Comprehensive Classification of QSFP28 Cable

Updated on Dec 22, 2021

From providing flawless, high-flow media to real-time connectivity with customers around the world, today's data centers require ultra-high-speed data transmission, promoting the development of the whole optical communication market. QSFP28 cable is a necessity for data transmission. How many types of QSFP28 cable are available in the market and what are they? Find answers in this article.

QSFP28 Cable: Definition and Types

QSFP28 cable contains two forms: one is a form of high-speed cable with QSFP28 connectors on either end, transmitting and receiving 100Gbps data over a thin twinax cable or a fiber optic cable, and the other is a form of breakout cable that can split one 100G signal into 4x 25G (QSFP28 to SFP28) or 2x 50G, enabling connectivity between network devices with different speed ports, while fully utilizing port bandwidth.

Types Data Rate Connector Type Cable Type
100G QSFP28 DAC 100Gbps QSFP28 to QSFP28 Passive Twinax Copper Cable
100G DAC Breakout Cables 100Gbps QSFP28 to 2xQSFP28 / QSFP28 to SFP28 Passive Twinax Copper Cable
100G QSFP28 AOC / 50G QSFP28 AOC 100Gbps QSFP28 to QSFP28 Optical Cable
100G AOC Breakout Cables 100Gbps QSFP28 to SFP28 / QSFP28 to 2xQSFP28 OM3

QSFP28 Cable: What Is 100G QSFP28 DAC?

100G QSFP28 DAC is generally divided into three types: 100G QSFP28 Passive Direct Attach Cable, 100G QSFP28 to 4× 25G SFP28 Passive DAC Cable, and 100G QSFP28 to 2x 50G QSFP28 Passive Direct Attach Cable.

100G QSFP28 Passive Direct Attach Cable

100G QSFP28 DAC is a 4-channel parallel passive copper cable that is combining four 28 Gbps SFP channels into one high-density cable. It offers 4 independent data transmitting channels and 4 data receiving channels via copper cable, providing a cost-effective way to establish a 100-Gigabit link between QSFP-100G ports of switches within racks and across adjacent racks, ideal for data centers, high-end servers and enterprise wiring closets. QSFP28 DAC is usually applied for ToR (Top of Rack) interconnections between 100G ToR switch and server or the stacking of 100GbE switches (as the figure below).

Figure 1: Application of 100G QSFP28 Passive Direct Attach Cable

100G QSFP28 to 4× 25G SFP28 Passive DAC Cable

QSFP28 to SFP28 Passive DAC Cable is a breakout cable providing a hybrid transition from a QSFP28 on one end to four individual SFP28 on the other end. It offers four parallel, bi-directional channels each operating at up to 25Gps. Featuring low crosstalk, small bend radius and low power consumption, the 100G to 25G breakout cable meets the ever-increasing demand for higher channel density with high-level signal integrity in high-performance computing, top-of-rack switching, and network storage deployments.

100G QSFP28 to 2x 50G QSFP28 Passive Direct Attach Cable

100G QSFP28 to 2x 50G QSFP28 breakout DAC is a 4-channel parallel copper direct attach cable offering 4 independent data transmission channels and 4 data receiving channels via the cable. The aggregate data rate of 100Gbps over 5m transmission can be achieved with this product. Designed for use in cost-effective 100GbE to 2x 50GbE Ethernet connectivity solution to meet the growing needs for higher bandwidth in data centers, this QSFP28 cable is suitable for the Infiniband EDR and 128G Fibre Channel.

Figure 2: 100G DAC Breakout Cables

QSFP28 Cable: What Is 100G AOC?

AOC (Active Optical Cable) is a communication cable that needs to use external energy to convert electrical signals into optical signals or conversely in the communication process. There are commonly two types of 100G AOC: 100G QSFP28 AOC and 100G QSFP28 to 4X 25G SFP28 AOC.


100G QSFP28 AOC cable is composed of multi-mode optical fiber and parallel optical modules. The QSFP28 transceivers at both ends provide photoelectric conversion and optical transmission functions to increase the transmission rate and distance of the optical cable without weakening the compatibility with the standard electrical interface. With no insertion loss and return loss, 100G AOC is mainly used for short-distance multi-channel data communication applications in several locations in the data center like ToR, EoR and MoR (as the figure below).

Figure 3: Application of 100G QSFP28 AOC

100G QSFP28 to 4X 25G SFP28 AOC

QSFP28 to SFP28 breakout AOC is a high data rate parallel active optical cable, to overcome the bandwidth limitation of traditional copper cable, terminated with a QSFP28 module at one end and four SFP28 modules at the other. It provides IT professionals with a cost-effective combination of 100G QSFP28 and 25G SFP28 interconnect solutions that enable host adapters, switches, and servers.

Figure 4: 100G AOC Breakout Cables

QSFP28 Cable: FAQs

Q: What is the operating temperature range and the standard of QSFP28 cable?

A: Generally, the operating temperature range of 100G cable is 0°C to 70°C. The standards of the QSFP28 cable are shown below.

QSFP28 Cable Standard
100G DAC IEEE 802.3, SFF-8665, QSFP28 MSA and InfiniBand HDR
100G DAC Breakout IEEE 802.3, SFF-8665, SFF-8636, QSFP28 MSA and InfiniBand EDR
100G AOC QSFP MSA compliant
100G AOC Breakout QSFP28 and SFP28 MSA compliant

Q: What is the maximum transmission distance of QSFP28 cable?

A: 100G DAC cable can achieve over 5m, and 100G AOC cable can provide links up to 100m MMF.

Q: Can 100G QSFP28 cables be used for 40G?

A: Yes, QSFP28 cables can be used for 40G, but not vice versa. There is the rule about mixing optical transceivers at different speed: both ends of the two modules have to match and the form factor needs to match as well. Additionally, port speed needs to be equal or greater than the optic used.

Q: What does breakout mode of QSFP28 cable mean?

A: Breakout mode refers to running a 100G port as 4 separate channels of 25G or 2 separate channels of 50G. When breaking out a single 100G port to 4x 25G or 2x 50G links, Forward Error Correction (FEC) mode on both ends of the link must be the same to ensure link-up.

Q: Can customers use third party QSFP28 Cable?

A: Yes, third-party 100G passive copper cables can be used but all the cables are required to comply with the associated IEEE specifications, as well as SFF-8636 management interface / EEPROM specifications to allow them to be correctly identified and recognized by the switch/router.


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