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Network Working Group D. Mavrakis Request for Comments: 2122 Monaco Telematique MC-TEL Category: Standards Track H. Layec

                                                         K. Kartmann
                                                          March 1997
                      VEMMI URL Specification

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

1) Abstract

 A new URL scheme, "vemmi" is defined. It allows VEMMI client software
 and VEMMI terminals to connect to multimedia interactive services
 compliant to the VEMMI standard (Enhanced Man-Machine Interface for
 Videotex and Multimedia/Hypermedia Information Retrieval Services),
 sometimes abbreviated as "VErsatile MultiMedia Interface".
 VEMMI is a new international standard for on-line multimedia
 services, that is both an ITU-T (International Telecommunications
 Union, ex.  CCITT)  International Standard (T.107) [2] and an
 European Standard (ETSI European Telecommunications Standard
 Institute) standard (ETS 300 382  [3], obsoleted by ETS 300 709 [1]).
 VEMMI could be described as an on-line multimedia protocol describing
 both the man-machine interface and the client/server exchange
 protocol.  VEMMI operates usually on a single continuous session
 between a client and a host and supports an object-oriented, event-
 driven, client/server oriented and platform independent multimedia
 interface. The well-known tcp port number 575 has been assigned by
 IANA to the VEMMI protocol [13].
 A description of the VEMMI standard along with its last approved
 version is publicly available on the Web: see the URL A presentation of
 VEMMI can be found on

Mavrakis, et. al. Standards Track [Page 1] RFC 2122 VEMMI URL Specification March 1997

2) VEMMI URL scheme utility and operability:

  1. VEMMI service selection: A VEMMI multimedia server will listen on

its VEMMI well-known port for incoming connections. The server

   could of course be engaged in many simultaneous connections, and
   after a connection is established, the terminal must be able to
   select the desired VEMMI application, as a same system may host
   different VEMMI applications.
   The best mechanism to fully describe the VEMMI service to activate
   is the URL mechanism.
   - Reporting user action to a remote server: The VEMMI protocol
   establishes a continuous TCP/IP link between the terminal and the
   server during the whole user session. During a session managing
   VEMMI objects, the user actions are usually reported back to the
   server using the VEMMI user data report mechanism that is an
   integral part of the VEMMI protocol.
   However, in some case, the URL mechanism may be required to send
   back reports to a remote host. VEMMI is for example able to display
   HTML documents within a multimedia display area in a VEMMI dialog
   box. these HTML documents may be managed either by the VEMMI server
   (acting as a proxy gateway) or directly by the client software that
   will issue itself the HTTP requests on the network and browse
   across documents on the Web as a standard Web browser (the link to
   the VEMMI server is kept and used for interacting with other VEMMI
   objects and components but the VEMMI server may not be informed of
   the user navigation on the Web inside the multimedia area).
   In such a case, the URL mechanism could also be used to report the
   user actions and commands within a HTML document to be reported to
   the VEMMI server or even another system.
 - Extension of Web browsers: The VEMMI protocol is quite
   complementary to HTTP/HTML used by Web browsers, and several
   networks operators have decided to support jointly Web and VEMMI
   (seen as complementary protocols). Thanks to the VEMMI URL, Web
   browsers will be able to activate a VEMMI client software module to
   start a VEMMI session to the requested service when the user
   activate a vemmi URL included in the HTML document.

3) Description of the VEMMI scheme

 The VEMMI URL scheme is used to designate multimedia interactive
 services conforming to the VEMMI standard (ITU/T T.107 and ETS 300
 A VEMMI URL takes the form:

Mavrakis, et. al. Standards Track [Page 2] RFC 2122 VEMMI URL Specification March 1997

 as specified in Section 3.1. of RFC 1738. If :<port> is omitted, the
 port defaults to 575 (client software may choose to ignore the
 optional port number in order to increase security). The
 <vemmiservice> part is optional and may be omitted.
 This URL does not designate a data object, but rather a multimedia
 interactive service. A VEMMI service starts a multimedia session
 managing multimedia objects and interacting with the user during the
 session. To the difference of other stateless protocols, the link
 between the client and the server is usually maintained during the
 whole session (although in some cases other mechanisms may be used,
 see below).
 The <vemmiservice> is the name of the VEMMI service to activate. This
 field is not mandatory and could be omitted for example if the remote
 host manages only one VEMMI service or activates a VEMMI service by
 default when no service is specified. If this field is omitted in the
 URL and the server requests it, it is assumed that the VEMMI client
 software will prompt the user for it.
 In addition, after the <vemmiservice>, optional attributes and values
 (parameters) associated with the VEMMI service may be specified as
 part of the URL. When present, each parameter (attribute/value pair)
 is separated from each other and from the rest of the URL by a ";"
 (semicolon). The name of the attribute and its value are separated by
 a "=" (equal sign). If present, these fields are used to transmit
 additional data useful for service selection or to request to perform
 a specific processing. For example, the $USERDATA field can be
 specified to transmit additional user-specified data to the VEMMI

