Service Location Working Group                            Erik Guttman
 Internet Draft                                  Sun Microsystems, Inc.
 Expires in six months

                         The service: URL Scheme

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   The service: URL scheme is used to provide service access information
   for arbitrary network services.  These URLs provide an extensible
   framework for client based network software to obtain configuration
   information required to make use of network services.  A service: URL
   may be accompanied by a set of well defined attributes which define
   the characteristics of the service.  These attributes may convey
   protocol configuration information to client software or service
   characteristics meaningful to end users.  This document describes how
   to define and standardize new service types and attributes for use
   with the service: scheme and provides examples.

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Table of Contents

      1. Introduction
         1.1. The service: Scheme
         1.2. Related work
      2. Use of service: URLs
      3. Specifying A New Service Type
         3.1. A Service Type specification defines:
              3.1.1. Service Type
              3.1.2. The service: 'urlpath' information
              3.1.3. Attributes
              3.1.4. Service Discovery Multicast Address
         3.2. Specifying Attributes
              3.2.1. A subtlety
              3.2.2. Types and String Encoding
              3.2.3. Attributes with multiple values
              3.2.4. Grouping attributes values together in records
         3.3. Special Attributes
              3.3.1. Service Discovery Multicast Address
              3.3.2. version
              3.3.3. Language tag
         3.4. Service Type templates
              3.4.1. Definition
              3.4.2. Manditory Attributes
              3.4.3. Attribute syntax for Service Type templates
              3.4.4. Use of templates by the Service Location Protocol
      4. A Process For Standardizing New Service Types
      5. Encoding Rules for Service Type URLs
      6. Examples
         6.1. NFS
              6.1.1. The NFS Service Type template
              6.1.2. Example: A 'pub' directory
              6.1.3. Example: A 'dist' directory
         6.2. LPR
         6.3. POP3
      7. Security Considerations
      8. Internationalization Considerations
         8.1. Character Set identification and use
         8.2. Language identification and translation
      9. Bibliography
     10. Author's Address

1. Introduction

   This document describes a URL scheme which will allow arbitrary
   network services to have a standard notation for defining their
   service access point.

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   In addition it describes how to define a set of attributes to
   associate with service: URLs.  These attributes will allow end users
   and programs to select between network services of the same type that
   have different capabilities.

   The use of these attributes is recommended but not required to make
   use of the service: URL.  The minimal encoding rules for attributes
   are specified.

   Service Type templates are used to describe services which use the
   service: URL in a standard way.  The rules for writing such a
   template are provided, as are three examples.

   All grammar encoding follows the Augmented BNF for syntax
   specifications [ABNF] with a few deviations.

1.1. The service: Scheme

   The service: scheme and all information which follows it MUST obey
   the URL conventions defined in [RFC1738].

   The scheme specific information following the service: scheme
   provides the service type and address of a network service.  It may
   additionally include service type specific information.  The form of
   a service: URL is as follows:

         serviceurl =  "service:" service-type ":" service-part

   The formal syntax for a serviceurl is given in Section 5.

   The service-type string indicates a specific protocol, such that
   client software can be expected to unambiguously make use of the
   service.  The Service Type determines semantics of the service-part
   and the attributes associated with the service: URL.

   The service-part includes an ip-schemepart.  This will define either
   a domain name or a numerical ip address for the service and possibly
   more, such as a port number to use.  The remainder of the service-
   part is intended to provide sufficient information for client
   software to be able to bind and make use of a service.

   The service-part allows for extensions to the basic tuple of Service
   Type and host (and possibly port number), so that more information
   may be provided to uniquely identify the resource. It is also
   possible, though less preferable, to provide uniquely identifying
   information in the attribute information associated with a service:
   URL.  This string will be referred to in this document as the
   'urlpath' to be consistent with [RFC 1738].

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   The attributes associated with the URL are not included in the URL.
   They are stored and retrieved using other mechanisms.  The service:
   URL serves as a unique identifier, to be used in registering or
   requesting the attribute information.  The Service Location Protocol
   [SLP] specifies how such information may be advertised by network
   services and obtained by client software.  Other facilities, such as
   Directory Services, could be used to distribute this information.

   Attributes are associated with service: URLs for three reasons:

      1. They allow configuration of the client.  Many servers have
         optional features.  Clients which require or prefer to make
         use of these features can proceed to do so without protocol
         negotiation or feature selection.  Client configuration
         parameters or server convention information may be obtained.

      2. Client software may have particular requirements.  The
         attributes associated with a given URL allow for automatic
         selection of services which have certain features.  For
         example, client software may require a server which has
         a particular version or which has access to specific

      3. Attributes support end user selection by characteristic
         as opposed to simply by type.  These attributes may be
         used to populate service browsing and choosing user
         interfaces, for example.

1.2. Related work

   The "Finding Stuff" work by Ryan Moats and Martin Hamilton uses
   service: URLs provide access information about arbitrary network
   protocols through DNS.  [FINDING]  They do not associate service
   attributes with these URLs.  The URLs allow them to provide
   nonstandard service port information and to relate several protocols
   to single abstract services, such as white pages and yellow pages.

2. Use of service: URLs

   The service: URL is intended to allow arbitrary client server and
   peer to peer systems to make use of a standardized dynamic service
   access point discovery mechanism.

   It is intended that service: URLs be obtained with their associated
   attributes.  In this way a client application may obtain the URLs of
   several services of the same type and distinguish the most preferable
   among them by means of their attributes.

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   These attributes will take the form specified by the "service-
   template", described below.  Each service: URL SHOULD be accompanied
   by all attributes in the template (except the template specific
   special attributes.)  The registration of this attribute information
   could be done using various mechanisms, one of which is the Service
   Location Protocol [SLP].

