SFP 40 km VS. DWDM SFP: Which to Choose?

Small Form-factor Pluggable (SFP) is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. It is also called mini-GBIC for its smaller size, which is the upgraded version of GBIC transceiver. These 1Gb SFP modules are capable of supporting speeds up to 4.25 Gbps. And they are most often used for Fast Ethernet of Gigabit Ethernet applications. It interfaces a network device motherboard (for a switch, router, media converter or similar device) to a fiber optic or copper networking cable. SFP modules are commonly available in several different categories: 1000BASE-T SFP, 1000BASE-EX SFP, 1000BASE-SX SFP, 1000BASE-LX/LH SFP, 1000BASE-BX SFP, 1000BASE-ZX SFP, CWDM SFP and DWDM SFP. These modules support different distance according to the different Gigabit Ethernet standard. Today’s main subject will discuss SFP 40 km vs. DWDM SFP.

SFP 40 km

SFP 40 km transceiver is designed for highly reliable fiber optic network links up to 40 km. It is a cost effective transceiver designed to enable 1Gb for data center and core network applications. 1000BASE-EX SFP is the most popular SFP 40 km transceiver which runs on 1310nm wavelength lasers and achieves 40km link length. Except that, 1000BASE-BX BiDi SFP, 1000BASE-LH SFP and 1000BASE-LX SFP can also realize the transmission distance up to 40 km. The following will introduce these 1GbE SFP 40 km transceivers respectively.

1000BASE-EX SFP 40 km

1000BASE-EX SFP transceiver module is designed to connect a Gigabit Ethernet port to a network and has dual LC/PC single mode connectors. It operates on standard single-mode fiber-optic link spans of up to 40 km in length. The SFP Ethernet module provides a dependable and cost-effective way to add, replace or upgrade the ports on switches, routers and other networking equipment. Cisco GLC-EX-SM1550-40 and Cisco GLC-EX-SMD are 1G single mode fiber SFP 40 km modules for 1000BASE-EX Gigabit Ethernet transmission. GLC-EX-SM1550-40 supports a 1550nm wavelength signaling, while GLC-EX-SMD supports a 1310nm wavelength signaling.

1000BASE-BX SFP 40 km

1000BASE-BX SFP is a kind of BiDi transceiver, which can be divided into 1000BASE-BX-D SFP and 1000BASE-BX-U SFP. These two SFP transceivers must be used in pairs to permit a bidirectional Gigabit Ethernet connection using a single strand of single mode fiber (SMF) cable. The 1000BASE-BX-D SFP operates at wavelengths of 1490nm TX/1310nm RX, and the 1000BASE-BX-U SFP operates at wavelengths of 1310nm TX/1490nm RX.

• 1000BASE-BX-D BiDi SFP 40 km

Cisco GLC-BX40-D-I and GLC-BX40-DA-I are pluggable fiber optical transceivers for Gigabit Ethernet 1000BASE-BX and Fiber Channel communications. They support link length of up to 40 km point to point on single mode fiber at 1Gbps bidirectional and use an LC connector. The GLC-BX40-D-I transceiver transmits a 1490nm channel and receives a 1310nm signal, whereas GLC-BX40-DA-I transmits at a 1550nm wavelength and receives a 1310nm signal.

• 1000BASE-BX-U BiDi SFP 40 km

Similar to 1000BASE-BX-D 40 km SFP , Cisco GLC-BX40-U-I and GLC-BX40-UA-I also support link length of up to 40 km point to point on single mode fiber at 1Gbps bidirectional and use an LC connector. The main difference is the wavelength: GLC-BX40-U-I transmits a 1310nm channel and receives a 1550nm signal, whereas GLC-BX40-UA-I transmits at a 1310nm wavelength and receives a 1490nm signal. A GLC-BX40-D-I or GLC-BX40-DA-I device connects to a GLC-BX40-U-I or GLC-BX40-UA-I device with a single strand of standard SMF with an operating transmission range up to 40 km.

