Gigabit Ethernet, Transmission Mechanism for 1000BASE Standards

Driven by growing Internet-based operations and the increasing delivery demands for time-sensitive applications, there appeared a boom in the deployment of 10/100M Ethernet or Fast Ethernet due to the low cost and compatibility with existing local area networks (LANs) over the past few years. Thanks to the advances in Ethernet technology, the Gigabit Ethernet, 1GbE, (1000M Ethernet) has been deployed as the later development of the Ethernet standard beyond the 100Base-T version. And this 1GbE has proven itself as an ideal solution for the increased bandwidth requirements of growing networks in data centers with the time passing by.

Gigabit Ethernet, 1GbE Development

1GbE is the evolutionary fruit of Ethernet standard. In computer networking, 1GbE is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second (1,000,000,000 bits per second), as defined by the IEEE 802.3-2008 standard.

The original development of Ethernet took place in 1970s at the Xerox Corporation. Since then Ethernet evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased speed from 10 to 100 megabits per second (Mbit/s). Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The initial standard for 1GbE was produced by the IEEE in June 1998 as IEEE 802.3z which required fiber optic cables. And in 1999, IEEE 802.3ab was ratified, defining 1GbE transmission over unshielded twisted pair (UTP) CAT5, 5e or 6 cabling, and known as 1000BASE-T. Although 1GbE is being replaced by even faster 10GbE or 40GbE versions, this 1GbE still sees bright future because of the widely planted 1000BASE-T variant at low prices.

Gigabit Ethernet, 1GbE Physical Layers

The 802.3ab specification details several 1000BASE standards that can operate over fiber, copper or other transmission media. The image below shows the 1GbE standard family.

1GbE standard family

  • 1000BASE-CX—It’s the initial 1GbE standard, intended for connections over short distances up to 25m per segment by using a balanced shielded twisted pair copper cable. In practical applications, 1000BASE-T has succeeded it for general copper wiring use.
  • 1000BASE-SX—It’s a fiber optic version of the standard that operates over multi-mode fiber (MMF), using a 770 to 860nm, near infrared (NIR) light wavelength. This standard specifies the distance reach between 220m (62.5/125µm fiber with low modal bandwidth) and 550m (50/125µm fiber with high modal bandwidth). Like 1783-SFP1GSX module, this Allen-Bradley compatible 1000BASE-SX SFP is able to realize 550m reach over OM2 MMF with LC duplex connector.

1783-SFP1GSX, 1000BASE-SX SFP

  • 1000BASE-LX—It’s also a fiber optic version, but it works over single-mode fiber (SMF), using a long wavelength (1,270-1,355nm), with distances ranging from 5km to 10km. It can also run over all common types of MMF with a maximum segment length of 550m.
  • 1000BASE-T—Also known as IEEE 802.3ab, this standard transmits signal over four pairs of CAT5 untwisted pair cables (UTP). Each 1000BASE-T network segment can be a maximum length of 100 meters. It can provide speed of 1000Mb/s—10 times the speed of Fast Ethernet- over CAT5 UTP.
  • The Telecommunications Industry Association (TIA) created and promoted a standard similar to 1000BASE-T that was simpler to implement, calling it 1000BASE-TX (TIA/EIA-854). The simplified design would have, in theory, reduced the cost of the required electronics by only using two unidirectional pairs in each direction instead of 4 bidirectional. However, this solution has been a commercial failure, likely due to the required Category 6 cabling and the rapidly falling cost of 1000BASE-T products. 1000BASE-T products are sometimes marketed as 1000BASE-TX despite the difference in standards.
Conclusion

Since the 1000BASE-T is backward compatible with 10BASE-T and 100BASE-T technologies, no costly hardware upgrading or expensive technical expertise is required in the 1GbE infrastructure deployment when using 1000BASE-T standard, a cost effective solution while ensuring network performance. Fiberstore offers various 1000BASE SPFs for 1GbE solutions, including GLC-EX-SMD, 1783-SFP1GSX, etc. For more information about 1GbE transceivers, you can visit Fiberstore.

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