4) Client/server dialog during service selection

 The VEMMI client will interpret the VEMMI URL to connect to the
 remote host and to access the specified VEMMI service. After
 connecting to the remote system, the host may prompt the VEMMI client
 for service name and user identification.
 Before starting the VEMMI session, a VEMMI terminal is in 'standard'
 mode and may display the data received from the network in a videotex
 or telnet terminal window. As the VEMMI session may be started
 anytime during an interactive videotex or telnet session, the VEMMI
 service selection is performed by a simple dialog between the client
 and the server.
 The service, username and password information are transmitted by the
 client software to the host in answer to the corresponding requests
 received from the host. The following behavior is expected from the

Mavrakis, et. al. Standards Track [Page 3] RFC 2122 VEMMI URL Specification March 1997

 - wait for the optional request strings from the host server
   ('service:', 'username:' and 'password:') and answer them
   (respectively by <vemmiservice> value defined in the URL and the
   <username> and <password> entered by the user if required).  The
   terminal answer may be sent automatically if the answers are known
   (that is if they are specified in the URL or terminal
   configuration) or it may prompt the user for the needed
   informations.  When parameters (attribute and value pairs) are
   present in the URL, these fields will be sent following the
   <vemmiservice> transmitted to the host in answer to the 'service:'
   request received from the host, separated from the <vemmiservice>
   value by a semicolon.
 - the client answers must always be followed by a Carriage Return
   (CR). If a Line Feed (LF) is transmitted after the CR, it will be
   ignored by the server.
 - in both cases, the server may echo the characters received from the
   client terminal, the received CR being echoed as CR LF. The server
   may echo the password characters as stars or any other scrambled
   output for safety purpose.
 - the client must also be ready to start the VEMMI session as soon
   as it receives the VEMMI_Open command. Before starting this VEMMI
   session, the terminal is in 'standard' mode and may display the
   data received from the network in a videotex or telnet terminal
   window (this is the reason why the service, username and password
   data are requested by the server using a telnet or videotex
   compatible dialog).
 Should an error occur during VEMMI service activation, the remote
 host may inform the user by displaying the error cause. It is
 recommended that, when possible and applicable, the status code
 syntax described in HTTP [8] [9] be used to facilitate automatic
 processing by the client of the host answer during error or normal
 If a VEMMI client software wants to request a VEMMI object without
 establishing a continuous VEMMI session, such a request may also be
 performed using a HTTP request for the vemmi object encoded using the
 Internet media type application/vemmi (pending registration by IANA
 [10]). In the same way, HTTP could be used in some cases to exchange
 data pertaining to a VEMMI session with or without setting the keep-
 alive keyword in the Connection header to request a persistent
 connection [9]. Protocol switching using the upgrade header field may
 be used in such case to switch to vemmi protocol [9]. This possible
 use of HTTP for VEMMI is not described in this document.

Mavrakis, et. al. Standards Track [Page 4] RFC 2122 VEMMI URL Specification March 1997

5) Proposed syntax

 The proposed BNF syntax is encoded as specified in RFC 1738 [5] [14]:

; vemmi (see ITU-T T.107 and ETSI ETS 300 709)

vemmiurl = "vemmi:" hostport [ "/" vemmiservice *[ parameter ] ] vemmiservice = *[ uchar | "/" | "?" | ":" | "@" | "&" | "=" ] parameter = ";" attribute "=" value attribute = *[ uchar | "/" | "?" | ":" | "@" | "&" ] value = *[ uchar | "/" | "?" | ":" | "@" | "&" ] This syntax: - allows the user to specify the remote host address by its name or numeric address. Although he could select a specific port, it is expected the information providers and VEMMI software will mostly use the port number assigned to VEMMI (575) [13]. For security reasons, the username and password could not be specified in the URL. - allows him to select a specific VEMMI service if the remote host manages several different VEMMI services. - allows also to send additional data to the service using the parameter syntax, either during the service selection phase or when the user selects a vemmi hyperlink within a HTML document displayed in a VEMMI multimedia area. To the difference of the params syntax used in [4], the parameter syntax requires each value to be labeled by an attribute. The parameter attribute names are case- insensitive. Parameter values may or may not be case-sensitive, depending on the attribute. All the values of fieldname beginning by a dollar ($) sign are reserved for specific use, including: - $COMMAND: VEMMI command to be returned to the host when the VEMMI session do not use a continuous link. - $CONTEXTDATA: context data. - $OBJECT_REQUEST: requests the retransmission of a given VEMMI object. - $USERDATA: user data specific by the user and to be processed by the VEMMI service. 6) Examples: Some examples of VEMMI URLs along with the corresponding client/server dialog are presented below, they are for information only: a) A simple VEMMI URL and the corresponding dialog for a VEMMI service that does not enforce access control might be: URL:

