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PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
PM7341 S/UNI-IMA-84
DATASHEET
PMC-2000223
ISSUE 4
INVERSE MULTIPLEXING OVER ATM
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
105
Read_delay
Reads a snapshot of the link-defect status and
link-delay information for all of the links within
the group. The delay information can be used to
determine differential delay, the link with the
most delay, and any other delay characteristics
of the group. The delay information is provided
in units of cells.
Adjust_delay
Adjusts the delay of a group by removing the
amount of specified delay. While the delay is
being adjusted, links cannot be added or
recovered for the group.
In addition to performing commands from PM, the RIPP processes the ICP cells
forwarded by the RDAT. When ICP cells arrive from a group, they may be out of
order in time due to differential delay between links. The RIPP must examine the
ICP cell and determine if it has any new information that needs processing. This
can be determined via the IMA frame number and the SSCI field. When
processing the ICP cells and the link states, attention must be taken not to violate
the group wide procedures. When link or group states are changed, updated ICP
cells are sent to the TIMA for transmission. Any state changes are also
communicated to the appropriate schedulers and round-robin processors.
10.2.5.1
Group Start-up and Differential Delay
On group start-up, when at least P
rx
Links obtain IMA frame synchronization, the
links will be evaluated. As each link is evaluated, the differential delay of the
accepted links is tracked. If a link cannot be accepted because the acceptance of
the link would violate the programmed maximum DCB threshold (fastest link
minus current data read pointer), the link will remain in the unusable state and
begin to report a LODS defect. Accepted links will begin to report a usable state.
At this point, as additional links acquire frame sync, they are evaluated and either
are accepted or begin to report an LODS defect. When all links have acquired
frame sync or the timer has expired, the accepted receive links are reported as
active. If at least P
rx
links have been accepted, the group state machine
transitions to operational..
If sufficient links are not accepted, the group will not become operational. Note
that within any collection of links that are targeted to form an IMA group the group
may not become operational even though there are combinations of P
rx
links that
meet the programmed maximum DCB threshold. This would occur in situations