rfc1240.txt

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RFC 1240                   OSI on top of UDP                   June 1991


   Data can only be read from a receive port after the port has been
   created.  This is a local matter.

   This memo reserves the use of UDP port 102 for the use of
   applications which realize the CLTS over UDP.  However as with RFC
   1006, other port values may be used by prior agreement (e.g., through
   use of the OSI Directory).

   This RFC describes how to use these services to emulate the following
   connectionless-mode network service primitives, which are required by
   [ISO8602]:

    N-UNIT-DATA.REQUEST     -  A NS-user requests unit data to be sent

    N-UNIT-DATA.INDICATION  -  A NS-user is notified that unit data
                               can be read from the NSAP

   The mapping between the UDP service primitives and the service
   primitives expected by the connectionless transport peer entity are
   quite straightforward:

    connectionless network service  UDP
    ------------------------------  ---

    N-UNIT-DATA.REQUEST             send datagram

    N-UNIT-DATA.INDICATION          read datagram


The parameter mapping is:

    connectionless network service  UDP
    ------------------------------  ---

    Source address                  source IP address from
                                    calling TS-address

    Destination address             destination IP address from
                                    called TS-address

    Quality of service              (ignored)

    NS-user data                    UD TPDU constructed from T-UNIT-DATA

   When the T-UNIT-DATA.REQUEST primitive is issued, the TS-peer
   constructs a UD TPDU and sends it as a single datagram to the desired
   IP address using UDP.




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RFC 1240                   OSI on top of UDP                   June 1991


   When UDP indicates that a datagram has been received, a UD TPDU is
   read from UDP, and a T-UNIT-DATA.INDICATION primitive is generated.

5.  Packet Format

   The following is the UD TPDU structure which is encapsulated in UDP
   data field:

          1       2         3                m m+1          n
          +--------------------------------------------------+
          |  LI  |  UD      |  Variable Part  |  User Data   |
          |      | 01000000 |                 |              |
          +--------------------------------------------------+

    LI (octet 1) -  the length of the header including parameters, but
                    excluding the LI and user data, with a maximum
                    value of 254

    UD (octet 2) -  the type of TPDU

    Variable Part (octets 3 to m) - the source and destination TSAP id's
          Parameter code:   source TSAP       11000001
                            destination TSAP  11000010
          Parameter length: the length of the parameter, not including
                            the parameter code or length fields, with a
                            maximum value of 254
          Parameter value:  source or destination T-selector

          The optional checksum parameter is not required in the
          variable part since the UDP checksum field in the UDP header
          already performs the checking.

    User Data (octets m+1 to n) -  all the data of the TSDU.

   The maximum NS-user data allowed in the OSI connectionless network
   service is 64,512 octets.  This limit is further constrained by the
   lesser maximum datagram size supported by the two communicating UDP
   peers, which should be known by a priori agreement.

6.  Conclusion

   There is a general trend towards support of the OSI protocol suite in
   the Internet.  This direction is being fostered by the Internet
   Activities Board (IAB) and its Internet Engineering Task Force, and
   by the Federal Networking Council.  By offering an OSI connectionless
   transport service on top of the Internet, this RFC will allow future
   applications to use the OSI connectionless upper-layer services,
   which are required to be conformant to the OSI upper layer



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RFC 1240                   OSI on top of UDP                   June 1991


   architecture.  Currently, T-UNIT-DATA, S-UNIT-DATA, P-UNIT-DATA, and
   A-UNIT-DATA have reached International Standard (IS).  As
   applications based on OSI connectionless services become widely
   available and OSI lower-layer service is widely implemented in the
   Internet, the underlying UDP/IP services can be simply replaced with
   the OSI lower layers.

7.  Acknowledgements

   Marshall T. Rose of PSI, Inc., provided many valuable comments and
   corrections.

8.  References

   [GOSIP88]  U.S. Department of Commerce/National Bureau of Standards,
   [FIPS146]  "Government Open Systems Interconnection Profile (GOSIP)",
              August 1988.

   [ISO7498/AD1]  ISO, "International Standard 7498 - Information
              Processing Systems - OSI:  Basic Reference Model
              Addendum 1: Connectionless-mode Transmission",
              May 1986.

   [ISO8072]  ISO, "International Standard 8072 - Information Processing
              Systems - OSI:  Transport Service Definition", June 1984.

   [ISO8072/AD1]  ISO, "International Standard 8072 - Information
              Processing Systems - OSI:  Transport Service Definition
              Addendum 1: Connectionless-mode Transmission",
              December 1986.

   [ISO8602]  ISO, "International Standard 8602 - Information Processing
              Systems - OSI:  Connectionless Transport Protocol
              Specification", December 1986.

   [ISO9548]  ISO, "International Standard 9548 - Information Processing
              Systems - OSI:  Connectionless Session Protocol
              Specification", April 1989.

   [ISO9576]  ISO, "Draft International Standard 9576 - Information
              Processing Systems - OSI:  Connectionless Presentation
              Protocol Specification", April 1989.

   [ISO10035]  ISO, "Draft International Standard 10035 - Information
              Processing Systems - OSI:  Connectionless ACSE Protocol
              Specification", April 1989.

   [ISOSC21/WG6 N184]  ISO SC21 WG6, "Justification for Connectionless



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RFC 1240                   OSI on top of UDP                   June 1991


              Services in the Upper Layers", June 1986.

   [RFC768]   Postel, J., "User Datagram Protocol", RFC 768,
              USC/Information Sciences Institute, September 1981.

   [RFC791]   Postel, J., "Internet Protocol", RFC 791,
              USC/Information Sciences Institute, September 1981.

   [RFC1006]  Rose, M., and D. Cass, "ISO Transport Service on top of
              the TCP - Version 3", RFC 1006, Northrop Research and
              Technology Center, May 1987.

Security Considerations

   Security issues are not discussed in this memo.

Authors' Addresses


   Chikong Shue
   Open Software Foundation, Inc.
   11 Cambridge Center
   Cambridge, MA 02142

   Phone: [phone]
   EMail: [e-mail]


   William Haggerty
   Wang Laboratories, Inc.
   1 Industrial Ave
   Lowell, MA 01851

   Phone: [phone]
   EMail: [e-mail]


   Kurt Dobbins
   Cabletron, Inc.
   35 Industrial Way
   Rochester, NH 03867

   Phone: [phone]








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