Subject: DLSw Version 0.13 Chapter 6, Protocol Flows (2 of 2)

From: "Alan K. Bartky, Manager of Technology" <[email-masked]>
Date: Mon, 3 Oct 94 15:39:57 PDT

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This is the second part of two of Chapter 6, DLSw Version 0.13

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

   Here is an example of a switched SDLC PU 2.0 device as the origin
   station.

    ======                            ___                           ======
    |    |        ---------        __/   \__       ---------        |    |
    |    |      __|  _|_  |__     /   IP    \    __|  _|_  |__      |    |
    ======        |   |   |      <  Network  >     |   |   |        ======
   /______\       ---------       \__     __/      ---------       /______\
    Origin       Origin DLSw         \___/        Target DLSw      Target
    Station        partner                          partner        Station

                 disconnected                     disconnected

   implementer's  DLC_RESOLVE_C   CANUREACH_ex
   choice (power  ----------->    ----------->
   up, configuration
   change, receipt                 ICANREACH_ex
   of XID, never, etc.)            <-----------

   XID(null)     DLC_XID(null)   CANUREACH_cs    DLC_START_DL
   ----------->  ----------->    ----------->    ----------->
                 circuit_start                   resolve_pending

                                   ICANREACH_cs    DLC_DL_STARTED
                                   <-----------    <-----------
               circuit_established                 circuit_pending
                                   REACH_ACK
                                   ----------->   circuit_established

                                   XIDFRAME      DLC_XID
                                   ----------->  ----------->

            XID        DLC_XID         XIDFRAME         DLC_XID
     <---------   <-----------     <-----------    <-----------

   XID           DLC_XID         XIDFRAME        DLC_XID
   --------->    ----------->    ----------->    ----------->

           SNRM    DLC_CONTACT       CONTACTED    DLC_CONTACTED
     <---------   <-----------    <-----------    <-----------
                 contact_pending                 connect_pending

   UA            DLC_CONTACTED   CONTACT         DLC_CONTACT
   --------->    ----------->    ----------->    ----------->
                    connected                      connected

      IFRAMEs      DLC_INFOs        IFRAMEs        DLC_INFOs
   <---------->  <------------>  <------------>  <------------>

AIW DLSw Related Interest Group                              [Page 57]

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

   Here is an example of a leased SDLC PU 2.0 device as the target station.

    ======                            ___                           ======
    |    |        ---------        __/   \__       ---------        |    |
    |    |      __|  _|_  |__     /   IP    \    __|  _|_  |__      |    |
    ======        |   |   |      <  Network  >     |   |   |        ======
   /______\       ---------       \__     __/      ---------       /______\
    Origin       Origin DLSw         \___/        Target DLSw       Target
    Station        partner                          partner         Station
                                                                    (SDLC)
                 disconnected                    disconnected

                 DLC_RESOLVE_C   CANUREACH_ex
                 ----------->    ----------->   reply if virtual MAC/SAP
                                                for SDLC station is
                                                configured, if SDLC
                                                station responds to
                                  ICANREACH_ex  TEST/SNRM/DISC, etc.
                                  <-----------

                 DLC_XID         CANUREACH_cs    DLC_START_DL    SNRM
                 ----------->    ----------->    ----------->    --------->
                 circuit_start                   resolve_pending

                                   ICANREACH_cs    DLC_DL_STARTED        UA
                                   <-----------    <-----------    <-------
             circuit_established                 circuit_pending
                                                                 RNR
                                 REACH_ACK                       --------->
                                 ----------->   circuit_established

                                 XIDFRAME        DLC_XID
                                 ----------->    ----------->  respond with
                                                               XID
                                                               configured
                                                               for station
                                                               or forward
                                                               XID to
                                                               station and
                                                               send
                      DLC_XID        XIDFRAME         DLC_XID  response
                 <-----------    <-----------    <-----------

                 DLC_CONTACTED   CONTACT         DLC_CONTACT     RR
                 ----------->    ----------->    ----------->    --------->
                connect_pending                contact_pending

                    DLC_CONTACT       CONTACTED    DLC_CONTACTED
                   <-----------    <-----------    <-----------
                   connected                        connected

                   DLC_INFOs        IFRAMEs        DLC_INFOs       IFRAMEs
                 <------------>  <------------>  <------------>  <------->

AIW DLSw Related Interest Group                              [Page 58]

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

   Here is an example of a switched SDLC PU 2.0 device as the target
   station.

