rfc2126.txt

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RFC 2126              ISO Transport on top of TCP             March 1997


   Class 2 Options Profile

   +--------------------------------------------------------------------+
   |  Bits     Service selected                                         |
   | 1 4 6 7                                                            |
   +--------------------------------------------------------------------+
   | 0 x x x   Non-use of Transport Expedited Data Service              |
   |           ---------------------------------------------------------|
   |                        Bits 4 6 7 are not applicable (*)           |
   +--------------------------------------------------------------------+
   | 1 x x x   Use of Transport Expedited Data Service                  |
   |           ---------------------------------------------------------|
   | 1 0 x x       Use of Expedited Data Service with Forward Connection|
   |               -----------------------------------------------------|
   | 1 0 1 0                Forward Connection with Expedited Data      |
   |                        Acknowledgement                             |
   | 1 0 1 1                Forward Connection with Expedited Data      |
   |                        Acknowledgement and use of Non-blocking     |
   |                        Expedited Data  (**)                        |
   |                        --------------------------------------------|
   | 1 0 0 0                Forward Connection with non-use of Expedited|
   |                        Data Acknowledgement  (***)                 |
   | 1 0 0 1                Forward Connection with non-use of Expedited|
   |                        Data Acknowledgement and use of Non-blocking|
   |                        Expedited Data                              |
   |               -----------------------------------------------------|
   | 1 1 x x       Use of Expedited Data Service with Reverse Connection|
   |               -----------------------------------------------------|
   | 1 1 1 0                Reverse Connection with Expedited Data      |
   |                        Acknowledgement                             |
   | 1 1 1 1                Reverse Connection with Expedited Data      |
   |                        Acknowledgement and use of Non-blocking     |
   |                        Expedited Data  (**)                        |
   |                        --------------------------------------------|
   | 1 1 0 0                Reverse Connection with non-use of Expedited|
   |                        Data Acknowledgement  (***)                 |
   | 1 1 0 1                Reverse Connection with non-use of Expedited|
   |                        Data Acknowledgement and use of Non-blocking|
   |                        Expedited Data                              |
   +--------------------------------------------------------------------+

   (*) Note the default (0000) provides an RFC1006-like service with
   Explicit Transport Disconnection.

   (**) Note in this case use of Expedited Data Acknowledgement with use
   of Non-blocking Expedited Data is a wasted effort (See section 6.5)





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   (***) Note in this case Normal and Expedited Data TPDU are not
   synchronised. (See section 6.6)

6.7 Class 2 Expedited Data Acknowledgement

   The Protocol specified in this document does not define any
   relationship between use of "Expedited Data Acknowledgement" option
   and use of "Non-blocking Expedited Data" service.

   However please note that when using "Non-blocking Expedited Data"
   service it is a wasted effort to use "Expedited Data
   Acknowledgement", since ED TPDUs are duplicated and sent on both the
   Normal Data and Expedited Data TCP connections.

6.8 Class 2 Normal Data and Expedited Data handling

   There exist two separate application requirements for using Expedited
   Data:

   1- Synchronisation of the order of delivery between Normal
      and Expedited Data TPDU.

   2- Independence of Normal and Expedited data channels. A busy
      Normal Data channel should not block an Expedited Data channel.

   The protocol described in this document can accommodate both
   requirements, separately or in combination.

   Synchronisation:
      If synchronised order of delivery between Normal and Expedited
      Data TPDU is required then use of either "Expedited Data
      Acknowledgement" TPDU or use of the "Non-blocking Expedited Data"
      service must be negotiated during connection establishment.

      If synchronised order of delivery between Normal and Expedited
      Data TPDU is not required then non-use of "Expedited Data
      Acknowledgement" need not be negotiated during connection
      establishment.

   Independence:
      If Independence of Normal and Expedited data channels is required
      then Forward or Reverse connection must be negotiated during
      connection establishment. Expedited data TPDU must be sent on the
      Expedited data channel.







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RFC 2126              ISO Transport on top of TCP             March 1997


      If Independence of Normal and Expedited data channels is not
      required then Forward connection should be negotiated during
      connection establishment and the Expedited data channels should
      never be established. Expedited data TPDU is then sent inband on
      the Normal data channel.

   Finally please note that independence of Normal and Expedited data
   channels without synchronisation relaxes the Transport Service
   definition of Expedited data and is not consistent with ISO 8072.

6.9 Class 2 Forward Connection procedure

   As defined in ISO 8073, when "Forward Connection" (Splitting and
   Recombining) procedure is used for Expedited Data transmission, ED
   TPDU must only be sent over an outgoing NS-provider TCP connection.

