llc2 - LLC2 Configuration file




     The llc2 files contain information needed by LLC2 to  estab-
     lish  the  appropriate  links  to  the  underlying MAC layer
     drivers as well as the parameters necessary to configure the
     LLC (Logical Link Control) Class II Station Component struc-
     tures for that link.

     The comments are made up of one or more lines starting  with
     the "#" character in column 1.

     The main section consists of keyword/value pairs of the form
     keyword=value, used to initialize the particular adapter.

     A sample of the llc2 is presented below:

     llc2_on=1         # LLC2: On/Off on this device
     timeinterval=0    # LLC2: Timer Multiplier
     acktimer=2        # LLC2: Ack Timer
     rsptimer=2        # LLC2: Response Timer
     polltimer=4       # LLC2: Poll Timer
     rejecttimer=6     # LLC2: Reject Timer
     rembusytimer=8    # LLC2: Remote Busy Timer
     inacttimer=30     # LLC2: Inactivity Timer
     maxretry=6        # LLC2: Maximum Retry Value
     xmitwindowsz=14   # LLC2: Transmit Window Size
     rcvwindowsz=14    # LLC2: Receive Window Size

  MAC specific Parameters
     The  llc2.ppa file contains 4 parameters directly related to
     the  underlying MAC-level driver.  These are the name of the
     physical device, the instance of the  device,  whether  LLC2
     can  be  used  with  this  device, and whether the device is
     capable of looping back data addressed to the node's  unique
     MAC address, broadcast address, or multicast addresses.

     Setting the llc2_on parameter to 1 means that  LLC2  can  be
     used with this device; setting it to 0 means otherwise. Set-
     ting the loopback parameter to 1 means that the LLC2  module
     will  loop  back  data  addressed  to this node's unique MAC
     address or to a broadcast/multicast address.

     The most likely use is for a media that cannot  receive  its
     own  transmissions  (for example, ethernet) or when the MAC-
     level driver intentionally does not loop back data addressed
     to the local node under the assumption that the upper layers
     have already done so.

  Host-Based LLC2 Parameters
     The LLC2 contains ten parameters in the  configuration  file
     (/etc/llc2/default/llc2.ppa)  that  apply  to configurations
     using the Host-Based LLC2 component for  connection-oriented
     operation over an Ethernet, Token Ring, or FDDI media.

     The ten  parameters  break  down  into  the  following  four

        o  Six parameters deal with timer settings  for  managing
           the flow of LLC elements of procedure (PDUs) on a data
           link connection.

        o  One parameter is the multiplier that is used to deter-
           mine the period of the interval timer for the station.
           A value of 1 means that each tick count represents 100
           milliseconds;  5  means  each  tick  count is 500 mil-
           liseconds.  Should  the  parameter  be  omitted,   the
           default  value is 5, except for Token Ring links which
           use a default of 1.

        o  One parameter indicates how many  times  an  operation
           should be retried on a data link connection.

        o  Two parameters  are  for  controlling  the  number  of
           unacknowledged  I  PDUs   to send or receive on a data
           link connection.

     Additional information on these parameters can be  found  in
     ISO 8802-2:1989, Section 7.8.

     The following table of Logical Link Control Parameters  pro-
     vides the LLC configuration parameter names, default values,
     and ranges.

     Parameter              Description           Default             Range
     timeinterval    The timer ticks in 100  ms   5, except TPR - 1   0 - 10
                     intervals.  This parameter
                     is used to scale the  fol-
                     lowing 5 timer parameters.

     acktimer        The connection acknowledg-   2                   > 0
                     ment  timer length in (100
                     * timeinterval) ms.

     rsptimer        The  response  acknowledg-   2                   > 0
                     ment  timer length in (100
                     * timeinterval) ms.

     polltimer       The connection poll  timer   4                   > 0
                     length  in  (100 * timein-
                     terval) ms.

     rejecttimer     The   connection    reject   6                   > 0
                     timer  length  in  (100  *
                     timeinterval) ms.

     rembusytimer    The connection remote busy   8                   > 0
                     timer  length  in  (100  *
                     timeinterval) ms.

