Can A Computer Connected to the PoE Switch?

PoE switches are commonly used in various networks. It can be low-cost unmanaged edge switches with a few ports or complex multi-port rack-mounted units with sophisticated management. When used in small or home networks, many people may wonder if it can be connected directly with a computer. This post will discuss this question in details.

What Are PoE and PoE Switch

Before the discussion, it is necessary to have a basic understand of what are PoE and PoE Switch:


As demands for connection from networking devices such as IP phones, IP cameras and access points increase, deployment complexity and cost rise as well. For less cable usage and investment, Power over Ethernet (PoE) technology is developed to provide both data connection and electrical power to devices through just one Cat5/Cat5e/Cat6 cable.

PoE Switch

PoE switch is a network switch that has Power over Ethernet injection built-in, which can transmit both power and data through an Cat5/Cat5e/Cat6 Ethernet cable at the same time. This kind of switch makes it easy for different sectors to deploy powered devices like VoIP phones, wireless access points and IP surveillance cameras in challenging places like ceilings, walls, outdoors, or wherever electrical outlets are not easily available.

poe switch connection

Can A Computer Connected Directly to the PoE Switch?

As shown below,PoE switch usually have the same RJ45 port as a computer. So many people will think they can be connected directly. But do not forget that PoE switch may also transmit electrical power through the RJ45 port and Cat5/Cat5e/Cat6 cable to the computer. Then can a computer be connected directly to the PoE switch? This is largely depend on the switch you have:

poe switch

If you have a PoE switch that conforms to 802.3af (the PoE standard) or 802.3at (the PoE Plus standard) and doesn’t claim to be “passive”, you can definitely connect your computer with it. This is because this kind of PoE switch has the function of PoE detection which is designed to avoid damage to non-PoE devices. In other words, when you connect other network devices to your PoE switch, it will communicate with the these devices whether they need power or not. Power is only injected if and when this negotiation is successful. Ethernet devices such as phones and access points are detected by the switch as accepting PoE and will receive the additional power feature from the PoE switch/port. Whereas a computer and other non-PoE devices will not be detected as having PoE capability and will just use the data communications features of the port.

computer connect to poe switch

However, there exists a class of PoE switches, usually referred to as “passive” or “always on”, which supply power without PoE detection. Why would anyone do this? Because this kind of PoE switch is significantly cheaper. Whether it damages your device depends on the voltage of the passive PoE switch and your devices. For a computer, it may be damaged for excessive voltage or current.


PoE switch is a dedicated device that contains multiple Ethernet ports to provide power and network communications. It is usually used in NVR/IP camera networks. For small or home networks, if you want to connect a computer to the PoE switch, make sure your switch follows the standard 802.3af or 802.3at PoE requirements. So can you connect a computer directly to your PoE switch?

How to Light a DWDM Ring Beyond 10G?

Network layout nowadays is no longer limited by old rules created for early Ethernet networks. The technology and infrastructure devices available currently allows for different network topologies, including bus, star, ring and mesh networks. Each of them has its benefits and drawbacks and can be combined to suit application needs. This article emphasizes on the DWDM ring network configuration, illustrating the approaches to build a fiber ring beyond 10G.

What Is a DWDM Fiber Ring?

A fiber ring refers to the network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node. A ring configuration is designed to withstand a single failure. If there happens to be a failure, the system automatically reconfigure itself.

Similarly, a DWDM ring network includes a fiber in a ring configuration that fully interconnects nodes. Two fiber rings are even presented in some systems for network protection. This ring DWDM topology is commonly adopted in a local or a metropolitan area which can span a few tens of kilometers. Many wavelength channels and nodes may be involved in DWDM ring system. One of the nodes in the ring is a hub station where all wavelengths are sourced, terminated, and managed, connectivity with other networks takes place at this hub station. Each node and the hub have optical add-drop multiplexers (OADM) to drop off and add one or more designated wavelength channels. As the number of OADMs increases, signal loss occurs and optical amplifier is needed.


How to Create a DWDM Fiber Ring Beyond 10G?

Assuming to build a higher than 10G optical ring using two strands of dark fibers, all nodes in this ring configuration are less than 10km apart and there are 8 nodes in total. Here we illustrate the options for achieving a DWDM ring beyond 10G.

20G Fiber Ring

For a 20G ring, the configuration is rather simple. There is no need for an OADM or Mux/Demux, it is recommend to use an Ethernet switch with two SFP+ ports and a pair of BIDI SFP+ optics.

