July 2017

A Brief Overview to Dense Wavelength Division Multiplexing (DWDM)

28. july 2017 at 13:38
In fiber optic communications, WDM (wavelength-division multiplexing) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over one strand of fiber as well as multiplication of capacity. Generally, WDM could be divided into CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing). Below part will give a brief introduction to DWDM.
Dense wavelength division multiplexing (DWDM) is a technology that puts data from different sources together on an optical fiber, with each signal carried at the same time on its own separate light wavelength. Using DWDM, up to 80 separate wavelengths or channels of data can be multiplexed into a light stream and transmitted on a single optical fiber. This process allows for multiple video, audio, and data channels to be transmitted over one fiber while maintaining system performance and enhancing transport systems. This technology responds to the growing need for efficient and capable data transmission by working with different formats, such as SONET/SDH, while increasing bandwidth.
The fiber optic amplifier in DWDM system provides a cost efficient method of taking in and amplifying optical signals without converting them into electrical signals. In addition, DWDM amplifies a broad range of wavelengths in the 1550nm region. For example, with a DWDM system multiplexing 16 wavelengths on a single optical fiber, carriers can decrease the number of amplifiers by a factor of 16 at each regenerator site. Using fewer regenerators in long-distance networks results in fewer interruptions and enhanced efficiency.
A basic Dense Wavelength Division Multiplexing contains five main components:
1. DWDM Terminal Multiplexer: This device contains one wavelength converting transponder for each wavelength carried. It receives an input optical signal, converts it to an electrical signal and then retransmits it as an optical signal (a process abbreviated as O/E/O) using a 1550nm laser beam. The MUX (multiplexer) takes a number of 1550nm optical signals and places them on a single optical fiber. This terminal multiplexer may also contain an EDFA (Erbium Doped Fiber Amplifier) to amplify the optical signal.
2. Intermediate Line Repeater: These are amplifiers placed every 80 to 100 kilometers to compensate for loss of optical power; amplification is done by an EDFA, usually consisting of several amplifier stages.
3. Intermediate Optical Terminal, or Optical Add/Drop Multiplexer: This is a remote site amplifier placed where the signal may have traveled up to 140 kilometers; diagnostics and telemetry signals are extracted or inserted.
4. DWDM Terminal Demultiplexer: This device breaks the multi-wave signal back into individual signals; these may be sent to O/E/O output transponders before being relayed to their intended destinations, i.e. client-layer systems.
5. Optical Supervisory Channel (OSC): This channel carries information about the multi-wave optical signal and may provide data about conditions at the site of the intermediate line repeater.
DWDM has several key advantages:
  • Transparency-Because DWDM is a physical layer architecture, it can transparently support both TDM (Time Division Multiplex) and data formats such as asynchronous transfer mode (ATM), Gigabit Ethernet, Enterprise System Connection (ESCON), and Fibre Channel with open interfaces over a common physical layer.
  • Scalability-DWDM can leverage the abundance of dark fiber in many metropolitan area and enterprise networks to quickly meet demand for capacity on point-to-point links and on spans of existing SONET/SDH rings.
  • Dynamic provisioning-Fast, simple, and dynamic provisioning of network connections give providers the ability to provide high-bandwidth services in days rather than months.
  • Robust and reliable-Well-engineered DWDM systems offer component reliability, system availability and system margin.
To sum up, DWDM system is very important in optical communication. If you are still confused about it, feel free to consult customer service at FS.COM. We are willing to solve your puzzles and offer the right solution for you. FS.COM provides various kinds of WDM products, such as 10GBASE DWDM, 40 channel DWDM Mux, CWDM Mux/Demux module and so on. It is an excellent option for choosing CWDM and DWDM equipment.

Do You Know About Twinax Cable?

21. july 2017 at 11:42
Introduction to Twinax Cable
A twinax cable (also called twinax or twinaxial cabling) is a type of cable similar to the common coaxial copper cable, but has two inner conductors instead of one. Twinax cable was initially designed by IBM, so it has been primarily used by IBM for its IBM3x and AS/400 computer systems. But until now, the cost-effective twinax cable has been widely used, especially for applications that require high-speed differential signaling in a short-ranged scenario. They are suitable for networking, storage, and telecom industries. They are used in applications such as data center cabling infrastructure, SAN, NAS, other storage servers.

Its main advantages were high speed (1 Mbit/s versus 9600 bit/s) and multiple addressable devices per connection. The main disadvantage was the large connectors that usually needed screws to stay in place. The twin conductors of the twinax cable do not carry individual signals. The cable works in a half-duplex mode, as both connectors are required to transmit data.

Difference Between Active and Passive Twinax Cable
Currently there is a twinax cable which comes in either passive or active copper cable. So what is the difference between them?

A passive twinax cable carries a 10 Gig Ethernet signal over short lengths (5m or under, like SFP+ passive cable) of copper with no additional components to boost signal. An active twinax cable carries a 10 Gig Ethernet signal over long lengths (5m or more, like XFP active cable) of copper with the use of signal boosting technology. Passive copper cables contain no electrical components. While active copper cables contain electrical components in the connectors that boost signal levels. This makes active copper cables slightly more expensive than passive copper cables; however, they can connect the Converged Network Adapter (CNA) to a Top of Rack (ToR) switch over longer distances than passive copper cables.

