RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
9.2.2.2.10
DBCES
Dynamic Bandwidth Circuit Emulation Service can be enabled to support the
dynamic adding and dropping of individual DS0s within a VC. DBCES is not
supported in conjunction with partially filled cells. When DBCES is enabled, the
RALP processes the incoming bit masks and adjusts the saved structure sizes,
and active connections.
When a channel changes its active state, an entry will be made into the
RCVN_STAT_FIFO., if the corresponding enable bit is set. At this point the
DBCES RX CHANNEL ACTIVE table, the DBCES_PENDING table and the
DBCES_PTR_TABLE will also be updated.
The DBCES RX CHANNEL ACTIVE table provides the active status for all of the
receive channels.
Using the bit mask, the number of active DS0s is calculated and the
R_TOT_SIZE, LAST_CHAN, R_DATA_LAST; R_CHAN_ACTIVE;
FRAMES_PER_CELL fields in the R_QUEUE_TABLE are updated.
If a queue implementing DBCES with active channels enters the underrun
condition, the normal underrun processing will occur. As individual time slots go
inactive, data will be played out as if the timeslot is in underrun.
If a DBCES queue has no active timeslots (all timeslots are inactive), the
underrun status from the RFTC is ignored and not counted as an underrun to
prevent a pointer search. When the queue transitions from all inactive to some
active channels, the write pointer is calculated as if resuming from an underrun.
If a sequence number error is detected and cells are inserted, the normal cell
insertion procedures apply except if the inserted cell should contain a bit mask.
In this case, the number of inserted bytes is adjusted for the bit mask.
If the bit mask is errored (parity error) the bit mask processing will be bypassed,
bit mask error sticky bit will be set and no changes made to the activity states of
the channels. If the errored bit mask should have contained a change in the bit
mask, all of the channels in that DBCES connection may be incorrectly mapped
until the next bit mask is received.
9.2.2.2.10.1 DBCES Receive Side Buffering
The amount of data that is buffered during DBCES mode is different than the
amount of data that is buffered in normal mode. In DBCES mode there must be
enough data to handle the case where the structure changes from the maximum
number of channels being active to only one channel being active without going
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
130
PMC [ PMC-SIERRA, INC ]
