5. Multicast > Error Management of Multicast Packets
118
Tsi578 User Manual
June 6, 2016
Integrated Device Technology
www.idt.com
Figure 26: Arbitration Algorithm for Multicast Port
5.4
Error Management of Multicast Packets
Multicast packets have four sources of error - packet TEA, packet STOMPing, exceeding the
maximum latency time, and exceeding the time-to-live timeout.
5.4.1
Packet TEA
A multicast packet at the head of the ingress queue is subject to TEA. The TEA function does not
differentiate between multicast and unicast packets. The assertion of TEA for a packet at the head of
the ingress queue causes the packet to be immediately dropped from the queue. The packet is not
forwarded to the destination port (see
“Multicast Work Queue” on page 107
).
5.4.2
Multicast Packet Stomping
Transfers from the ingress port through the multicast work queue into the broadcast buffers operate in
cut-through mode. It is possible for the ingress port’s link partner to stomp a packet, or terminate it due
to some other error condition. It is also possible for the ingress port to detect a CRC or some other error
with the packet. To handle these situations, the Tsi578 supports stomping of a packet while it is being
transferred from ingress port to broadcast buffer.
When a packet arrives at the Tsi578 and a stomp control symbol is received part way though the packet,
the packet is still multicast to the egress ports. However, the egress ports stomp the packet when they
transmit the packet.
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P
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Arbitration Result
SP
RR
Src Port 0 Packet
Src Port 15 Packet
Src Port 1 Packet
...
RR
Src Port 0 Packet
Src Port 15 Packet
Src Port 1 Packet
..
.
RR
Src Port 0 Packet
Src Port 15 Packet
Src Port 1 Packet
...
RR
Src Port 0 Packet
Src Port 15 Packet
Src Port 1 Packet
..
.
Priority 3
Packets
Priority 2
Packets
Priority 1
Packets
Priority 0
Packets
Multicast port