Tag: SFP

Understanding DWDM in Optical Communication

Without optical communication we might be still sending mail, going to the newsstand to buy a newspaper, sending mail and postcards and renting movies, no internet would have been possible, no digital communications as we know it.

Among the many unsung technologies that make all this possible, Dense Wavelength Division Multiplexing (DWDM) is without any doubt one of the most important. As a kind of WDM technology, DWDM has the capability to send multiple signals on the same fiber, using different wavelengths. DWDM devices combine the output from several optical transmitters for transmission across a single optical fiber. At the receiving end, another DWDM device separates the combined optical signals and passes each channel to an optical receive. One of the nice characteristics of the optical fiber is that different channel can travel one close to the other with very little, almost negligible in most cases, crosstalk. Thanks to DWDM, we’re now able to pack 10 TBits/s of traffic per single fiber and send it more than 1000Km.

DWDM started as high end transport technology, but made its way to regional and metropolitan network and finally into transceivers. Several generation of DWDM transceivers have already been released (XENPAK, X2, XFP, SFP, SFP+), providing networking equipment not only with the capability to transport a huge amount of data with a single fiber, simplifying cabling and reducing cost, but also reducing the number of equipment needed. Before, if an operator wanted to connect 2 switches located some tens of kilometers apart, it needed non-coloured optics on the switch, connected with the same kind of optics on the transport system transponder shelf, this last piece of equipment did the conversion from non-DWDM wavelengths to DWDM wavelengths before they were optically multiplexed and transported over the DWDM link, the opposite process at receiving site. With DWDM transceivers directly on the switch, they can be connected directly to the optical multiplexing gear. It is evident that this solution has numerous advantages.


If it is clear that DWDM optics come with great advantages, but the device is more complex and more optical variables comes into play. With uncoloured optics everything is pretty simple , they come with a “distance” tag attached (10km, 40km, 300m), power budget is pretty much the only parameter that the end user should care about. With DWDM there is no specific target distance power levels are of course still important, but other parameter, such as OSNR (optical signal to noise ratio) and CD (chromatic dispersion) come into play, in fact, often specifications are given in the form of a combination of the three mentioned parameters.

An optical signal travelling on a fiber experiences an attenuation of about 0.2dB/Km, so if you want to transmit it for long distances it needs to be amplified along the way and probably more than once. Erbium doped fiber amplifiers (EDFAs) do exactly this, but, at every amplifying stage, noise is added to the signal. The longer you want to go, the more amplifiers you need, the noisier the signal at the end of the line. Below a certain OSNR, which depends on the device to device, becomes impossible to detect the signal with an acceptable bit error rate.

DWDM is ready made for long-distance telecommunications operators that use either point-to-point or ring topologies. It provides ultimate scalability and reach for fiber networks. Without the capacity and reach of DWDM systems, most cloud-computing solutions today would not be feasible. Establishing transport connections as short as tens of kilometers to enabling nationwide and transoceanic transport networks, DWDM is the workhorse of all the bit-pipes keeping the data highway alive and expanding.


GBIC or SFP — Which One Is Your Choice?

As is known to all, fiber optical transceivers are developed along the way to achieve more compact sizes, such as GBIC, SFP, SFP+ and so on. Meanwhile, these transceiver modules are available with a variety of transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). In addition, there are a variety of interface types of GBICs and SFPs, like 1000Base-SX, 1000Base-LX/LH, 1000Base-EX or 1000Base-T etc. Faced with so many choices, some people are confused when choosing the proper one for their project.

Recently many users ask when they choosing a card for their switch/router, they should choose either cards that take SFP or cards that take GBIC. It seems to be a headache for them because they are not clearly know the differences of them. The following will tell you when it’s best to use GBIC or SFP.

GBIC (gigabit interface converter)

GBIC is a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot, linking the port with the network. GBIC is a standard for transceivers, commonly used with Gigabit Ethernet and fiber channel. GBIC module is hot pluggable, this feature allows a suitably designed enclosure to be changed from one type of external interface to another simply by plugging in a GBIC having the alternative external interface. Generally, GBIC is with the SC connector. The GBIC standard is non-proprietary and is defined by the Small Form Factor committee in document number 8053i. The first publication of the proposal was in November, 1995. A few corrections and additions were made in September, 2000.


SFP (small form-factor pluggable)

SFP is a specification for a new generation of optical modular transceivers. The form factor and electrical interface are specified by a multi-source agreement (MSA). SFP is also known as a Mini GBIC as its function is somewhat similar to the GBIC transceiver while SFP is smaller than it. SFP transceivers are designed to support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, SFP is now more and more widely used for both telecommunication and data communications applications.


