HomePNA: New uses for those plain old
telephone lines
By Steven Totolo and Franca Piccin
In June 1998, 11 companies formed the Home
Phoneline Networking Alliance (HomePNA). Their aim was to formulate
a single, unified phoneline networking technology that could be brought
to market quickly, providing interoperable home networking products. The
founding members were 3Com, AMD, AT&T, Compaq, Epigram, Hewlett Packard,
IBM, Intel, Lucent Technologies, Conexant, and Tut Systems. There are now
33 participant members and over 50 adopter members.
The original specification, published in the fall of 1998,
described an easy-to-use, cost effective and proven 1 Mbps (megabits per
second) home phoneline networking technology. With this technology, computers,
peripherals and other information devices would be able to communicate
to each other and the Internet using standard telephone wiring simultaneously
allowing normal telephone service. By December 1998 products displaying
the HomePNA logo became available. The logo provides a "seal of approval"
assuring purchasers that the products are compliant with the specification.
HomePNA adopted Tut Systems technology to work with the
existing phoneline network within today’s homes. To ensure success, several
issues needed to be addressed:
The telephone wiring structure within each home is unique
and can change on a day-to-day basis. Many network topologies require that
each node be wired to a central hub. The home phoneline topology is usually
a random connection of nodes. Telephone, faxes and modems can be connected
and disconnected from the phoneline changing the topology. With each of
these nodes, there are several connections that are not used and therefore
are not properly terminated. This results in impedance mismatches and signal
echoes that can lead to multi-path signals.
Random and varying levels of noise can be induced into
the phoneline from appliances, heaters, air conditioners, consumer appliances
and even telephones.
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Changing transmission line characteristics
Telephones and other phoneline devices can interfere
with data transmission by dynamically changing the line characteristics.
Simply answering the phone or sending a fax can cause the line impedance
to change.
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Coexistence with other phone line equipment
Connection to the phoneline must comply with FCC Part
68 regulation. This requires the phoneline network to use signals with
low power levels, which complicate the hardware design of the interfacing
electronics.
To entice consumer interest, any new technology must
provide a major increase in throughput over standard technologies, such
as 56k Baud modems. With network speed pegged at 1 Mbps, HomePNA provides
the capacity to reach near Ethernet performance in a home environment.
The first question on most people’s mind is How did HomePNA
do it? Since the technology will have to be compatible with Plain Old Telephone
Service (POTS) phone line devices, and Universal Asynchronous Digital Subscriber
Line (UASDL) technology, HomePNA resides in a frequency band above both
services.
Figure 2 illustrates how POTS, UADSL and HomePNA share
the same medium by operating in distinctive frequency bands.
HomePNA has its foundation in standard Ethernet technology.
It uses the IEEE 802.3 compliant Media Access Control (MAC) and Carrier
Sense Multiple Access/Collision Detect (CSMA/CD) access methods as used
in common office LANs. Standard Ethernet data frames transferred to the
phoneline have the first 8 bytes replaced with a header designed specifically
for the hostile phoneline-networking environment by the physical layer,
usually an integrated circuit such as AMD’s AM79C978. The receiver’s physical
layer reverses the process, passing the Ethernet frame to the standard
network software. This process allows home phoneline networking to utilize
the vast amount of Ethernet compatible software that exists today, while
providing a reliable transmission on home phone lines.
Figure 3 illustrates the HomePNA modification to the IEEE
802.3 Ethernet frame when it is transferred to the phoneline.
In March 1999, the HomePNA announced that the CEBus
Industry Council’s (CIC) PlugLab would begin testing for compliance
to the initial technical specifications. In the future, the PlugLab will
also host a series of "Plugfest" events to test the interoperability of
devices from different manufacturers. Uponn successful test completion,
a product will be deemed compliant and able to display the HomePNA
logo.
Despite the success of products such as Intel’s
AnyPoint Home Network and Farallon’s
HomeLINE now on sale in stores, their 1 Mbps performance is only the
dawn of phoneline network technology. Recently in July 1999, Epigram Inc.
proposed a technology that will push the speed of phoneline networking
to 10 Mbps while maintaining compatibility with the current 1 Mbps technology.
This technology will be adopted as HomePNA 2.0 and the specifications released
in the second half of 1999. Epigram’s technology employs a spectrally efficient
modulation technique that encodes up to 8 bits of data per symbol. In time,
this technology will have the ability to approach speeds of 100 Mbps.
As applications such as multi-user games, digital video
networking and video security become standard products in the home, higher
home network speeds will be a must to handle the increased traffic. With
HomePNA, home networks will have the capacity to meet theses future needs,
adding new life to those plain old telephone lines!
This protocol and others are documented and updated regularly
in the CABA Quarterly and in the CABA Standards Committee that meets quarterly
to discuss issues that affect the business of members in the automation
industry. The committee is open to all CABA members interested in up-to-date
issues involving communications standards, wiring practices, and regulations.
Steven Totolo is president of tvcAutomation, a home
automation specialist and a member of the CABA Standards Committee. He can
be reached at (613) 795-7117; fax (613) 737-5323; email: sales@tvcAutomation.com
