTP. Compared with POP3, IMAP is a more sophisticated delivery protocol. Its key objective is to let the e-mail server maintain a central mailbox to which the user can have access from any computer, such as a workstation in the office, a PC at home, or a laptop on the road. As a result, unlike POP3, IMAP does not copy e-mail to the user’s personal machine. In addition, IMAP has advanced features such as addressing mail not simply by arrival sequence but by attributes like subject and sender.

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