RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
clumping. It takes approximately 8 µs to build a cell normally but can take up to
15 us under worst case traffic and processor activity (Note this assumes a 38.88
MHz SYS_CLK). Therefore, each cell that is waited for could add up to 15 µs of
delay. When multiple queues are scheduled to send cells at the same time, the
cells will be built in sequential order, starting with 0 and going to 256. Therefore,
in a system that will be adding and dropping queues, the higher number queues
will experience more CDV than the lower number queues, depending on how
many queues are active at the time, and are scheduled within the same frame.
The AAL1gator-8 minimizes the effects of clumping by offsetting the schedule
point of each line by 1/8th of a frame. Also when queues are added, an offset
field can be supplied which will force multiple cells on the same line to be
scheduled at different times. See Add Queue FIFO section in the Processor
Interface section for more details.
3) For configurations that will require sending a cell every n frames where n is an
integer divisor of 128 (for E1) or 96 (for T1), the cells will always be scheduled in
the same frame unless the offset field is set differently for each cell.
4) The actual build time of a cell depends on microprocessor activity and
contention with other internal state machines for the AAL1gator-8 memory bus.
Therefore there will be some minor CDV that is added on a per cell basis, based
on current microprocessor/memory traffic. This CDV is usually less than 4 µs and
is not very noticeable.
6) If there is backpressure on the UTOPIA bus, cells will not be able to be sent
which also causes CDV.
7) Since OAM cells have higher priority than data cells the transmission of OAM
cells should be distributed. An OAM cell can add up to 8 us of CDV assuming a
38.88 MHz SYS_CLK under worst case processor load.
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
95
PMC [ PMC-SIERRA, INC ]
