HomePlug AV – ideal multimedia and data networking
over the household electricity circuit
200-Mbps bandwidth over existing infrastructure
Home networking via the electricity circuit is booming. Increases in bandwidth will accelerate this
development even further. In addition to the current specification HomePlug 1.0 with bandwidths of 14 Mbps
or 85 Mbps, sufficient for Internet access via DSL or audio transmissions, the latest standard HomePlug AV is
soon to be introduced to the marketplace. This enables transfer rates of up to 200 Mbps and guarantees high
quality performance of multimedia applications.
In future, applications such as TV transmissions via Internet protocol (IP-TV) and video-on-demand in DVD
quality will be cable of operation without problem. The household electricity circuit will become the backbone
supporting applications throughout the house and will enable Internet TV and video on demand to be
implemented throughout the home. The only requirement: Plug sockets. This means that even future forms of
home networking can become a reality with considerable ease.
Entertainment electronics equipment such as TVs, hard-disk recorders, set-top boxes or hi-fi systems can be
just as easily connected to networks as home servers or computers. Games consoles present no problem,
either. Market researchers agree: The desirability of home entertainment products in the home is continuously
increasing. House owners and tenants are well advised to consider how they can implement a powerful
broadband network in the most cost-effective manner possible. Unlike wireless LANs with their complicated
installation, and Ethernet that is inflexible and demands considerable efforts for installation, the electricity
networks are a true ―Plug&Play‖ solution. The structure is already present in every house or apartment, and
the adapters are ready to use within minutes!
There are further reasons why WLAN and Ethernet (as a transport medium) are not directly suitable as a
home network and backbone. Despite data rates of up to a gigabit per second, using Ethernet to transfer
audio and video data over a network yields results of a noticeably different quality to a direct connection via
analogue or digital cable. Depending upon the positioning within the household and the thickness of the
ceilings, WLAN often suffers from interrupted connections.
Alternative home-networking systems such as HomePNA (data links over telephone lines) or coax (data links
via TV and satellite cable) only provide satisfactory performance for shared browsing in the Internet or for
moving data between PCs.
Even the phased control of a loudspeaker pair, essential for stereo, is impossible with these technologies—a
fact which applies all the more when considering Dolby 5.1 or 7.1 Surround Sound systems.
Installation and security
Two questions are relevant here: How simple is it to set up a home network, and how secure is it? Home
users demand products that can be set up to form a functional home network even without expert knowledge.
At the same time, a new home-networking technology should be capable of providing high-definition television
(HDTV) with the same quality as a direct connection between the TV and the source (e.g. receiver, hard-disk
recorder, HDDVD/BlueRay players). What’s more, the system should cater for the needs of households
running more than just one audio/video device.
A home network must of course be able to handle the typical asynchronous networking of PCs and printers
with the Ethernet protocol. And even home automation systems—i.e. the measurement, control and
regulation of the central heating, roller blinds, lighting or surveillance systems—should be no obstacle to a
new, comprehensive home networking system.
The demand for home networking systems continues to increase. Up to one fifth of European
households are equipped with a home network already.
A study by Datamonitor in 2005 shows that a universal home-networking system has to be able to handle not
just data, but to be suitable for entertainment, communication and home automation as well.
Networks for data and entertainment are the main current drivers of growth in home networking
systems. Less pronounced is the development in home automation systems.
HomePlug AV – the key to multimedia home networking
After several years of development, the HomePlug Powerline Alliance (http://www.homeplug.org) has
at last succeeded in meeting all of these demands with one single network technology—HomePlug AV.
Thanks to chip manufacturers such as Intellon (http://www.intellon.com) and leading component
manufacturers such as devolo (http://www.devolo.com), the complex levels of technology required to
meet these demands can be offered at prices that suit the budgets of home users and computer and
With good reason, representatives of renowned chip, computer, networking and entertainment electronics
manufacturers have taken seats on the HomePlug Powerline Alliance Board of Directors
(http://www.homeplug.org/en/about/board.asp), including companies like Intel, Samsung, Motorola,
Sharp, Sony, Linksys, Cisco and GE Security (General Electric).
HomePlug AV provides a holistic approach for a true and comprehensive home-networking backbone.
HomePlug AV is a powerful network system available throughout the household and capable of supporting
multi-HDTV streams. It is easy to put into operation thanks to Plug and Play technology and auto-
configuration. It also offers impressive levels of security from intrusion and eavesdropping.
