Subject: DLSw Version 0.13, Chapter 4, Circuit Priority

From: "Alan K. Bartky, Manager of Technology" <[email-masked]>
Date: Mon, 3 Oct 94 15:31:39 PDT

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Here is Chapter 4 of DLSw Version 0.13

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RFC XXXX      DLSw: Switch-to-Switch Protocol              August 1994

4. Circuit Priority

   At circuit start time, each circuit end point will provide suggested
   priority information to its circuit partner.  The initiator if the
   circuit will choose which circuit priority will be effective for the
   life of the circuit.

4.1. Frame format:

   Circuit priority will be valid in the CANUREACH_cs, ICANREACH_cs, and
   REACH_ACK frames only. The relevant header field is shown below.  The
   Circuit Priority value is at offset 22 in an SSP Control Message.

   The following describes the format of the Circuit Priority byte.

     7   6   5   4   3   2   1   0
   +-----------------------+-------+
   |   reserved            |  CP   |
   +-----------------------+-------+

   CP: Circuit Priority bits
            00 - Low Priority
            01 - Medium Priority
            10 - High Priority
            11 - Highest Priority

   These values were chosen to correspond to the SNA INN FID4 TH TPF and
   NTWK_PRTY fields.

4.2. Circuit Startup:

   The sender of a CANUREACH_cs is responsible for setting the CP bits to
   reflect the priority it would like to use for the circuit being
   requested.  The mechanism for choosing an appropriate value is
   implementation dependant.  The sender of an ICANREACH_cs frame will set
   the CP bits to to reflect the priority it would like to use for the
   circuit being requested, with the mechanism for choosing the appropriate
   value being implementation dependant.  The receiver of the ICANREACH_cs
   will select from the 2 possible priorities and will set the value in the
   CP field of the REACH_ACK frame that follows to the value to be used for
   this circuit.  This priority will be used for the life of the circuit.

   Flow:

AIW DLSw Related Interest Group                              [Page 23]

RFC XXXX      DLSw: Switch-to-Switch Protocol              August 1994

        DLSw A               DLSw B

   CANUREACH_cs (CP=10) ------->                Circuit initiator requests
                                                   high Priority.

          <---------   ICANREACH_cs (CP=01)     Circuit target requests
                                                   medium priority.

   REACH_ACK (CP=01)   -------->                Circuit initiator sets
                                                   the priority for this
                                                   circuit to medium. The
                                                   circuit initiator could
                                                   choose any valid value.

AIW DLSw Related Interest Group                              [Page 24]