   The client will use the service: URL to bind directly to a service.
   The client must have a priori knowledge of how to use the network
   protocol associated with the Service Type included in the service:

3. Specifying A New Service Type

   A Service Type should be specified to be a close as possible to a
   particular protocol.  It may be tempting to create a Service Type for
   a 'class of services', such as 'printer'. This will complicate the
   specification later on, as the single service type must be
   differentiated between the different protocols at the level of
   service specific information or attributes.

   It is much clearer if the protocol is simply named by a service type.
   The urlpath is normally used to supply additional naming information
   to uniquely identify the service.  The attribute information can then
   be used to indicate configuration details, optional features
   available and characteristics (which may be relevant to a human user
   or to a program.)

3.1. A Service Type specification defines:

3.1.1. Service Type

   This is a string which will be prepended by the 'service:' scheme.
   It may be a name which is entirely invented or be the same as a well
   known service scheme.  For example, service:http: might refer to a
   HTTP server, whereas the http: scheme used in a URL generally refers
   to a document.

   The meaning of this service type must be fully described by service
   type specification.

   A network protocol specification should be cited as the definitive
   reference for the protocol to use when binding to the service access
   point provided by the service: URL.

3.1.2. The service: 'urlpath' information

   This information is included in the URL in order to provide uniquely

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   identifying information.  This mechanism is used in the examples
   which follow in order to identify a mountable filesystem (using the
   'nfs' service type) and an lpr print queue (using the 'lpr' service

   The syntax and interpretation of the urlpath must accompany the
   definition of a new Service Type.  The 'default' urlpath definition
   is that it is entirely omitted except possibly a terminating slash.
   The syntax is:

         urlpath = [ "/" ]

   Every effort to remain consistent with the syntax forms and styles of
   other standardized urlpaths should be pursued.  See [RFC1738] for
   examples and guidance.

3.1.3. Attributes

   This information provides information about the service's
   capabilities, characteristics and required client configuration.
   Each attribute which is defined must have a default value and
   definition of all values it can take.

   An attribute normally takes only one value, but optionally it may be
   defined to be able to take multiple values.

   The transmission of attributes is not described by this document.
   Attribute registration, deregistration and the use of attributes in
   queries may be accomplished using a number of different protocols.  A
   future document (or possibly a later version of this document) will
   describe how to encode attributes for use with different services.
   The Service Location Protocol [SLP] defines one method of encoding

3.1.4. Service Discovery Multicast Address

   Service Types may be registered with IANA and obtain a unique Service
   Discovery Multicast Address.  This address is to be used with the
   Service Location Protocol [SLP] as a means to specifically discover a
   single type of service in a network without burdening all other

   This is purely optional:  Services which use the service:  scheme do
   not need to have a unique Service Discovery Multicast Address
   assigned to them.

3.2. Specifying Attributes

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   Attributes are used to convey information about a given service for
   purposes of differentiating different services of the same type.
   They convey information to be used in the selection of which service
   to bind to, either for human consumption or for use by a program.

   Attributes may be encoded in different character sets and in
   different languages.  The procedure for doing this is described in
   Section 8.0.

   Attributes have two components.  The first is a 'tag'.  This is a
   string with certain encoding rules.  The second component is a set of
   values.  The set of values may be NULL, in which case the attribute
   is a 'keyword'.  The value or values of an attribute are typed, and
   must have the same type for each value if the attribute is
   multivalued.  The rules for typing and encoding of attribute values
   is given in the rest of Section 3.1.

3.2.1. A subtlety

    There is a subtlety in the definition of attributes.  A service
    may support 'feature A' and 'feature B'.  It may also have
    'enhancement C'.  Suppose the enhancement is only available
    when feature B is used, in this case.  If 'feature' is one
    attribute and 'enhancement' is a second attribute, we can
    describe the service with the following:

         feature = A, B
         enhancement = C

   It will be impossible to tell if there is any dependency between
   having feature B and enhancement C.  Since the data relationships are
   flat in the attribute encodings, it is necessary to explicitely state
   all combinations as distinct values.  This can be done in two ways.
   Either all combinations of features which may have dependencies must
   be given a well defined value or a 'record' format for an attribute
   value must be used.

   The combination method is only useful when there are very few values
   to be combined, as it will quickly become a very large set of values
   to define.  In the case of the example we can define feature's values

      feature can take:

         "A" | "A enhanced by C" | "B" | "B enhanced by C"

      In our example:

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         feature = "A" , "B enhanced by C"

   The suggested method for solving this problem with the 'record
   format' is described in Section 3.2.4. below.

3.2.2. Types and String Encoding

   Characters have been reserved in the specification of attributes in
   order to avoid ambiguity with respect to the delimiters in the string
   based protocol used in attribute lists.  Further limitations may be
   imposed if the attributes are to be encoded using another protocol.

