rfc2383.txt

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   The requirements for the AAL5 layer on the ST2+ over ATM user plane
   are as follows:

   o The SSCS must be null.

   o Implementations must use message-mode service.

     Note: Selection of the corrupted SDU delivery option on the
     receiver side depends on the implementation, so the receiver may or
     may not be able to select this option.

4.2.2 Overview of Interactions

   The AAL5 layer entity on the ST2+ over ATM user plane provides the
   following services to the ST2+ data layer.



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   o AAL5_UNITDATA.req

   o AAL5_UNITDATA.ind

4.2.2.1 AAL5_UNITDATA.req

   The AAL5_UNITDATA.req primitive sends a request for an AAL5 data
   (AAL5 CPCS_SDU) transfer from the ST2+ data layer entity to the AAL5
   layer entity.  The semantics of the primitive are as follows:

   AAL5_UNITDATA.req (
           DATA,
           CPCS_LP,
           CPCS_UU
           )

   The DATA parameter specifies the AAL5 data to be transferred.  The
   CPCS_LP parameter specifies the value of the CLP field in the ATM
   cell.  The CPCS_UU parameter specifies the user-to-user data to be
   transferred.

4.2.2.2 AAL5_UNITDATA.ind

   The AAL5_UNITDATA.ind indicates an AAL5 data (AAL5 CPCS_SDU) delivery
   from the AAL5 layer entity to the ST2+ data layer entity.  The
   semantics of the primitive are as follows:

   AAL5_UNITDATA.ind (
           DATA,
           CPCS_LP,
           CPCS_UU,
           STATUS [optional]
           )

   The DATA parameter indicates the delivered AAL5 data.  The CPCS_LP
   parameter indicates the value of the CLP field in the ATM cell.  The
   CPCS_UU parameter indicates the delivered user-to-user data.  The
   STATUS parameter indicates whether the delivered AAL5 data is corrupt
   or not.  The STATUS parameter is an optional parameter, and valid
   only when the corrupted SDU delivery option is selected.

4.3 AAL5 Encapsulation for ST2+ Data PDU

4.3.1 Mapping from st2_unitdata.req to AAL5_UNITDATA.req

   The ST2+ Data PDU is directly assigned to the DATA parameter in
   AAL5_UNITDATA.req.  That is, as shown in Fig. 4.1, the ST2+ Data PDU
   is mapped to the payload of AAL5 CPCS_PDU.



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   +-------+---------------------------+
   |  ST   |        ST2+ data          |               ST2+
   | header|                           |               Data PDU
   +-------+---------------------------+
   :                                   :
   :                                   :
   +---------------------------------------+--------+
   |             CPCS_PDU              |PAD|CPCS_PDU|  AAL5
   |             payload               |   |trailer |  CPCS_PDU
   +---------------------------------------+--------+

         Fig. 4.1: Mapping of ST2+ data to AAL5 CPCS_PDU payload.

   The value of CPCS_LP in AAL5_UNITDATA.req depends on the
   implementation: 1 (low priority) or zero (high priority) may be
   assigned permanently, or they may be assigned depending on the value
   of pri in st2_unitdata.req.

   The value of the CPCS_UU indication field in AAL5_UNITDATA.req is set
   to zero.

4.3.2 Mapping from AAL5_UNITDATA.ind to st2p_unitdata.ind

   The DATA parameter in AL5_UNITDATA.ind is directly assigned to the
   ST2+ Data PDU.  That is, the payload in AAL5 CPCS_PDU is mapped to
   the ST2+ Data PDU.

   If the value of STATUS in AAL5_UNITDATA.ind is valid, it is assigned
   to the status in st2p_unitdata.ind.

4.3.3 Value of MTU

   The value of MTU is Maximum CPCS_SDU size.

5. Protocol Specification of the Management Plane

   The management plane specifies the Null FlowSpec, the Controlled-Load
   Service FlowSpec, and the Guaranteed Service FlowSpec mapping rules
   for UNI 3.1 traffic management.