Mavrakis, et. al. Standards Track [Page 5] RFC 2122 VEMMI URL Specification March 1997

    In this case, the exchange between client and server will be as
    follow (the server requests are presented left, client answers
 service:        demo
 200 OK                     {status code returned by the VEMMI host}
 b) The service name may be omitted (for example if the remote server
    hosts only one VEMMI service), and the URL might then be:
      URL: vemmi://
    In this case, the VEMMI interactive session is started immediately
    by the host without requesting first the service name (should the
    client receive a service request from the host, it will prompt the
    user for service name).
 c) The URL could not include the username and password. In this case,
    should they be requested by the host, the VEMMI client may use a
    default value specified for this service or prompt the user for
    them (for example it could propose anonymous and user e-mail
    address as defaults):
      URL: vemmi://
    In this case, the exchange between client and server may be as
    follows (server requests at the left, client answers at the right):
 service:        demo
 login:          anonymous       {user has been prompted for username}
 password:  {user prompted for password}
 401 Unauthorized                {an anonymous user is not allowed to
                                  access the service}
 d) Some services may use additional data transmitted in the parameter
    fields, for example:
      URL: vemmi://;$USERDATA=smith;account=1234
    If no access check is done by the host, the dialog might be:
 service:        demo;$USERDATA=smith;account=1234
 200 OK
  ...starting VEMMI session...

7) Procedure to use when a VEMMI URL is encountered in a HTML document

  without VEMMI support:
 The VEMMI URL support may be built-in in some Web browsers, or
 offered by an associated software or plug-in interworking with the
 user browser, for example using the WWW_RegisterProtocol API command
 to register the new VEMMI protocol.
 When a Web browser encounters a VEMMI URL without having VEMMI support,
 two cases may occur:
 - some browsers will detect an unrecognized scheme and signal an
   unrecoverable error directly.

Mavrakis, et. al. Standards Track [Page 6] RFC 2122 VEMMI URL Specification March 1997

  1. others will manage it as a relative URL [4] and will build a

complete URL including the VEMMI URL and will request it from the

   host having sent the current document. In this case the host will
   usually return the error "not found".
 Among the mechanisms that could be used in order to offer a friendly
 interface to both users with and without VEMMI support:
 - when the second case occurs and the relative URL including the
   vemmi:// string is transmitted to the server, the HTTPD server may
   be modified in order to recognize such URL and to propose the
   downloading of a VEMMI client software.
 - the HTML document including the vemmi URL allowing to start the
   VEMMI session may propose both options, for example:
      If your browser supports VEMMI, directly
      <A HREF="vemmi://">start the interactive
      multimedia service</A>, otherwise
      <A HREF="">download first a VEMMI
      client software</A>.
 - the application/vemmi MIME type is defined below (to allow for
   example exchange of vemmi objects). A possible way is for the
   server to look in the HTTP Accept header field and to deduce that if
   application/vemmi is supported, then the VEMMI support exists (in
   this case, application/vemmi is to be defined in the browser and
   associated with the vemmi decoder).

8) Security Considerations:

 The VEMMI URL scheme is subject to the same security implications as
 the general URL scheme [5] [14], so the usual precautions outlined in
 [5] [14] apply (for example, it is not allowed to store the username
 and password in the URLs).
 Furthermore, among VEMMI objects that could be used during the
 interactive session, metacode objects (representing a sequence of
 VEMMI commands) and operative objects (they are executable programs
 to be run on the client platform) may be downloaded and/or started.
 In order to protect the user against the activation of an harmful
 operative object, it is strongly recommended that the users use the
 configuration menu of their VEMMI software to disable the option of
 running operative objects when receiving potentially unsafe VEMMI
 objects, or at least enable the option to request first user approval
 before starting the execution of an operative object.
 The VEMMI remote interactive services may vary widely in their access
 control policies; in practice, when a prompt for username or password
 is received, the VEMMI terminal should request them from the user.
 The VEMMI terminal implementation could support additional features,

Mavrakis, et. al. Standards Track [Page 7] RFC 2122 VEMMI URL Specification March 1997

 for example proposing by default "anonymous" as username and the user
 Internet e-mail address as password, or looking in an encrypted local
 database for user identification on this service.
 Such an identification mechanism using the username/password scheme
 is unsecure and is provided for backwards compatibility only. The
 VEMMI services requiring a safe identification procedure must rely on
 other alternative mechanisms (e.g. S/KEY or other). In numerous
 cases, the user identification procedure will be performed by the
 VEMMI service.

