Knowledge in one place.
Tatiane Figueiredo – Training Instructor
The decision to choose a transceiver is not always something quick and easy, as it involves several factors that need to be observed by the network analyst, ranging from physical characteristics, distance of the link to the model of equipment and technology that will be used. The idea of this article is to help you make the best choice.
However, first of all, let's start with the name. Some call them optical transceivers, others call them modules, we also find GBIC – Gigabit Interface Converter and Mini GBIC. Regardless of the nomenclature used, its objective is to transform or convert two different types of signals, for example, an electrical signal into an optical signal, so that it can be transmitted and received.
Thinking about the literal translation into Portuguese, transceiver is the combination of a transmitter and a receiver in a single device. Its use began a long time ago, with the GBIC, which is a larger transceiver, with its own standard and very similar to the image below. Note that the fiber connectors are wider than current ones and also take up a reasonable amount of space on the equipment.
Over the years, the technology has evolved, its size has reduced and its transmission capacity has increased along with the equipment. The applications where a transceiver can be used are as varied as possible, from 10Mbit/s links to many tera bit/s.
And from now on, we highlight ten points that are important to facilitate the choice of the best transceiver for your application.
1 – Technology
The need to deliver broadband to residential customers, dedicated links to corporate customers and the use of servers with the OCP concept – Open Compute Project in Datacenters, has increasingly encouraged the use of networks.
For all these applications, we find several technologies that can provide support, such as Ethernet and why not also the adoption or use of GPON and XGSPON, to provide access to all services?
And, we cannot leave out a whole legacy that also exists within the major telecommunications players, energy operators and Internet providers such as SDH - Synchronous Digital Hierarchy and PDH - Plesiochronous Digital Hierarchy.
For each model of equipment and technology, we have a transceiver, which follows the standards defined by the regulatory agency and is the first factor to be observed when choosing a network analyst.
2 – Encapsulation Standard - Form Factor
The transceiver encapsulation, called Form Factor, is directly related to the type of technology, the equipment used and the speed required. All parameterization follows the definitions established by the MSA - Multi-Source Agreement group, thus allowing compatibility and interoperability between suppliers, which complements the standards of the IEEE - Institute of Electrical and Electronics Engineers.
In the table below we check some types of encapsulation.
Datacom transceivers can be inserted and/or removed with the equipment energized, as they have the hot pluggable feature.
3 – Typical range
The operating distance involves criteria such as the type of fiber to be used, the classification of the transceiver whether short or long range and its power budget, which is simply defined as the result of the minimum transmission power minus the receiver sensitivity (OP = Ptx – Sorx).
With the increase in bandwidth, the power budget must also consider factors such as chromatic dispersion and signal-to-noise ratio, in addition to the traditional safety margin. Remember, the power budget needs to be greater than the attenuation or losses existing on that medium or link. If you have any questions about how to calculate the power budget, read our article on this subject.
Regarding the scope, the classification is observed in the following table.
Attention when testing long-range transceivers in a laboratory environment, we must always check the saturation threshold (RX overload) in the module description, and if necessary use the appropriate attenuator so as not to cause problems or burn out.
All DATACOM products with 100GbE interfaces have Host FEC functionality.
4 – Type of fiber and connector
Singlemode or Singlemode fiber is designed to propagate the signal in only one direction or by a single ray of light. Used for long distance applications and are categorized into OS1 (up to 10km) and OS2 (up to 200km) and have different characteristics.
Multimode or Multimode fiber allows the propagation of the signal in several different directions simultaneously and is used to cover shorter distances. Due to its larger diameter core, alignment becomes easier in case of splices. They are categorized into OM1, OM2, OM3, OM4 and OM5.
As for the connectors, there are several types, but for Ethernet transceivers, the LC - Lucent Connector type is used and for the PON and SDH/PDH universe, the SC - Standard Connector type.
Optical fibers and their respective connectors deserve special attention regarding dirt and contamination, as they can present a great attenuation, putting at risk the dimensioning of an optical network.
For the 40G (QSFP+) and 100G (QSFP28) Ethernet interfaces, we also find the MPO type connector – Multi-fiber Push On.