Items Description
S5800-48F4S High Performance Data Center Switch (48*1GE+4*10GE)
10GBASE-BX SFP+ Generic Compatible 10GBASE-BX SFP+ 1270nm-TX/1330nm-RX 10km DOM Transceiver
10GBASE-BX SFP+ Generic Compatible 10GBASE-BX SFP+ 1330nm-TX/ 1270nm-RX 10km DOM Transceiver
40G Fiber Ring

There are three options for creating a 40G DWDM ring.

1. Use a switch with QSFP+ ports, and using QSFP+ optics in accordance. This can be the most cost-effective option for 40G if you have no future plan for more than 40G on the ring.

Items Description
S5850-48S6Q High Performance Data Center Switch (48*10GE+6*40GE)
40GBASE-LR4 Generic Compatible 40GBASE-LR4 and OTU3 QSFP+ 1310nm 10km LC Transceiver for SMF

2. Use four 10G SFP+ optics and a CWDM OADM. You could even scale up to 18 channels giving you a 180G ring if you were use all 18 CWDM channels and had that large of a OADM or Mux/Demux. First four channels with lower cost SFP+ optics, wavelength 1270nm through 1310nm. Then the next 14 channels 1350nm to 1610nm adopts SFP+ with relatively higher cost. You would need a SFP+ port per channel on both ends, and a passive CWDM OADM.

Items Description
CWDM OADM Single Fiber/ Dual Fiber CWDM OADM, East and West
10GBASE-LR SFP+ Generic Compatible 10GBASE-LR SFP+ 1310nm 10km DOM Transceiver
10GBASE-ER SFP+ Generic Compatible 10GBASE-ER SFP+ 1550nm 40km DOM Transceiver

3. Use 10G DWDM SFP+ optics and a DWDM OADM. You can choose less expensive 100Ghz optics that have up to 40 or 44 channels, or the expensive 50Ghz optics that can reach up to 80 or 88 channels.

Items Description
DWDM OADM Single Fiber/ Dual Fiber DWDM OADM, East and West
10G DWDM SFP+ Generic C40 Compatible 10G DWDM SFP+ 100GHz 1545.32nm 40km DOM Transceiver
10G DWDM SFP+ Generic H50 Compatible 10G DWDM SFP+ 50GHz 1537nm 40km DOM Transceiver
100G Fiber Ring

As for a 100G fiber ring, you can count on Ethernet switches that have 100G QSFP28 uplink ports, along with 100G QSFP28 optics. This would allow a 100G connection each way around the ring.

Items Description
S5850-48S2Q4C Carrier Grade 100G-uplink Switch (48*10GE + 2*40GE + 4*100GE)
100GBASE-LR4 Generic Compatible QSFP28 100GBASE-LR4 1310nm 10km Transceiver

Fiber ring enables more reliability and survivability: if a single link failure should occur – the traffic can simply be sent the other way around the ring. With the pervasiveness of Ethernet technology, the ring architecture is widely adopted to construct a Metropolitan Area Network (MAN), Metro-Ethernet service and school district that uses municipal fiber pathways. Several options for creating fiber ring beyond 10G are presented, along with the optical components needed. Hope this could be informative enough.

40G vs 100G: Which One Is Worth the Investment?

Today, the trend for high-speed data transmission and high-bandwidth is overwhelming. Some years ago, people had witnessed upgrading from 10Mbps Ethernet to 100Mbps Ethernet. And the migration from 1G to 10G was happened not very long ago. But now, whether you believe it or not, prepared or not prepared, 40G and 100G have already on the way. To upgrade to 40G or skip it and directly migrate to 100G has become a question for many data center mangers and IT engineers. Here, in this article, you may find some clue you want.

The Rise of 100G

To begin with, it has to be made clear that the market trend is 100G Ethernet, which will eventually become the mainstream in the future. The strong demand in 100G Ethernet is being driven by cloud services and hyper-scale data centers. And there is a demand for lower-priced 100G pluggable transceivers from data center customers. Currently, the market transition to 100GE is in full swing, fueled primarily by the seemingly insatiable need for networking bandwidth by hyper-scale data centers and cloud services. As it has been shown in the picture below, 100G Ethernet transceivers will exceed 15 million units a year.

100G market

This tremendous growth in deployments by a small number of key customers, together with a large number of suppliers competing for these orders, will undoubtedly drive down the cost of 100GE modules rapidly. It is predicted that the cost of 100G transceiver is expected to decline by 75% in the next couple of years. In the meantime, Facebook has publicly set a target cost of $100 for a 100G transceiver with a reach of less than 2km. While the Facebook target appears to be years away, we believe that a 70% cost reduction in 2 years is possible. By that time, the 100G transceivers will be more affordable.

