5NP4G
Egress Enqueuer / Dequeuer / Scheduler
6.4 The Egress Scheduler
The Egress Scheduler provides shaping functions in the network processor. The Egress scheduler manages
bandwidth on a per frame basis by determining the bandwidth a frame requires (that is, the number of bytes
to be transmitted) and comparing this against the bandwidth permitted by the configuration of the frame’s flow
queue. The bandwidth used by the first frame affects when the Scheduler permits the transmission of the
second frame of a flow queue. The Egress Scheduler characterizes flow queues with the parameters listed in
Table 6-2. Table 6-3 lists valid combinations of the parameters described in Table 6-2.
Table 6-2. Flow Queue Parameters
Parameter
Description
Provides guaranteed bandwidth with qualitative latency reduction.
Low -latency sustainable bandwidth (LLS)
LLS has higher service priority than NLS. Flow queues connected to LLS have bet-
ter latency characteristics than flow queues connected to NLS.
Normal-latency sustainable bandwidth (NLS)
Peak bandwidth service (PBS)
Provides guaranteed bandwidth.
Provides additional bandwidth on a best-effort basis.
Allows the scheduler to assign available (that is, not assigned or currently not used
by LLS and NLS) bandwidth to flow queues using best effort or PBS services.
Assignment of different ratios of the available bandwidth is accomplished by assign-
ing different queue weights to queues that share the same target port.
Queue Weight
Table 6-3. Valid Combinations of Scheduler Parameters
QoS
Low Latency with Guaranteed BW Shaping
Normal Latency with Guaranteed BW Shaping
Best Effort
LLS
X
NLS
X
Weight
PBS
X
X
Best Effort with Peak Rate
X
X
Normal Latency with Guaranteed BW Shaping
and Best Effort
X
X
X
X
Normal Latency with Guaranteed BW Shaping
and Best Effort and Peak Rate
Figure 6-7 on page 183 presents a graphical representation of the Egress Scheduler.
Egress Enqueuer / Dequeuer / Scheduler
Page 182 of 607
5NP4G Network Processor, Data Sheet, DS-0125-02
January 2006
EXAR [ EXAR CORPORATION ]