GBIC & SFP Interface Types

For every type of GBIC and SFP transceivers, it works with different wavelengths at a designated location or distance. For examples, SX SFP uses 850nm for a maximum of 550 meters, LX SFP uses 1310nm for a maximum 10km, ZX SFP could reach 80km or copper SFP uses a RJ45 interface. We can easily distinguish via the information in their names or models, ie. 1000BASE-T, 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, 1000BASE-CWDM, or 1000BASE-DWDM. In addition, the DOM function for an SFP is discretionary. It supports the users to locate the real-time working status of SFP. The famous brand of GBICs or SFPs are Cisco, Finisar, HP, Juniper, Extreme Network and so on. There is a little difference in the features of each brand’s GBICs and SFPs and they support their corresponding brand’s switches/routers.

When it’s best to use GBIC and When to use SFP?

According to the above definitions of GBIC and SFP, you may have a further understanding on both of them. There is only one difference of them. SFP is smaller than GBIC. Because the smaller size of SFP (almost half the volume of GBIC), we can configure double number of ports on the same panel which increases the utilization rates of switches/routers. Other basic functions of SFP is almost the same with the GBIC and they are equal in performance. Though there are some users still using the GBIC as their old divice which can not be updated to support SFP, GBIC will gradually be obsoleted and replaced by SFP. So the answer to the question “When it’s best to use GBIC and When to use SFP?” is very noticeable.

1000BASE-SX SFP Modules Provided by FS.COM

Introduction to Gigabit Ethernet

In order to accelerate speeds from 100 Mbps Fast Ethernet up to 1 Gbps, many changes have been made to the physical interfaces. Gigabit Ethernet uses the same 802.3 frame format as 10Mbps and 100Mbps Ethernet systems. It runs ten times faster than the speed of Fast Ethernet, backward compatibility is assured with earlier versions, increasing its attractiveness by offering a high bandwidth connectivity system to the Ethernet family of devices.

Defined by IEEE 802.3z standard, Gigabit Ethernet originally launched three different physical layers: 1000Base-LX and 1000Base-SX using fiber and 1000Base-CX using copper. These physical layers were originally developed by IBM for the ANSI Fibre Channel systems and used 8B/10B encoding to reduce the bandwidth required to send high-speed signals. The IEEE merged the fibre channel to the Ethernet MAC using a gigabit media independent interface (GMII), which defines an electrical interface, enabling existing fibre channel PHY chips to be used and enabling future physical layers to be easily added.

1000Base-SX for Horizontal Fiber

1000Base-SX is a physical layer specification for Gigabit Ethernet over fiber optic cabling as defined in IEEE 802.3z. SX stands for short wavelength. And 1000Base-SX uses short wavelength laser (850nm) over multimode fiber as opposed to 1000Base-LX, which uses long wavelength laser over both multimode and single-mode fiber. The maximum distance of (multimode) fiber, based on 1000Base SX is 550m.

This Gigabit Ethernet version was developed for the short backbone connections of the horizontal network wiring. The SX systems operate full-duplex with multimode fiber only, using the cheaper 850nm wavelength laser diodes. The maximum distance supported varies between 200 and 550 meters depending on the bandwidth and attenuation of the fiber optic cable used. The standard 1000Base-SX NICs available today are full-duplex and incorporate LC fiber connectors.

1000BASE-SX SFP Optical Module Selection Guide

SFP transceiver is a hot-swappable input/output device that plugs into a Gigabit Ethernet port/slot, linking the port with the fiber-optic network. SFP can be used and interchanged on a wide variety of Cisco products and can be intermixed in combinations of IEEE 802.3z compliant 1000Base-SX interfaces on a port-by-port basis. 1000BASE-SX SFP (eg. Cisco GLC-SX-MM) supports link length of up to 550m on multimode fiber at 1Gbps. This optic works at 850nm wavelength and uses a LC connector.

SFP modules have now become an indispensable component in networks. Thus, it is very necessary to use quality assured modules. If you want to purchase cheaper and 100% compatible 1000Base-SX SFP modules online, FS.COM may be your good choice. You would not worry about the compatibility of the optics you have bought here. Because there is a perfect system from the production to shipment. Compatible SFP transceiver modules offered by FS.COM are test-assured and fully compatible with major brands (such as Cisco, HP, NETGEAR, Finisar, Juniper, etc.) and supported by a lifetime warranty. Besides, all these SFP modules can be customized according to your specific requirements.