Copper Twisted-Pair versus Optical Fibre at 10Gb/s


This write up entry is taken from this wonderful article from Corning titled “The Real Facts About Copper Twisted-Pair at 10 Gb/s and Beyond” (pdf)

    1. The IEEE 802.3an 10GBASE-T Standard was  approved in July 2006. This standard provides guidance for data transmission of 10 Gb/s in which multi-gigabit rates are sent over 4-pair copper cable within a 500 MHz bandwidth.
    2. CAT 6A is intended to support 10G Operation up to 100m.
    3. For 10GB require 500 Mhz frequency range requires power consumption (10-15KW) of the 10G interfaces due to increased insertion loss, as well as needing to overcome internal and external cross talk issues.
    4. 10G optical PHY latency has 1000 times better latency performance than 10G copper. 10G optical has typical PHY latency measurable in the nanosecond range, whereas 10G copper has PHY latency in microseconds.
      • What is Latency?  Extensive data encoding and signal processing is required to achieve an aceptable bit error rate (BER). Electronic digital signal processing (DSP) technique are required to corrct internal noise impairments, which contributes significantly to an inherent time delay while recovering the transmitted data packets.
    5. According to Sun Microsystems IEEE 302.3an Task Force, states that “PHY latency should not exceed one microsecond … it may start affecting Ethernet over TCP/IP application performance in the foreseeable future.”
    6. CAT 6A cable has a larger diameter, designed to alleviate internal and external cross talk noise issues. The 0.35 in maximum cable diameter is 40 percent larger than CAT 6 (0.25 in).This contributes to significant pathway and space problems when routing in wire baskets, trays, conduits, patch panels and racks. A typical plenum CAT 6A UTP cable weighs 46 lbs per 1000 ft of cable.
    7. 10G optical electronics provide clear advantages over copper twisted-pair.
      • 10G X2 transceivers support up to 16 ports per line card. Maximum power dissipation is 4 W per port.
      • 10G XFP optical transceivers support up to 24-36 ports per line card. Maximum power dissipation is 2.5 W per port.
      • Emerging 10G SFP+ optical transceivers will support up to 48 ports per line card. Maximum power dissipation will be 1 watt per port. The SFP+ transceiver will offer significantly lower cost compared to the X2 and XFP transceivers.
    8. High Port Density for Fibre provides a higher 10G port density per electornic line card and patch panel as compared to copper. One 48-port line card equals 6 9-port copper line cards
    9. Fibre provide less congestion in pathways and spaces. The high-fiber density, combined with the small diameter of optical cable, maximizes the raised floor pathway and space utilization for routing and cooling

         

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