Subject: Valid SSP messages for flow control information

From: "Gene Cox ((444) 919-254-5075)" <[email-masked]>
Date: Mon, 11 Jul 94 15:31:02 EDT

I've given some thought to which SSP messages should be allowed to carry
valid flow control information, and used a generic connect/disconnect
model to help in my proposal thought process. The goal is to eliminate
any requirement to send a flow control only message.

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

 May have valid
  FCI/FCA/FCO    Data carrying

       Y*            N          CANUREACH_cs
                                ----------->
       Y             N            ICANREACH_cs
                                  <-----------
       Y             N          REACH_ACK
                                ----------->
       Y             Y            XIDFRAMEs
                                <------------>
       Y             Y            DGRMFRAMEs
                                <------------>
       Y             N          CONTACT
                                ----------->
       Y             N               CONTACTED
                                  <-----------
       Y             Y             IFRAMEs
                                <------------>
       Y             N          RESTART_DL
                                ----------->
       Y             N               DL_RESTARTED
                                  <-----------
       Y             N          CONTACT
                                ----------->
       Y             N               CONTACTED
                                  <-----------

       N             N          HALT_DL
                                ----------->
       N             N               DL_HALTED
                                  <-----------

* - CANUREACH_cs cannot carry FCA, as there could not be an outstanding
    FCI.