What Does BASE-“n” Mean for Fiber Optic Transceiver?

The networking is a very complicated field. Especially, when it intertwines with many terms, it’s easy to make beginners get lost in it. In this article, we will explore the Ethernet network naming system as Base-“n” and its applications in fiber optic transceiver.

Network Basics

Before the subject, there are two terms we need to have a clear mind. The first one is “megabit”. Put it in a simple way, the “megabit” refers to the data transfer rates of computer networks or telecommunications systems, also called network speed or Internet connection bandwidth. Usually, the “megabit” is measured by the second, which is used as megabits per second. The common network speeds as “megabit” and their relations with Ethernet speed are displayed below:

·10 megabits
·100 megabits – Fast Ethernet
·1000 megabits – Gigabit Ethernet, GbE, including 1000BASE-X, 1000BASE-T, etc.
·10,000 megabits – 10 Gigabit Ethernet, 10GbE, including 10GBASE-X, 10GBASE-T, etc.
·40,000 megabits – 40 Gigabit Ethernet, 40GbE, or 40GBASE-X.
·100,000 megabits – 100 Gigabit Ethernet, 100GbE, or 100GBASE-X.

The other term is “BASE”, also called baseband. Under Ethernet physical layer standards, for example, 10BASE5, 100BASE-TX and 1000BASE-SX, the “BASE” implies the transmission is an unfiltered line not requiring a digital modulation scheme. In the early days, the 10PASS-TS version of Ethernet was used for a signaling scheme similar to a modem but now is baseband instead.

An Overview of BASE-“n”

In this part, we will have an overview of BASE-“n”. Here, “n” refers to the variable symbols after BASE. The commonly used symbols with “BASE” are listed below:

1. The first letter tells us which kind of wire we are talking about:

  • “T” means twisted-pair cable (e.g. Cat5e and Cat6 are popular for today).
  • “K” means a copper backplane.
  • “C” means balanced copper cable.
  • “F” means optical cable.
  • “B” uses two wavelengths over a single optical cable.
  • “S” means short-range multimode optical cable (less than 2 km).
  • “L” means the long-range single mode or multimode optical cable (less than 10 km).
  • “E” means extended-range optical cable (10 km to 40 km).
  • “Z” means long-range single mode cable at a higher wavelength (up to 80 km).

2. Next is the coding scheme for data on the wire:

  • “X” means 4B/5B block coding for Fast Ethernet or 8B/10B block coding for Gigabit Ethernet.
  • “R” means 64B/66B block coding.

3. Finally, we have a number representing the number of parallel “lanes” for data:

  • “1” would mean serial (non-parallel) but is omitted instead.
  • “4” or “10” are available for copper wire.
  • Just about any other number could be used for optical lanes or wavelengths.

BASE-“n” Applied in Fiber Optic Transceiver

After having a basic idea about “BASE”, we will use some examples to explain what the BASE-“n” means for fiber optic transceiver.

1. In the old days, 10BASE-T was preferred instead the coaxial 10BASE2. It was a simple 10 megabits baseband signal over common twisted-pair.

2. Later, the fast Ethernet emerged, people concerned that the previous cable versions (usually Cat3) couldn’t support 100 megabits. Then, some chose to use four copper pairs (100BASE-T4) or fiber optics (100BASE-FX). However, currently, nearly every 100 megabits Ethernet connection is 100BASE-TX, using plain two pairs on plain Cat5 cable.

transceiver picture
Figure 1: 1000BASE-T SFP Fiber Optic Transceiver

3. As for the Gigabit Ethernet, it had a similar history. In case that two pairs on unshielded Ethernet cables wiring could not handle 1000 megabits per second, the optical (1000BASE-SX) and balanced shielded wiring (1000BASE-CX) were specified. Although the standard of unshielded two pairs was developed (1000BASE-T), it still couldn’t meet the need. Therefore, in today’s Gigabit applications, the 1000BASE-T uses all four pairs of unshielded twist pair wiring on Ethernet cables. For example, the connection for 1000BASE-T SFP fiber optic transceiver is such a case.

4. After the Gigabit Ethernet, the Ethernet world embraces the 10Gigabit technology. It has mostly shifted to the block coding scheme from Fibre Channel, 64B/66B, which is denoted by the letter “R”. The 10Gigabit technology extends the family of fiber optic cables (10GBASE-SR, LR, ER, etc), and a copper backplane interconnects (10GBASE-KR). In applications of 10Gigabit Ethernet, the 10Gb Ethernet switch is popular.

5. With technology moving on, the higher-speed Ethernet has arrived: 40GBASE-KR4 for backplane use, multimode optical 40GBASE-SR4 and 100GBASE-SR10, and long-range single mode optical 40GBASE-LR4 and 100GBASE-LR10. The mostly seen applications of 40G/100GBASE technologies as fiber optic transceivers are 40G QSFP+ fiber optic transceiver and 100G QSFP28 fiber optic transceiver.

Figure 2: 40GBASE Fiber Optic Transceivers


In this post, we can see the naming rule of BASE-“n” from 1000BASE to 100GBASE in a more clear way. With this naming system, we can have a better understanding of the naming system for fiber optic transceiver and the development of the Ethernet world.


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