Archive | November 2017

Power over Ethernet Switch: Passive PoE Vs Active PoE

Power over Ethernet (PoE) is a technology for wired LANs. This allows a single cable usually Ethernet cable to provide both data connection and electric power to devices such as IP cameras, NVR recorders, wireless access points, etc. A PoE switch, compared with other Gigabit network switches, has power over Ethernet injection built in. This feature allows end-user to power PoE capable devices without the need for a separate power supply or the need for an electrical outlet near the powered device. If you have read about the how-to-understand-poe-and-poe-switches, you must know clearer about the difference between PoE and PoE+ switches. However, today’s article will help you understand active PoE and passive PoE.

What is PoE Switch?

As mentioned before, a PoE switch not only supply power to devices but also carries network connection. In general, a PoE switch usually contains multiple Ethernet ports, e.g. a PoE switch with 8 ports, PoE switch with 16 ports, 24 ports PoE switch, or PoE switch with 48 ports. If you are looking for PoE switch to cover all your devices, it’s important to check the port number first.

8-port PoE managed siwtch

The following image shows the 8-port PoE managed switch.


Passive Power over Ethernet vs. Active PoE

To safeguard a voltage range, the Power over Ethernet devices must communicate according to established procedures. In simple terms, active PoE refers to any type of PoE that negotiates the correct voltage between the switch and PoE-powered device. Passive PoE does no such negotiation, and as such is always sending electric current out over the Ethernet cable at a certain voltage regardless of the device it’s going to.

Active PoE

If your PoE switch uses 48V 802.3af or 802.3at standard, it is considered to be active PoE. The power supply unit inside the active PoE switch usually tests the connection before providing the supplying voltage, meaning that PoE switch will check the power coming in, and if it doesn’t meet the device requirement, it won’t power up.

Passive PoE

Passive PoE refers to any devices using PoE that is not 802.3af or 802.3at. Unlike active PoE switch, In passive PoE, no negotiation takes place between the two devices, but instead the known cable layout is used from Standard 802.3af, mode B. Therefore, it is extremely important to know what PoE voltage your devices requires before plugging in the Ethernet cable and powering it up. If you connect the wrong voltage, you may cause permanent electrical damage. Passive PoE is like plugging a 120V appliance into a 240V outlet, but with devices than cost much more than a simple toaster.


The big advantage of Power over Ethernet switch is that it allows greater flexibility in locating devices, as you don’t have to be situated near a power source—power is carried to them right in the Ethernet cable. That also frequently results in significantly lower installation costs, especially where many Access Points must be setup. The difference between Passive PoE and active PoE switch is quite obvious. For more, you can go through previous articles.


The ABCs of Tunable SFP+ & Tunable XFP DWDM Optics

Tunable XFP transceiver and tunable SFP+ transceiver are the hot-swap DWDM Tunable optics used in 10Gbps SONET/SDH, Fibre Channel and Gigabit Ethernet applications. Tunable DWDM transceiver is a unique device which allows customers to set the channel that the laser emits. Generally, the tunable optics is for C-Band 50GHz, starting from channel 16 up to 61 (depends on the manufacturer of the Router/Switch and which channels it supports). This article will shed light on the revolutionary Tunable DWDM transceivers.

Tunable Optics Gives You a lot of Flexibility

The introduction of these new optical components enable telecom, datacom, and enterprises operating a DWDM network to significantly reduce their sparing costs, improve their operational efficiencies, and turn up new customers or circuits in a fraction of the time it would normally take.

  • SFP+ Tunable Transceiver

10G DWDM tunable SFP+ transceiver is compliant to SFP+ MSA. This flexible transceiver can be tuned to any one of C-band channels with 50GHz spacing, supporting data rate of 10 Gbit/s-11.3 Gbit/s. DWDM tunable SFP+ transceiver operates over LC singlemode fiber for a max linking length of 80km.

Tunable SFP+ transceiver

  • XFP Tunable

Tunable XFP can be tuned from channel 1561.83 to 1530.33. This tunable optic has a reach of around 80km depending on the fiber quality and the mux type. The Cisco version is the “ONS-XC-10G-C” and there are more brands like Juniper, Ciena, Extreme and Brocade which are offering these optics.

Tunable Optics in DWDM networks

Typically, a DWDM network is set up with fixed wavelength DWDM transceivers. The laser hardware inside a DWDM optics has a fixed wavelength for transmitting over a DWDM channel. That means if one channel fails, you need this specific channel device in your spare part stock.

10G DWDM Tunable SFP+ & DWDM Tunable XFP+

A DWDM network can be used with 40 channels, so you need to stock 40 fixed wavelength DWDM modules. However, with Tunable SFP+ or XFP modules, you have the possibility to reduce OPEX or be flexible in terms of spare parts and stock.

To build a well-organized DWDM networks, you are supposed to scale up a wavelength planning for ordering the right types. There needs to be a documentation which specific channel is already in use at different locations. By the use of Tunable module, you just need to count the unused DWDM ports instead of each wavelengths and order the needed amount of only this one product. This reduces a lot of complexity and makes the planning so much easier.

Three Tips Before Using Tunable Optics

More expensive Than Fixed Wavelength DWDM Optics

Tunable transceivers renown as spare-optics, provide the flexibility to customers and reduce the amount of spare optics you need r to hold in stock. Owing to the special tunable laser in tunable optics, they are between two and four times more expensive than the regular static DWDM optics.

The following figure shows the cost comparison between DWDM SFP+ and Tunable SFP+ optics from FS.COM and Flexoptics.

