Cutting all Cables: Phoneline vs. Wireless Networkingby Eric Hagen on October 30, 2001 4:10 AM EST
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- IT Computing
The phoneline networking standard known as HomePNA 2.0 was developed by the Home Phoneline Networking Alliance and offers 10Mbps of throughput over the copper wires already installed in your home. The HomePNA standard does not interfere with normal telephone service or any other phone based technologies such as Caller ID, DSL or analog modem service.
In theory, the networking standard operates on a similar principle to the standard IEEE 802.3 10Mbps Ethernet standard, transmitting over existing copper wires (phone lines), allowing automatic detection of collisions in order to wait and continue transmission. However, the PNA standards must obviously be very resistant to external noise and signal degradation within a medium which is not ideal for high speed data communication.
The actual data rate of a HomePNA 2.0 network is in fact not 10Mbps, however; this number was chosen as a rough equivalent to its standard IEEE 802.3 10 Mbps Ethernet cousin. Technically, it operates at a variable rate of either 2Mbaud or 4Mbaud and on a variable 4-256 QAM (Quadrature Amplitude Modulation). Put simply, this means that the system can operate on any data rate between 4Mbps and 32Mbps. Under ordinary conditions, a HomePNA 2.0 link will be probably operate around 16Mbps.
One of the more interesting side effects of the "bus" topology of a HomePNA 2.0 network is the ability to establish ad-hoc networks by directly connecting standard phone cables (RJ-11) together, regardless of whether there is any sort of phone service installed on the lines. This may be useful for locations that have in-wall wiring that is not currently used for telephone service. This also means that HomePNA 2.0 connections can be cascaded so that multiple computers can share a single wall jack as if there were multiple.
A common myth about phoneline networking is that the network traffic can be sniffed remotely, using the lines that run from your home to the Telephone Company. Under most circumstances, this is not true and all network traffic remains within your home. A phoneline network can be sniffed just as easily as a phone line can be tapped, however; just like tapping a telephone conversation, the tapping of a HomePNA network requires a physical connection to your home's wiring.
A truly secure system always utilizes some sort of software-layer encryption. If there is sensitive data to protect, relying on the boundaries of a physical medium is generally not sufficient. While this applies to Ethernet as well, HomePNA is especially vulnerable because of the large volume of unprotected phone lines in a building. That said, the average home user will not have to worry about his or her phoneline network being disrupted by attackers.