Gigabit Ethernet Technology and applications

1. Introduction

The IEEE 802.3z Gigabit Ethernet Standard, adopted in June 1998, describes 3 physical layer interfaces (1000BASE-SX, 1000BASE-LX, and 1000BASE-CX) that are used for a universal link encoding and can be 1000mb/s transmitted. 1000BASE-SX, 1000BASE-LX interface using optical fiber as a medium, the farthest transmission distance of up to 5000 meters, so can be used in buildings or campus backbone network. The 1000BASE-CX interface is planned to be used to limit connections within a computer room within 25 meters.

IEEE 802.3AB Gigabit Ethernet standard was certified in June 1999, which describes additional physical layer interfaces (1000BASE-T) for different line encodings. The 1000BASE-T interface is transmitted over a maximum distance of 100 m through 5 types of unshielded twisted pair (UTP) media and is mainly used for desktop-facing network connections.

In March 1999, an IEEE 802.3 research group was formally established to develop standards for the transmission of Wanchaubi Ethernet through optical fiber media.

2. Copper cable Wiring System

In fact, all buildings using structured cabling systems have twisted-pair copper horizontal subsystems to connect each layer of communication wiring and wall information exits. And these wiring system installs most uses 5 kind of product, therefore 1000BASE-T is the design applies in the 5 kind of wiring system.

The 1000BASE-T uses all 4 pairs of cables in a cable to transmit, and the effective transfer rate of each pair of lines is 250mb/s to achieve Full-duplex transmission. In order to apply to 5 kinds of bandwidth cabling system, the 1000BASE-T adopts 5-level coding transmission, and the receiver uses digital signal processing (DSP) technology to reduce the impact of reflection and near-end Crosstalk (NEXT) from the wiring system.

1000BASE-T Cabling system requirements include additional transmission performance not described in the original 5 system, such as elfext (remote crosstalk at the same level) and loop loss. This can be strongly recommended by the latest professional tester testing, recognition, most of the installed 5 types of cabling system can support 1000base-t to confirm. ---http://bianceng.cn (computer science)

The specification of the 1000BASE-T cabling system will be fed back to the new procedures that evolve with Ansi/tia/eia. "4 to 100 ohms 5 cabling System of additional transmission performance parameters" is expected to be promulgated by TSB-95 by the end of this year.

Ansi/tia/eia also issued a draft stating "4 to 100 ohm enhanced 5 wiring system transmission Performance parameters", now is the 12th draft, which is expected to be promulgated as Appendix 5 to the ANSI/TIA/EIA568A standard at the end of this year. The draft is similar to the TSB-95 description, but the loop loss and next performance index are good 2db~3db. ANSI recommends that the new cabling installation should at least meet the performance requirements of the enhanced 5-class cabling.


In the past two years, the term "enhanced Category 5" has been very common, but the draft of the enhanced 5 category has changed a lot. It is therefore recommended that users who wish to designate an enhanced 5-class cabling system refer to the latest draft ansi/tia/eia-568-a-5 and now the 12th draft. User reference a defined performance requirement should be better than accepting the manufacturer's view of the enhanced 5 performance, and can consult the latest data from the manufacturer to confirm that its products conform to the current enhanced 5-class draft standards.

Ansi/tia/eia also published an article explaining "4 to 100 ohms 6 cabling System transmission Performance". Class 6 systems have a bandwidth of twice times 5, with better loop loss (reflection) and next performance metrics.
The development recommendations for 1000MB/S interfaces for Class 6 systems are designed to better apply their advanced performance compared to 1000base-t to reduce the complexity and cost of electrical interfaces.

3. Fiber Cabling System

At Gigabit data transmission rates, the use of light-emitting diodes (LEDs) as 10base-f and 100base-fx light sources will no longer be applicable, but requires the use of conventional lasers or recently recommended low-cost cylindrical laser (VCSEL). The 1000BASE-SX interface uses a short wavelength (850nm) Vcsel, which is more widely used than the 1000base-lx of a long wavelength (1300nm) conventional laser. Each interface has a different distance limit, depending on the type and level of fiber (bandwidth) shown in the following table.

Table. Comparison of maximum transmission distances between 1000BASE-SX and 1000BASE-LX in different fiber bandwidth
In recent years, 62.5/125mm fibers have been used as the backbone of buildings in a large number of installations, while others have been fitted with single-mode fibers to meet future requirements. This orthodoxy is changing as Gigabit Ethernet is involved. Due to bandwidth constraints, the use of standard 160/500mhz.km62.5/125mm optical fiber, the farthest transmission distance of 220 meters, and for the backbone of the building system, 220 meters of transmission distance is not long enough. Although it can be used the farthest transmission distance of up to 550 meters of 1000base-lx, but extremely expensive. As a candidate, a higher-priced 1000BASE-LX is recommended to be installed in some industrial environments using 50/125mm fiber because it has a higher bandwidth than 62.5/125mm fiber, but costs almost as much.

For distance of more than 550 meters of campus network backbone, with 1000BASE-LX can only choose single mode fiber.

Work on the specification of Wanchaubi Ethernet has just begun, so it is premature to discuss its changes, but Vcsel is very similar to the choice of conventional lasers. The difference is that both 62.5/125mm and 50/125mm cannot have enough bandwidth to support Wanchaubi Ethernet over a distance of practical significance. For this reason, the international wiring Standards Working Group, ISO/IEC jtc1/sc25/wg3, wrote to the IEEE802.3 committee, saying that they would work with the IEC SC86A Committee to develop a new multimode optical fiber protocol. The new code multimode fiber will support the Vcsel transmission distance of at least 300 meters based on Wanchaubi Ethernet. The new procedures are for bandwidth-enhancing 50/125mm fibers, as well as for 62.5/125mm fibers.

4. Conclusion

While 1000base-t can run on most installed 5-class cabling systems, the industry has consistently recommended the adoption of at least an enhanced 5-type cabling system for new installations. Compared to the enhanced 5 class systems, 6 types of systems will support 1000base-t more forcefully, and in the future, it supports new gigabit-specific interfaces that are not supported by the Enhanced 5 class system.

The single mode fiber is the only choice when applied to the 1000BASE-LX interface and the transmission distance is over 550 meters. And for the short distance of the campus network or building trunk, the choice is not unique. Because at 850nm, the 50/125mm fiber with higher bandwidth is better than the 62.5/125mm fiber, especially when the transmission distance is over 220 meters. When porting to Wanchaubi Ethernet, it is possible to consider the parallel operation of Single-mode fiber and multimode fiber. This is the best option until the new multimode fiber that supports Wanchaubi Ethernet is developed.