Some switches, routers and network cards have pluggable transceiver ports. In common Ethernet equipment, SFP is used for 1 Gbps, SFP+ for 10 Gbps and SFP28 for 25 Gbps. Identify the exact port and supported module before choosing the fiber or copper connection; a matching physical shape alone does not establish compatibility.
What is an SFP Transceiver
The SFP transceiver stands for Small Form-factor Pluggable Transceiver , it is also known as simply “SFP” or “Mini-GBIC”. SFP modules allow us to interconnect different devices that use SFP ports, they are generally used to connect switches or routers to each other through single-mode or multimode fiber optics, there are also SFP transceivers to “convert” this type of port into an RJ-45 port for use the normal and current Ethernet network cable.
This type of SFP modules become a convenient bridge device to use in small spaces, and to make the most of the SFP ports that the equipment has. Among the characteristics of this type of transceivers we have:
- They are compatible with copper and fiber optic media, although fiber optics are generally used, either in single mode or multimode, depending on our needs.
- They can be used in both 1000BASE-T (Gigabit Ethernet) and 10GBASE-T (10Gigabit) networks.
- They are hot-swappable, allowing network engineers to create or swap connections between networks on the fly, there is no need to shut down computers to remove the SFP, although of course we don’t recommend having network traffic traveling through here because we will produce a break in the connection.
SFP transceivers allow us bi-directional data movement with a transmit side (Tx) and a receive side (Rx). For Ethernet connections, these transceivers will simplify bridging of network switches by providing fast copper connectivity without having to configure additional network devices or equipment. In addition, they can also support standards such as SONET, Fiber Channel, GB Ethernet, and Passive Optical Networks (PON).
In the previous photo you can see that we have two fiber optic inputs, one of these fibers will be for reception and the other for transmission, it is very important to place the fibers in the correct position, otherwise the communication will not work. These types of SFP transceivers are the most common, so we must take into account the characteristics of the transceiver itself and whether it supports single-mode or multimode fiber optics. Next, we are going to show you how to choose a transceiver depending on your needs.
How to choose an SFP transceiver
To choose an SFP transceiver we must take into account several aspects, otherwise, we might not get the most out of its performance, and even directly it might not even work correctly. Therefore, we must pay special attention to the following.
Speed
One very important thing to keep in mind is that network hardware vendors offer their own version of an SFP transceiver, which means you’re going to have a plethora of options. In this aspect, one of the most important things that we must do is a classification between SFP, SFP+ and QSFP/QSFP+. As we will see below, these nomenclatures are closely related to speed:
- SFP: they provide a speed of 1Gbps Full Duplex, that is, they are the typical Gigabit networks. These types of ports are widely used by managed switches, and even managed switches aimed at small offices.
- SFP+: They provide a speed of 10Gbps Full Duplex, that is, they are typical 10G networks. These ports are on the rise due to the Multigigabit networks with the NBASE-T standard, in this way, we will be able to interconnect several switches via SFP+ so as not to have a bottleneck or excessive oversubscription.
- SFP28: commonly provides 25 Gbps Ethernet. It is different from the larger QSFP28 form factor. See Cisco’s 25G SFP28 specifications.
- QSFP+: Provides a speed of 40Gbps Full Duplex, they are aimed at datacenters and medium and large companies.
- QSFP28: commonly provides 100 Gbps Ethernet using four 25 Gbps lanes. It is not the fastest transceiver family available.
Before buying an SFP transceiver, we must know what type of SFP the switch or router is using, so that they have exactly the same speed. Generally the switches that support SFP+ (for example) also support SFP, however, we should look at it in the technical specifications to make sure 100%, but it does not make much sense to use an SFP when a port supports SFP+, because logically the speed that we will achieve will be that of the SFP which is 1Gbps instead of 10Gbps.
Type of fiber optic to use
In SFP transceivers, single-mode or multimode optical fiber is generally used, depending on the transceiver, we will have to use one or the other. To know which one we should use, we have to go to the technical specifications of the specific SFP transceiver. Usually multimode fiber optic (multi-mode) is used because it is cheaper, unless you have to make a fiber cable run of several kilometers, in this case you will have to use single-mode fiber optic because we will have a greater distance.
Check the connector and fiber requirements of the particular module. The two D-Link SFP+ examples shown below use duplex LC connections, with one fiber for transmit and one for receive; that does not mean every optical module uses duplex LC. Match the fiber type, wavelengths, reach and compatible module at the other end.
Therefore, we must not only look at the speed, but also if it is singlemode or multimode, and even also at the size of the fibers, which are also defined in the technical specification sheet.
SFP to RJ-45 port
Today there are SFP and SFP+ transceivers that convert the signal to an RJ-45 port to connect an Ethernet network cable. Let’s imagine that we have a switch with 2 10GBASE-T ports and two other SFP+ ports, but we want to connect a NAS server to one of these SFP+ ports. We have two options: we buy an SFP+ card for the NAS, two SFP+ transceivers and fiber optics, or we buy a compatible RJ-45 transceiver and use the copper cable category and maximum length specified by its manufacturer. These types of devices are really useful for these scenarios where we don’t have enough 10GBASE-T ports that we need.
For an RJ-45 module, check supported link speeds, switch compatibility, cable length, power consumption and cooling requirements. There is no fiber cable to select, but speed alone is not the complete compatibility check.
If we buy an SFP then we must bear in mind that we will have a Gigabit Ethernet network, and if we buy an SFP+ we must bear in mind that we will have a high-speed 10Gigabit network, so the equipment should also support (they must have a 10G network).
Other considerations
An important consideration when choosing the right SFP transceiver is that we must be very vigilant if we come across a situation where old and new network devices are mixed. In this aspect, it must be taken into account that most SFP modules accept LC fiber connectors, but this is not always true in all cases.
On the other hand, we must not forget that they are also electronic components, so they are sensitive to environmental conditions. In this aspect we must verify that our transceiver supports the pressure, humidity and temperature of the site that is going to be placed. This can be perfectly verified in the technical specification sheet.
Before buying our SFP transceiver we must check the compatibility between providers so that we can use all our network equipment without problems. Although generally everyone always uses the standards, so we should not have too many problems when using them, but it is better to review it before buying it.