RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
• SDF-FR Partial cell configurations with bytes_per_cell/num_chan = an
integer: 0 us.
• All other configurations: 125 us.
The following items affect transmit CDV:
• Cell scheduling
• Contention with other cells scheduled at same time
• Actual cell build time
• UTOPIA contention
• OAM cell generation
1) The scheduler has a resolution of 125 µs. In other words, it works off a frame-
based clock to determine whether or not a cell should be sent during the current
frame. Therefore, if the ideal rate of cell transmission is not a multiple of 125 µs,
there will be 125 µs of CDV. The scheduler will never add more than 125 µs of
CDV.
For example, a single DS0 queue with no signaling and using full cells, will need
to build a cell every 47 frames. Therefore, a cell will be scheduled every 47
frames, and the scheduler will add no CDV. Also in UDF mode all cells are sent
every time 47 bytes are received so no CDV is added.
However, if signaling were added to the single DS0 queue, the extra byte that
occurs every 24 bytes (assuming T1 mode) requires compensation. In this case,
a cell will be sent every 46 or 47 frames. Therefore, there will be up to 125 µs of
CDV due to the scheduler.
Note that for UDF lines there is a LOW_CDV bit which can be set in the
LIN_STR_MODE memory register which will cause cells to be scheduled every
47 bytes instead of frame based. This eliminates the CDV caused by the
scheduler. This mode can only be used in UDF-ML mode when
BYTES_PER_CELL is 47. In High Speed mode cells are always scheduled
every 47 bytes which assumes that partial cells are never used in HS mode.
2) Only one cell can be built at a time. Thus if multiple queues are scheduled to
send cells during the same frame, additional delay will be incurred. If queues are
activated and deactivated so that the number of queues scheduled ahead of a
specific queue in the same frame changes, the resulting change in delay
translates to CDV. The scheduling of multiple cells at the same time is known as
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
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