RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 80

• Manufacturer Part Number: RS8234EBGC
• Description: RS8234EBGC ATM XBR SAR
• Manufacturer: Mindspeed Technologies

4.0 Segmentation Coprocessor
4.2 Segmentation Functional Description
4.2.1 Segmentation VCCs
4-2
4.2.1.1 Segmentation
VCC Table
4.2 Segmentation Functional Description
A VCC specifies a single VC or VP in the ATM network. The RS8234 supports
up to 64 K segmentation VCCs, referenced by a unique index, VCC_INDEX. The
VCC_INDEX identifies a location in the Segmentation VCC Table, an array of
10-word segmentation VCC channel descriptors.
single descriptor in the table (10 words). Due to the large number of specified
parameters for ABR traffic, ABR VCCs occupy two descriptors (20 words) in the
Segmentation VCC Table. The VCC_INDEX for ABR VCCs points to the first of
the two descriptors, and must be evenly divisible by two.
specific VCC Table Entry (seven words) and a service class specific Schedule
State (SCH_STATE). For non-ABR VCCs, the remaining three words of the
channel descriptor form the SCH_STATE entry. For an ABR VCC, the
SCH_STATE entry contains 13 words, which require an additional descriptor
location.
Figure 4-1
VCC located at VCC_INDEX 0x1000, and a non-ABR VCC at VCC_INDEX
0xFFFD. The host allocates the VCC Table in SAR shared memory and provides
an address to the SAR in a base register field, SEG_VBASE(SEG_VCCB). For
the most efficient ABR performance, all ABR VCCs should be placed in the
upper half of the VCC Table (i.e., with smaller VCC indexes). The only reason
not to put ABR VCCs at the lowest address range is to place CBR VCCs in the
first 32k of VCC addresses. Valid VCC indexes for CBR traffic range from
0x0000 to 0x7FFE, due to the limit imposed by a 15-bit address. A VCC index of
0xFFFF for non-CBR and 0x7FFF for CBR indicates a NULL VCC.
Indexes, the actual number of segmentation VCCs allowed by the SAR is limited
by the amount of SAR shared memory available in which to allocate and create
segmentation VCC Tables, transmit queues, etc.
Except for ABR service category VCCs, each segmentation VCC occupies a
A Segmentation VCC Table channel descriptor consists of two parts: an AAL
While the RS8234 will accept any VCC Index within the range of 64 K VCC
Mindspeed Technologies
shows a VCC Table with a CBR VCC at VCC_INDEX 3, an ABR
ATM ServiceSAR Plus with xBR Traffic Management
™
28234-DSH-001-B
RS8234