L-ET4148-50C-DB LSI, L-ET4148-50C-DB Datasheet - Page 289

• Manufacturer Part Number: L-ET4148-50C-DB
• Manufacturer: LSI

Specifications of L-ET4148-50C-DB

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Preliminary Data Sheet
April 2006
Agere Systems Inc.
Appendix B: Configuration
Quality of Service
Likewise, the supervisor_queue_buffer_limit[14:0] and queue_buffer_limit[14:0] fields in the
Packet_Buffer_Queue_Buffer_Limit register are global limits used to restrict the number of buffers
(128 bytes) that a queue may occupy during packet buffer congestion. For these limits, the packet buffer is consid-
ered congested, if buffer_queue_global_congestion_threshold[14:4] in the
Packet_Buffer_Queue_Management_Thresholds register is exceeded.
When this global threshold is reached and a queue is occupying more buffers than its allocated limit, the ET4148-
50 prevents further enqueues to that queue until the packet buffer is no longer congested or until the number of
buffers occupied by the queue goes below its allocated limit. The packet buffer is no longer considered congested
for these limits when the total number of buffers used by the queue drops below
buffer_queue_global_congestion_threshold[14:4] minus
global_congestion_hysteresis[9:4].
Multicast/Broadcast Rate Limiting
The ET4148-50 has the ability to track the rate at which it is forwarding multicast and/or broadcast packets. If that
rate exceeds a configurable maximum, the excess multicast and/or broadcast packets are discarded. A single rate-
limiting function is shared by all Ethernet ports.
This packet rate limiting may be applied to either multicast packets or broadcast packets exclusively, or it may be
applied to both multicast and broadcast packets. Multicast rate limiting is enabled by asserting the
multicast_rate_limit_en bit in the Multicast_Rate_Mode register. Broadcast rate limiting is enabled by
asserting the broadcast_rate_limit_en bit in the same register.
A leaky bucket style rate limiting function is used to measure the global rate of multicast packets and compare that
rate against a configurable limit. If that limit is exceeded, a mask is applied to the destination bit map for all multi-
cast and/or broadcast packets for as long as the condition persists.
The maximum multicast rate is established via the Multicast_Rate_Decrement_Period register. This register
determines how often the Multicast_Rate_Accumulator is decremented. The period is calibrated in eight nano-
second units. So, setting this register to a value of one enables a multicast packet rate of 125,000,000 per second.
A value of F_FFFF
The Multicast_Rate_Limit register is used to establish the ET4148-50’s multicast burst tolerance. A higher
value in this register implies a higher tolerance for bursts of multicast packets. Once the value in
Multicast_Rate_Accumultor exceeds that of Multicast_Rate_Limit, the multicast packet rate is determined
to be in excess of the established limit.
When this condition is true, the mask in Multicast_Rate_Discard_Mask is applied during bridging operations to
all received multicast packets. This mask is typically configured to exclude certain destinations from the masking
operation. An example of such a destination is the supervisor queue that has been configured to be dedicated to
the reception of BPDU packets.
16
results in maximum rate of 119 multicast packets per second.
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Single-Chip 48 x 1 Gbit/s + 2 x 10 Gbits/s Layer 2+ Ethernet Switch
(continued)
Agere Systems - Proprietary
ET4148-50
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