request-id in each request to a unique value or a constant value,
   such as 1, depending on what the client does with the request-id




 
RFC 2565            IPP/1.0: Encoding and Transport           April 1999


   returned in the response. The value of the request-id MUST be greater
   than zero.

3.7 Tags

   There are two kinds of tags:

      - delimiter tags: delimit major sections of the protocol, namely
        attributes and data
      - value tags: specify the type of each attribute value

3.7.1 Delimiter Tags

   The following table specifies the values for the delimiter tags:

      Tag Value (Hex)   Delimiter

      0x00              reserved
      0x01              operation-attributes-tag
      0x02              job-attributes-tag
      0x03              end-of-attributes-tag
      0x04              printer-attributes-tag
      0x05              unsupported-attributes-tag
      0x06-0x0e         reserved for future delimiters
      0x0F              reserved for future chunking-end-of-attributes-
                         tag

   When an xxx-attributes-tag occurs in the protocol, it MUST mean that
   zero or more following attributes up to the next delimiter tag are
   attributes belonging to group xxx as defined in the model document,
   where xxx is operation, job, printer, unsupported.

   Doing substitution for xxx in the above paragraph, this means the
   following. When an operation-attributes-tag occurs in the protocol,
   it MUST mean that the zero or more following attributes up to the
   next delimiter tag are operation attributes as defined in the model
   document.  When an job-attributes-tag occurs in the protocol, it MUST
   mean that the zero or more following attributes up to the next
   delimiter tag are job attributes or job template attributes as
   defined in the model document.  When a printer-attributes-tag occurs
   in the protocol, it MUST mean that the zero or more following
   attributes up to the next delimiter tag are printer attributes as
   defined in the model document. When an unsupported-attributes-tag
   occurs in the protocol, it MUST mean that the zero or more following
   attributes up to the next delimiter tag are unsupported attributes as
   defined in the model document.






 
RFC 2565            IPP/1.0: Encoding and Transport           April 1999


   The operation-attributes-tag and end-of-attributes-tag MUST each
   occur exactly once in an operation. The operation-attributes-tag MUST
   be the first tag delimiter, and the end-of-attributes-tag MUST be the
   last tag delimiter. If the operation has a document-content group,
   the document data in that group MUST follow the end-of-attributes-
   tag.

   Each of the  other three  xxx-attributes-tags defined above is
   OPTIONAL in an operation and each MUST occur at most once in an
   operation, except for job-attributes-tag in a Get-Jobs response which
   may occur zero or more times.

   The order and presence of delimiter tags for each operation request
   and each operation response MUST be that defined in the model
   document. For further details, see section 3.9 "(Attribute) Name" and
   section 9 "Appendix A: Protocol Examples".

   A Printer MUST treat the reserved delimiter tags differently from
   reserved value tags so that the Printer knows that there is an entire
   attribute group that it doesn't understand as opposed to a single
   value that it doesn't understand.

3.7.2 Value Tags

   The remaining tables show values for the value-tag, which is the
   first octet of  an attribute. The value-tag specifies the type of the
   value of the attribute. The following table specifies the "out-of-
   band" values for the value-tag.

      Tag Value (Hex) Meaning

      0x10            unsupported
      0x11            reserved for future 'default'
      0x12            unknown