28236-DSH-001-B Datasheet, PDF (54/443 Pages) M/A-COM Technology Solutions, Inc. – ATM ServiceSAR Plus with xBR Traffic Management

2.0 Architecture Overview
2.5 Advanced xBR Traffic Management
CN8236
ATM ServiceSAR Plus with xBR Traffic Management
2.5.6 xBR Cell Scheduler
The xBR Scheduler slates traffic for transmission according to a Dynamic
Schedule table maintained in SAR-shared memory. The table contains a
user-programmable number of schedule slots. The duration of a single slot is a
user-programmable number of system clock cycles. The xBR Scheduler
sequences through this table in a circular fashion to schedule traffic. By
configuring the number of slots in the table and the duration of each slot, the
system designer chooses a range of available rates. A specific rate for any channel
is determined by how many slots in the table to which that channel is assigned.
Schedule slots not reserved for CBR during table setup are used for the rest of the
service categories.
The xBR Scheduler implements Mindspeed’s proprietary per-VCC
rate-shaping algorithms. The predecessor to the CN8236, the Bt8230 SAR,
proved the core algorithms. The CN8236 extends algorithms use to other service
classes. The CN8236 xBR Scheduler shapes all traffic classes, including CBR,
single leaky bucket VBR, dual leaky bucket VBR, ABR, and UBR. The host
configures the Dynamic Schedule table during system initialization, defining the
table size in number of schedule slots and the length of each schedule slot in clock
cycles. After setup, the CN8236 dynamically manages the entire table.
Some key features of the xBR Scheduler are as follows:
1. Per-VCC rate control guarantees conformance to GCRA UPC/policing
2. Dynamic reallocation of link bandwidth to active channels
3. Dynamic, fair sharing of bandwidth on oversubscribed lines
4. Multiple scheduling priorities
5. Fine-grained rate control
6. Rate based on a user-supplied reference clock
Dynamic management provides on-the-fly reallocation of link bandwidth
without host intervention. The CN8236 fairly distributes the link bandwidth to
channels based upon their QoS parameters and assigned transmission priority. As
covered previously, the CN8236 supports 16 priorities in addition to preallocated
CBR time slots.
The xBR Scheduler facilitates advanced network traffic management
topologies. The CN8236 rate shapes VCs or VPs. Additionally, CBR tunneling
allows UBR, VBR and/or ABR traffic management schemes to operate under a
preallocated CBR limit.
2-20
Mindspeed Technologies™
28236-DSH-001-B