WhatisSFPDirectAttachCopperCable

  SFP  DAC 电缆成为云计算与云存储中的主流主要连接工具，但是关于什么是 SFP DAC cable ，不同的 SFP  DAC cable 的生产厂商对此也有不同的介绍和描述，今天，我们整理了一些相关的资料，主要说说什么是 SFP  DAC cable 及其它的背景，同时也会谈到有源和无源的 SFP  DAC cable 之间的优缺点和 SFP  DAC cable 与10GBASE-T的比较。
SFP  Direct Attach Copper Cable background （ SFP  DAC cable 的背景）

The SFP  interface offers the highest density, lowest cost, and lowest power 10 Gigabit Ethernetsolution commercially available today. Further SFP  enables mass migration of the 1GbE network to10 GbE by offering a very low cost 10GSFP Cu (direct attached copper cable assembly) option for short reach interconnects along with multimode and single mode fiber options. The SFP  interface accepts along with hot-pluggable, small-footprint, optical transceivers, a Direct Attach Cable “10GSFP Cu”, which replaces two optical modules and a connectorized optical fiber with a twinaxial copper cable assembly. The 10GSFP Cu option is defined for 10GbE applications over passive copper with a reach of 8.5m. The 10GSFP Cu link utilizes a receive equalizer in the host PHY/SerDes in order to compensate for the Inter Symbol Interference (ISI) introduced by the cable. Electrical and mechanical specifications for SFP  optical modules, 10GSFP Cu, and hosts are defined in the SFF-8431 specification developed by the SFF Committee, with broad industry participation.
What is SFP  Direct Attach Copper Cable?（SFP  DAC Cable 的介绍）
10GSFP Cu (SFP  Direct Attach) is a copper interconnect using a passive twin-ax cable assembly that connects directly into an SFP  housing. It has a range of 10 meters and like 10GBASE-CX4, is low power, low cost and low latency with the added advantage of having the small form factor of SFP , and smaller, more flexible cabling.
SFP  Direct Attach is known as the successor technology to 10GBASE-CX4. SFP  Direct Attach, as implied in the name, uses SFP  MSA and by using the inexpensive copper twinaxial cable with SFP  connectors on both sides, provides 10 Gigabit Ethernet connectivity between devices with SFP  interfaces. SFP  Direct Attach has a 10 meter distance limitation, thus the target application is interconnection of top-of-rack switches with application servers and storage devices in a rack.
Pasive and  Active SFP  DAC Cables ？（有源和无源的SFP  DAC Cables）
Passive cables are much less expensive but require the host to do the work of driving it properly.
– Benefits:
• Lower Costs
• Higher Reliability
– Fewer Components (No Active Tx /Rx Components)
– Only Capacitors, Resistors, EEPROM, Cable
– Tradeoffs:
• No LOS
• No TX Disable
• No Interrupts
• Limited Management Interface
• Host must drive Cu cable
Active cables offer the added benefit of being "optical-module" like.
Benefits:
• Enhanced Signal Integrity
• Longer Cable Lengths
• Transmit Pre-emphasis
• Active/Adaptive Receive Equalization
• Tx Disable
• Loss of Signal (LOS)
• Interrupts
• Management Interface
• Looks like an optical module
• Don’t have to worry about host Tx/Rx for Cu cables
– Tradeoffs:
• Higher Cost
How does SFP  Direct Attach Copper compare with 10GBASE-T?
10GBASE-T will work with Cat 6 and Cat 7 cables that are commonly used for 1Gb network connections and also support much longer distances than SFP  Direct Attach Copper. 10GBASE-T is currently not supported for OneConnect adapters due to power requirements and high latency of 10GBASE-T PHY chips. 10GBASE-T PHY technology continues to evolve and could be suitable for adapter products by the end of 2010.