100G QSFP28 To 4x25G SFP28 DAC Cable

Signal Integrity ：

(ITEM)		(REQUIREMENT)	(TEST CONDITION)
	Cable	105+5/-10Ω
	Impedance
(Differe	Paddle Card	100±10Ω	Rise time of 25ps
ntial	Impedance		(20 % - 80 %).
Impedan	Cable
ce)	Termination	100±15Ω
	Impedance
		Return_loss(f)≥ 16.5-2√f 0.05≤f﹤4.1 10.66-14log10(f/ 5.5) 4.1≤f≤19 Where f is the frequency in GHz Return loss(f) is the return loss at frequency f
[Differential (Input/Output)Return			10MHz≤f ≤19GHz
loss SDD11/SDD22]
[Differential to common-mode (Input/Output)Return loss SCD11/SCD22]		Return_loss(f)≥ 22-(20/25.78)f 0.01≤f﹤12.89 15-(6/25.78)f 12.89≤f≤19 Where f is the frequency in GHz Return_loss(f) is the Differential to common-mode return loss at frequency f	10MHz≤f ≤19GHz

 

[Common-mode to Common-mode (Input/Output)Return loss SCC11/SCC22]	Return_loss(f)≥2dB 0.2≤f≤19 Where f is the frequency in GHz Return_loss(f) is the common-mode to common-mode return loss at frequency f							10MHz≤f ≤19GHz
[Differential Insertion Loss (SDD21 Max.)]	(Differential InsertionLoss Max. For TPa to TPb Excluding Test fixture )							10MHz≤f ≤19GHz
	F AWG	1.25GHz	2.5GHz	5.0GHz	7.0GHz	10Ghz	12.89Ghz
	30(1m) Max.	4.5dB	5.4dB	6.3dB	7.5dB	8.5dB	10.5dB
	30/28( 3m)Ma x.	7.5dB	9.5dB	12.2dB	14.8dB	18.0dB	21.5dB
	26(3m) Max.	5.7dB	7.2dB	9.9 dB	11.9dB	14.1dB	16.5dB
	26/25( 5m)Ma x.	7.8dB	10.0dB	13.5dB	16.0dB	19.0dB	22.0dB
Differential to common-mode Conversion Loss-Differential Insertion Loss(SCD21-SDD21)	10 0.01≤f﹤12.89 Conversion _loss(f) – IL(f)≥ 27-(29/22)f 12.89 ≤ f ﹤ Where f is the frequency in GHz Conversion_loss(f ) is the cable assembly differential to common-mode conversion loss IL(f) is the cable assembly insertion loss							10MHz≤f ≤19GHz
[MDNEXT(multiple disturber near-end crosstalk)]	≥26dB @12.89GHz							10MHz≤f ≤19GHz

Other Electrical Performance：

 

(ITEM)	(REQUIREMENT)	(TEST CONDITON)
[Low Level Contact Resistance]	70milliohms Max. From initial.	EIA-364-23:Apply a maximum voltage of 20mV And a current of 100 mA.
Insulation Resistance	10Mohm(Min.)	EIA364-21:AC 300V 1minute
[Dielectric Withstanding Voltage]	NO disruptive discharge.	EIA-364-20:Apply a voltage of 300 VDC for 1minute between adjacent terminals And between adjacent terminals and ground.

 

Environment Performance

 

(ITEM)	(REQUIREMENT)	(TEST CONDITON)
[Operating Temp. Range]	-20°C to +75°C	Cable operating temperature range.
Storage Temp. Range (in packed condition)]	-40°C to +80°C	Cable storage temperature range in packed condition.
[Thermal Cycling Non-Powered]	No evidence of physical damage	EIA-364-32D, Method A, -25 to 90C, 100 cycles, 15 min. dwells
[Salt Spraying]	48 hours salt spraying after shell corrosive area less than 5％.	EIA-364-26
Mixed Flowing Gas	Pass electrical tests per 3.1 after stressing. (For connector only)	EIA-364-35 Class II,14 days.
Temp. Life	No evidence of physical damage	EIA-364-17C w/ RH, Damp heat 90℃ at 85% RH for 500 hours then return to ambient
Cable Cold Bend	4H,No evidence of physical damage	Condition: -20℃±2℃, mandrel diameter is 6 times the cable diameter.

