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2–Planning
Performance
2-4 59229-05 A
Regardless of how many credits are borrowed, extending credits requires a
minimum cable length that is dependent on transmission speed. Extending credits
over short cables can result in excessive port resets. Table 2-2 describes the
distances that are possible for a port with 30 credits and the minimum cable
lengths.
Bandwidth
Bandwidth is a measure of the volume of data that can be transmitted at a given
transmission rate. An SFP port can transmit or receive at nominal rates of 1-, 2-,
4-, or 8-Gbps depending on the device to which it is connected. This corresponds
to full duplex bandwidth values of 212 MB, 424 MB, 850 MB, and 1700 MB
respectively. X2 ports transmit at a nominal rate of 10-Gbps, which corresponds to
a full-duplex bandwidth value of 2550 MB.
For optimal performance, devices connected to the same I/O blade should have
the same transmission speed. Connecting devices of different transmission
speeds on the same I/O blade can reduce the maximum bandwidth by as much as
10%.
Multiple source ports can transmit to the same destination port if the destination
bandwidth is greater than or equal to the combined source bandwidth. For
example, two 2-Gbps source ports can transmit to one 4-Gbps destination port.
Similarly, one source port can feed multiple destination ports if the combined
destination bandwidth is greater than or equal to the source bandwidth.
When additional bandwidth is needed between devices, increase the number of
links between the connecting switches. The switch guarantees in-order-delivery
with any number of links between chassis.
Table 2-2. Extended Credit Distances and Cable Lengths
Transmission Speed Range for 30 Credits Minimum Cable Length
1-Gbps 50 Km (30÷0.6) 3 Km
2-Gbps 25 Km (30÷1.2) 1.5 Km
4-Gbps 12 Km (30÷2.4) 750 m
8-Gbps 6 Km (30÷4.8) 370 m
10-Gbps 4 Km (30÷7.2) 250 m