   The Service Location Protocol [SLP], for example, has several
   reserved characters that are not to be used in attributes.  SLP
   provides an escape sequence to allow these characters to be used in
   attribute values (not attribute tags.)  The same character escape
   mechanism is proposed here.

         esc-char     = "&" "#" 1*DIGIT ";"

   The escaped character is replaced by a character sequence with no
   spaces.  The digits are a decimal representation of the character
   value to be replaced, in the character set used for the attribute

   There are only three heavy handed syntactic devices used:

      1. Blank lines are used to separate attributes.  To add a
         blank line to text, one would have to escape the CRLF
         with &#13;&#10;

      2. Commas are used to separate attribute values.  To use a
         comma in attribute encodings, escape the comma with &#44;

      3. Sets of colons are used to mark a default value (see
         Section 3.4.3.)  This means the string "::" must be
         escaped in attribute values to &#58;&#58;

      Attributes have the following grammar:

      attribute  =  keyword / tag "=" 1#value CRLF CRLF

      safe-chars =  <any character except "," which is reserved.>
      white-sp   =  SPACE / CR / LF / TAB
      key-chars  =  <any safe-chars except for white-sp which is
                     not allowed.>

      tag        =  1*safe-chars

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      keyword    =  1*key-chars
      value      =  string / integer / boolean / opaque

      string     =  1*safe-chars

      integer    =  [-] 1*DIGIT
                      ; The integer MUST fall within the range of
                      ; values a 32 bit integer may take, ie.
                      ; "-2147483648" to "2147483647".

      boolean    =  "TRUE" / "FALSE"
                      ; These values are the only exception to the
                      ; Internationalization rules in Section 8.0.
                      ; Independent of the translation of the
                      ; attributes, the boolean values remain the
                      ; indicated strings.

      rad64-char =  ALPHA / DIGIT / "+" / "-" / white-sp

      opaque     =  1*DIGIT ":" 4*rad64-char
                      ; The digits define the original length of the
                      ; opaque value. The restricted character string
                      ; is the radix-64 encoding of the opaque value.
                      ; See [RFC 1521], Section 5.2.

                      ; NOTE:  White space is ignored in decoding
                      ; radix-64 values.

   Note on the use of white space:

   A string is considered to be a token in the case of a tag or <string>
   value.  In this case, the string is 'trimmed'.  White space interior
   to a string token is left alone, while white space between the tokens
   is removed.  For example:

         "  some  name  =  some  value , another  example "

      would be trimmed to

         "some  name" '=' "some  value" and "another  example".

   Note on string matching:

   Attribute tags and values may be used by some protocols for directory
   look-up.  In this case, the following rules should be applied for
   string matching of attribute strings.

   String matching MUST be done after character escape encoding has been

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   removed, white space has been trimmed.  In addition, string matching
   SHOULD be case insensitive.

3.2.3. Attributes with multiple values

   Attributes with multiple values must be defined so that the type of
   each value is the same.  Attributes with a boolean value may not take
   multiple values.

3.2.4. Grouping attribute values together in records

   In order to make use of this value encoding strategy, the record
   format must be explicitely described.  A 'delimiter' is used to
   separate the fields in the record, a 'tab' is suggested, but others
   are possible.

   Each field in the attribute 'record' value must be defined
   separately, as though it were an attribute value of its own.  This
   means it needs to have a type, default value, whether it can have
   multiple values and a definition for all values it can take.  If a
   field is omitted, it is assumed to take its default value.  It is
   wise to have the default value be "NONE" or "NOT APPLICABLE", to make
   it possible to explicitely declare only the relevent field values and
   ignore the others.  It is also possible to declare that the field has
   no default value, if it MUST be defined in each record.

   Following the example in Section 3.1, we can define the attribute
   "feature" to have a record structure, delimited by tabs.  Both fields
   are single valued strings.   The first field is the "feature name",
   and has no default value.  The second field is the "enhancement
   name", with "NO ENHANCEMENT" as the default value.  The resulting
   value would be:

         "feature =" "A" TAB "," "B" TAB "C"

   The string "feature =" indicates the attribute 'feature' takes the
   value to the right of the equals sign.  The quotes will be used to
   indicate that this is not an ABNF syntax but rather a string encoding
   resulting from rules given elsewhere.  (In this case the rules were
   given in Section 3.1.1.).

   The feature "A" has no second field value, the first value record is
   A with NO ENHANCEMENT.  The second value record that feature may take
   is B with the enhancement C.

3.3. Special attributes

3.3.1. Service Discovery Multicast Address

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   This attribute is always included in Service Type templates.

   It takes a single valued which takes a numerical IP address
   specification.  This should take the value of the assigned Service
   Discovery Multicast Address.  If the service has not been assigned
   one, this attribute should take the value NONE.  The value that this
   attribute takes is defined by the following syntax:

         discovery-addr = ipv4-addrport / ipv6-addrport / "NONE"

         byte          = 1*3DIGIT
                         ; This value MUST be between 0..255
         ipv4-addrport = byte "." byte "." byte "." byte [":" 1*DIGIT]

         hex           = DIGIT / "A" / "B" / "C" / "D" / "E" /
                                 "a" / "b" / "c" / "d" / "e"
         ipv6-addrport = 32hex [":" 1*DIGIT]

   The address must be a valid multicast address (according to either
   IPv4 or IPv6 addressing rules.  The port number identifies the port
   number for the service discovery protocol. The Service Location
   Protocol [SLP] uses port 427, which is the default if no port number
   is given.

3.3.2. Version

   This attribute has a string value of the form:

         version = 1*DIGIT '.' 1*DIGIT

   This is the version of the Service Type template.

   This attribute MUST be included in every collection of attributes so
   as to identify which version of the template it used to determine the
   set of attributes and attribute definitions.  Client software can use
   these version numbers potentially to support old attributes, allowing
   a smooth migration to new template definitions.

   A Service Type template proposal starts at 0.0, and the minor number
   increments once per revision.

   A standardized template starts at 1.0.  Additions of attributes add
   one to the minor number, where changes of definition or removal of
   attributes or values adds one to the major number.  See Section 4 for
   more detail on how to use the Version attribute.