5.1 Mapping of the Null FlowSpec

   The Null FlowSpec is mapped to the UBR (VBR with the Best Effort
   Indicator).

   The value of the PCR (CLP=0+1) is shown in section 6.7.2.





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5.2 Mapping of the Controlled-Load Service FlowSpec

   The Controlled-Load FlowSpec is mapped to the VBR whose PCR
   (CLP=0+1), SCR (CLP=0+1), and MBS (CLP=0+1) are specified.

   The value of the PCR (CLP=0+1) is shown in section 6.7.2.

   Let scr be the calculated value of the SCR (CLP=0+1).  Based on the
   value of the [r] field in the Controlled-Load FlowSpec, it is given
   by:
                           scr = ([r] / 48) * S,

   where S is the coefficient of segmentation, and in an implementation,
   it must be configurable to any value between 1.0 and 56.0.  The
   recommended default value is 1.2.  The value of the SCR (CLP=0+1) is
   a minimum integer equal to or more than the calculated value of the
   scr.

   Let mbs be the calculated value of the MBS (CLP=0+1).  Based on the
   value of the [b] field in the Controlled-Load FlowSpec, it is given
   by:
                           mbs = ([b] / 48) * S.

   The value of the MBS (CLP=0+1) is a minimum integer equal to or more
   than the calculated value of the mbs.

   The values of the [p] and [m] fields in the Controlled-Load FlowSpec
   are ignored.

5.3 Mapping of the Guaranteed Service FlowSpec

   Note: The UNI 3.1 version of the ST2+ over ATM protocol does not
   support Guaranteed Services. It will be supported by the UNI 3.1/4.0
   version.

6. Protocol Specification of the Control Plane

   This section specifies the rules for encapsulating the ST2+ SCMP PDU
   into the AAL5 PDU, the relationship between ST2+ SCMP and PVC
   management for ST2+ data, and the protocol interaction between ST2+
   SCMP and UNI 3.1 signaling.

6.1 AAL5 Encapsulation for ST2+ SCMP PDU

   This subsection describes AAL5 PDU encapsulation for the ST2+ SCMP
   PDU.  ST2+ Data PDU compatible encapsulation, AAL5 encapsulation
   based on RFC 1483, and on the RFC 1483 extension are specified.
   Selection of which one to use depends on the implementation.



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   The ST2+ over ATM protocol does not cover a VC (SVC/PVC) that
   transfers ST2+ SCMP. VCs for IPv4 transfer may be used for ST2+ SCMP
   transfer, and implementations may provide particular VCs for ST2+
   SCMP transfer. Selection of these VCs depends on the implementation.

6.1.1 ST2+ Data PDU compatible encapsulation

   The ST2+ Data PDU compatible encapsulation is shown in Fig. 6.1: the
   ST2+ SCMP PDU is mapped to the payload of AAL5 CPCS_PDU.
   Implementors should note that this encapsulation is not applicable
   when the ST2+ SCMP PDU is multiplexed with other protocols.

   +-------+---------------------------+
   |  ST   |        ST2+ SCMP          |               ST2+
   | header|                           |               SCMP PDU
   +-------+---------------------------+
   :                                   :
   :                                   :
   +---------------------------------------+--------+
   |             CPCS_PDU              |PAD|CPCS_PDU|  AAL5
   |             payload               |   |trailer |  CPCS_PDU
   +---------------------------------------+--------+

             Fig. 6.1: ST2+ Data PDU conpatible encapsulation.

6.1.2 RFC 1483 base encapsulation

   The RFC 1483 base encapsulation is shown in Fig. 6.2: the ST2+ SCMP
   PDU with the RFC 1483 LLC encapsulation for routed protocol format is
   mapped to the payload in AAL5 CPCS_PDU.

