cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 190

• Manufacturer Part Number: cn8236
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

6.0 Traffic Management
6.2 xBR Cell Scheduler Functional Description
Figure 6-11. Another Possible Scheduling Priority Scheme with the CN8236
6.2.7 Guaranteed Frame Rate
6-22
VBR_OFFSET
HIGH
LOW
=3
Priority
Levels
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
GFR is a new service category defined by the ATM Forum to provide an MCR
QoS guarantee for AAL5 CPCS-PDUs (or frames) not exceeding a specified
frame length. This class of service is designed specifically to utilize the UBR
service category. A GFR service connection is thus treated as UBR with a
guaranteed MCR.
using both the VBR1 scheduling procedure (for the MCR rate value) and a UBR
priority queue, thereby providing fair sharing for all GFR connections to excess
bandwidth. The VBR1 queue priority (the PRI field in the SEG VCC table entry)
must be set to a higher priority than the UBR queue (the GFR_PRI field in the
SEG VCC table entry). The priority level entered in the GFR_PRI field can only
be one of the lower eight scheduling priorities. This establishes the condition
where those GFR connections sharing the same GFR_PRI would fair-share any
excess bandwidth above the MCR limits. Call control must not oversubscribe
MCR on GFR channels and other rate-guaranteed services.
mechanism to trigger an increase in the scheduling priority by one priority level,
if the transmit rate on that channel falls below its specified MCR. This is done
using the MCRLIM_IDX field in that VCC’s SCH_STATE entry in the SEG
VCC table entry. MCRLIM_IDX is an 8-bit index into a table containing 256
The CN8236 implements GFR by scheduling or shaping the connections
The CN8236 helps guarantee MCR on a GFR channel by providing a
Tunnel A
nrt-VBR
rt-VBR
ABR
UBR
Mindspeed Technologies
Example of Multi-Service Tunnels
Tunnel B
rt-VBR
nrt-VBR
UBR
ABR
ATM ServiceSAR Plus with xBR Traffic Management
Tunnel C
nrt-VBR
rt-VBR
UBR
ABR
™
Tunnel D
nrt-VBR
rt-VBR
ABR
UBR
28236-DSH-001-B
CN8236
8236_043