Why not 40G?

If you ask me why 40G Ethernet will be obsolete? The short answer is “cost”. From the technical point, The primary issue lies in the fact that 40G Ethernet uses 4x10G signalling lanes. On UTP, 40G uses 4 pairs at 10G each. Early versions of the 40G standard used 4 pairs, but rapid advances in manufacturing developed a 4x10G WDM on a single fiber optic pair. Each 40G SFP module contains a silicon chip that performs multiplexing so that the switch see 40 gigabits in and 40 gigabits out. It’s similar to Coarse Wave Division Multiplexing when using fiber. When you buy a 40G cable or QSFP, you are paying for the cost of the chip and software, plus the lasers, etc. When using 25/50/100G, the “lane speed” is increased to 25 gigabits per second. For 100G Ethernet, there are four 25G signalling lanes. It’s cheaper to buy 100G with four lanes rather than 40G with a four-lane MUX.


Scale up to 100G with FS 100G Optics Solution

As one of the leading providers in optical communication , FS provides customers with 100G optics that are manufactured at the highest quality of standards in the industry, including QSFP28, CFP, CFP2, CFP4, 100G patch panels, 100G switches, etc. Part of the products are listed as follow:

Model ID Description    Price


Juniper JNP-QSFP-100G-SR4 Compatible 100GBASE-SR4 850nm 100m Transceiver

   US$  269


Cisco Compatible QSFP28 100GBASE-SR4 850nm 100m Transceiver

   US$  269


Juniper Networks CFP-100GBASE-SR10 Compatible 100GBASE-SR10 850nm 150m Transceiver

   US$  1,500

100G Ethernet are racing to market and will finally takeover the 40G market. Don’t hesitate to migrate your network to the 100G Ethernet to embrace the future technology.

100G Coherent CFP Modules for Metro Network Applications

Due to the rapid increase of communication traffic, the requirement for core networks to handle larger capacity and longer distance on their links has led to a spread of 100G optical networks. For this environment, service providers are adopting coherent transceivers for their 100G DWDM backbone applications. Until recently, coherent CFP/CFP2 DWDM optical transceivers had been the technology of choice for transporting 100G traffic over long distances or as part of a DWDM network. This paper will mainly discuss 100G coherent CFP modules for metro network application.

Coherent Technology: Making 100Gb/s Available

Moving from 10Gb/s to 100Gb/s line speeds comes with technical challenges. Coherent technology had been investigated for optical transmission since the 1980s as a means to increase transmission distances. By 2010 to 2011, the technology had reached a point of market maturity. At this time, it could genuinely allow 100G coherent signals. This result forms the foundation of the industry’s drive to achieve transport speeds of 100G and beyond, which helps to deliver Terabits of information across a single fiber pair at a lower cost. Until now, coherent technology has been mainly deployed in long-haul networks, and it is now starting to be deployed in metro networks.

Capacity Enabled by Coherent Technology

Figure 1: Capacity Enabled by Coherent Technology

Metro Requirements for 100G

100G rates were initially deployed in the long-haul and core networks. In the Metro, 10G is still the most dominant rate. In the coming years, the trend toward aggregation into 100G in the larger metro areas or data center connectivity will become more significant. The metro covers a broad range of distances: the metro regional and metro core cover distances of 500-1000 km and 100-500 km respectively, while the metro access links are generally point-to-point connections shorter than 100 km. Although these distances are shorter than long-haul links, the characteristics of metro network- including flexible protocol support, higher granularity of signal rates and increased number of nodes- create the requirements for 100G rates.

Three Types of Metro Network

Figure 2: Three Types of Metro Network

100G Coherent CFP Modules for Metro Network Applications

While metro and long haul applications have different requirements, the lower-cost 100G technology for the metro is demanded for service providers. To achieve this feat, equipment vendors consider coherent CFP as the ultimate solution for metro 100G deployments. Coherent CFP 100G can overcome optical transmission impairments and still achieve acceptable performance.

Scenario 1: 100G Multi-Channel DWDM Networking

An Architecture of Coherent CFP for 100G Deployment

Figure 3: An Architecture of Coherent CFP for 100G Deployment

As shown in Figure 3, since the 100G rates are more susceptible to dispersion, they would require extra dispersion compensation and optical power boost. Thus an extra 100GHz DWDM multiplexer is first used to combine all the 100G rates together followed by a combined dispersion compensation and amplification stage. This architecture conveniently supports the ‘pay-as-you-grow’ model for service providers. When the bandwidth is exhausted, the existing legacy 10G channels may be seamlessly interchanged with 100G services. The same remaining components can even be reused to extend the data rate up to 2.4 Tb/s.