     inacttimer      The connection  inactivity   30                  > 0
                     timer  length  in  (100  *
                     timeinterval) ms.

     maxretry        The  maximum   number   of   6                   0 - 100
                     retries  of an action on a
     xmitwindowsz    The  maximum   number   of   14                  0 - 127
                     unacknowledged    I-format
                     protocol data  units  that
                     can  be  transmitted  on a
                     connection before awaiting
                     an acknowledgment.
     rcvwindowsz     The  maximum   number   of   14                  0 - 127
                     unacknowledged    I-format
                     protocol data  units  that
                     can  be received on a con-
                     nection  before  an   ack-
                     nowledgment is sent.

     Default values are set when  the  following  conditions  are

        o  The parameter is not set by the user.

        o  The       user        requests        a        default
           /etc/llc2/default/llc2.instance  file,  where instance
           is the  sequence  number,  starting  with  0,  of  the
           adapter  as detected by ifconfig(1M).  For example, if
           there are 3 adapters on the machine, the default  con-
           figuration   files   will   be   named   in  order  as
           /etc/llc2/default/llc2.0,    /etc/llc2/default/llc2.1,
           and /etc/llc2/default/llc2.2.

        o  The user codes a value of 0 for a parameter.

  Timer Parameter Descriptions
           The acktimer parameter is used to manage the following
           sample sequences:

           1. Attempting to establish,  reset,  or  disconnect  a

                  SABME     start acknowledgment timer
                   or   -------------------------------->

              The acknowledgment timer expires before the receipt
              of a response.

                  SABME     start acknowledgment timer
                   or   -------------------------------->

                     stop acknowledgment timer
                  <-------------------------------- UA

           2. Sending an FRMR in response to a  received  PDU  of
              dubious distinction:

                                       PDU with invalid N(R)
                                       I PDU with invalid N(S)
                  <------------------- PDU of invalid length
                                       unexpected UA PDU
                                       response PDU with
                                       invalid P/F setting

                             start acknowledgment timer
                  FRMR  -------------------------------->

              Acknowledgment timer expires before the receipt  of
              a PDU.

                             start acknowledgment timer
                  FRMR  -------------------------------->

                   stop acknowledgment timer
                                                     SABME, FRMR
                  <-------------------------------   DISC, or DM

           3. There is also a special case of the  acknowledgment
              timer,  referred  to  in this implementation as the
              response acknowledgment  timer  (rsptimer).  It  is
              used when sending an I PDU.

                     start response acknowledgement timer
                  I  -------------------------------------->

              Response acknowledgment timer  expires  before  the
              receipt of an  acknowledgment.

                             start poll timer
                  RR  -------------------------------->

           The polltimer parameter is used to  manage  situations
           where  a  Supervisory command PDU (RR, RNR, or REJ) is
           sent with the P/F bit set. This type of PDU  is  typi-
           cally sent when:

              o  There has been a period of inactivity on a  con-
                 nection in information  transfer mode.

              o  The remote node must be notified of a local busy
                 condition  occurring   in  information  transfer

           The expiration of the poll timer causes another Super-
           visory  command  PDU (which may be of a different type
           than the first) to be sent with the P/F bit set,  pro-
           vided  the  retry  count  has not exceeded the maximum
           retry value. This timer, then,  provides  an  extended
           retry   mechanism  for  a  connection  in  information
           transfer mode.

           The rejecttimer parameter controls the frequency  with
           which a REJ PDU is sent to a remote node from which an
           I PDU with an unexpected N(S) was received  and  which
           has  not  corrected  the situation by sending an I PDU
           with the expected N(S).

                  <-----------------------  I PDU with
                                            unexpected N(S)
                        start reject timer
               REJ  ------------------------>

           Reject timer expires before the receipt of  an  I  PDU
           with an expected N(S).

                     start reject and poll timer
               REJ  ----------------------------->
                     stop reject and poll timer
                   <---------------------------   I PDU with
                                                  expected N(S)

           The rembusytimer parameter is used  to  determine  how
           long the local node should wait, after the remote node
           sends an RNR to indicate it is busy, before sending  a
           Supervisory  PDU  with  the P/F bit set to solicit the
           current state of the remote node. If the  remote  node
           indicates  that  it  has  cleared  its  busy condition
           before the timer expires, the  local  node  stops  the
           remote busy timer.

