Dear Professor Phil,
My background is in telecom and I work now in the IT department of an insurance company. I’ve used devices with RS-232 interfaces for years. In researching a Contemporary Research device that converts RS-232 to Ethernet, my department raised a few questions. What advantage does Ethernet provide over RS-232? Which is the more current standard? Can IP be used with both?
—Ian, Manchester, UK
Let’s look at each question, but in an order that is different from the order in which you asked the questions. The newer technology is Ethernet. First ratified as a standard in 1982 by the IEEE (Institiute of Electrical and Electronic Engineers), it has constantly been undated. The latest version supports 40 and 100 Gb/sec transmissions and is IEEE 802.3ba (2010). RS-232 version C, the first widely used version, was ratified in 1969. The latest version, RS-232-F, derived from the EIA/TIA (Electrical Industries Alliance and Telecommunications Industry Association) in 1997. The original purpose of Ethernet was to connect over a common medium a small group of computers that were close to each other. Also, it is likely that users needed to share laser printers, which at the time were very expensive. On the other hand, the purpose of RS-232 was to interface data and signaling between terminal devices and a telephone modem. Notice that only Ethernet targeted the idea of a local network of more than two devices.
Turning now to the first question, Ethernet generally operates over inexpensive category cabling for distances up to 300 feet and over fiber optic cables for longer distances. RS-232 uses a variety of cabling options but typically depends on 3-, 5-, 9-, or 25-wire cables. When category cable is used with Ethernet, the connector is always an RJ-45 connector. RS-232 can use a variety of connectors but the D-shaped 9-pin is the most common. A significant advantage of Ethernet is that it can be repeated by switches to reach virtually any distance across a city or region. And, it supports much higher data rates.
Finally, let’s answer the last question. Any circuit capable of carrying signals for standards data characters can carry IP. So, in this case both Ethernet and RS-232 will carry IP. However, designs that use RS-232 to carry IP are often limited in speed to an order of magnitude of around 10kb/sec or 100kb/sec. Here, the TELNET protocol is often used. TELNET is notoriously inefficient. Conversely, Ethernet will support the entire suite of TCP/IP applications up to the 100Gb/sec rate we mentioned.
Dr. Phil Hippensteel has spent more than 40 years in higher education and now teaches at Penn State Harrisburg. Email your questions to firstname.lastname@example.org.