RFC 830                                                       October 1982

4.1  Command Structure

     The basic command structure begins with two octets indicating
command type and the number of items in the command.  They are followed
by the indicated number of items.  The type of an item is indicated in
its first octet, followed by a one-octet content length, and then the
item content.  Required presence or absence and order of the items for
each component pair are specified in this section.

	Command Type   Number of Items

	Item Indicator   Content Length   Item Content
          .
          .

Command Type

     This type coded in binary number indicates whether this command is
a request, an affirmative response, or some other type of response (see
Appendix A for the command types and their corresponding code).  This
type specification implies the presence or absence and order of the
following items.

Number of Items

     This number is expressed in binary number.  It specifies the number
of following items.  Owing to the possibility of a multiple response,
this number may vary for a particular command.

Item Indicator

     This indicator defines the item type.  The possible types include:
service, name, address, and comment.  The type of an item implies its
content structure.

Content Length

     This length specification, in binary, indicates the length of the
following content in octets.  The maximum can be specified is 255, thus
the maximum length of the content.  However, this maximum may also be
constrained by the total length of the command (Section 4.3).

Item Content

     The contents for different items are:
     Service -- Transport protocol/service protocol/service type
                (ASCII). (See Appendix A for standard identifiers for
                service specifications.)
     Name -- Whole or partial name string according to Internet Naming
             Convention [1] (ASCII).
     Address -- The address is presented in binary form.  In this
                writeup, double quotes, " ", are used around decimal
                values separated by a space to represent octets of the
                binary form.

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RFC 830                                                       October 1982



                Parsing of the address is implied by the specified
                transport protocol.  In the case of TCP, the first
                four octets gives the 32-bit IP address, the 5th octet
                the IP-specific protocol number, and the 6th the TCP or
                UDP port number for the application service.

     Comment -- The item is mostly optional.  Its presence may allow
                an intermediate server passing comment to the end user.
                Error comments explaining resolution failure is an
                example of its use.


4.2  Command Specification

     In this section, we define the name service commands for the
various communication pairs.


4.2.1 Application Process/AIP Communication

     From the name service point of view, there is no need for
communication between the AIP and an application process at the
destination.  Thus, here we discuss communications at the originating
domain.

     An application process initiates a dialogue by making a request for
name service to its local AIP.  It provides the requested application
service and a destination name for resolution.

REQUEST

   Command Type   Number of Items

   Service Indicator   Length   Transport Protocol/Service/Service Type

   Name Indicator   Name Length   Name String