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Unit 4: Ethernet and CablingLesson 4.5 (5 of 9 in this unit)20 of 84 in the Network Fundamentals course

Ethernet physical layer standards

Reading names like 1000BASE-T and 10GBASE-LR, and matching speeds to media and distances.

Beginner · 7 min read

An Ethernet physical layer standard is an IEEE 802.3 specification that defines how Ethernet runs over one kind of medium: its speed, the type of copper cable or fibre, the signalling and the maximum distance. The name, such as 1000BASE-T or 10GBASE-LR, encodes the speed, the baseband signalling and the medium.

In simple terms: Each standard is a recipe for one kind of Ethernet link. For example, the name 1000BASE-T tells you that the link runs at 1000 Mbps over twisted-pair copper cable.

Reading a standard's name

An Ethernet standard's name contains the speed, the signalling and the medium. For example, take 10GBASE-LR:

10G
Speed: 10 Gbps
BASE
Baseband signalling
-L
Long wavelength (1310 nm)
R
64B/66B encoding family

The first letter after the dash tells you the medium:

SuffixMeaningExample
TTwisted-pair copper1000BASE-T, 10GBASE-T
SShort wavelength, multimode fibre1000BASE-SX, 10GBASE-SR
LLong wavelength, usually single-mode fibre1000BASE-LX, 10GBASE-LR
EExtended reach (1550 nm), single-mode fibre10GBASE-ER

Common standards

NameIEEESpeedMediumTypical max distance
10BASE-T802.3i10 MbpsCat3+ copper100 m
100BASE-TX (Fast Ethernet)802.3u100 MbpsCat5+ copper100 m
1000BASE-T (Gigabit)802.3ab1 GbpsCat5e+ copper100 m
1000BASE-SX802.3z1 GbpsMultimode fibre~550 m
1000BASE-LX802.3z1 GbpsSingle-mode fibre5 km (10 km with LX10 optics)
2.5G / 5GBASE-T802.3bz2.5 / 5 GbpsCat5e / Cat6 copper100 m
10GBASE-T802.3an10 GbpsCat6a copper100 m
10GBASE-SR802.3ae10 GbpsMultimode fibre300 m (OM3), 400 m (OM4)
10GBASE-LR802.3ae10 GbpsSingle-mode fibre10 km

Faster standards (25, 40, 100 and 400 Gbps) follow the same naming pattern. For example, 100GBASE-SR4 uses four lanes over multimode fibre. Real distances depend on the exact cable grade and optics, so always check the transceiver's datasheet.

Matching the standard to the job

1000BASE-T · 40 m10GBASE-SR · 150 m10GBASE-LR · 2 kmDesk PCAccess switchDistributionOther building
  1. 1. Desk to access switch: low-cost copper cable works for runs up to 100 m.
  2. 2. Access to distribution: multimode fibre covers a few hundred metres at 10 Gbps.
  3. 3. Between buildings: single-mode fibre covers distances of several kilometres.

Copper port or SFP slot?

On a real switch, you see these standards as two types of port:

  • An RJ45 port is for twisted-pair copper cable (the -T standards).
  • An SFP or SFP+ slot is empty until you plug in a module for the standard you want (SX, LX, SR, LR and so on).

The speed a link actually runs at is agreed by the devices at both ends.

Learn more: Copper CablingFibre-Optic CablingSpeed and Duplex

✅ Key takeaways
  • Names follow the pattern speed + BASE + medium: 1000BASE-T is 1 Gbps over twisted-pair copper.
  • -T means copper (up to 100 m), -S means short-wavelength multimode fibre, and -L means long-wavelength, usually single-mode, fibre.
  • Use copper to the desk, multimode fibre inside buildings and single-mode fibre between buildings.

Check yourself

Predict · scenario 1

You need to connect a server to a switch at 10 Gbps over a 60 m run of Cat6a copper cable. Which standard does the link use?

Predict · scenario 2

Two buildings are 3 km apart. Which is the right choice for a 10 Gbps link between them?