1000BASE-LX SFP 40 km

1000BASE-LX is a standard specified in IEEE 802.3 Clause 38 which uses a long wavelength laser. The “LX” in 1000BASE-LX stands for long wavelength, indicating that this version of Gigabit Ethernet is intended for use with long-wavelength transmissions (1270 - 1355nm) over long cable runs of fiber optic cabling. Allied Telesis AT-SPLX40 and Allied Telesis AT-SPLX40/1550 are 1000BASE-LX SFP single-mode modules supports Gigabit Ethernet over single-mode cables at distances up to 40 km. AT-SPLX40 operates over a wavelength of 1310nm for 40 km, whereas AT-SPLX40/1550 operates over a wavelength of 1550nm.

1000BASE-LH SFP 40 km

Unlike 1000BASE-LX, 1000BASE-LH is just a term widely used by many vendors. Long Haul (LH) denotes longer distances, so 1000BASE-LH SFP modules operate at a distance up to 70 km over single mode fiber. Cisco Linksys MGBLH1 is a easy-to-install modules that provide a simple way to add fiber connectivity or to add an extra Gigabit Ethernet port to switches. The MGE transceiver can support distances up to 40 km over single-mode fiber at a 1310nm wavelength.

DWDM SFP

DWDM SFP transceivers are used as part of a DWDM optical network to provide high-capacity bandwidth across an optical fiber network, which is a high performance, cost effective module for serial optical data communication applications up to 4.25Gb/s. DWDM transceiver uses different wavelengths to multiplex several optical signal onto a single fiber, without requiring any power to operate. There are 32 fixed-wavelength DWDM SFPs that support the International Telecommunications Union (ITU) 100-GHz wavelength grid. The DWDM SFP can be also used in DWDM SONET/SDH (with or without FEC), but for longer transmission distance like 200 km links and Ethernet/Fibre Channel protocol traffic for 80 km links. Cisco C61 DWDM-SFP-2877-40 is a 1000BASE-DWDM SFP 40km transceiver, which is designed to support distance up to 40 km over single-mode fiber and operate at a 1528.77nm DWDM wavelength (Channel 61) as specified by the ITU-T.

SFP 40 km VS. DWDM SFP

• Transmission Medium

Generally, the standard SFP 40 km transceivers transmit through the single mode fiber, while DWDM SFP carries signals onto a single optical fiber to achieve maximum distances by using different wavelengths of laser light. So the DWDM SFP transceivers do not require any power to operate.

• Wavelength

The standard SFP 40 km transceivers support distances up to 40 km over single-mode fiber at a 1310nm/1550nm wavelength. (the BiDi SFP has 1490nm/1550nm TX & 1310nm RX or 1310nm TX & 1490nm/1550nm RX ). However, DWDM SFP operates at a nominal DWDM wavelength from 1528.38 to 1563.86nm onto a single-mode fiber. Among them, 40 km DWDM SFP operates at a 1528.77nm DWDM wavelength (Channel 61).

• Application

DWDM SFP is used in DWDM SONET/SDH, Gigabit Ethernet and Fibre Channel applications. These modules support operation at 100Ghz channel. The actual SFP transceiver offers a transparent optical data transmission of different protocols via single mode fiber. And for back-to-back connectivity, a 5-dB inline optical attenuator should be inserted between the fiber optic cable and the receiving port on the SFP at each end of the link.

• Price

DWDM provides ultimate scalability and reach for fiber networks. Boosted by Erbium Doped-Fiber Amplifiers (EDFAs)  - a sort of performance enhancer for high-speed communications, DWDM systems can work over thousands of kilometers. Most commonly, DWDM SFP is much more expensive than the standard SFP. You can see the price more clearly in the following cable.

Conclusion

1000BASE SFP transceiver is the most commonly used component for Gigabit Ethernet application. With so many types available in the market, careful notice should be given to the range of differences, both in distance and price of multimode and single-mode fiber optics. Through SFP 40 km vs. DWDM SFP, if you are looking for SFP modules over long distance and with better scalability, DWDM SFP module is the ideal choice.

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