Use Direct Attach Cable(DAC) for Data Center Interconnection
Home Data Center Use High Speed Direct Attach Cable for Data Center Interconnection

Use High Speed Direct Attach Cable for Data Center Interconnection

Posted on by FS.COM

Cat5e copper cabling and 1000BASE-T have dominated data center interconnection application for several years, however, the upgrading to 10GE, 40GE and beyond poses a significant hindrance in both power consumption and cost. That’s when high speed direct attach cable (DAC) snucks in and becomes an integral part for inter rack cabling and Top of rack switching.

High Speed Direct Attach Cable—Definition, Structure and Specification

A direct attach cable, short for DAC cable, is a type of factory terminated twinax cable used to connect switches to routers or servers. These cables consist of fixed lengths of shielded copper coaxial or fiber optic cable with fixed pluggable transceivers on either end with varying gauges from 24 to 30AWG. DAC cable can achieve interconnection up to 15m via twinaxial copper cable, and reach 100m over active optical cable at 10Gbps, 40Gbps or beyond.

Types of High Speed Direct Attach Cables

High speed direct attach cable can be classified into direct attach copper cable(DACC) and direct active optical cable (DAOC). The following figure shows leading types of passive and active direct attach cables for data center ToR interconnection:

active optical cable vs passive optical cable

The direct attach copper cable is a fixed copper assembly that connects directly into “transceivers” and can be brought in several lengths for short distances of up to 15 meters. DACC can be either passive or active. direct active optical cable bonds the fiber connection inside the transceiver ends, creating a complete fiber cable assembly much like a direct attach copper cable, but with a 3-200 meter reach capability.

Passive DAC Cable vs. Active DAC Cable

Passive DAC cable contains no electrical components, so it has minimal power consumption of <0.15w, but the linking distance is limited to 5m. While active copper cable (ACCs) contains electrical components in the connectors that can boost signal levels, allowing reaching greater distances (5m or more) via copper media and ensure better transmission quality. This makes active copper cables slightly more expensive and consumes more power than direct attach passive copper cables. The details can be seen in the following table.

Reach Cable Type Power Consumption Weight Bend Radius Application Price

Passive DAC Cable

<5m Twinax copper cable <0.15w Heaviest 24 AWG=38 mm
26 AWG=33 mm
28 AWG=25 mm
30 AWG=23 mm
ToR, Adjacent racks Lowest

Active DAC Cable

5-15m Twinax copper cable 0.5-1w Heaviest 24 AWG=38 mm
26 AWG=33 mm
28 AWG=25 mm
30 AWG=23 mm
ToR, Adjacent racks Low

DAC Cable vs. AOC Cable

The following list highlights some of the advantages and disadvantages of DAC cable.

Advantages of DAC Cable:

Higher data transmission rate: The DAC cable can support data transmission rates from 4Gbps to 10Gbps, which is higher than traditional copper cable.
Strong interchangeability: With the development of copper technology, DAC cable and optical transceiver are interchangeable and hot swappable.
Low cost: Copper cable is cheaper than fiber, and using DAC cable will reduce wiring cos.
Good heat dissipation: The DAC cable is made of copper core and has good heat dissipation effect.

Disadvantages of DAC Cable:

Short transmission distance, heavy weight, large volume, difficult to manage.
Susceptible to electromagnetic interference, such as adverse response and degradation etc.

The following list highlights some of the advantages and disadvantages of AOC cable.

Advantages of AOC Cable:

Larger bandwidth: Device upgrades are not required, with throughput up to 40Gbps.
Lightweight: Much lighter than DAC cable.
Low electromagnetic interference: because optical fiber is a dielectric, it is not easy to be affected by electromagnetic interference.

Disadvantages of AOC Cable:

More expensive than DAC cable.

High Speed Direct Attach Cable vs. Optical Transceiver Module

When considering whether to use high speed direct attach cable or optical transceiver for a particular cabling infrastructure, one must know the key differences between them.

Reach Cable Type Power Consumption Weight Bend Radius Application Price

High Speed Direct Attach Cable

Around 1m-100m Twinax copper cable or fiber optic cable 0.15w-1w DAC:Heaviest
AOC: Lightest
24 AWG-30 AWG ToR, Adjacent racks, Middle of Row, End of Row, Zone to Zone Low

Optical Transceiver Module

Per TIA/IEEE standard (Up to 160km) Twinax copper cable or fiber optic cable Up to 4.5w Depend on transceivers & cabling used Depend on cabling used ToR, Middle of Row, End of Row, Zone to Zone High

According to the table, it’s obvious that high speed direct attach cable costs less, consume less power. But it usually has a limited distance compared to transceiver attached with cabling. Thus for any short range connection measuring from 5m to 100m, a better performing DAC cables offer easier and more affordable solution. But when the distance range is beyond 100m, optical transceivers are preferred.

High Speed Direct Attach Cable for Different Use

The following table displays the list of popularly used 10G/25G/40G/56G/100G DAC and AOC cables along with respective prices.

