I understand the number in the naming convention. The number represents how many Megabits per second can the standard support. However, I do not understand the rest of the naming convention. What do "BASE," "T," "X," etc. mean?

Can someone explain what do names mean and how did these standards come into effect?

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    – Ron Maupin
    Jan 3, 2021 at 4:27

2 Answers 2


BASE indicates baseband signaling - there is no modulated carrier, the frequency starts near zero and extends to a certain cut-off frequency.

BROAD indicates broadband modulation - there is a wide frequency band with a number of carriers modulated with the data (similar to xDSL).

The X in -TX, -SX, ... stands for 4b/5b (100 Mbit/s) or (improved) 8b/10b line code (PCS block code). The R in 10GBASE-SR or -LR stands for more efficient 64b/66b line code (laRge block). A line code is required to enable clock recovery and bit-level synchronization. Without line code, the receiver would lose track of the bit boundaries when many same bits are transmitted.

-T indicates a twisted-pair medium, two used pairs for 10/100 Mbit/s, four pairs for 1 Gbit/s upwards. Speeds beyond 100 Mbit/s use specialized line codes plus scrambling. Mostly, only -T is used - the X in 100BASE-TX was added since it competed with the differing variants 100BASE-T2 and 100BASE-T4 at the time. Modern, single-pair variants use -T1.

-S stands for Short wavelength optical (~850 nm), -L for Long wavelength (~1300 nm), -E for Extra long wavelength (~1500 nm) and so on. With few exceptions, short wavelength is used with multi-mode fiber for short distance (less than 1 km), longer waves with single-mode fiber for long distance (1 km to 100 km). These three wavelengths are selected from the low-absorption bands of silica glass.

I've compiled a comprehensive and fairly complete list for Wikipedia a while back, all taken from IEEE 802.3.


The first number represents the speed.

If the next part is "BASE", then it is baseband. If it is "BROAD", then it is broadband. This is the original meaning of baseband/broadband, not the government idea (any speed at or above an arbitrary speed) of broadband.

The last part is tricky. "2" means about (185) 200 meters. "5" means 500 meters. "36" means 3600 meters. "T" means twisted-pair cable (limited to 100 meters). "TX" is a variation of twisted-pair". Things like "SX" or "LX" are for fiber. "SX" is for short range, "LX" is for long range. There are other variations of fiber, too.

Ethernet (and other LAN standards) is developed by the IEEE. The ethernet IEEE working group is 802.3. There are other working groups, e.g. 802.11 for Wi-Fi, some of which have been disbanded, e.g. 802.5 for token ring, and the standards are frozen.

  • What do "baseband" and "broadband" mean in this context? Aug 29, 2017 at 21:06
  • 1
    Baseband uses the full bandwidth to send data, while broadband only uses part of the bandwidth, allowing simultaneous signals on the same physical link (think cable TV, where you have multiple channels being sent at the same time on the same cable).
    – Ron Maupin
    Aug 29, 2017 at 21:08
  • 1
    I've seen PASS as the second part as well - meaning a specific band that is not a baseband. (10PASS-TS appears to be a thing)
    – user253751
    Aug 29, 2017 at 23:58

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