How does DH+ compare to Ethernet?

When it comes to industrial communication protocols, an inevitable question is: how does it compare to Ethernet? It’s a fair question because it demands an answer, and here are my thoughts on it.
Baud Rates <br>Ethernet is very fast and getting faster every day. Currently 1GB and 10GB are supported, with 100GB coming soon. DH+ supports a much lower set of baud rates; 57.6, 115.2K, and 230.4K baud. Unlike Ethernet, there are no switches to allow lower baud rate devices to join the network. All DH+ devices must use the same baud rate.

wiring
CAT5 and CAT6 cables are typical for Ethernet systems. CAT5 consists of four twisted pairs of copper wires. This is probably what you used in your office before you started using wireless connections. CAT5E and CAT6 are enhanced cabling types that offer higher bandwidth and speeds up to 10Ghz. DH+ uses a very simple cable with one twisted pair surrounded by a shield.

Cable length

CAT5 is typically rated for less than 400 feet, much less than the 10,000 feet of trunk cable supported by DH+. This is one area where DH+ has an advantage over Ethernet, although the Ethernet backbone makes this advantage superficial.

Supported controllers

DH+ supports all original Allen-Bradley PLCs, PLC2, and PLC3. Some controllers in the PLC5 family support DH+, others support Ethernet, and some support both.

Number of devices

DH+ networks are limited to 64 devices, while Ethernet networks have virtually no limit.

Device Addressing

Ethernet uses standard dot-decimal addressing, and station numbers between 0 and 63 are used to address DH+ devices. It is illegal to have duplicate station numbers on any one network.

cost

Due to the limited number of possible clients, DH+ was an expensive solution at the time and was initially used only by the largest Allen-Bradley customers. Ethernet, on the other hand, was a mass consumer product used by millions of people and was inexpensive due to commercial scale.

Network Architecture

The network architecture of Ethernet is much more complex than that of DH+. Ethernet uses a layered approach using physical layer, data link layer, network layer, and application layer for communication. DH+ uses few layers (physical layer, link layer, and application layer) and the DH+ layers are much more complex than Ethernet layers.

Network Communication

Ethernet and its switching infrastructure allows for maximum network throughput, with many devices able to send messages simultaneously. DH+ is more like the original version of Ethernet, where only one device can talk and the rest can listen.

Network Mastery

Ethernet itself does not use the concept of a network master, but some Ethernet application layer protocols do.

With Ethernet, any device can send a message to any other device at any time. In DH+, there is a strict protocol that only devices holding a token can send a message. Devices receiving messages hold their responses until the token is rotated to them, at which point they send out a response to the previously received message.

Because DH+ predates Ethernet by many years, it is not nearly as fast, sophisticated, or flexible as Ethernet. However, it supported the manufacturing applications of the time very well.