DWDM SFP+ Vs Tunable SFP+

Some Switches/Routers Do Not Support CLI Command

In fact, the Tunable XFP/SFP+ can be tuned in different ways. It is such a new technology that currently, most high-end devices make it possible to tune over the command line interface, but not every switch or router is capable of this. For example the ASR9000 and the MX80 can be used for this but the EX4200 series from Juniper does not support this, which is indeed the biggest challenge in the tuning of these optics.

Not the mainstream in Metro & OTN Networks Now

Metro Ethernet network mainly consists of IP nodes, e.g. switches and routers interconnected by numbers of 10G interfaces. Network installers usually implement DWDM connectivity by using colored WDM transceivers in 10G ports and directly connect to dark fiber to line through passive optical multiplexer. According to the above description, only few of the IP node (optical switches and routers) support tuning wavelength of CLI commands.

And as for Optical Transport Networks (OTN), it is focusing on carrying payload and multiplexing, switching and supervising networks in optical Layer 1 domain. But how about tunable optical transceivers in OTN network..? Still, the mainstream is conventional fixed wavelength DWDM transceivers.

This compact device allows end-users to self-select any DWDM channel for each tunable SFP+ transceiver, tune it, and set it as a fixed-channel DWDM optic on demand. The whole DWDM sparing costs can be substantially reduced through the use of Tunable optics. Therefore, it would be popular in the near future.


In fiber optical networks where fixed DWDM channel XFP/SFP+ transceivers are currently used, changing to Tunable XFP/SFP+ transceivers offers the potential for large inventory stock reduction since all wavelengths can now be covered with one transceiver module. Tunable module will make itself a desirable choice to replace the fixed wavelength used in many networks.

10GBASE-T SFP+ Copper Module up to 200m – Is It Possible?

The introduction of 10gb SFP+ copper modules made people rethink 10G optical network, and was treated as the thrive of copper cabling. Vendors like Cisco, HPE, Amazon, prolabs and FS.COM provides 10GBase-T SFP+ module around $300 with 30m linking length and 2.5W power consumption, but it is a controversial and expensive copper devices. Today’s article decodes the 10GBASE-T SFP+ copper modules that can support up to 200m, and auto-negotiate to 1G, 2.5G, 5G data rate.

beautiful view

10GBASE-T Copper Can Auto-negotiate to 5G, 2.5G, 1G, 100Mbps, 10Mbps

10GBASE-T SFP+ transceivers, terminated with RJ45 connectors, allow 10G bandwidth over existing infrastructure and reuse Ethernet cables. However, owing to the high price and unstable performance, 10GBASE-T is not usually the type when competing with cost-effective DAC cables, and reliable SFP+ fiber modules. Customers use ideally DAC twinax cables for shorter reach transmission, or if they need longer distance, they would go for fiber SFP+ or SFP+ AOC cables.

10GBASE-T can auto-negotiate to 5G, 2.5G, 1G, 100Mbps, 10Mbps data rate, which is the highlight of this product. For 2.5GBASE-T/5GBASE-T networks, you can use this module.

Is It Possible to Support up to 200m?

The regular 10G copper modules launched by fiber optic vendors are specified to support up to 30m over Cat6a/Cat7 cables. According to wikipedia, 10GBASE-T, or IEEE 802.3an-2006 standard is released to provide 10G connections over unshielded or shielded twisted pair cables, with distances up to 100 meters (Cat6a), 55m (Cat6). What’s more, 10GBASE-T cable infrastructure can also be used for 1000BASE-T allowing a gradual upgrade from 1000BASE-T using auto-negotiation to select which speed to use.

Therefore, 10GBASE-T copper modules can auto-negotiate to lower data rate e.g. 10 Mbps, 100 Mbps, 1 Gbps, 2.5 Gbps, 5 Gbps, 10 Gbps. A new type 10GBASE-T SFP+ from Mikrotik can support all the above five data rates over different link length. The max power consumption is 2.4W, and can only be used in SFP+ ports.

Mikrotik 10Gig SFP+ copper

Table 2 shows the 10GBASE-T Cable Types and max supported lengths.

According to the above table, we can see that it can reach up to 200m over 1000BASE-T network, or at 2.5G 200m using Cat6a STP cables. So please be mindful of where you want to use them.

Isn’t 10GbE Copper Power Hungry?

10GBASE-Cu DAC twinax cables consumes 4-8 Watts power during the operation, while SFP+ 10GBASE-T copper modules draw less (2.5W), and it is not a standard compliant transceiver, hence the shorter distance of 30m. But if dig deeper, we will find that if there were more power, they would use it. So, in order to be fully compatible with 10GBASE-T standard, you need more power.

10GBASE-T SFP+ Module

Today’s fiber SFP+ modules like 10GBASE-SR draw less than 1W, much lower than the 5 to 8 Watts per 10GBASE-T port. Drawing an increase in power by a factor of 5 can seem like an expensive upgrade cost. When factored against servers that can draw up to 1000W or more, the overall proportion is low. For small to mid-sized (SMB) organization switch-server installations, short reach cable runs of less than 45 meters will apply and use even less power and therefore cost less.

Future-Proof 10GBase-T Technology

Although fiber becomes popular with the benefit of delivering flexible cabling, lowest latency, many IT departments still adopt copper cables for switch-to-switch or switch-to-server connections in 10G Ethernet applications. 10GBase-T Copper SFP+ is backward compatible with Fast Ethernet and Gigabit Ethernet and can automatically negotiate to lower speed connections. More importantly, 10GBase-T provides a cost-effective method for migrating from your current network to 10G Ethernet by utilizing your existing RJ-45 copper short connections. Amazon, FS.COM, Prolabs, Mikrotik and HPE supply 10GBAST-T copper transceivers, you can get what you want from them.