 

Mechanical and Physical Characteristics

(ITEM)	(REQUIREMENT)	(TEST CONDITON)
Vibration	Pass electrical tests per 3.1 after stressing.	Clamp & vibrate per EIA-364-28E, TC-VII, test condition letter – D, 15 minutes in X, Y & Z axis.
Twist	No evidence of physical damage	Twist cable 180° (±90° from nominal position) for 100 cycles at 30 cycles per minute with a 0.5kg load applied to the cable jacket. Clamp position: 300mm
Cable Flex	No evidence of physical damage	Flex cable 180° for 20 cycles (±90° from nominal position) at 12 cycles per minute with a 1.0kg load applied to the cable jacket. Flex in the boot area 90º in each direction from vertical. Per EIA-364-41C
Cable Plug Retention in Cage	90N Min. No evidence of physical damage	Force to be applied axially with no damage to cage. Per SFF 8661 Rev 2.1 Pull on cable jacket approximately 1 ft behind cable plug. No functional damage to cable plug below 90N. Per SFF-8432 Rev 5.0
Cable Retention in Plug	90N Min. No evidence of physical damage	Cable plug is fixtured with the bulk cable hanging vertically. A 90N axial load is applied (gradually) to the cable jacket and held for 1 minute. Per EIA-364-38B
Mechanical Shock	Pass electrical tests Per 3.1 after stressing.	Clamp and shock per EIA-364-27B, TC-G,3 times in 6 directions, 100g, 6ms.
Cable Plug Insertion	40N Max.(QSFP28) 18N Max.(SFP28)	Per SFF8661 Rev 2.1 Per SFF-8432 Rev 5.0
Cable plug Extraction	30N Max. (QSFP28) 12.5N Max. (SFP28)	Place axial load on de-latch to de-latch plug.Per SFF8661 Rev 2.1 Measure without the aid of any cage kick-out springs. Place axial load on de-latch to de-latch plug. Per SFF-8432 Rev 5.0
Durability	50 cycles,No evidence of physical damage	EIA-364-09, perform plug &unplug cycles:Plug and receptacle mate rate: 250times/hour. 50times for QSFP28/SFP28 module (CONNECTOR TO PCB)

 

High-speed data transmission has become the backbone of modern data centers and enterprise networks. As bandwidth demands continue to surge, Direct Attach Copper (DAC) cables have emerged as a cost-effective, reliable solution for short-reach connectivity. Understanding the capabilities and applications of DAC cable technology is essential for network engineers and IT professionals seeking optimal performance.

What Makes DAC Cable Technology Essential for Modern Data Centers

Direct Attach Copper cables represent a sophisticated evolution in network connectivity. Unlike traditional copper cabling, DAC cable assemblies integrate transceivers directly into the cable assembly, eliminating the need for separate optical modules. This integration delivers significant advantages in power consumption, latency reduction, and overall system cost.

The architecture of a quality DAC cable encompasses precision-engineered components working in harmony. The differential impedance must maintain tight tolerances throughout the cable assembly, from the connector interface through the transmission line to the termination point. This consistency ensures signal integrity across the entire transmission path, preventing reflections and maintaining data fidelity.

Signal Integrity: The Foundation of Reliable DAC Cable Performance

When selecting a DAC cable for demanding applications, signal integrity stands as the paramount concern. High-speed data transmission at rates up to 25Gbps per lane requires exceptional electrical characteristics. The return loss performance across the frequency spectrum determines how effectively the cable minimizes signal reflections that could compromise data transmission.

Insertion loss represents another critical parameter in DAC cable selection. As signal frequencies increase, copper's inherent resistance causes attenuation. Premium DAC cable designs employ advanced conductor materials and optimized geometry to minimize these losses. The relationship between cable length, conductor gauge, and maximum operating frequency must be carefully balanced to achieve optimal performance.

Common-mode rejection capabilities distinguish superior DAC cable assemblies from mediocre alternatives. External electromagnetic interference can induce common-mode noise on differential pairs. A well-designed DAC cable converts minimal differential signal to common-mode, maintaining clean data transmission even in electrically noisy environments.

Environmental Resilience: DAC Cable Performance Under Stress

Data center environments present numerous challenges that DAC cable assemblies must withstand. Temperature fluctuations from cooling system variations require cables to maintain electrical performance across wide thermal ranges. Quality DAC cable construction ensures stable impedance and low insertion loss whether operating in arctic server room conditions or during thermal stress events.

Mechanical durability proves equally important in real-world deployments. During installation and maintenance activities, DAC cable assemblies experience bending, twisting, and tension forces. Robust mechanical design with appropriate strain relief prevents conductor damage and maintains connector integrity. The cable jacket material must provide flexibility for routing while offering protection against abrasion and chemical exposure.

Humidity resistance ensures long-term reliability in data center environments where condensation may occur during cooling system maintenance. Properly sealed connectors and moisture-resistant materials prevent corrosion that could degrade contact resistance and signal quality.

Application Scenarios: Where DAC Cable Excels

Top-of-rack switching represents the quintessential application for DAC cable technology. The short distances between servers and switches perfectly match the optimal reach of copper direct attach solutions. Compared to optical alternatives, DAC cable assemblies deliver equivalent bandwidth at a fraction of the cost while consuming less power.

Storage area networks benefit tremendously from DAC cable deployments. The low latency characteristic of copper transmission becomes crucial when microseconds matter in storage transactions. High-quality DAC cable assemblies ensure consistent performance during intensive storage workloads.

High-performance computing clusters leverage DAC cable technology for inter-node communication. The combination of low latency, high bandwidth, and cost efficiency makes DAC cable the preferred choice for building scalable computing fabrics. Proper cable management and selection ensures these demanding applications achieve maximum throughput.

