Advantages of Enhanced Tx/T2 Proposal for 1000BASE-T
                       Sailesh K. Rao
                 Level One Communications, Inc.

1. 125MHz ADC and 125MHz clocking throughout.
  -> 5.5bit effective ADC for 3dB margin.
  -> Simplest ADC among all proposals.
  -> No latency losses at clock domain boundaries.

2. Uses 1Volt per level effective separation at transmitter with 2V ptp
launch level.
  -> Best noise margin under Crane Test == 100BASE-Tx.
  -> 33-level PR requires 32.0V ptp.
     = 32.0Volts (for 1Volt separation between levels)
      X 0.707    (3dB gain from 1+D decorrelator)
      X 1.4      (loss due to increased symbol rate from 125 to 167MHz)
      X 1.0      (no gain from FEC due to hard decision decoding)
  -> 17-level PR requires 16.0V ptp.
     = 16.0Volts (for 1Volt separation between levels)
     X 0.707     (3dB gain from 1+D decorrelator)
     X 1.4       (loss due to increased symbol rate from 125 to 167MHz)
  -> 9-level PR requires 8.0V ptp.
     = 8.0Volts  (for 1Volt separation between levels)
     X 0.707     (3dB gain from 1+D decorrelator)
     X 1.4       (loss due to increased symbol rate from 125 to 167MHz)
     X 1.0       (no gain from FEC due to hard decision decoding)
  -> CAP-12 requires 6.0V ptp.
     = 2.0Volts  (original CAP-9 ptp voltage)
     X 3/2       (to go from 3-levels to 4-levels per dimension)
     X 4.0       (to go from CAP-9 noise immunity to 100BASE-Tx noise
immunity)
     X 0.5       (assumed 6dB gain due to 24-D block coding)
  -> QAM-25 requires 5.1V ptp.
     = 1.8Volts  (QAM-25 ptp voltage)
     X 4.0       (to go from QAM-25 noise immunity to 100BASE-Tx noise
immunity)
     X 0.707     (3dB gain from 4-D block coding)
  -> QAM-36 requires 4.5V ptp.
     = 1.8Volts  (QAM-25 ptp voltage)
     X 5/4       (to go from 5-levels to 6-levels per dimension)
     X 4.0       (to go from QAM-25 noise immunity to 100BASE-Tx noise
immunity)
     X 0.5       (6dB gain from 8-D block coding)
  -> Dual CAP-64 requires 24.0V ptp.
     = 2.0Volts  (CAP-9 ptp voltage)
     X 7/2       (to go from 3-levels to 8-levels per dimension)
     X 4.0       (to go from CAP-9 noise immunity to 100BASE-Tx noise
immunity)

3. Packet Delimiters are much better protected codes than normal data.
  -> Impossible to achieve this by just adding one more level in a
16-level code!

4. Falls back to 100BASE-Tx by design.
  -> No overhead for 100/1000 designs.

5. Complies with the requirement of Ethernet to handle packets of any
length.
  -> CAP-12 with 24-D coding requires packet length to be a multiple of
36 bits?
  -> RS-Coded PR requires packet length to be a multiple of 120 bits?