This scenario would require 24 differently colored CFP 100G transceivers deployed together with the already existing 48 channel 100 GHz DWDM multiplexer. All the 100G services are first multiplexed together such that only one dispersion compensation and amplification stage suffices. Clearly, such a network architecture provides higher density with capability to reuse existing infrastructure with flexibility while remaining cost friendly.

Scenario 2: 100G Distance Extension Solutions

100G Coherent DWDM Transport by Using SFP+ OEO Transponder

Figure 4: 100G Coherent DWDM Transport by Using SFP+ OEO Transponder

In this scenario, the switch was tested with SFP+ OEO transponders for simple distance extension solutions. The 100G output signals from the switch are converted to DWDM signals that can be transmitted over longer distance. The solution removes the distance limitations by using a coherent CFP module to connect the output signal to the line fiber and carry the signal over longer distances.

As shown in Figure 4, to achieve higher cabling density with Cisco CFP 100G optics, the architecture mixed a 16 channels dual fiber DWDM Mux Demux which can be used for CWDM/DWDM hybrid and 8 channels dual fiber CWDM Mux Demux, by adding MTP harness cable and WDM SFP+ OEO converter to transfer the regular SR wavelength to DWDM wavelengths. Therefore, building a long distance 2500km DWDM networks in coherent CFP 100G transceiver and cost effective way will be achieved.


Coherent CFP 100G transceivers provide cost-effective electronic equalization of fiber impairments and extensive performance monitoring capabilities that enable easy installation and network management. These benefits help service providers meet bandwidth demand growth while reducing the total cost of ownership.

10G Ethernet: 10GBASE-T or 10G SFP+?

10GBASE-T has been available as an add-in card in servers, switches and network interface cards (NICs) since 2008, and it has been widely adopted since 2012. It is highly praised for its advantages which include lower cost than 10G fiber, cost-efficiency of using existing MAC (Media Access Control), easier migration from 1GBASE-T to 10GBASE-T, and the ability to deliver PoE (Power over Ethernet). Does that mean we should all turn to use 10GBASE-T now? And what are the 10GBASE-T cable requirements? Every application differs, let’s see some specific cases in short-reach applications.

10G copper or fiber

Where Can 10GBASE-T Be Used?

When building a 10G network, the link can be either copper or fiber. If using 10GBASE-T cable, the places are required to be in the Data Center or Horizontal areas (in building, including wiring closet). But it is not suited for Vertical (riser links) applications within building, or campus & metro applications.

Cases for 10G Ethernet Connections

Case 1: Connecting a switch with only SFP+ ports to a switch with only 10GBASE-T ports.

10GBASE-T cable 1

When the distance of these two switches are less than 30 m, which is the max. link distance for 10GBASE-T copper SFP+ module, the desired connection for them can be made by using a 10GBASE-T module and a Cat6a cable. It’s the simplest solution for this case.

Case 2: Connecting two switches with only 10GBASE-T ports.

10GBASE-T cable 2

Connecting two switches with all 10GBASE-T ports are as simple as placing the plug into its mating socket. One Cat6a Ethernet cable is born for such a connection and that is why it is called the standard 10GBASE-T cable. By using a Cat6a cable for 10GBASE-T, it can reach up to 100m distance.

Case 3: Connecting two switches with only SFP+ ports.

10GBASE-T cable 3

There are three choices for connecting two complete SFP+ switches. For distances between 30 m to 400 m, it is recommended to get two 10GBASE-SR SFP+ modules for each switch and connect them with a OM3/4 LC duplex multimode fiber patch cable. The second is to use two 10GBASE-T SFP+ modules and Cat6a cable. If the link is as short as 7 m, it is suggested to use a low cost 10G SFP+ direct attach copper (DAC) cable.

Case 4: Connecting switches with both SFP+ and 10GBASE-T ports.

10GBASE-T cabling 4

When the two switches both have SFP+ and 10GBASE-T ports, you will be free to use methods from Case 1 to Case 3 above. But in my experience, it would be better to use the 10GBASE-T copper ports first, and save the SFP+ ports for possible future connections to an optical network for longer transmission distance.

Words in the End

10GBASE-T is taking its way to being more extensively used on network gears without a doubt, and cost for deploying 10GBASE-T equipment will be lowered with its wide spreading. Know the requirements for 10GBASE-T cabling is necessary for correctly choosing between 10GBASE-T or 10G SFP+ in practical usage. After all, cost-efficiency is very important in large-scale deployment.