Microtronix Access User Guide
Window Modulus:
LAPB may be set to standard (
Modulo-8
) or extended (
Modulo-128
)
sequencing. Modulo-8 allows for up to 7 unacknowledged packets to be transmitted before
receiving an acknowledgment. Modulo-128 will allow up to 127 packets to be transmitted before
receiving an acknowledgment. This MUST match the peer device. The usual default is Modulo-
8.
Window Size (K):
The maximum number of unacknowledged frames that may be transmitted.
This MUST match the peer device. For Modulo-8, the valid values are 1-7, for modulo-128, 1-
127. The usual default is 7.
Maximum Information Frame Size (N1 Count):
The maximum number of bits (expressed as
bytes) in an Information (I) frame that the port is willing to accept. This value should include the
following:
●
maximum data packet size desired (minimum 128 bytes, maximum 4096)
●
packet header (3 bytes for modulo-8, or 4 bytes for modulo-128)
●
frame header (2 bytes for modulo-8, or 3 bytes for modulo-128)
●
checksum (2 bytes)
Retransmit Attempts (N2 Counter):
The maximum number of attempts made to complete the
successful transmission of a frame before attempting recovery.
Retransmit Timeout (T1 Timer):
The period of time which must pass before a retransmission
of an unacknowledged frame may occur. The normal default is 3 seconds, but this may be
increased for slower links (less than 4800 baud) to avoid unnecessary retransmissions.
Acknowledgment Hold Back Timeout (T2 Timer):
The period of time, in seconds, before an
acknowledgment is transmitted. This allows outbound information (I) frames to “piggyback” any
outstanding acknowledgments thereby canceling the timer. This should always be less than the
attached peer's T1 timer.
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