   As defined in ISO 8073, this document does not mandates use of the
   Splitting procedure for Expedited Data transmission. The
   Recombination procedure, which associates Data (normal and expedited)
   TPDUs arriving for a transport connection over two TCP connections
   must be handled.

   It is legal to send Expedited Data TPDU inband on the Normal Data TCP
   connection.

   Please note that the protocol specified in this document does not
   define when an Expedited Data TCP connection should be established.
   This is an implementation choice.

   When using "Non-blocking Expedited Data" service it is recommended to
   not delay establishing Expedited Data TCP connection.

6.10 TPKT

   This document specifies the value of the TPKT reserved field.

   Implementation should not interpret and act upon any value in a
   reserved field. To avoid Interoperability issues with RFC1006, this
   field should be ignored on input.

7. Rationale - Interoperability with RFC1006

   We have chosen to maintain the same TPKT protocol version in ITOT as
   in RFC1006 (version 3). The reason for this decision is that the
   changes in this document do not conflict with RFC1006. If we were to
   change the protocol version we would prevent existing RFC1006
   implementations which mandate version 3 from interoperating with the
   protocol defined in this document.



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RFC 2126              ISO Transport on top of TCP             March 1997


   One consequence of this decision relates to class negotiation.  The
   protocol described in this document introduces Class 2 over TCP, and
   it therefore introduces the need to be able to perform class
   negotiation between Class 2 and Class 0.  While all Transport
   implementations should be able to handle Class negotiation, we
   recognise that some RFC1006 implementations cannot. Therefore
   Implementors should be aware that Class 2 Connect Request (with no
   Alternative class) could be accepted with a Class 0 Connect Confirm,
   at which point the Connect Confirm should be rejected as specified in
   ISO 8073.

8. Security Considerations

   Security issues are not specifically addressed in this document.
   Operation of this protocol is no more and no less secure than
   operation of TCP and ISO 8073 protocols. The reader is directed there
   for further reading.

Acknowledgements

   The authors are pleased to acknowledge the suggestions and comments
   of Harald T. Alvestrand, Jim Bound, John Day, Mike Dyer, Peter
   Furniss, Dan Harrington, Steve Kille, Keith G. Knightson, Keith
   Sklower, Matt Thomas, Robert Watson and many other members of the
   IETF TOSI mailing list. The support of Allison Mankin of the IESG was
   essential.

References

   [ISO8072]  ISO. "International Standard 8072.  Information Processing
              Systems - Open Systems Interconnection: Transport Service
              Definition."

   [ISO8073]  ISO. "International Standard 8073.  Information Processing
              Systems - Open Systems Interconnection: Transport Protocol
              Specification." ISO 8073:1992 and 8073:1992/Amd.5:1995.

   [ISO8348]  ISO. "International Standard 8348.  Information Processing
              Systems - Open Systems Interconnection: Network Service
              Definition."

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC793]   Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.





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RFC 2126              ISO Transport on top of TCP             March 1997


   [RFC896]   Nagle, J., "Congestion Control in IP/TCP Inertnetworks",
              RFC 896, January 1984.

   [RFC1006]  Rose, M., and D. Cass, "ISO Transport Services on Top of
              the TCP Version 3", STD 35, RFC 1006, May 1987.

   [RFC1277]  Hardcastle-Kille, S., "Encoding Network Addresses to
              support operation over non-OSI lower layers", RFC 1277,
              November 1991.

   [RFC1278]  Hardcastle-Kille, S., "String encoding of Presentation
              Address", RFC 1278, November 1991.

              A string encoding of Presentation Address
              update to RFC1278, Work in Progress.

   [RFC1859]  Pouffary, Y., "ISO Transport Class 2 Non-use of Explicit
              Flow Control over TCP - RFC1006 extension", RFC 1859,
              October 1995.

   [IPV6]     Deering, S., and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 1883, December 1995.

              Hinden,, R., and S. Deeing, "IP Version 6 Addressing
              Architecture", RFC 1884, December 1995.

              Bound, J., Carpenter, B., Harrington, D., Houldsworth, J.,
              and A. Lloyd, "OSI NSAPs and IPv6", RFC 1888, August 1996.























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RFC 2126              ISO Transport on top of TCP             March 1997


Authors' Addresses

   Yanick Pouffary
   End Systems Networking
   Digital Equipment Corporation
   Centre Technique (Europe)
   B.P. 027
   950 Routes des colles
   06901 Sophia antipolis, France

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


   Alan Young
   ISODE Consortium
   The Dome
   The Square
   Richmond, UK

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



























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