This response indicates no compatible application and/or transport
service is available at the destination.  For example, the requested
application service may be SMTP, while only FTP-mail is available at the
destination.  Return with this command is the available corresponding
available service, if any, and its address.  If no service is available
for that service type, an empty string for service specification is
returned.

   Command Type   Number of Items

   Service Indicator   Length   Transport Protocol/Service/Service Type

   Name Indicator   Name Length   Name String

   Service Indicator   Length   Transport Protocol/Service/Service Type

   [Address Indicator   Address Length   Address]

Examples:

   9  3
   3 14 TCP/NIFTP/mail
   1 21 Postel@F.ISI.USC.ARPA
   3  0

   9  5
   3 13 TCP/NIFTP/RFT
   1 12 TSC.SRI.ARPA
   3 11 TCP/FTP/RFT
   2  6 "10  3  0  2  6 21"
   2  6 "39  0  0  5  6 21"



                                   10
 
RFC 830                                                       October 1982



4.2.2 AIP/AIP Communication

     Communication between the AIPs accomplishes the "what-can-you-do-
for-me" negotiation.  Examples in this section correspond to those of
Section 4.2.1.

REQUEST

   Command Type   Number of Items

   Service Indicator   Length   Transport Protocol/Service/Service Type

Examples:

   1  1
   3 13 TCP/SMTP/mail

   1  1
   3 13 TCP/NIFTP/RFT

AFFIRMATIVE RESPONSE

   Command Type   Number of Items

   Service Indicator   Length   Transport Protocol/Service/Service Type

   Address Indicator   Address Length   Address

Examples:

   2  2
   3 13 TCP/SMTP/mail
   2  6 "10  2  0 52  6 25"

   2  3
   3 14 TCP/NIFTP/RFT
   2  6 "10  3  0  2  6 47"
   2  6 "39  0  0  5  6 47"

     An affirmative response implies that the destination offers the
same service as that of the originator.  A multi-resolution response is
possible.  The parsing of an address is implied by the indicated
transport protocol.  In the second example, the transport protocol is
TCP.  Thus, the address is composed of three fields: the internet
address (10 2 0 52), the protocol number (6 for TCP), and the port
number (25 for SMTP).  The returned address(es) is to be relayed to the
originating application process.






                                   11
 
RFC 830                                                       October 1982

INCOMPATIBLE SERVICE

   Command Type   Number of Items