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7.0 OAM Functions
7.2 Segmentation of OAM Cells
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
essential that a range of flexibility be provided in the processing of network man-
agement overhead. To provide this flexibility, the RS8234 includes an optional
local processor interface.
Since the RS8234 is capable of SAR shared memory segmentation and reas-
sembly, it can route OAM traffic including PM traffic to and from this local pro-
cessor, thereby off-loading ATM network management from the Host. Thus, host
processing power is focused on the user applications specifically concerned with
processing ATM user data traffic.
To accomplish this, the RS8234 provides global OAM buffer and status
queues (OAM_BFR_QU and OAM_STAT_QU, addresses for both assigned in the
RSM_CTRL1 register). If the OAM_QU_EN bit in the RSM_CTRL1 register is
set to a logic high, then the RS8234 routes OAM traffic to these global queues.
And with SAR shared memory addresses assigned to these global queues, the
RS8234 processes OAM traffic through the local processor, thereby freeing the
Host from these management functions. In addition, global OAM segmentation
status queue, SEG_CTRL(OAM_STAT_ID), is used if the OAM_STAT bit in the
segmentation buffer descriptor is a logic high.
7.2 Segmentation of OAM Cells
The host (or local processor) places OAM cells in a single buffer, and thus allo-
cates a single segmentation buffer descriptor (SBD) for the OAM cell data buffer,
not a linked list of SBDs.
The host (or local processor) then writes a pointer to that SBD in the next
available transmit queue entry, and sets the VLD bit to one.
When the segmentation coprocessor processes that transmit queue entry, it
submits the OAM cell data buffer to the xBR Traffic Manager and the cell thus is
scheduled for transmission.
7.2.1 Key OAM-Related Fields for OAM Segmentation
7.2.1.1 Segmentation
Buffer Descriptors
There are several fields in the SBD entry that are used to facilitate segmentation
of OAM cells.
Set the 2-bit AAL_OPT field to SINGLE (value = 01). This enables read-
ing 48 octets from a single buffer to form a single ATM cell.
Set the OAM_STAT bit to a logic high. The RS8234 will now report status
to the OAM-dedicated OAM_STAT_ID identified in the SEG_CTRL reg-
ister, instead of the STAT specified in the Seg VCC Table entry.
Set the single-bit HEADER_MOD field to a logic one. This activates the
WR_PTI and WR_VCI bits in the buffer descriptor, which signal the
RS8234 to overwrite the ATM header PTI and VCI fields for that cell with
the values from the PTI_DATA and VCI_DATA fields. In this way, F4 and
F5 flow OAM cells can be generated by the RS8234.
The VCI_DATA field set to a value of three (segment cell) or four (end-to-
end cell) generates an F4 flow OAM cell.
The PTI_DATA field set to a value of 100 (segment cell) or 101 (end-to-
end cell) generates an F5 flow OAM cell.