9) application/vemmi MIME type

 VEMMI is a multimedia interactive service and VEMMI objects are
 usually exchanged through a continuous VEMMI multimedia session.
 However, VEMMI objects could also be transmitted and exchanged using
 other mechanisms, for example using HTTP, through e-mail, and so
 on... The assignment of a MIME media type application/vemmi will
 allow this transport and exchange of VEMMI objects, and this
 paragraph describes this MIME type.
 Furthermore, for Web browsers not supporting the addition of new URL
 protocol scheme, the VEMMI MIME type may also be used to transmit,
 instead of a VEMMI object, a text file containing the VEMMI URL to
 activate to connect to a VEMMI server.


 MIME media type name: "application"
 MIME subtype name: "vemmi"
 Required parameters: none
 Optional parameters:
 - version:
   an optional version number may be specified, in the format:
   The version number is a numeric integer whose is encoded as the
   <version> parameter defined in ETS 300 709 (e.g. version=100), and
   whose the first digit represents the major VEMMI version number.
   It must be pointed out that the VEMMI objects includes the VEMMI
   version and a timestamp.

Mavrakis, et. al. Standards Track [Page 8] RFC 2122 VEMMI URL Specification March 1997


 The "base64" mechanism is preferred because VEMMI use a native 8-bit
 binary file format. However, as VEMMI includes its own 7-bits
 encoding mechanisms, VEMMI data could also be transmitted in 7-bit


 Refer to paragraph 8.


 VEMMI is designed to be fully platform independent, and the VEMMI
 objects and contents could interoperate between any platform. The
 only exception are the VEMMI operative objects that could be binary
 programs specific to a given hardware platform and operating system.

10) Liaison address:

 For all technical questions regarding this request, please contact:
         Daniel Mavrakis
         Monaco Telematique MC-TEL
         P.O. Box 225
         MC 98004 Monte-Carlo Cedex
         Tel: (+377) 9216 8860
         Fax: (+377) 9330 4545
 Comments may also be addressed to:
         Mr. Herve Layec,
         ETSI STC TE1
         06921 SOPHIA ANTIPOLIS Cedex
         Tel: (+33) 2 99 12 73 01
         Fax: (+33) 2 99 38 49 61

Mavrakis, et. al. Standards Track [Page 9] RFC 2122 VEMMI URL Specification March 1997

         Mr. Kurt Kartmann
         Gabelsbergerstr. 2
         D-64807 DIEBURG
         Tel: (+49) 6071 1528
         c/o Deutsche Telekom AG
         Tel. (+49)6151 834965, Fax (+49) 6151 834284
 The authors thank the other members of the ETSI TE1 VEMMI Working
 Group for their comments:
  1. Michael Blaschitz (
  2. Agnelo Fernandes (
  3. Daniel Allonsius (
  4. Stefaan Herrebout (
  5. Francisca Oliva (
  6. Herwart Wermescher (

11) References:

 [1] "Enhanced Man-Machine Interface for Videotex and
     Multimedia/Hypermedia Information Retrieval Services (VEMMI
     revision 1)", ETS 300 709 standard (European Telecommunications
     Standards Institute), September 1996.
     This document is available on the Web in HTML format: see
 [2] "Enhanced Man-Machine Interface for Videotex and Other
     Information Retrieval Services (VEMMI)", ITU-T T.107 standard
     (International Telecommunications Union), March 1995.
 [3] "Videotex Enhanced Man-Machine Interface service (VEMMI)",
     ETS 300 382 standard (European Telecommunications Standards
     Institute), February 1995.
 [4] Fielding, R., "Relative Uniform Resource Locators", RFC 1808, UC
     Irvine, June 1995.
 [5] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform Resource
     Locators (URL)", RFC 1738, December 1994.
 [6] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
     October 1994.

Mavrakis, et. al. Standards Track [Page 10] RFC 2122 VEMMI URL Specification March 1997

 [7] Mavrakis, D., "VEMMI and Internet", TD 44, ETSI TE1 plenary
     meeting in Brussels, October 20, 1995.
 [8] Berners-Lee, T., Fielding, R., and H. Frystyk: "Hypertext Transfer
     Protocol - HTTP/1.0", RFC 1945, MIT/LCS, UC Irvine, May 1996.
 [9] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
     Berners-Lee, Transfer Protocol - HTTP/1.1", RFC 2068, UC Irvine,
     January 1997.
 [10] Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
      Mail Extensions (MIME) Part Four Registration Procedures", BCP
      13, RFC 2048, November 1996.
 [11] Masinter, L., Zigmond, D., and H. Alvestrand, "Guidelines and
      Process for new URL Schemes", Work in Progress.
 [12] Berners-Lee, T., and D. Connolly, "Hypertext Markup Language
      Specification - 2.0", RFC 1866, MIT/LCS, November 1995.
 [13] "Port Numbers",
 [14] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource
      Locators (URL)", Work in Progress.

Mavrakis, et. al. Standards Track [Page 11]

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