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llc2(4)                          File Formats                          llc2(4)



NAME
       llc2 - LLC2 Configuration file

SYNOPSIS
       /etc/llc2/default/llc2.*

DESCRIPTION
       The  llc2  files  contain  information  needed by LLC2 to establish 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 structures 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 key-
       word=value, used to initialize the particular adapter.

       A sample of the llc2 is presented below:

       devicename=/dev/dnet
       deviceinstance=1
       llc2_on=1         # LLC2: On/Off on this device
       deviceloopback=1
       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 under-
       lying 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. Setting 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 trans-
       missions (for example, ethernet) or when the  MAC-level  driver  inten-
       tionally  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 groups:

         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  determine  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 milliseconds. 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 provides the LLC
       configuration parameter names, default values, and ranges.


       tab();    lw(1.294118i)   cw(2.588235i)   lw(0.970588i)   lw(0.647059i)
       lw(1.294118i) lw(2.588235i) lw(0.970588i) lw(0.647059i).   ParameterDe-
       scriptionDefaultRange  timeintervalT{  The timer ticks in 100 ms inter-
       vals. This parameter is used to scale the following 5 timer parameters.
       T}5,  except  TPR  -  10  - 10 acktimerT{ The connection acknowledgment
       timer length in  (100  *  timeinterval)  ms.   T}2>  0  rsptimerT{  The
       response  acknowledgment timer length in (100 * timeinterval) ms.  T}2>
       0 polltimerT{ The connection poll timer length in (100 *  timeinterval)
       ms.   T}4> 0 rejecttimerT{ The connection reject timer length in (100 *
       timeinterval) ms.  T}6> 0 rembusytimerT{  The  connection  remote  busy
       timer  length in (100 * timeinterval) ms.  T}8> 0 inacttimerT{ The con-
       nection inactivity timer length in (100 * timeinterval)  ms.   T}30>  0
       maxretryT{  The maximum number of retries of an action on a connection.
       T}60 - 100 xmitwindowszT{ The maximum number of unacknowledged I-format
       protocol  data  units  that  can  be transmitted on a connection before
       awaiting an acknowledgment.  T}140 - 127 rcvwindowszT{ The maximum num-
       ber of unacknowledged I-format protocol data units that can be received
       on a connection before an acknowledgment is sent.  T}140 - 127


       Default values are set when the following conditions are true:

         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 configuration 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
       acktimer        The  acktimer parameter is used to manage the following
                       sample sequences:

                           1.  Attempting to establish, reset, or disconnect a
                               connection.

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


                               The  acknowledgment  timer  expires  before the
                               receipt of a response.

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

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



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

                                                        PDU with invalid N(R)
                                                                or
                                                        I PDU with invalid N(S)
                                                                or
                                   <------------------- PDU of invalid length
                                                                or
                                                        unexpected UA PDU
                                                                or
                                                        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 acknowledg-
                               ment  timer, referred to in this implementation
                               as the response  acknowledgment  timer  (rspti-
                               mer). 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  -------------------------------->






       polltimer       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 connec-
                            tion in information  transfer mode.

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


                       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  trans-
                       fer mode.



       rejecttimer     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)




       rembusytimer    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.



       inacttimer      The  inacttimer  parameter  controls  how  much time is
                       allowed to elapse on a connection in information trans-
                       fer  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 restarted.



       The following rules of thumb should apply for the timer parameters:

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

         o  The rejecttimer and rembusytimer parameters should have intermedi-
            ate   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 estab-
       lishment requests or handle information flow.

   Maximum Retry Parameter Description
       The  maxretry parameter determines the number of times a recovery oper-
       ation 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 connection, the SABME is resent
            each time the acknowledgment timer expires, up to maxretry  number
            of times.

         o  In information transfer mode, if the response acknowledgment 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 sent.


       In general, the maxretry value should not need to be large.  Since  the
       acknowledgment  and  poll  timers are typically used in recovery opera-
       tions 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
       rcvwindowsz     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 window
                       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
                       internally.



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



       In  many cases, the values assigned to rcvwindowsz and xmitwindowsz for
       adapters on a server node will depend on the transmit and receive  win-
       dow 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 connections  are entering local or remote  busy
       state frequently.

FILES
       /etc/llc2/default/llc2.*

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



SunOS 5.10                        7 Feb 2000                           llc2(4)