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FEATURE COPPPER CABLING


increase. Instead of defining very high modulation density over a narrower frequency band, an alternative approach is to send signals over a very wide frequency band. As the information of the signal


is now spread over a much wider frequency spectrum, modulation density can be contained to a manageable level. One study has recommended using 1.6GHz bandwidth to make standard CAT6A cables capable of transmitting at 40 Gbps. Another option is to define the operation for a shorter length of cable. Attenuation in twisted pair cables rapidly increases with frequency, and by using shorter lengths, much higher frequencies can be transmitted with detectable signal levels.


Standardisation activities


Standardisation bodies are actively looking into various aspects of higher than 10G transmission on structured copper cables. TIA has started a new project to define next generation cabling systems. As part of the project, four task groups have been formed to study different aspects. The first is the ‘Capacity task group’. Its objective is to determine technical parameters like the overall noise model (NEXT, FEXT, reflection, external noise) and capability of PHY devices to cancel noise, power consumption, and bandwidth requirements. The second is the ‘Application space task group’, which attempts to determine what applications will be served, and what constraints they will face. The other two task groups, ‘Cable


task group’ and ‘Connector task group’ will translate the capacity and application requirements into cable and connector requirements. Similar work has also started in ISO. IEEE will have the ultimate responsibility of defining 40GBASE-T specifications, and the progress there is driven by equipment manufacturers and cabling companies.


Field testing


While cabling and semiconductor technologies can ensure feasibility of supporting 40Gbps Ethernet over twisted pair copper cables, wide spread


20 NETCOMMS europe Volume II, Issue 1 2011


market adoption calls for additional considerations. One key element is the availability of field test instruments to characterise and certify installed cabling for suitability for 40GbE. Unlike laboratory grade vector network analysers, field testers are constrained by several limitations. They need to be small, handheld, light weight, low cost devices. They also need to be battery operated with long battery life, so that the installation technicians can avoid the hassle of recharging the testers in the middle of their work day. This essentially means that the power consumption of the measurement hardware must be minimised. It is because of these factors that until recently field testers could only support 1GHz or smaller bandwidth. With the advent of recent


innovations in semiconductor devices, driven by proliferation of consumer grade mobile RF gadgets, a tester that provides accurate measurements over a wide frequency range from 1 MHz to 1600 MHz (1.6 GHz) is commercially available. It represents not only a significant increase in achievable test frequency range, but also better performance than currently available test instruments. The characterisation of parameters for field testers is defined in IEC 61935-1 and TIA 1152 standards. While discussing standards that


determine field tester performance, it should be noted that the highest level of accuracy spec defined till date, so called level IV spec, only covers 600MHz bandwidth. It will become important for standards committees to come up with field tester accuracy specifications covering a broader frequency range in coming months and years.


Conclusion


Despite the growth in wireless and fibre infrastructures, copper cabling will still be the dominant media for enterprise networks in the foreseeable future. When designing infrastructures for use over the next 15 to 20 years, one must consider the fact that there is a high likelihood that 40GBASE-T systems will be defined, and become commonplace in 5 to 10 years.


There are technical challenges in


supporting such high data rates, such as the complexity of physical layer devices. Studies and test data suggest that cabling available today should work for 40GBASE-T. This would be made possible by extending the bandwidth usage over a cable link. In order to create a complete eco system for adoption of technologies like 40GBASE-T, the industry will need cabling systems, networking devices, standardisation, and also field test instruments suitable for that technology. Field testing over a wider bandwidth


has been constrained in the past due to several factors, but now at least one commercially available field tester features capability of certifying cabling to bandwidths as high as 1600 MHz, which is expected to meet field testing needs for future 40GBASE-T systems.


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