Home PNA "Phoneline Networking" Round Upby Greg Hanna on July 21, 2000 11:10 PM EST
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Although this tech brief is largely reprinted from our February 2000 review of the D-Link DHN-910 kit, there is new some new material. So, even if you read that review, you will probably want to check this out.
The three products up against one another in this round-up are all based on the recently ratified HomePNA 2.0 standard. HomePNA (Home Phoneline Network Alliance) is a group of over 100 companies, which have come together to produce a single home phoneline networking standard. Some of the founders are IBM, AT&T and Compaq. Add to that the fact that several large producers of networking equipment are members (3com, Cisco, Xircom, etc, and the three manufacturers featured in this article) and you can be pretty sure that their standard will be the standard. This means that if you buy one company's home phoneline network hardware it must work with another company's equipment, as long as they both adhere to the standard.
To test that theory, we took one card from each company and put them together on a network. We found that not only did each card communicate flawlessly with its competitors, but we were actually able to get the Intel card to talk to the Netgear card using the D-Link driver stack (on the Intel card). This isn't mind-boggling considering that all the competing cards are built with the same Broadcom HomePNA chipset, but it still shows a degree of compatibility that isn't universally available… even with regular Ethernet cards.
The high-level technology itself is not new. Telephone providers have used it for many years to provide two separate telephone 'lines' when only one pair of physical wires is available, and is the same technology behind ADSL. The basic premise is that you can pass several signals over the same pair of wires using separate frequency ranges. Your phone conversation, for instance, is passed at relatively low frequencies (4kHz and below) and is not actually even the same kind of signal used by ADSL or HomePNA. The two latter technologies use a much higher frequency range (up to 1.1 MHz in the case of ADSL, and between 5.5 and 9.5 MHz in the case of HomePNA) and are modulated onto the carrier frequency using shifts in phase and amplitude. The upshot of all this is that your telephone wire can handle a voice conversation, ADSL data, and HomePNA data all at one time, with no disruption or interference between them.
One of the neatest things about how the HomePNA technology works is the fact that the network traffic is built as Ethernet and passed to the HomePNA network card for conversion into HomePNA-compliant traffic. The conversion is done by circuitry on the network card which strips off the preamble and delimiter fields and replaces them with a header designed for HomePNA. When the packet is received at the other end, the receiving network card converts the frame back by reversing the original process. It then hands the data up to the higher layers for processing.