Table 3.5 Conditions For Cut-Through Transfers - Renesas IDT 89HPES48H12G2 User Manual

IDT Switch Core
Notes
PES48H12G2 User Manual
and egress link bandwidth is determined by the negotiated speed and width of the links. Table 3.5 shows
the conditions under which cut-through and adaptive-cut-through occur. When the conditions are met, cut-
through is performed across the IFB, crossbar
Note that a packet undergoing a cut-through transfer across the Switch Core may be temporarily
delayed by the presence of prior packets in the IFB and/or EFB. In this case, the packet starts cutting-
through as soon as it becomes unblocked by prior packets.
When cut-through routing of a packet is not possible, the packet is fully buffered in the appropriate IFB
prior to being transferred to the EFB and towards the egress link (i.e., store-and-forward operation). Once
the packet is stored in the IFB, there is no necessity to fully store it in the EFB as it is transferred towards
the egress link.
Ingress Ingress
Link Link
Speed Width
2.5 Gbps x8
x4
x2
x1
Table 3.5 Conditions for Cut-Through Transfers (Part 1 of 2)
1.
During cut-through transfers, the crossbar maintains the connection between the appropriate IFB and EFB
through-out the duration of the transfer.
1
, and EFB.
Egress Egress
Link Link
Speed Width
2.5 x8, x4, x2, x1
5.0 x4, x2, x1
x8
2.5 x4, x2, x1
x8
5.0 x2, x1
x4
x8
2.5 x2, x1
x4
x8
5.0 x1
x2
x4
x8
2.5 x1
x2
x4
x8
5.0 x1
x2
x4
x8
3 - 7
Conditions for Cut-
Through
Always
Always
At least 50% of packet is in IFB
Always
At least 50% of packet is in IFB
Always
At least 50% of packet is in IFB
At least 75% of packet is in IFB
Always
At least 50% of packet is in IFB
At least 75% of packet is in IFB
Always
At least 50% of packet is in IFB
At least 75% of packet is in IFB
At least 100% of packet is in IFB
Always
At least 50% of packet is in IFB
At least 75% of packet is in IFB
Never (100% of packet is in IFB)
At least 50% of packet is in IFB
At least 75% of packet is in IFB
Never (100% of packet is in IFB)
April 5, 2013