3.3.3. Language tag

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   The Language tag attribute must be included with each template and
   with each set of attributes associated with a particular service:
   URL.  This allows client applications to identify if the attributes
   which will be comprehensible for a given user and retrieve them.  See

3.4. Service Type templates

3.4.1. Definition

   The Service Type for the Service Type template is "service-template".
   The service type specific information which follows is the location
   and path information of a hypertext document which describes the
   Service Type template, which is to be accessed using http.

   For example, this template would be encoded as:


      The document would be accessed by using:


3.4.2. Mandatory Attributes

   The service-template Service Type has 3 mandatory attributes. The
   template must also support the two special attributes version and
   Service Discovery Multicast Address, as defined in Section 3.3.
   These attributes are NOT specified in attributes which accompany
   service: URLs.  These attributes are only to be specified in Service
   Type templates.

      service type

         The value of this attribute is a service type string.

      Service Discovery Multicast Address

         See section 3.3.1.


         The service type is described here.   This is a paragraph or
         so of text which describes how to interpret the service: URL
         for this particular service type.  It should be clear what
         protocol or protocols can bind to the service access point

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         which the service: URL resolves to.

   Of these attributes tags, only "description" may be translated into
   another language (see Section 8.0.)

3.4.3. Attribute syntax for Service Type templates

   For each attribute the service type supports, an additional attribute
   is added to the service type template.   This attribute has the same
   tag as the service type's attribute.  The value of the attribute has
   the following syntax:

      tmpl-attr   =  attr-tag attr-val

      safe-char   =  Any character other than "," and ":"
      attr-tag    =  1*[safe-char]
      attr-val    =  [type] [m] [l] "::" default "::" description

      type        =  ["STRING" | "BOOLEAN" | "INTEGER" | "OPAQUE"]
      default     =  1*[safe-char]
      description =  1*[safe-char]
      m           =  SPACE "M"
      l           =  SPACE "L"

      The default is "STRING" if type is omitted.

      "M" indicates the attribute can have multiple values.  If this
          field is omitted it is assumed the attribute can have only
          one value.

      "L" indicates the attribute and its values must be considered
          literally, that is, they must not be translated to other
          languages.  (See Section 8).

   The default field provides the default value for the attribute.

   The description field should be a paragraph of text describing the
   attribute and the all the values it can take on.  This information
   will be used by those who develop user interfaces to display service
   information and those who advertise services using attributes
   associated with the service: URL.

3.4.4. Use of templates by the Service Location Protocol

   Service templates may be used by the Service Location Protocol [SLP]
   in three important ways:

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   First, those who program user interface front ends may use the
   template to understand the format, range and meaning or attributes
   available from Attribute Queries from Service Location.

   Second, the template provides requirements for those who program
   Service Agents for a particular Service Type.  The attributes in the
   Service Template must be assigned values to be associated with the
   service: URL advertisement.

   Finally, the template provides a mechanism for the Service Location
   Protocol to discover Service Type specific Service Discovery
   Multicast Addresses.  The template itself is a service of type
   "service-template".  A User Agent obtains the template in order to
   discover which multicast address to use for issuing requests to
   Service Agents.  Service Agents obtain the template to discover which
   multicast group to join in order to receive multicast User Agent
   requests.  Both the Directory Agent and Service Agent will use the
   templates in order to associate the Service Type string with the
   correct Service Discovery Multicast Address in the SLP's Service Type

   All that is required to make this work, is to run a Service Agent
   which advertises the set of templates of all services supported in
   the network.  ("The network" here refers to a network which has
   multicast routing support with a maximum multicast TTL of 32.  That
   is, a "site.")

4. A Process For Standardizing New Service Types

   New Service Types can be suggested simply by providing a Service Type
   template and a short description of the use for the service:  URL.
   This should have its 'Version' attribute set to "0.0" initially.

   The minor version number will increment once with each change until
   it achieves 1.0.  There is no guarantee any version of the service
   template will be backwards compatible before it reaches 1.0.

   Once a service template has reached 1.0, the definition is "frozen"
   for that version.  New templates may be defined, of course, to refine
   that definition, but they must follow these rules:

      - Any new attribute defined for the template will increase
        the minor version number by one.  All other attributes
        for the version must continue to be supported as before.
        A client which supports 1.x can still use later versions
        of 1.y (where x<y) as it will ignore attributes it doesn't
        know about.

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      - Deprecating or changing the definition of an attribute
        requires changing the major version number of a service
        template.  The client may be unable to make use of this
        information, or it may need to obtain the most recent
        service template to help the user interpret the service

   The template should be posted to the Service Location Working Group
   mailing list for review.  Ideally, experts in the implementation and
   deployment of the particular protocol will be consulted so as to add
   more attributes or change their definition to make them as useful as

   All published versions of the template must be available on-line,
   including obsolete ones.

   Once there is no more active dissent the Service Type should be
   reissued with possible corrections, having its Version number set to
   "1.0".  If there is no comment on the template after 3 months, it
   should be considered to have been accepted.

   At that time, the a Service Discovery Multicast address may be
   obtained from IANA for use with the Service Type.