HomePlug AV in brief
Transfer medium: 50/60 Hz AC wiring or coax cable
Link rate and data rate: 200 Mbps
TCP data rate: 60 Mbps
UDP data rate: 85 Mbps
Coverage: up to 300 metres -> the complete household
Transfer method: Yes (TDMA)
Ethernet compatibility: Yes (CSMA)
Security: 128-bit AES encryption
Co-existence with HomePlug 1.0 / HomePlug 1.0 Highspeed: Yes
Co-existence with home automation: Yes (X10, LonWorks, CEBus)
Frequency range PHY: 2 - 28 MHz
Number of carrier frequencies: 1155
Modulation: OFDM and Turbo Convolutional Code (TCC)
HomePlug as the backbone for home networking. At last, all networking equipment can be linked over
HomePlug AV architecture
To meet the demands of QoS for entertainment electronics and for VoIP, the HomePlug AV system functions
with connection-oriented and connectionless communications channels. Connection-oriented communications
channels represent logical point-to-point connections—similar to an ISDN line—in which data traffic
commands a defined bandwidth which is guaranteed for the duration of the connection. More precisely: Once
an application has reserved the connection between transmitter and receiver, no other applications can
access this bandwidth as long as the connection is in place. The disadvantage: To realise this, all
communicating parties need to be synchronised on a precise, network-wide basis, and this can only be
achieved with a central control mechanism. The advantage: All data packets arrive in the same order as they
were transmitted, and each was travelling for the same time as the others.
Connectionless communications channels are familiar from standard (W)LANs, where applications send out
data packets in an uncoordinated manner with the (wireless) Ethernet protocol. If two data packets collide en
route, they are lost and have to be transmitted again. To avoid a repeat collision, the transmitters first wait for
a brief pause of random length. The advantage: There is no need of a centralised timing mechanism,
meaning that the system can be less complex and thus less susceptible to disturbance. The disadvantage:
The order in which the packets arrive at the receiver varies, as does the travel time across the network.
To combine these contradicting techniques into a single network, HomePlug AV has had to adopt a similar
tactic as used by telecommunications companies (with ATM, asynchronous transfer mode) and later Apple
(with the Firewire bus) in the past:
The system’s control pivots on the Central Coordinator (CCo). This primarily ensures that all stations (STA) in
the network are synchronised with one another. The CCo then allocates time, dividing up the entire bandwidth
(i.e. the gross transport capacity of the transmission channel in bits per second) into several periods which
are dynamically assigned to the various stations in the network.
CCo—the central co-ordinator
Where are the various types of information stored? Since HomePlug AV networks are designed to function
without a super-ordinate entity, each and every station has to be capable of storing this information itself. For
this reason, every HomePlug AV adapter is equipped with a central coordinator (CCo).
The question is; how do multiple stations agree on which one is the network’s CCo? HomePlug AV
pragmatically resolves the issue of its ―sole representative‖ the moment that an adapter is connected to the
electricity circuit: Once fed with the current, a HomePlug AV station scans the medium (electrical wiring) to
search for control information in the form of beacons from other HomePlug AV stations . If it fails to detect
anything, it automatically assumes the role of CCo and sends out beacons to inform other stations of its
A second HomePlug AV station subsequently plugged into the circuit detects the beacons being transmitted
through the electrical wiring. It assumes a subordinate status to the existing CCo by entering information
about itself (MAC address, network key, etc.) into the CCo's Discovered Stations List (DSL), a type of routing
The CCo has control over at least one AV logical network (AVLN). An AVLN consists of multiple AV stations
(STAs), all of which share the same Network Membership Key (NMK). It is important to know that the NMK
provides the stations with exclusive access to an AVLN, enabling them to communicate unimpaired and
securely with one another.
Gradually the CCo learns about the topology of its AVLN, and also about the topology of neighbouring
AVLNs. The CCo gains this information from periodic beacon transmissions from the AV stations (in time
windows allotted by the CCo). These ―discover beacons‖ contain information about each AV station and the
AVLN it belongs to.
Each station detecting a discover beacon enters the information into its own DSL. Information from stations
which are in another AVLN is additionally entered into a second list, the Discovered Network List (DNL).
The CCo periodically queries the stations for their DSLs and DNLs and uses these to build up its own
information on topology.
The CCo uses the topology map, as compiled from the various DSLs and DNLs, to decide whether there is
another station which would be better suited as CCo than itself. This decision is based on the following
1. Selection by a user
2. Capabilities of the CCo
3. Number of STAs in the Discovered Station List
HomePlug 1.0 adapters are also detected
Power savers—even though they’re always on
If all stations are inactive, the CCo will place the entire AVLN on standby by instructing the stations to fall
back to a power-saving mode. In this state, activity is confined to the CSMA region, enabling stations to
initiate a connection if required, and also to a small PCF region just long enough to be able to receive
discovery and proxy beacons. The stations remain a part of an AVLN as long as their receivers are active
during these brief periods. The transmitters and receivers can remain inactive for the remainder of the beacon
time interval. This makes it easier for manufacturers to certify their products in line with the Energy Star
Ample bandwidth despite poor cables
For a single shared medium—the AC wiring—to support multiple logical networks with AV streams each
transmitting several Megabits of data per second, a significant quantity of bandwidth amounting to hundreds
of Mbps is necessary.
