40GE Data Center Cabling Options – Transceivers & Direct Attach Cables

Updated on Jan 8, 2021 by

40GbE (Gigabit Ethernet) era is already upon us and makes a contribution to satisfying the increasing demands of higher throughput and bandwidth. In today’s data center, especially in medium-sized and large ones, 40G cabling networks coming with QSFP+ transceivers, QSFP+ DAC/AOC and MTP/MPO fiber cables are very common, which enhance the booming of 40G optical module market. This article intends to provide a detailed products analysis of the general 40GE data center cabling solutions including 40G direct short-reach connectivity cabling, 40G long-reach connectivity cabling and 40G breakout cabling.

40G Short-Reach Cabling Solution

In most 40G data centers, usually server to server connections require 2-5 meters, while rack to rack connections are required to be connected by 8-12 meters of cables. And distance between data center switches can be far away to hundred meters. Therefore, there are several types of 40G products used in those short-reach connections: 40G QSFP+ Direct Attach Cables (passive copper cable and active copper cable), QSFP+ AOC cable, QSFP 40G SR4 and QSFP+ CSR4 module.

40G QSFP+ to QSFP+ Connectivity via DAC AOC SR4 Modules.png

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 Cost of 3m link length
Cisco QSFP-40G-SR4 Compatible Module Up to 150m MTP/MPO fiber Cable Yes About $96=$49 (QSFP+ SR4) + $47 (3m OM4 MTP cable)
Cisco 40GBASE-CSR4 Compatible Module Up to 400m MTP/MPO fiber Cable Yes About $106=$59 (QSFP+ CSR4) +$47 (3m OM4 MTP cable)
Cisco Compatible 40G QSFP+ to QSFP+ Passive DAC cable (3m) Up to 7m MTP/MPO fiber Cable No About $49
Cisco Compatible 40G QSFP+ to QSFP+ Active DAC cable (3m) Up to 10m No No About $140
Cisco Compatible 40G QSFP+ to QSFP+ AOC cable (3m) Up to 100m No No About $130

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 FS.com, 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.

40G Long-Reach Cabling Solution

When link length is beyond 400m, the above 40G QSFP+ SR4 transceivers, direct attach cable and AOC cables are no longer suitable to use. For those applications that are up to thousand meters, only QSFP+ transceivers, such as 40GBASE-PLRL4, 40GBASE-PLR4, 40GBASE-LR4L and 40GBASE-ER4/LX4/LR4, can realize.

40G QSFP+ to QSFP+ Connectivity via LR4 Modules.jpg

In fact, these long-reach 40G transceivers come with MTP/MPO interface or LC interface. The QSFP+ transceivers with LC interface do not support 4x10G connectivity as they use four wavelengths on a pair of single mode fibers, while QSFP+ transceiver with MTP/MPO interface can. All the long-reach 40G optical modules work on single mode fiber cable (SMF). Different QSFP+ optical module supports different transmission distances which decides 40G QSFP+ module price. However, the price of MTP/MPO fiber patch and LC fiber patch cable is different, so does the total cost. Take the link length of 1 kilometers as an example, here is the price of Cisco compatible 40G QSFP+ modules and fiber cables from FS.com.

40G QSFP+ Module Interface Max Transmission Distance Cost of 1km link length
Cisco QSFP-4X10G-LR-S Compatible Module MTP/MPO 10km over SMF About $1143.6=$380 (QSFP-4X10G-LR-S) + $763.6 (8-Fiber MTP/MPO SMF)
Cisco 40GBASE-LR4-S Compatible Module LC Duplex 10km over SMF About $542.6 =$340 (40GBASE-LR4-S) + $202.6 (LC duplex SMF)
Cisco 40GBASE-LR4 OTU3 CFP Compatible Module LC Duplex 10km over SMF About $1402.6=$1200 (40GBASE-LR4 CFP) + $202.6 (LC duplex SMF)

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

40G-10G Breakout Cabling Solution

As we know, 40GbE port can be split into four 10GbE ports, which offers an effective way for connection between 10G and 40G. Usually in 40G-10G breakout cabling networks, the following two types of solutions are available:

40G QSFP+ optical module: 40G QSFP+ SR4, 40G QSFP+ PLRL4 and 40G QSFP+ PLR4, MTP-LC harness cable
40G breakout cable: QSFP+ to 4xSFP+ DAC, QSFP+ to 4xSFP+ AOC, QSFP+ to 8xLC AOC

40G to four 10G connectivity.jpg

Similar to the 40G short-reach connectivity, users can choose different QSFP+ products according to different application requirements. However, when using 40G transceiver like QSFP+ SR4 module to achieve 40G breakout cabling, four 10G SFP+ modules and an MTP-LC harness cable are needed. While 40G breakout DAC cable and 40G breakout AOC cable can connect QSFP+ switch to four 10G switches directly, which is more simple and cost-saving in short distance transmission. In addition, 40G QSFP+ to 8xLC AOC is terminated with 40GBASE QSFP+ port on one end, while on the other end, it can be terminated with LC, SC, FC, and ST connectors, providing an effective way for port extension applications. Here is a simple comparison between the two 40G breakout cabling solutions.

40G Optical Module/Cable Fiber Cable needed Max Distance Cost of 1m link length
40G QSFP+ SR4 Transceiver MTP-LC Harness Cable Up to 150m About $78=$49 (QSFP+ SR4)+ $29 (1m 8-fiber MTP-LC harness cable)
QSFP+ to 4xSFP+ Breakout DAC (1m) No Up to 5m About $40
QSFP+ to 4xSFP+ Breakout AOC (1m) No Up to 100m About $190
QSFP+ to 8xLC Breakout AOC (1m) No Up to 100m About $140

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


When designing a networking system, it is important to plan the cabling system in advance. With speeds in the data center now increasing from 10Gbps to 40Gbps, 40G cabling network consolidates into more complex. A single cabling solution can no longer meet the 40G data center deployment which is growing complex. From the analysis of the three types of 40GE data center cabling solutions above, we can see the optics market for 40GbE connectivity is now mature. When buying 40G QSFP+ transceivers, DAC Twinax cable and 40G QSFP+ AOCs, it’s imperative to address current network requirements as well as accommodate future growth.

Related article:

40G QSFP+ Direct Attach Copper Cabling

Active Optical Cable (AOC)–Rising Star of Telecommunications & Datacom Transceiver Markets

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