llc2(4)
NAME
llc2 - LLC2 Configuration file
SYNOPSIS
/etc/llc2/default/llc2.*
DESCRIPTION
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:
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 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
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 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
connection.
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
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 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
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 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 -------------------------------->
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 con-
nection 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
transfer 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
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-
tarted.
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 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
sent.
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
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 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
internally.
xmitwindowsz
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.
FILES
/etc/llc2/default/llc2.*
SEE ALSO
llc2_autoconfig(1), llc2_config(1), ifconfig(1M), llc2(7D)
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