| Full titles | IEEE 802.3an-2006, Amendment 1: Physical Layer and Management Parameters for 10 Gb/s Operation, Type 10GBASE-T. IEEE 802.3bz-2016, Amendment 7: Media Access Control Parameters, Physical Layers, and Management Parameters for 2.5 Gb/s and 5 Gb/s Operation, Types 2.5GBASE-T and 5GBASE-T |
| Publisher | IEEE Standards Association, IEEE 802.3 Ethernet Working Group |
| Approved | 802.3an: 8 June 2006 (amendment to IEEE 802.3-2005). 802.3bz: September 2016 (amendment to IEEE 802.3-2015) |
| Current home | Both are now incorporated in IEEE 802.3-2022, IEEE Standard for Ethernet. 10GBASE-T is Clause 55. 2.5GBASE-T and 5GBASE-T are Clause 126 |
| Status | IEEE 802.3-2022 is the active edition, with later amendments and corrigenda. The amendments are superseded by IEEE 802.3-2022 |
| Related documents | ISO/IEC 11801-1, ANSI/TIA-568.2, TIA TSB-155, ISO/IEC TR 24750, CLC/TR 50173-99-1, TIA TSB-5021, ISO/IEC TR 11801-9904 |
What they cover
IEEE 802.3an and IEEE 802.3bz are amendments to IEEE 802.3, the Ethernet standard. They define BASE-T physical layers that run over four-pair balanced twisted-pair structured cabling with RJ45-type interfaces.
- 802.3an-2006 added 10GBASE-T: 10 Gb/s over balanced twisted-pair cabling up to 100 m.
- 802.3bz-2016 added 2.5GBASE-T and 5GBASE-T: intermediate rates aimed at cabling already installed for 1000BASE-T, such as Cat 5e and Cat 6.
Amendments are folded into the next revision of IEEE 802.3. Both are now part of IEEE 802.3-2022, so references to “802.3an” or “802.3bz” today point to clauses of the base standard.
Where they sit in IEEE 802.3
| PHY | Original amendment | Clause in IEEE 802.3 |
|---|---|---|
| 10GBASE-T | 802.3an-2006 | Clause 55 |
| 2.5GBASE-T | 802.3bz-2016 | Clause 126 (overview in Clause 125) |
| 5GBASE-T | 802.3bz-2016 | Clause 126 (overview in Clause 125) |
All three are full duplex only, keep the standard Ethernet frame format and support Clause 28 auto-negotiation. The 802.3an objectives required coexistence with 802.3af PoE. The 802.3bz objectives required support for PoE (Clause 33), including the 4-pair work in 802.3bt.
Cabling and reach
10GBASE-T
The 802.3an objectives set reach as at least 100 m on Class F cabling and 55 m to 100 m on Class E cabling. Augmented Category 6 (Cat 6A, TIA) and Class EA (ISO/IEC) were developed to support 10GBASE-T over a 100 m channel. For new installations intended to run 10GBASE-T to 100 m, specify Cat 6A / Class EA or higher.
IEEE 802.3 Clause 55 also supports Class E / Category 6 cabling, but over shorter lengths: 55 m for unscreened Category 6, with longer links depending on alien crosstalk. The assessment and mitigation of installed Category 6 / Class E is covered by separate guidance documents:
| Document | What it says about Cat 6 / Class E |
|---|---|
| TIA TSB-155 | 10GBASE-T is expected to run on Category 6 channels up to 37 m, and from 37 m to 55 m depending on the alien crosstalk environment. Channels over 55 m may need mitigation. TSB-155 is a guideline, not a standard |
| ISO/IEC TR 24750 and CLC/TR 50173-99-1 (2007) | Assessment and mitigation of installed Class E and Class F channels. After assessment and mitigation, unscreened Category 6 Class E channels are expected to support 10GBASE-T from 55 m up to 100 m, screened Category 6 Class E channels up to 100 m. Class F channels support 10GBASE-T up to 100 m without mitigation |
The limiting factor is alien crosstalk between neighbouring cables. TSB-155 gives field testing to 500 MHz, including power sum alien crosstalk.
2.5GBASE-T and 5GBASE-T
| PHY | 802.3bz reach objective |
|---|---|
| 2.5GBASE-T | At least 100 m on four-pair Class D (Cat 5e) |
| 5GBASE-T | At least 100 m on four-pair Class E (Cat 6) |
| 5GBASE-T, additional objective | Up to 100 m on four-pair Class D (Cat 5e) |
The objectives are qualified “on defined use cases and deployment configurations”. The cabling side is covered by two guidance documents:
- TIA TSB-5021 (2017): guidelines for using installed Category 5e and Category 6 cabling for 2.5GBASE-T and 5GBASE-T, with visual inspection and field test guidance.
- ISO/IEC TR 11801-9904:2017: assessment and mitigation of installed Class D and Class E channels. It states that higher classes support 2.5GBASE-T and 5GBASE-T without mitigation up to 100 m.
How they relate to other standards
| Document | Relationship |
|---|---|
| ISO/IEC 11801-1 and BS EN 50173-1 | Define the channel classes (D, E, EA, F) that the IEEE PHYs are specified to run over |
| ANSI/TIA-568.2 | Defines Category 5e, 6 and 6A cabling and their test limits |
| IEEE 802.3af/at and 802.3bt | PoE can be delivered over the same four pairs. Bundle heating limits are covered by ISO/IEC TS 29125 |
| IEEE 802.3ab (1000BASE-T) | The earlier four-pair PHY that 2.5GBASE-T and 5GBASE-T were designed to follow on installed cabling |
What it means in practice
- For new 10GBASE-T links to 100 m, specify Cat 6A / Class EA channel performance and test to it.
- Do not assume an existing Cat 6 link supports 10GBASE-T beyond 37 m. Alien crosstalk testing is needed to confirm it.
- 2.5GBASE-T and 5GBASE-T are intended for higher speeds on installed Cat 5e and Cat 6. Field test results to the original category give a baseline; the TSB-5021 or TR 11801-9904 guidance covers further assessment.
- Large bundles carrying PoE run warmer, which increases insertion loss. Check bundle size and PoE class together.
Related reading: The complete guide to Cat6A cable · Cat5e vs Cat6 vs Cat6A.