What is the Crosstalk?
"Crosstalk" means unwanted signals produced by coupling between different pairs of wires in a cable. It is simply the electromagnetic interference between two wires and can cause a signal on one pair of twisted wires to affect another. Crosstalk exists between different wire pairs in the same cable harness, and a pair of twisted wires will be interfered by multiple pairs. It has a great influence on signal transmission, which may lead to the loss of communication confidentiality, even the interruption of communication. Therefore, "crosstalk" is an important index to judge the quality of communication cable.
Crosstalk can be divided into Far End Crosstalk and Near End Crosstalk.
Far End Crosstalk (FEXT)
FEXT means that in a same cable harness, the transmitter which working at the far end of other pair of twisted wires interferes to the receiver at the other end of the twisted pair in the same direction. This kind of crosstalk will be smoothly attenuated through loop transmission, so it causes less influence, especially the long-distance cable. As the picture following:
Near End Crosstalk (NEXT)
NEXT occurs at the same end. It means that in a same cable harness, the transmitter which working in other twisted pairs interferes to the receiver located at the same end in the opposite direction of the twisted pair. This kind of crosstalk is not smoothly attenuated through the loop transmission, so it affects greater than FEXT. As the picture following:
terminal A --- transmitter, terminal B --- receiver, The signal strength received by terminal C is Near End Crosstalk, and the signal strength received by terminal D is the Far End Crosstalk.
What is the PROFINET？
PROFINET is a communication standard for automation developed by Siemens and PROFINET & PROFIBUS. Based on IEEE Ethernet protocol, it has the flexible structure of linear, ring and star topology.
PROFINET has the characteristics of great real-time performance, high security and reliability, it also achieves high compatibility and low cost, which is widely used in industrial automation.
According to Ethernet protocol, PROFINET cable generally adopts the star twisted structure. In different application environments, it can be divided into type A (fixed installation), type B (occasional movement), type C (drag chain application) and type R (robot application).
How to Improve Cable Crosstalk
As the band width and transmission frequency of data cable communication continue to expanding, people’s demands for the quality of data transmission become increasingly high. It is all known that crosstalk is one of the important indexes to affect the quality of communication cable. So how to improve cable crosstalk?
1. Choose reasonable pair twisted pitch. In theory, the smaller pitch of twisted pair is, the smaller problem of crosstalk is. However, when the pitch becomes smaller, the attenuation of cable also gets worse, and the longer the transmission delay will lower the production efficiency. Therefore, it is necessary to consider various indicators to choose the most reasonable pitch design.
2. Take a rational use of pair distance effect. Theoretically, when the relative distance is fixed, the further distance between pairs is, the smaller problem of crosstalk is. For example, add the cross skeleton in the middle of CAT6.
3. Increase shielded pairs. Each pair of core wire can add a shielding outside such as aluminum foil shield to improve the crosstalk between pairs. This is also a common structural design in CAT7.
4. Control the manufacturing process. For example, the concentricity of insulation, the consistency of outer diameter (OD), twisted pitch and cabling pitch. A smaller fluctuation of each link can make better crosstalk performance of a cable.
In a word, the crosstalk problem of communication data cable is closely related to the design, production, processing, usage and other aspects. Through 28 years of R & D and manufacturing, Zhaolong continuously improves the cable technology and product performance.
What is a DAC high-speed cable?
DAC high-speed cable (Direct Attach Cable) is generally translated as direct cable or direct-attached copper cable. It is usually a fixed-length cable assembly with fixed connectors at both ends, with ports not being able to be replaced and module heads and copper cables not being able to be separated. High-speed cables are accepted and used by more and more users due to their significant advantages such as high price-quality ratio, high performance, high speed, high composite, and low loss. They have become the first choice for high-speed data communication solutions. And they are widely used in storage area’s networks, data center and the connection between high-performance computers.
What are the advantages and characteristics of DAC high-speed cables?
