PLAP(3)                                                   PLAP(3)

     NAME
          plap - USR/3Com Edgeserver packet bus link access protocol

     SYNOPSIS
          bind -a '#X' /net

          /net/plap/clone
          /net/plap/n/ctl
          /net/plap/n/data
          /net/plap/n/local
          /net/plap/n/remote
          /net/plap/n/status
          /net/plap/n/listen

     DESCRIPTION
          The plap driver serves a three-level directory giving access
          to the link level protocol used by an Edgeserver card to
          communicate with other cards in a USR/3Com chassis.  On
          first attach (usually by a bind(1) to /net) the driver opens
          a connection to the packet bus device #Y described in
          pbus(3). It multiplexes that connection using a specialised
          member of the LAP family of protocols.

          The top level directory contains a single directory naming
          the protocol, plap.  It contains a clone file and a set of
          conversation directories numbered from 0 to 127; only active
          conversation directories are present.

          Opening the clone file allocates a new conversation direc-
          tory n. The file descriptor will point to the control file,
          ctl, of that directory.  Reading the file returns a text
          string giving the conversation number.

          Each conversation directory contains six files.  The connec-
          tion is controlled by writing text strings to the ctl file.
          Once a connection has been established, data is exchanged
          with the remote peer by reading and writing the data file.

          A plap address has the form:

               [ slot.  ] chan!sap

          where slot is a chassis slot number, chan is a logical chan-
          nel (eg, a modem number), and sap is a number representing a
          `service access point'.

          The following control messages are supported:

          connect remoteaddr [ localaddr ]
               Make a connection to the given remote address (of the

     PLAP(3)                                                   PLAP(3)

               form given above).  If a local address is not speci-
               fied, the system will assign an unused address dynami-
               cally (the local chassis slot number is of course
               fixed).  Connect fails if the connection is already
               announced or connected, or localaddr is already in use.

          announceaddress
               Set the local address to address and accept incoming
               calls to that address.  If no address is specified, all
               incoming calls to addresses not explicitly announced
               will be accepted by this connection.  Announce fails if
               the connection is already announced or connected, or
               the local address specified is already in use.

          The remote and local files contain the remote and local
          addresses for the connection in the full address form
          slot.chan!sap.  The status file returns a line giving the
          directory name, number of active opens, and the state of the
          connection.

          A process listens for incoming calls by opening the listen
          file using sys-open(2). The open will block until a call
          arrives, when it will return a file descriptor open on the
          ctl file of the newly accepted connection, which can be read
          to find the directory number and thus the other files.

          The device follows the conventions that allow dial, announce
          and listen of sys-dial(2) to do the work needed to establish
          and manipulate network connections.

     SOURCE
          /os/pc/devplap.c

     SEE ALSO
          pbus(3)

     BUGS
          The driver cannot be included in the public distribution.