IEEE Std 802.3bq “Standard for Ethernet Amendment 3: Physical Layer and Management Parameters for 25 Gb/s and 40 Gb/s Operation, Types 25GBASE-T and 40GBASE-T” was developed by the IEEE P802.3bq 25G/40GBASE-T Task Force and approved by the IEEE-SA Standards Board on June 30, 2016. Industry profiles of server uplink speeds required in the data center led to the prediction that 40 Gb/s and even higher Ethernet speeds would be required to support these connections. In addition, trends for cloud servers and forecasts on server port speeds demonstrated that 25 Gb/s would be a critical point on the speed migration road map to 40 Gb/s. The unique features and benefits of Ethernet operation over balanced twisted-pair cabling, including backward compatibility, auto-negotiation, and small connector form factor, drove the need for faster BASE-T applications targeted for deployment in the data center. This amendment defines two new Physical Layer (PHY) specifications for 25GBASE-T and 40GBASE-T and supports Energy Efficient Ethernet (EEE) operation for both PHYs.

The link segment for 25G/40GBASE-T consists of up to 30m of ISO/IEC class I or II or TIA category 8 balanced twisted-pair cabling, including two connectors.

Features for 25G/40GBASE-T operation include:

  • MultiGBASE-T is used to describe the set of PHYs operating at speeds in excess of 1000 Mb/s (e.g. 10GBASE-T, 25GBASE-T and 40GBASE-T)
  • MultiGBASE-T transmits in full duplex over four pairs of balanced twisted-pair cabling
  • 25GBASE-T employs baseband 16-level PAM signaling with a modulation rate of 2000 Megasymbols per second over each of the pairs
  • 40GBASE-T employs baseband 16-level PAM signaling with a modulation rate of 3200 Megasymbols per second (4x faster than 10GBASE-T) over each of the pairs

Goals and Objectives for 25G/40GBASE‑T operation:

  • Support full duplex operation only
  • Preserve the 802.3 / Ethernet frame format utilizing the 802.3 MAC
  • Preserve minimum and maximum Frame Size of current 802.3 standard
  • Support a BER better than or equal to 10-12 at the MAC/PLS service interface
  • Support Auto-Negotiation (Clause 28)
  • Support Energy Efficient Ethernet (Clause 78)
  • Support local area networks using point-to-point links over structured cabling topologies, including directly connected link segments
  • Do not preclude meeting FCC and CISPR EMC requirements
  • Support a data rate of 40 Gb/s at the MAC/PLS Service Interface
  • Support a data rate of 25 Gb/s at the MAC/PLS Service Interface
  • Define a link segment based upon copper media specified by ISO/IEC  JTC1/SC25/WG3 and TIA TR‑42.7 meeting the following characteristics:
    • 4-pair, balanced twisted-pair copper cabling
    • Up to 2 connectors
    • Up to at least 30 m
  • Define a single 40 Gb/s PHY supporting operation on the link segment
  • Define a single 25 Gb/s PHY supporting operation on the link segment

The IEEE 802.3 Next Generation BASE-T Call-For-Interest Consensus Presentation can be found here: http://www.ieee802.org/3/cfi/0712_1/0712_next_gen_BASE-T_CFI_2.0.pdf

The Project Authorization Request (PAR), approved on September 25, 2012, with changes from January 13, 2013, March 20, 2013, May 10, 2013, and September 3, 2015 can be found here: http://www.ieee802.org/3/bq/P802.3bq.pdf

IEEE P802.3bq Resources

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