Half Duplex vs. Full Duplex, Symmetrical & Asymmetrical Bandwidth, Latency, Crosstalk, and More

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Half Duplex vs. Full Duplex

When evaluating Power over Ethernet switches, it’s important to understand full duplex and half duplex. When a switch is connected to an IP device, information is transferred in both directions. The switch sends information to the endpoint device and vice versa. Full duplex (FDX) switches allow for the simultaneous transmission of information between the switch and the endpoint. In a half duplex (HDX) system, communication flows in one direction at a time.

For example, let’s say two files need to be exchanged. One file is at the head end (switch end), and the other is at the endpoint. The two files are 150Mb in size, and the switch can deliver 100Mbps, full duplex. In this scenario, it would take 1.5 seconds to transfer BOTH files to their destinations.

Let’s now analyze this scenario from a half duplex perspective. In this situation, the first file must be transferred before the other can be sent. Assuming the same file size and the same delivery of 100Mbps, the time required to transfer the two files is approximately doubled. Both files are transferred at the same speed, but not simultaneously, creating a very different overall experience.

The above example is a bit of an oversimplification of a real-world example. Full duplex and half duplex switches will vary in performance. Collision management, the directionality of traffic, the number of endpoints in a network, and cable length/type will also have an impact. It is not uncommon to see performance of less than half of a full duplex network.

A half duplex system can be compared to the “push-to-talk” nature of a walkie talkie. When the button is pressed, the receiver is turned off, and the transmitter is activated. When the button is released, the transmitter is turned off, and the receiver is turned back on. The device cannot transmit and receive simultaneously. A full duplex system is like talking on the telephone, in which both parties can speak and listen at the same time.

The entire NVT Phybridge CHARIoT Series of products are full duplex switches. Data is transferred simultaneously from the switch to the endpoint, and vice versa, to ensure optimal network performance and speed.

Symmetrical vs. Asymmetrical Bandwidth

Like full duplex and half duplex, symmetrical and asymmetrical bandwidth will play a significant role in the network’s overall performance and reliability. A switch that can deliver 100Mbps symmetrical, full duplex can transmit and receive at a rate of 100Mbps. Even if it is full duplex, a network switch with asymmetrical bandwidth cannot send AND receive at 100Mbps. Asymmetrical switches will use an uneven split to transmit at 70Mbps and receive at 30Mbps, for example.

Using the same example of moving two 150Mb files, a 100Mbps symmetrical, full duplex switch will deliver both files in 1.5 seconds. A 100Mbps asymmetrical half duplex switch with a 70/30 split will take 7.14 seconds to deliver both files. Even though both devices can be marketed as a 100Mbps switch, real-world performance is significantly different.

The NVT Phybridge CHARIoT series of products all have symmetrical bandwidth capabilities, ensuring fast and consistent data delivery through the network.

Latency

In addition to transmission speed, latency also plays a significant role in network performance and service quality. Latency is the time it takes a piece of information (a packet) to reach its destination. Latency may not be as crucial for certain endpoints, such as data terminals. However, for real-time applications like voice calls or live video monitoring, low latency is critical to ensure good user experience.

To illustrate latency, we tested our long reach Ethernet over Coax switch against a competing product. Both switches were tested at 100Mbps, symmetrical, full duplex over 2,000ft of RG6 cable.

Latency was tested using the Siama GENEM-X 10G Ethernet/IP Test Application at various frame sizes ranging from 64 bytes to 1518 bytes. The average delay, or latency, of the NVT Phybridge CLEER24 switch, was 64 microseconds. The average delay of the competing product was 4,685 microseconds, which is 73-times more latency that the CLEER24 switch. See the full performance comparison between these two products.

Even at 2,000ft, NVT Phybridge Power over Ethernet switches have extremely low latency, on par with standard reach Ethernet solutions from market leaders like Cisco. Many long reach Power over Ethernet solutions on the market have higher latency levels, which are not suited to support real-time applications.

Noise/Crosstalk

Finally, there is the issue of noise, also known as crosstalk. Crosstalk occurs when a signal transmission results in undesired electromagnetic waves that interfere with surrounding equipment or wiring.

Noise production makes a big impact on large deployments where there is a lot of equipment and cabling in one physical space. This issue can be overlooked when testing equipment with just a few devices. However, as the deployment size increases, so does the noise produced, and therefore the interference with other devices. As a result, devices will slow and experience packet loss.

NVT Phybridge Power over Ethernet solutions are FCC Class B certified and produce very minimal noise interference. This makes our equipment safe and effective, even around extremely sensitive devices like pacemakers. Our long reach Power over Ethernet switches are used onboard many luxury cruise ships to enable thousands of endpoints inside the noisy metal walls of a ship’s networking closets – without issues. This makes our solutions very scalable, especially for large scale deployments with many endpoints.

There are several Power over Ethernet switches on the market, and they are far from equal. Clever marketing tactics can sometimes hide the real story behind a Power over Ethernet switch’s expected performance. It’s important to understand what the numbers mean and how that translates into a better experience.

Are you interested in diving deeper into the performance of NVT Phybridge long reach Power over Ethernet solutions? Visit our performance comparison page to see how we compare to industry-leading Cisco switches, and how we crush the competition!

NVT Phybridge Power over Ethernet Switches

NVT Phybridge long reach Power over Ethernet switches and extenders deliver symmetrical, full duplex, and PoE over any new or existing network infrastructure. We provide industry-leading solutions to make digital transformation projects as simple and rewarding as possible for our customers and partners. Leave the technology to us. All you need to think about is what devices and applications will you enable?

Related Resources

Power over Ethernet Explained

Managed vs. Unmanaged Power over Ethernet Switches Explained

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