5. Encoding Rules for Service Type URLs

   Much of this material is directly adapted from [RFC1738].  Note that
   the syntax for the urlpath depends upon the Service Type definition.
   See Section 3.  The ABNF for a serviceurl is:

      serviceurl    = "service:" service-type ":" service-part

      service-type  = 1*[ low-alpha / DIGIT / "+" / "-" / "." ]
      service-part  = "//" login [ "/" urlpath ]

      login         = [ user [ ":" password ] "@" ] hostport
      hostport      = host [ ":" port ]
      host          = hostname / hostnumber
      hostname      = *[ domainlabel "." ] toplabel
      okchar        = ALPHA / DIGIT
      domainlabel   = okchar / okchar *[ okchar / "-" ] okchar
      toplabel      = ALPHA / ALPHA *[ okchar / "-" ] okchar
      hostnumber    = ipv4-number / ipv6-number
      ipv4-number   = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
      ipv6-number   = 32hex
      port          = 1*DIGIT
      user          = *[ uchar / ";" / "?" / "&" / "=" ]
      password      = *[ uchar / ";" / "?" / "&" / "=" ]

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      urlpath       = *xchar ; each Service Type must define its own
                             ; syntax.  See Section

      safe          = "$" / "-" / "_" / "." / "+"
      extra         = "!" / "*" / "'" / "(" / ")" / ","
      hex           = DIGIT / "A" / "B" / "C" / "D" / "E" /
                              "a" / "b" / "c" / "d" / "e"
      escape        = "%" hex hex
      reserved      = ";" / "/" / "?" / ":" / "@" / "&" / "="
      unreserved    = ALPHA / DIGIT / safe / extra

      uchar         = unreserved / escape
      xchar         = unreserved / reserved / escape

6. Examples

   The purpose of these examples is demonstrate the manner of specifying
   new Service Types described in this document.  In addition, it will
   provide a useful starting point for using service: URLs in

   In the case of file servers, print spoolers and POP3 servers, the
   client software often requires the user to know the name and even
   parameters of the server before being able to use the service.  A
   client which can obtain service: URLs and associated attributes
   dynamically will be able to bind to the server without any knowledge
   of the network at all, even the name of the server host.

   Values given for specific attribute assignments will be given in
   quotes.  The syntax for attribute definitions are given in Section
   3.2.2.  The syntax used to assign and interpret the values for
   attributes in the template (other than the mandatory attributes) is
   given in section 3.4.3.

   Note that in the templates commas are used to separate attributes and
   that commas themselves must be escaped.  The templates are assumed to
   be in the [ASCII] character set, so escape values are expressed in
   that character set.

   Default values are given when they exist, otherwise the value MUST be
   assigned for each set of attributes associated with a service: URL.
   String values are to be assigned descriptive values in the absence of
   a standardized set of identifiers. The strings without standardized
   identifiers or integer values are intended to be read by human

   Tabs in the example strings are represented by "\t".

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6.1. NFS

   The service type for NFS is "NFS".

   The protocol it refers to is defined in [RFC2055] and [RFC2054].

   The URL has service specific information which specifies the mount
   path.  The syntax for the urlpath for specifying this is given in

6.1.1. NFS Service Type template

     "Service Discovery Multicast Address = NONE

      service type = NFS

      version      = 0.0

      Language tag = en

      description  =
        The NFS service type provides attributes which define the
        contents and policies of server mount points.  It defines
        three types of storage:
           (1) installations (software ready to use)
           (2) distributions (software ready to install)
           (3) space         (ready for others to use)
        Each of these attributes have record structured attribute
        values which are described below.

      authorization policy = :: NONE ::
        A text description of any authentication requirements for
        use of the NFS exported filesystem.  For example:  Only
        groups x&#44; y and z - only users a&#44; b&#44; c and so on.

      use policy = :: NONE ::
        The nfs exported file system may be intended for certain
        purposes or contain software with license restrictions.
        This text description will make this clear.

      distributions = M :: NONE ::
        Software distributions&#44; ready to install on other systems.
        The value will have 5 fields&#44; separated by a tab.
        The fields are:
          - distribution name including relative path from the mount
            point (could be the name of a tar file&#44; a self
            extracting archive&#44; etc. (String)
          - platform the distribution is intended to be run on.

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          - the size of the distribution in KB (required to install it).
          - the date and or version number of the distribution. (String)
          - a description of the distribution. (String: default = NONE)

      installations = M :: NONE ::
        An installation is a program which is available on a file
          - relative path and name of executable. (String)
          - platform the installed program is intended to be run on.
          - the date and version number of the installed program.
          - required configuration to use the program (set environment
            variables&#44; required libraries&#44; etc.) (String:
            default = NONE)
          - a description of the installed program.  (String)

      documents = M :: NONE::
        A document or group of documents can be advertised on a server
        so as to allow distributed search for the document.
          - relative path and name of the document or document directory
          - format the document(s) are in (String)
          - a list of keywords (separated by semicolons).  These
            keywords may be determined by an organization which has an
            indexing policy&#44; or done in an ad hoc manner.  These
            keywords do not have to be guessed&#44; they can be
            accumulated and presented to a user or queried for.)
          - date and or version of the document. (String)
          - description of the document (String: default = NONE )

      space = M :: NONE ::
        Space indicates that a filesystem has room for temporary files.
          - Available space (in KB). (Integer)
          - Policy statement (how long can files be left on the server&#44;
            will files be considered temporary and removed when convenient?)

6.1.2.  Example: A 'pub' directory

   Suppose I have an NFS server which exports two filesystems.  The
   first one is a 'pub' directory with some documents, the second one is
   a 'dist' directory with both installed software and software ready to
   download and install.

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   For the pub directory I will assign the following values to the
   attributes above:

     "version = 0.0

      Language tag = en

      authorization policy = world readable

      use policy = Documents here are for internal company use only

      documents =
        ./slides \t powerpoint \t marketing&#44; quarterly reports \t
          10/15/96 \t This directory contains slides are from
          presentations made over the last year.
        ./meeting-notes \t text \t planning&#44; update \t 10/22/96 \t
          This directory is a repository for all group meetings.
          We keep it up to date and hold our meetings once every
          25 days.,
        ./cartoons \t gif \t silly \t 3/23/96 \t This directory has
          a bunch of silly cartoons from a website I like.




