Subject: DLSw version 0.15 Chapter 4

From: "Alan K. Bartky, Manager of Technology" <[email-masked]>
Date: Tue, 1 Nov 94 16:26:34 PST

----------
X-Sun-Data-Type: text
X-Sun-Data-Description: text
X-Sun-Data-Name: text
X-Sun-Content-Lines: 1
X-Sun-Content-Length: 31

This is the third part of 11.

----------
X-Sun-Data-Type: default
X-Sun-Data-Description: default
X-Sun-Data-Name: dlsw4.txt
X-Sun-Content-Lines: 124
X-Sun-Content-Length: 3385

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

4. Circuit Priority

   At circuit start time, each circuit end point will provide priority
   information to its circuit partner.  The initiator of the circuit will
   choose which circuit priority will be effective for the life of the
   circuit.  If Priority is not implemented by the Data Link Switch, then
   "Unspecified" priority is used.

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 a byte value 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
           000 - Unspecified       (note 1)
           001 - Low Priority      (note 2)
           010 - Medium Priority   (note 2)
           011 - High Priority     (note 2)
           100 - Highest Priority  (note 2)
           101 to 111 are reserved for future use

   Note 1: Unspecified means that the Data Link Switch that originates the
   circuit does not implement priority.  Actions taken on Unspecified
   priority are vendor specific.

   Note 2: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 dependent.  The sender of an ICANREACH_cs frame will set
   the CP bits to reflect the priority it would like to use for the circuit
   being requested, with the mechanism for choosing the appropriate value
   being implementation dependent.  The receiver of the ICANREACH_cs will
   select from the 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.
   A CANUREACH_cs or ICANREACH_cs with the circuit priority value set to
   Unsupported (CP=000) indicates that the sender does not support the
   circuit priority function.

AIW DLSw Related Interest Group           DLSw version 0.15 [Page 24]

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

   Flow:

      DLSw A               DLSw B

   CANUREACH_cs (CP=011) ----->           Circuit initiator requests
                                          high Priority.

        <--------- ICANREACH_cs (CP=010)  Circuit target requests
                                          medium priority.

   REACH_ACK (CP=010) -------->           Circuit initiator sets
                                          the priority for this
                                          circuit to medium. The
                                          circuit initiator could
                                          choose any valid value.

AIW DLSw Related Interest Group           DLSw version 0.15 [Page 25]