    ======                            ___                           ======
    |    |        ---------        __/   \__       ---------        |    |
    |    |      __|  _|_  |__     /   IP    \    __|  _|_  |__      |    |
    ======        |   |   |      <  Network  >     |   |   |        ======
   /______\       ---------       \__     __/      ---------       /______\
    Origin       Origin DLSw         \___/        Target DLSw       Target
    Station        partner                          partner         Station
                                                                    (SDLC)
                 disconnected                    disconnected

                 DLC_RESOLVE_C   CANUREACH_ex
                 ----------->    ----------->    reply if virtual MAC/SAP
                                                 for SDLC station is
                                                 configured, if SDLC
                                                 station responds to
                                   ICANREACH_ex  TEST/XID/SNRM/DISC, etc.
                                   <-----------

                 DLC_XID         CANUREACH_cs    DLC_START_DL    XID
                 ----------->    ----------->    ----------->    --------->
                 circuit_start                   resolve_pending

                                   ICANREACH_cs   DLC_DL_STARTED        XID
                                   <-----------   <-----------    <--------
             circuit_established                 circuit_pending
                                 REACH_ACK
                                 ----------->   circuit_established

                                   XIDFRAME        DLC_XID
                                   ----------->    -----------> respond
                                                                with XID
                                                                received
                        DLC_XID        XIDFRAME        DLC_XID  above
                   <-----------    <-----------     <---------

                DLC_CONTACTED   CONTACT         DLC_CONTACT     SNRM
                ----------->    ----------->    ----------->    --------->
                connect_pending                  contact_pending

                   DLC_CONTACT       CONTACTED    DLC_CONTACTED          UA
                  <-----------    <-----------    <-----------    <--------
                   connected                        connected

                   DLC_INFOs        IFRAMEs        DLC_INFOs       IFRAMEs
                 <------------>  <------------>  <------------>  <-------->

AIW DLSw Related Interest Group                              [Page 59]

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

   Here is an example of an SDLC T2.1 device as the target station.  (SDLC
   T2.1 origin station would look just like the LAN T2.1 origin station)
    ======                            ___                           ======
    |    |        ---------        __/   \__       ---------        |    |
    |    |      __|  _|_  |__     /   IP    \    __|  _|_  |__      |    |
    ======        |   |   |      <  Network  >     |   |   |        ======
   /______\       ---------       \__     __/      ---------       /______\
    Origin       Origin DLSw         \___/        Target DLSw      Target
    Station        partner                          partner        Station

                 disconnected                    disconnected

                 DLC_RESOLVE_C   CANUREACH_ex
                 ----------->    ----------->    implementers choice
                                                 (virtual MAC/SAP
                                                  configured,
                                                  check to see if station
                                                  is powered up using
                                   ICANREACH_ex   TEST/XID/DISC, etc.)
                                   <-----------

                 DLC_XID         CANUREACH_cs    DLC_START_DL    null XID
                 ----------->    ----------->    ----------->    --------->
                 circuit_start                   resolve_pending

                                   ICANREACH_cs    DLC_DL_STARTED       XID
                                   <-----------    <-----------    <-------
             circuit_established                 circuit_pending
                                 REACH_ACK
                                 ----------->   circuit_established

                                 XIDFRAME        DLC_XID
                                 ----------->    ----------->  respond with
                                                               XID received
                        DLC_XID        XIDFRAME        DLC_XID above
                   <-----------    <-----------    <----------

                    DLC_XIDs       XIDFRAMEs        DLC_XIDs         XIDs
                 <------------>  <------------>  <------------>  <-------->

                 DLC_CONTACTED   CONTACT         DLC_CONTACT     SABME
                 ----------->    ----------->    ----------->    --------->
                 connect_pending                 contact_pending

                    DLC_CONTACT       CONTACTED    DLC_CONTACTED         UA
                   <-----------    <-----------    <-----------    <-------
                   connected                        connected

                   DLC_INFOs        IFRAMEs        DLC_INFOs       IFRAMEs
                 <------------>  <------------>  <------------>  <-------->

AIW DLSw Related Interest Group                              [Page 60]

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

6.2. Link Restart Protocols

   The following figure depicts the protocol flows that result from
   restarting the end-to-end connection.  This causes the Data Link
   Switches to terminate the existing connection and to enter the Circuit
   Established state awaiting the start of a new connection.