   Notice that there are multiple values for the attribute "documents."
   I use a tab delimited format in order to group 5 items together in
   the same value. Carriage returns and white space is basically ignored
   BETWEEN values, but is relevent IN values.

6.1.3. Example: A 'dist' directory

   Here is an example of where I use an NFS server to provide access to
   software.  I will include software in distributed format and
   installed format.  The distributed format allows someone to either
   download the distribution or install directly off the fileserver.
   The installation is already ready to run on the fileserver (ie. it is
   a distribution which has been installed and resides on the
   fileserver, in my meaning of the word 'distribution.')

   This form of software distribution is unnecessary if you are using an
   'applet' approach, but is still absolutely required if you are
   distributing full applications, scripts, documentation packages, etc.

   Say we have two pieces of software, a word processor WP and a

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   Calendar program CP.  The sofware runs on 3 platforms, Solaris 2.5
   and up, Windows 95 and NT 4.0, and MacOS 7.5 and up.  We will call
   these platforms Sol2.5, Win32 and MacOS7.5.  Our file server will
   offer these preinstalled for Sol2.5 and MacOS7.5 but not for Windows
   - as software configuration for this platform very often requires
   modification of the individual host's registry file.  The attributes
   for this content on the file server could be:

     "version = 0.0

      Language tag = en

      authorization policy=
         The files available here should be accessed only by the
         Sales Dept. of Acme Corp.

      use policy=
         The Sales Dept of Acme Corp. (and no one else) has a
         software license for all software available here.



       ./wp-zog/distrib/wp-zog-1-31-sol25.tar.Z \t Sol2.5 \t
          2054 kb \t 01/13/96 \t version 1.31 \t
          Word processor from Zog Corp - for X/Motif.,
       ./wp-zog/distrib/ \t Win32 \t
          3056 kb \t 01/13/96 \t version 1.31 \t
          Word processor from Zog Corp - for Windows NT and 95,
       ./wp-zog/distrib/wp-zog-1-31-mac.hqx \t MacOS7.5 \t
          1980 kb \t 02/23/96 \t version 1.31m \t
          Word processor from Zog Corp - for Macintosh,
       ./cp-foo/distrib/cp-foo-2-01-sol25.tar.Z \t Sol2.5 \t
          1044 kb \t 08/02/95 version 2.01 \t
          Calender Program from Foo - for Solaris 2.5,
       ./cp-foo/distrib/ \t Win32 \t
          2096 kb \t 11/30/95 \t version 2.11 \t
          Calander Program from Foo - for Windows 95,
       ./cp-foo/distrib/cp-foo-1-4-mac.hqx \t MacOS7.5 \t
          733 kb \t 03/23/95 \t version 1.4 \t
          Calander Program from Foo - for Macintosh

       ./wp-zog/sol-inst/wp-zog \t Sol2.5 \t 01/13/96 version 1.31 \t
          \t Word processor from Zog Corp - for X/Motif.,
       ./wp-zog/mac-inst/wp-zog \t MacOS7.5 \t 02/23/96 version 1.31m \t

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            Word processor from Zog Corp - for Macintosh,
       ./cp-foo/sol-inst/cp-foo \t Sol2.5 \t 08/02/95 version 2.01 \t
           Set CP-HOME environment variable to ./cp-foo/inst/cp-foo \t
           Calander Program from Foo - for Solaris 2.5,
       ./cp-foo/mac-inst/MyCal \t MacOS7.5 \t 03/23/95 version 1.4 \t
           \t Calander Program from Foo - for Macintosh"

   This could be registered as an attribute string associated with the
   URL "service:nfs://".

   The attribute values MUST supply a complete 'record'; they declare
   the contents of the file repository, the installation or the
   distribution.  The notation used for platform name, configuration
   requirements and so forth is informal and MAY be formalized in the
   service template text.

   Note that in the example above, only the third installation had any
   special configuration to be done on the client.  The other
   installations had a blank field where configuration details would
   normally be.  In this case these take on the default value given in
   the template (NONE).

6.2. Line Printer Daemon Protocol

   The service type string for the Line Printer Daemon Protocol is

   The protocol it refers to is defined in [RFC1179].

   The URL has service specific information which specifies print queue
   name.  The syntax for the urlpath for specifying this is:

      name    = 1*[ DIGIT / ALPHA ]
      urlpath = "/" name

   The attributes for the lpr service are largely derived from the
   Printer MIB [RFC1759].  The attributes specified are a subset of
   those in the MIB document, as the goals of service attributes are
   different than that of system management.  The attributes specified
   here are intended to facilitate automatic and user selection of
   services not to provide service statistics or notification.  In
   short, the target audience of service attributes are users, either
   processes or people, where the audience of MIB statistics are network

   In all cases the values and terms in [RFC1759] take precedence over
   those listed below.  Some default "unknown" values have been added
   which are not part of the Printer MIB specification.

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   The service template for LPR follows:

      "Service Discovery Multicast Address = NONE

       service type = LPR

       version = 0.0

       Language tag = en

       Description =
          The LPR service provides line printer spooling&#44; using
          the BSD Unix print spooling protocol&#44; formalized in
          RFC 1179.  The attributes associated with the LPR
          service refer to the printer actual printing service
          will be performed.

       Status = INTEGER L :: 1 ::
          The status is taken from the Printer Status object of the
          host MIB&#44; hrDeviceStatus.  The enumerated values have
          the following definitions:
             1 = unknown    The state is unknown.
             2 = running    The device is up:  No known errors.
             3 = warning    Still operational: Agent has been warned.
             4 = testing    Not available:  In the 'testing' state.
             5 = down       Not available.

