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:

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:

IEEE P802.3bq Resources

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