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What is the maximum length of QSFP cable?
Knowledge Base + 2023.12.04

The maximum length of a QSFP (Quad Small Form-factor Pluggable) cable can vary depending on the type and specification of the cable. In general, active QSFP cables can reach lengths of up to 10 meters (33 feet), while passive QSFP cables typically have a maximum length of around 7 meters (23 feet). However, it is important to refer to the specific manufacturer's specifications for the exact maximum length of a QSFP cable.

As shown in the solutions above, QSFP+ DAC Twinax cable, AOC cable and 40GBASE-SR4 QSFP+ module are able to provide a simple and useful way to establish a 40G-40G link between QSFP+ switches within racks and across adjacent racks. What’s the differences between these cabling solutions? Here take Cisco QSFP+ compatible optical modules and cables as an example to make a straightforward comparison.

                40G Optical Module/Cable                Max Transmission Distance                Fiber Cable Needed                Insertion Loss
                Cisco QSFP-40G-SR4 Compatible Module                Up to 150m                MTP/MPO fiber Cable                Yes
                Cisco 40GBASE-CSR4 Compatible Module                Up to 400m                MTP/MPO fiber Cable                Yes
                Cisco Compatible 40G QSFP+ to QSFP+ Passive DAC cable (3m)                Up to 7m                MTP/MPO fiber Cable                No
                Cisco Compatible 40G QSFP+ to QSFP+ Active DAC cable (3m)                Up to 10m                No                No
                Cisco Compatible 40G QSFP+ to QSFP+ AOC cable (3m)                Up to 100m                No                No

Notes: Prices may vary from different vendors and change over time.

From the table we can see that the QSFP+ direct attach passive copper cable price is lower than others, but its max transmission distance is only 7 meters. QSFP+ SR4 and QSFP+ CSR4 module are relatively cheap in, and their total cost is less than QSFP+ active copper cable and AOC cable at the same transmission length. Therefore, users can choose the suitable products for their 40G cabling networks on the basis of distance and products price. And sometimes insertion loss caused by fiber patch cables also need to be taken into account.