       Location Description = :: NONE ::
          This is a text description of the location of the printer.
          It may make use of office landmarks and so forth to guide

       Location Address = :: NONE ::
          This is the Postal Address of the printer as a minimum.
          It should also include any office number or other location
          notation used within an organization.

       Operator = :: NONE ::
          The name and possibly telephone number of the person
          responsible for operating the printer.  This value should
          be obtained from the prtGeneralTable of the Printer MIB&#44;
          from the prtGeneralCurrentOperator object of the
          prtGeneralEntry if possible.

       Service Person = :: NONE ::
          The name and possibly telephone number of the person
          responsible for servicing the printer if it breaks down.
          This value should be obtained from the prtGeneralTable of

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          the Printer MIB from the prtGeneralCurrentOperator object
          of the prtGeneralEntry&#44; if possible.

       Use policy = :: NONE ::
          Any restrictions to use&#44; such as intended users should be
          described here.

       Feed type = INTEGER :: 2 ::
          This describes the feeder mechanism of the printer. The
          value should be assigned from the prtInputDefaultIndex
          entry of the prtInputTable of the Printer MIB if possible.
          This attribute takes the value of the prtInputType item
          in the prtInputEntry sequence.  The textual definition of
          the integer type values are:
             1 = other
             2 = unknown
             3 = sheetFeedAutoRemovableTray
             4 = sheetFeedAutoNonRemovableTray
             5 = sheetFeedManual
             6 = continuousRoll
             7 = continuousFanFold

       Media length = INTEGER  :: -2 ::
          This value indicates the length (in the direction of the
          printer feed) of the media.  The value -2 indicates that
          the length is unknown&#44; -1 means there is no limit.  All
          other values are in the Media units given below.  This
          value should be obtained from the default prtInputEntry
          (see Feed type) from the prtInputMediaDimFeedDirDeclared

       Media width = INTEGER :: -2 ::
          As for Media length.  This value indicates the width
          (across the feed path) of the Media.  The item to use
          is prtInputMediaDimXFeedDirDeclared.

       Media units = INTEGER :: -1 ::
          -1 indicates the units are unknown.  The value from the
          default prtInputEntry should be used (see Feed type).
          The prtInputDimUnit item should be used.  The values
          are defined as:
             3  =  .0001 inches
             4  =  micrometers

       Media type =  L :: stationary ::
          The Media type describes what is to be printed upon.
          The value from the default prtInputEntry should be used
          (see Feed type): the item is prtInputMediaType.  The

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          defined values are:
          stationery       Separately cut sheets of an opaque material
          transparency     Separately cut sheets of a transparent
          envelope         Envelopes that can be used for conventional
          mailing purposes
          envelope-plain   Envelopes that are not preprinted and have no
          envelope-window  Envelopes that have windows for addressing
          continuous-long  Continuously connected sheets of an opaque
                           material connected along the long edge
          continuous-short Continuously connected sheets of an opaque
                           material connected along the short edge
          tab-stock        Media with tabs
          multi-part-form  Form medium composed of multiple layers not
                           pre-attached to one another; each sheet may
                           drawn separately from an input source
          labels           Label stock
          multi-layer      Form medium composed of multiple layers which
                           are pre-attached to one another; e.g.&#44;
                           for use with impact printers

       Media color =  L :: unknown ::
          The Media color describes the color of what is printed upon.
          The value from the default prtInputEntry should be used
          (see Feed type): the item is prtInputMediaColor.  The
          defined values are:
           other         unknown         white
           pink          yellow          buff
           goldenrod     blue            green
          According to [RFC1759]:
             Implementors may add additional string values. The naming
             conventions in ISO 9070 are recommended in order to avoid
             potential name clashes.

      Max speed = INTEGER :: -1 ::
         The maximum speed of the printer expressed in Speed units.
         This value should be obtained from the prtMediaPathMaxSpeed
         object in the default prtMediaPathEntry .  -1 indicates
         'other'&#44; or 'unknown'.

      Speed units = INTEGER :: 8 ::
         This value determines unit of speed for the Max speed.  The
         value should be obtained from the prtMediaPathMaxSpeedPrintUnit
         of the default prtMediaPathEntry.  The definitions of the

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         values are:
             3  =  tenThousandthsOfInchesPerHour -- .0001/hour
             4  =  micrometersPerHour
             5  =  charactersPerHour
             6  =  linesPerHour
             7  =  impressionsPerHour
             8  =  sheetsPerHour
             9  =  dotRowPerHour
             16 =  feetPerHour
             17 =  metersPerHour

      Interpreter Language = M :: 37 \t 1 \t 1 ::
         The Interpreter Language determines what forms of input the
         printer can accept and interpret.  Multiple values are
         each of which has a tab delimited form with three values.
         The table is populated by a complete traversal of the
         prtInterpreterTable.  The items to use for the fields are
         given below.  See [RFC1759] for their definitions.
          - prtInterpreterLangFamily (INTEGER: Default value is 37
            or langAutomatic.)
          - prtInterpreterLangVersion (INTEGER: Default value is 1.)
          - prtInterpreterLangLevel (INTEGER: Default value is 1.)"

6.3. POP3

   The POP3 service type is "POP3".

   The protocol it refers to is defined in [RFC1936].

   The 'urlpath' has the default syntax.  (See Section 3.1.2.)

   The service template for POP3 is as follows:

     "service type = POP3

      Service Discovery Multicast Address = NONE

      version = 0.0

      Language tag = en

      Description =
         Clients which wish to make use of POP3 services need to
         be configured to use the correct POP3 server.  The server
         may or may not be able to use the APOP authentication
         mechanism.  Clients are able to discover which POP3 server
         is the correct one for them and whether they can use APOP

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         to authenticate themselves.  Finally&#44; the POP3 server
         policy statement may be included.