How to Tell Active From Passive Twinax Cable?
Active and Passive Twinax Cable
We can see from the above picture that they look totally the same, and there isn't a truly visual way to tell the difference between active and passive twinax cables. The connectors are the same and the cable jackets are identical. So how do you tell? Most manufacturers including FS.COM will have some sort of marking on the cable connector head which will distinguish the cable as active or passive. But it is also not simply to tell by just looking at it.

Which to Choose?
With all cables, length and signal strength are always something to consider. For shorter distances, passive twinax cables are preferred, they are rated for ranges up to 5m and provide a good working solutions at a great cost. When the distance between connection points exceeds 5m, it is highly recommended to use active twinax cables to ensure that signal is transferred smoothly. The cost may be a bit higher, but the signal is strengthened.

Typically, we see twinax copper cable being used between the server and the Top of Rack switch. In regards to active versus passive twinax cables, it depends on what you are connecting together. For example, if you are connecting a CNA to a Cisco ToR switch (Nexus) and the cable length is 1, 3, or 5m, you can use a Cisco-supplied 1, 3, or 5m passive twinax cable, which is offered by FS.COM at a great cost and performance. If you are connecting a CNA to a Cisco ToR switch (Nexus) and the cable length is 7 or 10m, you need to use a Cisco-supplied 7 or 10m active twinax cable. If you are connecting a CNA to a Brocade ToR switch (8000) and the cable length is 1, 3, or 5m, you can use a Brocade-supplied 1, 3, or 5m active twinax cable.
Cisco Nexus 9300 Series
This post gives a brief introduction to twinax cables, including its definition, application, the difference between active and passive twinax cables, how to tell from them and which to choose when they are needed. However, there isn't a truly visual way to tell the difference between active and passive twinax cables. Therefore when you are requiring a twinax cable, please follow the instructions that I have listed above or you should ask your vendors for expertise suggestion. FS.COM offers a large variety of SFP+ Twinax cables and QSFP+ cables that are well tested and compatible with major brand.

What is an Optical Transceiver?

8. july 2017 at 5:04
Optical transceiver, also known as fiber optic transciever, is a device that uses fiber optic technology rather than conventional electrical wire to send and receive data. It is made of optoelectronic devices, functional circuits and optical interfaces. Optoelectronic devices include two parts: transmitter and receiver. To put it simple, a fiber optic transceiver serves as a photoelectric converter. The transmitter converts an electrical signal into a light signal, and then the receiver converts the light signal into an electrical signal after transmission through the optical fiber. Fiber optics is a rapidly growing field and can communicate complex information faster than conventional methods of transferring data.
optical module
How Does It Work?
The optical transceiver module is composed of both a transmitter and a receiver that are arranged in parallel so that they can operate independently. In the fiber optics, the transmission of data is in the form of light, because the transceiver has electronic components to encode or decode data into light pulses and then sends them to the other end as electrical signals in order to be utilized by an electronic device. The transmitter converts an electrical signal into an optical signal, which is connected with a connector and transmitted through a fiber optic cable. The light entering from the end of the cable is connected to a receiver where a semiconductor detector converts the light back into an electrical signal.
According to the package, there are six common types of fiber optic transceivers popular in the market, namely GBIC, XFP, SFP, SFP+, XENPAK, and X2.

1. GBIC (Gigabit Interface Converter). GBIC is designed for hot-plug. It is an interchangeable product meeting international standards. GBIC optical modules are used widely before SFP package.

2. SFP (Small Form-factor Pluggable). SFP is an upgraded version of the early GBIC module. It features smaller volume and higher integration than GBIC fiber module. It is currently the most popular optical module in the market.

3. SFP+. SFP+ optical module has been upgraded based on SFP with a higher transmission rate, usually up to 8.5G or 10G.

4. XFP. XFP transceiver (10 Gigabit Small Form Factor Pluggable) is a hot-swappable, independent of the communication protocol optical transceiver. XFP is usually used for 10Gbps SONET/SDH, Fibre Channel, Gigabit Ethernet and other applications, but also for CWDM DWDM link.

5. XENPAK. XENPAK is a multisource agreement (MSA), instigated by Agilent Technologies and Agere Systems. It's a 10 Gigabit Ethernet optical transceiver which is independent of transceiver circuits and optical components. It can be plugged into a router or switch. But now XENPAK has been replaced by more compact devices providing the same functionality.

6. X2. X2 transceiver is a 10Gbps modular fiber optic interface intended for use in routers, switches and optical transport platforms. X2 modules are smaller and consume less power than XENPAK modules, but larger and consume more energy than XFP and SFP+ transceivers.
differen types of transceivers
Optical Transceivers are Used in a Variety of Applications
One of the most important attributes of optical transceivers is their ability to be compatible in a variety of communication applications. Most manufacturers choose them because they fit in a small footprint, and they are reliable. Besides, compatibility is one of the most common considerations in fiber optic transceivers. Take SFP fiber optic transceiver as an example, a SFP fiber optic transceiver on a network device (such as a switch, router, media converter, or similar devices) provides the device with a modular interface so that the user can easily adapt to various fiber optic or copper networking standards. They are designed to support SONET (Synchronous Optical Networking), Gigabit Ethernet, Fibre Channel, and other communications standards.

This article briefly tells about what an optical transceiver is, comprising its definition, its working mode, different types according to package and its usage. I hope it may be helpful to you!