Bandwidth; Extended Credit Distances And Cable Lengths - Qlogic 5800V Series Installation Manual

2–Planning
Performance
Extending credits requires a minimum cable length that is dependent on
transmission speed. Extending credits over short cables can cause excessive port
resets.
with 30 credits.
Transmission Speed

Bandwidth

Bandwidth is a measure of the amount of data that can be transmitted at a
specified transmission rate. An SFP port can transmit or receive at nominal rates
of 1, 2, 4, or 8Gbps depending on the device to which it is connected. These rates
correspond to full-duplex bandwidth values of 212MB, 424MB, 850MB, and
1700MB respectively. XPAK ports transmit at a nominal rate of 10Gbps, which
corresponds to a full-duplex bandwidth value of 2550MB. With a 20Gbps license
key, XPAK ports can transmit at a nominal rate of 20Gbps (5100MB bandwidth).
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 2Gbps source ports can transmit to one 4Gbps 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.
In multiple chassis fabrics, each link between chassis contributes 424, 850, 1700,
2550, or 5100MB of bandwidth between those chassis, depending on the speed
of the link. 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.
2-4
Table 2-3 lists the possible distances and minimum cable lengths for a port
Table 2-3. Extended Credit Distances and Cable Lengths
1Gbps
2Gbps
4Gbps
8Gbps
Range for 30 Credits
50 Km (30÷0.6)
25 Km (30÷1.2)
12 Km (30÷2.4)
6 Km (30÷4.8)
Minimum Cable Length
3 Km
1.5 Km
0.75 Km
0.37 Km
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