      Mailboxes = M L :: NONE ::
         This is a list of all users (by user name) which the
         POP3 server supports.

      APOP = BOOLEAN L :: FALSE ::
         This attribute determines whether the POP3 server supports
         the POP3 AUTHentication command [RFC1734].

      Policy = :: NONE ::
         This describes the POP3 policy regarding use.  In particular
         users may be dissuaded from keeping mail on the server or
         keeping more than a certain amount of mail on the server."

   Mail clients may discover POP3 servers which support these attributes
   in a new way.  A user need only supply her user name and the client
   can proceed to use a dynamic configuration protocol, such as Service
   Location, to determine the server and whether to use APOP.  If the
   POP3 server is down, a backup server may be discovered using the same
   mechanism, transparently to the user.

   An example of service attributes associated with a particular POP3
   server might be:


     "version = 0.0

      Language tag = en

      Mailboxes = larry, curly, moe, shemp

      APOP = FALSE

      Policy = Mail should not be left on the server."

   A translation of these attributes could be associated with the same
   URL to make the policy readable to non-English speakers.  For
   example, the following is a translation to German:

     "version = 0.0

      Language tag = de

      Mailboxes = larry, curly, moe, shemp

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      APOP = FALSE

      Anweisung = Mail darf nicht auf dem Server bleiben."

   Note that only the last attribute is translated.  That is because
   version and Language tag are not translated (see Section 3.4.2.) and
   Mailboxes and APOP are marked with a 'L' in the POP3 template.

7. Security Considerations

   Security considerations are not discussed in this memo.

8. Internationalization Considerations

   The service: URL itself must be encoded using the rules set forth in
   [RFC1738].  The character set encoding is limited to specific ranges
   within the US-ASCII character set [ASCII].

   The attribute information associated with the service: URL may be
   expressed in any character set, and in any language.

8.1. Character Set identification and use

   The way of identifying the character set used is the IANA Character
   Set registry official name. [CHAR-REG]

   It can be assumed that US-ASCII [ASCII] will be supported.

   For other encodings, the repository of the service template or the
   protocol which transmits attributes (for registration or query
   purposes) must be able to identify the encoding using an external
   mechanism.  It would make no sense to use an 'internal' designation
   for marking the character encoding, as the attribute information is
   itself string encoded.   The Service Location Protocol [SLP] makes
   the character encoding for each registration, query and query result
   explicit in the protocol header, for example.

   All attribute information in a single transmission, file, etc. MUST
   be in the same character encoding.

8.2. Language identification and translation

   The language used in attribute string should be identified using a
   Language tag as defined by [RFC1766].

   All strings used in attributes (tags and values) are assumed to be
   able to be translated unless explicitely defined as should be
   literal, so that best effort translation (see below) will not

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   obfuscate strings which are meant to be interpreted by a program, not
   a person.

   There are two ways to go about translation:  Standardization and best

   When the service type is standardized, more than one document may be
   submitted for review.  One service type description is registered for
   each language.  These descriptions must be kept in sync, so that when
   a service type template is updated in one language, all the
   translations are (or eventually are) reflect the same semantics.

   If no document exists describing the standard translation of the
   service type, a 'best effort' translation for strings may be done.

   A given service: URL may have several sets of attributes associated
   with it.  Each set may be localized to a particular language.
   Mechanisms for obtaining service attributes MUST be parameterized to
   allow selection of language by Language tag.  This way, users may
   access the same information in their own language.

9. Bibliography

   [ABNF]      D. Crocker, "Augmented BNF for Syntax Specifications:
               ABNF", Work in progress, November 1996.

   [ASCII]     "Coded Character Set -- 7-bit American Standard code
               for Information Interchange", ANSI X3.4-1986.

   [CHAR-REG]  IANA Character Set registry, <URL:

   [FINDING]   R. Moats, M. Hamilton, "Finding Stuff (Providing
               information to support service discovery)", Work in
               progress, November 1996.

   [NFSURL]    B. Callaghan, "NFS URL Scheme", Work in progress,
               October, 1996.

   [RFC2055]   B. Callaghan, "WebNFS Server Specification", RFC 2055.
               July 1996.

   [RFC2054]   B. Callaghan, "WebNFS Client Specification", RFC 2054.
               July 1996.

   [RFC1939]   J. Myers, M. Rose, "Post Office Protocol - Version 3",
               RFC 1939.  May 1996.

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   [RFC1759]   R. Smith, F. Wright, T. Hastings, S. Zilles, J.
               Gyllenskog, "Printer MIB", RFC 1759.  March 1995.

   [RFC1766]   H. Alvestrand, "Tags for the Identification of
               Languages", RFC 1766.  March 1995.

   [RFC1738]   T. Berners-Lee, L. Masinter & M. McCahill,  "Uni-
               form Resource Locators (URL)", RFC 1738.  December

   [RFC1734]   J. Myers, "POP3 AUTHentication command", RFC 1734.
               December 1994.

   [RFC1179]   L. McLaughlin III, "Line Printer Daemon Protocol",
               RFC 1179.  August 1990.

   [SLP]       J. Veizades, E. Guttman, C. Perkins & S. Kaplan,
               Service Location Protocol", Work in progress,
               November 1996.

10. Author's Address

         Erik Guttman

         Sun Microsystems, Inc.
         Gaisbergstr. 6
         D-69115 Heidelberg

         Phone: +1 415 336 6697

      This memo expires on May 20, 1997

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