     Data Link   Data Link                     Data Link   Data Link
      Control     Switch                        Switch      Control
     ---------------------                     ---------------------
          +-----------+                             +-----------+
          | Connected |                             | Connected |
    SABME +-----------+                             +-----------+
   ----------->                 RESTART_DL
      DM           ------------------------------------->     DISC
   <-----------                                               -------->
                                                               UA
                         DL_RESTARTED (Case 1)              <--------
                   <-------------------------------------
          +-----------+                             +-----------+
          |Circuit Est|                             |Circuit Est|
          +-----------+                             +-----------+
                        ........... or ...........
    SABME
   ----------->           DL_RESTARTED (Case 2)
       UA          <-------------------------------------
   <-----------                                     +-----------+
                                                    |Circuit Est|
                                CONTACT             +-----------+
      RNR           ------------------------------------>
   <----------

             Figure 5.  DLSw Link Restart Message Protocols

   Upon receipt of a SABME command from the origin station, the origin DLSw
   will send a RESTART_DL message to the target DLSw.  A DM response is
   also returned to the origin station and the data link is restarted.

   Upon receipt of the RESTART_DL message, the target DLSw will issue a
   DISC command to the target station.  The target station is expected to
   return a UA response.  The target DLSw will then restart its data link
   and send an DL_RESTARTED message back to the origin DLSw.  During this
   exchange of messages, both Data Link Switches change states from
   Connected state to Circuit Established state.

   If the origin station now resends the SABME command, the origin DLSw
   will send a CONTACT message to the target DLSw.  If the SABME command is
   received prior to the receipt of the DL_RESTARTED message (case 2 in the
   figure), the CONNECT message is delayed until the DL_RESTARTED message
   is received.  The resulting protocol flows at this point parallel those
   given above for the connect sequence.

AIW DLSw Related Interest Group                              [Page 61]

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

6.3. Disconnect Protocols

   The following figure depicts the protocol flows that result from the end
   system terminating an existing connection.  Not only is the connection
   terminated, but the circuit between the Data Link Switches is taken
   down.

     Data Link  Data Link                      Data Link  Data Link
      Control    Switch                         Switch     Control
     --------------------                      --------------------
          +-----------+                             +-----------+
          | Connected |                             | Connected |
          +-----------+                             +-----------+
      DISC
   ---------->                  HALT_DL
       UA         ------------------------------------->      DISC
   <----------                                              --------->
                                                               UA
                               DL_HALTED                    <--------
                  <-------------------------------------
          +-----------+                             +-----------+
          |Disconnectd|                             |Disconnectd|
          +-----------+                             +-----------+

                          ......... or ..........

          +-----------+                             +-----------+
          | Connected |                             | Connected |
          +-----------+                             +-----------+
       DISC              TCP Connection Failure               DISC
   <--------     <------------------------------------>    --------->
        UA                                                     UA
    -------->                                               <--------
          +-----------+                             +-----------+
          |Disconnectd|                             |Disconnectd|
          +-----------+                             +-----------+

              Figure 6.  DLSw Disconnect Message Protocols

   Upon receipt of a DISC command from the origin station, the origin DLSw
   will reply with a UA response and issue a HALT_DL message to the target
   DLSw.  Upon receipt of the HALT_DL message, the target DLSw will send a
   DISC command to the target station.  The target station will then
   respond with a UA response, causing the target DLSw to return a
   DL_HALTED message to the origin DLSw.  During this exchange of messages,
   both Data Link Switches change states from the Connected state to the
   Disconnected state.

   If the TCP connection between two Data Link Switches fails, all
   connections that are currently multiplexed on the failed TCP connection
   will be taken down.  This implies that both Data Link Switches will send
   DISC commands to all the local systems that are associated with the
   failed connections.  Upon sending the DISC command, the Data Link Switch
   will enter the DISCONNECT state for each circuit.

AIW DLSw Related Interest Group                              [Page 62]