               +------+----------------+
               |  ST  |   ST2+ SCMP    |               ST2+
               |header|                |               SCMP PDU
               +------+----------------+
               :                       :
   +---+---+---+-----------------------+
   |LLC|OUI|PID|     Information       |               IEEE 802 SNAP
   |   |   |   |                       |               ISO 8802-2 LLC
   +---+---+---+-----------------------+
   :                                   :
   +---------------------------------------+--------+
   |             CPCS_PDU              |PAD|CPCS_PDU|  AAL5
   |             payload               |   |trailer |  CPCS_PDU
   +---------------------------------------+--------+

                  Fig. 6.2: RFC 1483 base encapsulation.




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   The value of the LLC is 0xAA-AA-03, the value of the OUI is 0x00-00-
   00, and the value of the PID is 0x08-00.  The classification of the
   IPv4 and the ST2+ SCMP is determined by the IP version number, which
   is located in the first four bits of the IPv4 or ST headers.

6.1.3 RFC 1483 extension base encapsulation

   The RFC 1483 extension base encapsulation is the same as for RFC 1483
   base encapsulation, except that the value of the OUI is 0x00-00-5E
   (IANA) and the value of the PID is 0xXX-XX (TBD).

   The RFC 1483 base encapsulation for the SCMP is ideal, but requires
   modifying the IPv4 processing in the driver software of the WS or PC.
   Therefore, the RFC 1483 base encapsulation may be difficult to
   implement.  This encapsulation is designed to solve this problem.

6.2 Service Primitives Provided by Control Plane

   RFC 1819 ST2+ does not specify SCMP state machines.  And the ST2+
   over ATM protocol does not correspond to SCMP state machines.
   Therefore, the control plane specification assumes the following.

   o The ST2+ agent has ST2+ SCMP layer entities that correspond to the
     next hops and the previous hop in the stream.

   o The SCMP layer entity terminates ACK, ERROR, and timeout processing
     and provides reliable SCMP delivery.

   o The origin consists of an upper layer entity, ST2+ SCMP layer
     entities for next hops, and a routing machine that delivers SCMP
     messages between these entities.

   o The intermediate agent consists of ST2+ SCMP layer entities for a
     previous hop and for next hops and a routing machine that delivers
     SCMP messages between these entities.

   o The target consists of an upper layer entity, an ST2+ SCMP layer
     entity for a previous hop, and a routing machine that delivers SCMP
     messages between these entities.

   At least, the ST2+ SCMP layer entity for the next hop provides the
   following services to the routing machine.

   o connect.req
     This primitive sends a request for a CONNECT message transfer to
     the ST2+ SCMP layer entity.





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   o change.req
     This primitive sends a request for a CHANGE message transfer to the
     ST2+ SCMP layer entity.

   o accept.ind
     This primitive indicates an ACCEPT message delivery from the ST2+
     SCMP layer entity.

   o disconnect.req
     This primitive sends a request for a DISCONNECT message transfer to
     the ST2+ SCMP layer entity.

   o refuse.ind
     This primitive indicates a REFUSE message delivery from the ST2+
     SCMP layer entity, or indicates detection of an abnormal status
     such as an illegal message or timeout in the ST2+ SCMP layer
     entity.

   At least, the ST2+ SCMP layer entity for the previous hop provides
   the following services to the routing machine.

   o connect.ind
     This primitive indicates a CONNECT message delivery from the ST2+
     SCMP layer entity.

   o change.ind
     This primitive indicates a CHANGE message delivery from the ST2+
     SCMP layer entity.

   o accept.req
     This primitive sends a request for an ACCEPT message transfer to
     the ST2+ SCMP layer entity.

   o disconnect.ind
     This primitive indicates a DISCONNECT message delivery from the
     ST2+ SCMP layer entity, or indicates detection of an abnormal
     status such as an illegal message or timeout in the ST2+ SCMP layer
     entity.

   o refuse.req
     This primitive sends a request for a REFUSE message transfer to the
     ST2+ SCMP layer entity.

6.3 Service Primitives Provided by UNI 3.1 Signaling

   The UNI 3.1 signaling layer entity on the ST2+ over ATM control plane