DAC Type Description Price
10G SFP+ to SFP+ DAC 1m Cisco SFP-H10GB-CU50CM 10G SFP+ Passive DAC Twinax Cable $11.00
40G QSFP+ to QSFP+ DAC 1m Cisco QSFP-H40G-CU50CM 40G QSFP+ Passive DAC Cable $30.00
40G QSFP+ to SFP+ DAC 1m Cisco QSFP-4SFP10G-CU1M 40G QSFP+ to 4x10G SFP+ Passive DAC Breakout Cable $40.00
56G QSFP+ to QSFP+ DAC 1m Mellanox MC2207130-001 56G QSFP+ Passive DAC Cable $52.00
25G SFP28 to SFP28 DAC 1m Cisco SFP-H25G-CU1M 25G SFP28 Passive DAC Twinax Cable $52.00
100G QSFP28 to QSFP28 DAC 1m Cisco QSFP-100G-CU1M 100G QSFP28 Passive DAC Cable $67.00
100G QSFP28 to SFP28 DAC 1m Cisco QSFP-4SFP25G-CU1M 100G QSFP28 to 4x25G SFP28 Passive DAC Breakout Cable $88.00
10G SFP+ to SFP+ AOC 1m Cisco SFP-10G-AOC1M 10G SFP+ Active Optical Cable $42.00
40G QSFP+ to QSFP+ AOC 1m Cisco QSFP-H40G-AOC1M 40G QSFP+ Active Optical Cable $120.00
40G QSFP+ to SFP+ AOC 1m Cisco QSFP-4X10G-AOC1M 40G QSFP+ to 4x10G SFP+ Breakout Active Optical Cable $190.00
100G QSFP28 to QSFP28 AOC 1m Cisco QSFP-100G-AOC1M 100G QSFP28 Active Optical Cable $480.00
25G SFP28 to SFP28 AOC 1m Cisco SFP28-25G-AOC1M 25G SFP28 Active Optical Cable $220.00

SFP Cable—10G SFP+ DAC vs. 25G SFP28 DAC

The 10G SFP+ cable offers the highest density, lowest cost, and lowest power 10 Gigabit Ethernet solution commercially available today. Furthermore, SFP+ enables mass migration of the 1GbE network to10GbE by offering a very low cost SFP+ 10GBASE-Cu (direct attached copper cable assembly) option for short reach interconnects. For more information about 10G SFP+ direct attach cable, you can read SFP+ DAC Twinax Cable Deployment Considerations

25G SFP28 DAC utilizes the same familiar form factor as 10G SFP+ cable, but the electrical interface has been upgraded internally to support 25-Gigabit data rates for 25G Ethernet applications and future standards such as 32G Fibre Channel. 25G SFP28 DAC cable offers a faster migration to 100G. Compared to 40G using four 10G lanes and 100G using ten 10G lanes, now with 25G SFP28 DAC cables, only four 25G lanes are needed to upgrade to 100GbE.

QSFP+ Cable—40G QSFP+ vs. 56G QSFP+

40G QSFP+ direct attach twinax copper cables come in QSFP+ to QSFP+ direct attach cooper cables and QSFP+ to 4 SFP+ breakout cables. 40G QSFP+ to QSFP+ direct attach copper cables are suitable for very short distances (within 10m) and offer an efficient 40G link between QSFP+ ports of QSFP+ switches within racks and across adjacent racks. While QSFP+ to 4x10G SFP+ breakout cables split a 40 Gigabit port on a switch or a server into four 10 Gigabit ports, which is ideal for 10G to 40G short-reach migration.

56G QSFP+ cables supports up to 4x14G per lane, are marked as the efficient and lower power alternative to short length interconnects between 40G InfiniBand 4x FDR, and 56G Ethernet network. 56G QSFP+ DAC cables have the same construction as 40G DAC cables, therefore the operation of 56G QSFP+ DAC and 40G QSFP+ DAC in 40G network deployment is the same.

100G QSFP28 Cable

QSFP28 to QSFP28 direct attach cable and 100G QSFP28 to 4×SFP28 breakout DAC cable are the popularly used cable types for 100G interconnection cabling. QSFP28 to QSFP28 direct attach cooper cable contains four high-speed copper pairs, each operating at data rates of up to 25Gb/s for a total of 100G. While QSFP28 to 4 SFP28 Breakout DAC cables can support 100G to 4x 25G Ethernet interoperability. It is commonly used in 100G to 25G migration.

100G QSFP28 DAC cable

Where to Find A Reliable High Speed Direct Attach Cables Supplier?

With so many options and vendors on the market, which one should I choose and trust? FS.COM offers the most fully-featured DAC and AOC cables in various form factors and different data rates including 10G, 25G, 40G, 100G and also 56G. We can customize direct attach cable assemblies of various lengths, compatibility with all major brands, different wire AWG ranges and so on, to meet any requirement of customers.

Direct Attach Cable factory

In addition, we are able to make the form factors on either end with different brands. For example, if you are in want of interconnecting Cisco to Juniper switch, then we are capable of making the form factor to Cisco on one end and the other to Juniper (as shown in the above picture). Most importantly, each of our DAC cable is strictly tested to ensure 100% compatibility with all major vendors and systems, and guarantee its smooth function on network devices.

Conclusion

According to aforementioned details, we know that high speed direct attach cable is an ideal short-reach solution for high density, high speed I/O data center applications in the networking. It can be either DAC or AOC cable type and in different data rates such as 10G/25G/40G/56G/100G.

Related articles:

SFP+ DAC Twinax Cable Deployment Considerations
How to Install/Remove QSFP+ Transceivers and DAC/AOC Cables

Copyright © 2002-2018. All Rights Reserved.