Technical Considerations for DAC Cable Deployment

Compatibility verification stands as the first step in successful DAC cable implementation. Modern network equipment supports various form factors including QSFP28 and SFP28 interfaces. Each form factor presents unique electrical and mechanical requirements that the DAC cable must satisfy.

Cable length selection requires careful analysis of network topology and performance requirements. Shorter DAC cable assemblies naturally exhibit lower insertion loss and better signal integrity. However, practical routing considerations may necessitate longer lengths. Understanding the insertion loss budget for your specific application helps determine maximum acceptable cable length.

Electromagnetic compatibility becomes increasingly important as data rates climb. Quality DAC cable designs incorporate shielding strategies that prevent both emission of electromagnetic interference and susceptibility to external noise sources. This becomes particularly critical in dense server environments where numerous high-speed signals operate in close proximity.

Quality Standards and Testing Protocols

Rigorous testing separates reliable DAC cable products from those prone to field failures. Comprehensive electrical characterization across the operating frequency range validates that the cable meets stringent return loss and insertion loss specifications. Time-domain reflectometry helps identify impedance discontinuities that could compromise signal integrity.

Mechanical testing ensures the DAC cable withstands the rigors of installation and operational stress. Insertion and extraction force testing verifies smooth connector mating while retention testing confirms adequate pull-out strength. Durability testing through repeated mating cycles demonstrates long-term reliability.

Environmental stress testing subjects DAC cable assemblies to temperature cycling, humidity exposure, and corrosive atmospheres. These tests validate that the cable maintains performance specifications throughout its intended service life despite environmental challenges.

Future-Proofing Your Infrastructure with DAC Cable

As network speeds continue their relentless march toward higher bandwidth, DAC cable technology evolves to meet emerging requirements. The transition from 25Gbps to 50Gbps per lane and beyond demands even tighter electrical specifications and more sophisticated cable designs. Selecting DAC cable products from manufacturers committed to supporting future standards protects infrastructure investments.

Backward compatibility considerations help maximize deployment flexibility. Well-designed DAC cable assemblies often support multiple speed grades, allowing the same cable to function across various equipment generations. This flexibility simplifies inventory management and provides upgrade paths without complete cable infrastructure replacement.

Frequently Asked Questions About DAC Cable

What is the maximum recommended length for a DAC cable?

The optimal length depends on the specific data rate and cable design. For 25Gbps applications, quality DAC cables typically support lengths up to 5 meters. At 10Gbps, reliable operation extends to 7 meters or more. Always consult manufacturer specifications for your specific application requirements.

How does a DAC cable differ from standard Ethernet cables?

Unlike standard Ethernet cables, DAC cable assemblies integrate active or passive circuitry directly into the connector assembly. This integration optimizes impedance matching and signal conditioning for high-speed serial data transmission. Standard Ethernet cables lack these specialized components and cannot reliably support modern 25Gbps+ applications.

Can DAC cables be used in outdoor environments?

Standard DAC cable assemblies are designed for controlled data center environments. Outdoor deployment requires cables specifically rated for extended temperature ranges, UV exposure, and moisture ingress. Always verify environmental ratings match your deployment conditions.

What causes signal degradation in DAC cables?

Multiple factors contribute to signal degradation including conductor resistance, dielectric losses, impedance mismatches, and external interference. Higher frequencies suffer greater attenuation, which explains why longer cables support lower maximum data rates. Quality cable design minimizes all these degradation mechanisms.

How do I select between active and passive DAC cables?

Passive DAC cables contain no active components and rely purely on optimized copper transmission for signal integrity. They offer lower cost and power consumption but are limited to shorter lengths. Active DAC cables incorporate signal conditioning circuitry enabling longer reach at the expense of increased cost and power requirements.

What maintenance do DAC cables require?

DAC cable assemblies require minimal maintenance beyond periodic inspection for physical damage. Keep connectors clean and protected when not in use. Avoid exceeding minimum bend radius during installation and ensure adequate strain relief at connection points.

Are DAC cables compatible across different vendor equipment?

Most DAC cables follow industry-standard specifications enabling multi-vendor interoperability. However, some equipment vendors implement proprietary enhancements. Always verify compatibility with specific equipment models before large-scale deployment.

What role does impedance matching play in DAC cable performance?

Proper impedance matching throughout the signal path minimizes reflections that cause signal integrity problems. Any impedance discontinuity creates reflections that interfere with the transmitted signal. Quality DAC cables maintain consistent impedance from connector through cable to termination.

Conclusion: Making Informed DAC Cable Decisions

Selecting the appropriate DAC cable for your infrastructure requires understanding the interplay between electrical performance, mechanical reliability, and application requirements. By focusing on proven designs from reputable manufacturers, implementing proper installation practices, and matching cable specifications to actual needs, you can build a reliable, high-performance network infrastructure that supports current demands while providing headroom for future growth.

 

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