5 – Number of fibers
The unidirectional type transceiver uses one fiber for the transmission and another one for the reception of the optical signal. The link must be formed with transceivers of the same model and wavelength.
The bidirectional type uses a single fiber for transmission and reception. The link is formed by transceivers of different wavelengths, as they transmit on one length and receive on another.
6 – Polishing
Polishing is the type of finish that the ferrule receives at its end or surface, so that light propagation occurs properly in a connector.
The connections differ according to the type of polishing and can be PC - Physical Contact, UPC - Ultra Physical Contact and APC - Angled Physical Contact.
It is not recommended to combine types of polish, ie a UPC polish with an APC, as it causes greater attenuation in the optical signal.
Datacom transceivers are PC-type polished and meet INF-8074i (SFP MSA), SFF-8431 (SFP+ MSA), SFF-8436 (QSFP+ MSA), SFF-8679 (QSFP28 MSA), and IEC/EN 60825- 1 (LASER safety).
7 – Technical Specifications
The transceivers have a range of technical specifications that help in the construction of the power bugdet or power budget for the desired link, in the appropriate choice when referring to distance and also in the performance of the network analyst to investigate possible failures. We will use a 40G Datacom transceiver as an example.
In your description we find:
Detailing the technical specifications we have:
Transforming the transmit and receive power information from the table above to a graph, we observe:
The optical module will transmit between the minimum value of -2.70dBm and the maximum value of +4.50dBm. Through the CLI of the equipment with the DmOS operating system, this information can be consulted through the syntax show interface transceivers digital-dignostics, as seen in the image below.
Datacom uses feedback technology (closed loop), where a sensor is tuned to the same transmit frequency and measures everything being transmitted. If the reading is above or below the expected, the transmitter current will be changed to stay within acceptable parameters. This operation compensates for the degradation that occurs over time and also for changes in the operating temperature.
The overload parameter refers to the highest optical power level that the device can receive or detect and the sensitivity parameter, the lowest optical power level to be received by the device.
When we talk about power budget, we need to keep in mind that there are different losses or attenuations for each of the wavelengths used (850nm, 1330nm, 1490nm, 1550nm), that the attenuation of multimode fiber is greater than that of singlemode, in addition to all connectorization and splicing.
You can view all models and specifications of Datacom's optical modules on our website: Optical and Electrical Transmission Modules.
8 – Temperature classification
The environment where the equipment and the transceiver will be installed must also be taken into account, especially when addressing the temperature issue. Datacom offers extended temperature options, up to 85C.
9 – Colored transceivers
The so-called color transceivers are dedicated for use in DWDM solutions, which operate from channel 17 to 61. The choice of “color” or wavelength is related to the channel number used according to the multiplexer/demultiplexer.
10 – Tunable or Dual Density Transceiver
The so-called tunable transceiver has coherent technology, which allows it to operate in long-distance solutions without the need for amplifiers, as it makes better use of the optical spectrum. It can also be used in DWDM applications, as in the following topologies.
Datacom has the QSFP-DD 100GE DWDM Coherent transceiver, and its main features are:
*DD = Dual Density/Dual Density, which allows twice the modulation capacity.
It is also possible to use the passive 32-channel DWDM – DM936 32CH19, with the objective of transmitting 32 channels of 100Gb, totaling 3.2Tbps in a single pair of fibers, up to a distance of 80km without amplification. With amplification, a range of up to 152km is possible.
See more details about this solution in the following articles: 100Gb aggregation switch for long-distance links and Coelho Tecnologia and Ampernet invest in DM4770 for long-distance links.
Datacom has a complete portfolio of transceivers for the most diverse applications, as well as equipment that can be positioned from the access to the network core. See the models on our website.
We emphasize that Datacom has a complete structure in its headquarters where on-site training is offered (check availability with the commercial team), as well as an online training platform (DATACOM EAD). In the trainings, it will be possible to configure different topologies and application scenarios, in addition to being able to count on the help of our professionals in a series of good practices that will greatly help in the operation of your network.
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For questions and request for proposal, please contact Datacom's commercial team. We are available to assist you in choosing the most suitable product for your needs.