Application Application data rate
High-definition television (HD-TV) 12 - 27.8 Mbps
Standard television (SD-TV) 2 - 4 Mbps
Digital audio (MP3, Ogg, etc.) 0.128 Mbps
CD audio 1.6 Mbps
VoIP 0.16 Mbps
Network printer 1 Mbps
Home automation 0.04 Mbps
Picture telephone 1 Mbps
Time-slip TV recording 8 Mbps
IP data traffic (LAN, Internet) 4 Mbps
Total requirement 30 to 47 Mbps
Any home network to be used for transmitting audio, video and HD-TV has to be equipped with ample bandwidth.
HomePlug AV reaches 200 Mbps (gross). Specialised Cat-5 twisted-pair cabling is not necessary.
HDTV streaming works with HomePlug AV without problem.
Quality of Service guaranteed
As described above, HomePlug AV provides connection-oriented Contention Free (CF) service to support the
Quality of Service (QoS) requirements (guaranteed bandwidth, latency and jitter requirements) of demanding
audio-video (AV) and IP (Internet protocol) applications.
This Contention Free service is based on periodic Time Division Multiple Access (TDMA) allocations of
adequate duration to support the QoS requirements of a connection.
Synchronisation within the network is achieved by periodic beacons transmitted by the central co-ordinator.
One beacon period covers two full 50/60-Hz AC cycles and lasts for 40 or 33 1/3 milliseconds respectively.
Secure encryption and easy installation
Data transfer via electrical wiring cannot rely upon physical borders, such as those that cable structures offer
to Ethernet. For this reason, security (from interception) has to be assured by other, logical means.
Access control functions need to ensure that only authorised devices can log on to a HomePlug AV network
(AVLN). HomePlug AV stations can manage multiple security keys, which enables them to join multiple
What does this mean, exactly? For example, AVLN number 1 links an LCD TV with a satellite receiver; AVLN
number 2 connects six (active) loudspeakers of the 5.1 Dolby Surround system, which is also connected with
an AV network player or an IPTV set-top box via AVLN 3. The PC in the study uses AVLN number 4 to
communicate with the notebook in the living room (possibly via WLAN) and with the storage server in the
cellar, which also serves as a data source for the LCD TV over AVLN number 3.
All of the data transport and the majority of the control traffic in an AVLN are secured by powerful 128-bit AES
encryption. The only exceptions are a small selection of control commands which cannot be encrypted. This
encryption uses the Network Encryption Key (NEK) and is performed on individual network segments as the
MPDUs (MAC Protocol Data Units) are created.
Keys are assigned in the following ways: When installing the gear for the first time, a factory programmed key
in all stations provides users with a true Plug&Play experience. This is by no means secure, as all HomePlug
AV adapters are programmed with this key. The user defines a network password (NPW) and enters this
directly into a new station. A hash algorithm uses this to generate the NEK, a 128-bit AES key.
As mentioned previously, HomePlug AV stations may be members of multiple logical networks in a single
physical network. In addition, HomePlug AV can co-ordinate several Neighbouring Networks (NN). As soon
as a central co-ordinator (CCo) detects a neighbouring network, it takes up negotiations with its CCo to
negotiate a schedule for the transmission of data, so avoiding disturbance.
Conclusion: Better, faster, more precise
HomePlug AV is powerful technology which is almost unparalleled in its ability to distribute audio, video and
Ethernet packets over the AC wiring in the home.
The gross bandwidth at 200 Mbps is sufficient, for example, to simultaneously transport three HDTV signals
(66 – 84 Mbps), three digitised standard television streams via network player (18 – 42 Mbps), home-theatre
audio or CD audio into two rooms (9 - 11 Mbps) and six VoIP telephone calls (1 Mbps) throughout the home
network—and even then it still has the capacity to transfer IP data at 10 Mbps.
When compared with the costs of structured LAN cabling (four twisted pairs), along with the additional cables
for a television network (coax) and telephone lines (two twisted pairs), plus the labour costs for the
installation, the costs for a HomePlug AV network appear to be relatively low.
However, HomePlug AV is absolutely unbeatable where changes in the home situation are involved. Unlike
the cabling which may need to be installed at other locations, devices controlled by HomePlug AV can be
addressed from any plug socket in the home—be they playback devices such as IP TVs, beamers or
loudspeakers, feeder devices such as satellite receivers, CD/DVD players, media servers, computers or even
other distributing networks such as WLAN access points or Ethernet LANs.
ComTek (Communications Technologies): www.comtekbroadband.com
Current Communications Group: www.currentgroup.com
devolo AG: www.devolo.com
DS2 (Design of Systems on Silicon): www.ds2.es
HomePlug Powerline Alliance: www.homeplug.org
Main.net Communications: www.mainnet-plc.com
National Association of Amateur Radio (ARRL): www.arrl.org
Schneider Electric: www.schneider-electric.com
United Power Line Council: www.uplc.utc.org
Universal Powerline Alliance: www.upaplc.com
Web article; well worth reading
Large Maury Wright, Riding the sine wave: Broadband data hitches a ride with an unlikely carrier.