L-ET4148-50C-DB LSI, L-ET4148-50C-DB Datasheet - Page 34

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

Specifications of L-ET4148-50C-DB

• Lead Free Status / RoHS Status: Supplier Unconfirmed

ET4148-50
Preliminary Data Sheet
Single-Chip 48 x 1 Gbit/s + 2 x 10 Gbits/s Layer 2+ Ethernet Switch
April 2006
Functional Description
(continued)
Retrieval
(continued)
A token bucket method is used for transmit bandwidth management. On a periodic basis, credit is applied to an
accumulator. The period is set to be proportional to the port speed. In other words, the period of accumulation for a
10 Mbits/s Ethernet port is 100 times greater than the period for 1 Gbit/s Ethernet port. Hence, the credit applied
each period is equivalent to a percentage of the total bandwidth available on a port. An accumulator limit is estab-
lished that is used to set a maximum amount of credit that may be accumulated.
Whenever the accumulator is greater than zero, the associated queue is enabled to arbitrate against the other
queues of the same transmit port. Each successful arbitration causes the length (byte count) of the transmit packet
to be subtracted from the accumulator. The accumulator limit establishes the longest burst of transmit packet bytes
that is allowed.
Packets may be destined for multiple queues or ports. This being the case, not every packet retrieval results in the
deallocation of the buffer used for packet storage. Only after the completion of the last retrieval of a packet may its
buffers be deallocated and made available for future storage operations.
The deallocation of buffers may result in the crossing of a congestion threshold towards the uncongested side. If
this is the case, the appropriate congestion indications are removed.
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Agere Systems Inc.
Agere Systems - Proprietary