It has become a preferred solution for users in short-distance application scenarios. It is widely used in data center’s interconnection scenarios such as SATA storage devices, RADI system scenarios, core routers, 10G or 40G Ethernet, etc.. In data centers, copper cables are generally used to connect servers and storage area’s networks. The most commonly used is Direct Attach Copper Cable (DAC), and among which passive copper cables are most particularly used. Since passive copper cables are of low price and of fast transmission speed, they have become the best solution for short-distance transmission. For example, 40G QSFP+ passive cable is one of passive copper cables. Because of its low power consumption, high efficiency, low cost and low latency, it is widely used in 40G LAN, HPC and SAN. And 40G QSFP+ passive cable is also suitable for flexible wiring; we can say that 1 SFP+ high-speed cable is equal to 2 SFP+ 10 Gigabit optical modules and 1 pair of OM3 10 Gigabit fiber jumpers.
What is the basic structure of DAC high-speed cable?
Our DAC high-speed cable mainly takes silver-plated conductors and foamed insulated core wires as materials while some manufacturers use special PTFE films instead of insulating materials, foamed PE. Because this cable has high requirements for materials and processes, there are currently very few manufacturers that can produce them. The method of shielding and total shielding make our high-speed cables have excellent attenuation performance, low delay and anti-interference, and have the capability of realizing high-frequency broadband transmission. Our high speed cables range from 30AWG to 24AWG, with various structures such as 2P, 4P or 8P. And it can be used in many different applications.
What is 400ZR?
400ZR, also known as 400G ZR, is a specification defined by the Optical Internetworking Forum (OIF). The specification uses a combination of the plans of Dense Wavelength Division Multiplexing (DWDM) and high-order modulation. Due to 400ZR, 400G can be transmitted on the interconnect (DCI) link of the data center. Its purpose is to ensure long-term and stable implementation based on single carrier 400G. This single carrier uses complex polarization multiplexing’s 16-level quadrature amplitude modulation (DP-16QAM) with a rate of approximately 60 Gbaud.
What is SFP optical module?
SFP optical module is an interface device that converts gigabit electrical signals into optical signals. Our SFP optical module is an industry-standard small and pluggable gigabit optical transceiver module which can be plugged into the SFP ports of network equipment such as switches, routers, and media converters. It can be used to connect optical or copper network cables for data transmission. Usually we can find it in Ethernet switches, routers, firewalls and network interface cards.
Differences between QSFP-DD and QSFP+/QSFP28/QSFP56
In terms of structure, QSFP-DD and QSFP+/QSFP28/QSFP56 have some differences in depth of mechanical interface of motherboard, number of channels of electrical interface, and number of integrated circuits.
Depth of Mechanical Interface of Motherboard - When MSA team members are designing QSFP-DD, the mechanical interface on the motherboard is slightly deeper than the ones of QSFP+ /QSFP28/QSFP56 in order to make QSFP-DD and QSFP+/QSFP28/QSFP56 have the same port density and have the capability of accommodating an extra row of contacts.
The Number of Channels of the Electrical Interface -- as can be seen from the above, the QSFP-DD’s package is equipped with an 8-channel electrical interface. Compared with the QSFP+/QSFP28/QSFP56 package with a 4-channel electrical interface, the number of channels of the electrical interface is doubled, which is also due to the reason that QSFP - DD package has an extra row of contacts.
Number of Integrated Circuits—Although QSFP-DD has the same size as QSFP+/QSFP28/QSFP56, compared with QSFP+/QSFP28/QSFP56 with 4-channel electrical interface, the number of integrated circuits(i.e. ASIC) and density are doubled since QSFP-DD has 8-channel electrical interfaces.
Bandwidth & Application
It can be seen from the above that the maximum bandwidth of QSFP-DD can reach 400Gbps, while the maximum bandwidth of QSFP+/QSFP28/QSFP56 can only reach 40Gbps/100Gbps/200Gbps respectively. The maximum bandwidth of QSFP-DD is much higher than the ones of QSFP+/QSFP28/QSFP56. Because of this, QSFP-DD is generally used as a package for 400G optical modules and 400G high-speed cables (i.e. DAC and AOC), is applied for the interconnection of 400G data center and to solve the problem of high-speed migration of massive data between data centers; and QSFP+/QSFP28/QSFP56 are respectively used for the packaging of 40G/100G/200G optical module and high-speed cable and for 40G/100G/200G network interconnection.
Advantages of SFP Port
With strong flexibility, the SFP port is a hot-swappable I/O interface (refers to input/output interface). It is suitable for a variety of products, for example, it can be switched with 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX or 1000BASE-BX10-D/U ports. Besides, the SFP port is backward compatible, supporting 10/100/1000Mbps.