           The inacttimer parameter controls  how  much  time  is
           allowed  to  elapse  on  a  connection  in information
           transfer mode between the issuing of command  PDUs  by
           the  local  node.  If  the  inactivity  timer  expires
           because a command PDU has not been  generated  in  the
           configured  time  interval, a Supervisory PDU with the
           P/F bit set is sent to the remote node to solicit  its
           current  state,  provided  that  the  connection is in
           information transfer mode. Each time a command PDU  is
           sent  by  the local node, the inactivity timer is res-

     The following rules of thumb  should  apply  for  the  timer

        o  The  acktimer,  rsptimer,  and   polltimer  parameters
           should  have  small relative values to allow for quick
           recovery from common transient error conditions  on  a

        o  The rejecttimer  and  rembusytimer  parameters  should
           have  intermediate  relative values to allow the local
           and remote nodes time to recover without resorting  to
           possibly unnecessary polling cycles.

        o  The inacttimer parameter should  be  set  to  a  large
           relative  value to provide a safety net in information
           transfer mode.

     You may need to shift the values for the timer parameters to
     higher  values  if  bridges are included in the network or a
     user application requires a substantial amount  of  time  to
     respond  to  connection  establishment  requests  or  handle
     information flow.

  Maximum Retry Parameter Description
     The  maxretry parameter determines the  number  of  times  a
     recovery  operation  is  performed before notifying the user
     that an error has occurred on a connection. Typical examples
     of its use include the following:

        o  When the remote node fails to respond to a SABME  sent
           by  the  local  node to establish or reset the connec-
           tion, the SABME is resent each time the acknowledgment
           timer expires, up to maxretry number of times.

        o  In information transfer mode,  if  the  response  ack-
           nowledgment  timer  expires  after  an  I PDU has been
           sent, an RR with the P/F bit set is sent  (and  resent
           each  time  the  poll  timer expires) until the remote
           node responds or maxretry  number  of  RRs  have  been

     In general, the maxretry value should not need to be  large.
     Since  the acknowledgment and poll timers are typically used
     in recovery operations that involve the maxretry  parameter,
     the  product  of  maxretry and either acktimer, rsptimer, or
     polltimer gives a rough  estimate  of  the  length  of  time
     allotted  for  the  connection  to  attempt  internal  error
     recovery before notifying the user.

  Window Size Parameter Descriptions
           The rcvwindowsz parameter is used to set  the  receive
           window  size  for I PDUs received locally on a connec-
           tion.  This value should agree with the transmit  win-
           dow size set for the connection at the remote node. If
           the local  rcvwindowsz  is  greater  than  the  remote
           transmit  window  size, I PDUs sent by the remote node
           are not acknowledged quickly. If the local rcvwindowsz
           is less than the remote transmit window size, there is
           a greater risk of the local node generating FRMR PDUs,
           requiring  intervention  by  the user application when
           transient errors on the connection require the  remote
           node  to  retransmit  an I PDU. REJ PDUs are recovered

           The xmitwindowsz parameter  sets  the  local  transmit
           window  size  for a connection.  It denotes the number
           of unacknowledged I PDUs that the local node may  have
           outstanding.  The  configured  value  should match the
           receive window size for the connection at  the  remote
           node,  based  on the same reasoning as for the rcvwin-
           dowsz parameter.

     In many  cases,  the  values  assigned  to  rcvwindowsz  and
     xmitwindowsz  for  adapters  on a server node will depend on
     the transmit and receive window sizes specified for  another
     LLC implementation on a client node. In cases where this LLC
     implementation is resident in both nodes, larger values  for
     these  parameters  are  useful in environments where much of
     the activity on  a  connection  consists  of  file  transfer
     operations.   Smaller  values  are  warranted if analysis of
     LLC2 connection component statistics  reveals  that  connec-
     tions  are entering local or remote busy state frequently.




     llc2_autoconfig(1), llc2_config(1), ifconfig(1M), llc2(7D)

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