Introduction

Today there are a lot of different technologies for building of local networks, with the main one being Ethernet. First there was 10-Mbit Ethernet, then 100 Mbit one and now you can find 1-GB Ethernet networks. But the requirements to the communication medium are also growing: simple cables are now replaced with already 7-category ones! As a result, the price is growing both for network equipment and cables. Besides, an update of a network requires replacement of an older cable with a newer one. But is there another way-out, i.e. without changing requirements to the network cables? Is it possible to create a technology which would work only on cables of a lower category? The experience shows that it is. In mid-90s the company Tut Systems offered its own technology for transferring data on a telephone cable. Although the speed was only 1 Mbit/s, it became anyway popular. And then different companies among which there are such as AMD founded an alliance named HomePNA (Home Phoneline Networking Alliance) and developed a data transfer standard based on the Tut Systems' technology for telephone lines and called it HomePNA 1.0. The first version of this standard was identical to the Tut Systems' technology - 1 Mbit/s, 25 computers in the HomePNA 1.0 network and a communication range about 150 m. Then they released network cards (PCI and USB), different communicators, Ethernet-to-HomePNA bridges etc. The speed of 1 Mbit/sec is sufficient for many tasks, for example, for connection of a computer or a local network to the Internet. So, the HomePNA 1.0 standard was used for connection of small offices, hospitals, apartments where the telephone cables were already laid. Since this standard was developed for data transfer via phonelines, it didn't affect telephone signals. In the enhanced version of the HomePNA - HomePNA 2.0 - the developers managed to prevent affecting also many other signals and not only in telephone lines. The frequency distribution of basic signals - voice, xDSL and HomePNA signal is shown on fig. 1:

Fig. 1. Frequency range for telephony, xDSL equipment and HomePNA 1-2. W- signal's power, F - signal's frequency .

The HomePNA technology is a usual Ethernet with 1 Mbit/s (HomePNA 1.0) and 10 Mbit/s (HomePNA 2.0) in all aspects. The CSMA/CD, IEEE-802.3, MAC addresses are applicable not only for the Ethernet but also for both HomePNA standards. This technology differs from the Ethernet only on a physical level. And installation of HomePNA cards doesn't differ from that of HomePNA adapters. Operating systems operate with these adapters as with usual Ethernet ones.

Now let me examine the first version of the HomePNA standard in detail -

HomePNA 1.0

Well, this technology is a usual Ethernet working at 1 Mbit/s. Since this version is older, there are much more equipment for it than for the HomePNA 2.0. A hub is a heart of networks based on this technology. As a rule, hubs contain both HomePNA 1.0 and Ethernet ports. That is why you can easily join Ethernet and HomePNA 1.0 networks. While the HomePNA 1.0 places a limitation on the quantity of working devices in such network (up to 25 devices), usage of hubs changes these limitations. For example, for a hub from CityNetek the maximum number of simultaneously working devices mustn't exceed 8192 MAC addresses. The hubs can have ports of a different size - a maximum of 12 HomePNA and 4 Ethernet for the most advanced hub of the CityNetek series - CN-1412(M) (fig 2).

Fig. 2. CityNetek HomePNA 1 CN1412(M) Hub.

Why so many MAC addresses? Because you can make stacks of HomePNA hubs, i.e. combine several hubs into one. Besides, the HomePNA hubs support VPN (but only on the level of ports). Ports can be grouped to form VPN networks. Moreover, each port has its own statistical data, i.e. the number of transferred and received bytes, and it can be enabled or disabled alone or together with several other ports. The most advanced models, with index M, have SNMP control, supports telnet and http configuring. Besides, there are network cards - all manufacturers have PCI and USB versions of the cards and HomePNA <-> 10/100 Ethernet bridges (fig. 3.).

Fig.3a CityNetek HomePNA 1.0 PCI Card CN-10;

Fig.3b CityNetek HomePNA 1.0 USB Card CN-201;

Fig.3c CityNetek HomePNA 1.0 <-> Ethernet Converter CN-101.

The HomePNA 1.0 standard doesn't adapt to quality of a line. If a packet is lost, it is to be resent. The distance where the real speed of 1 Mbit/s is present is about 150 m. But the increased power of the signal, which can be enabled or disabled in the hub, allows reaching 500 m. But in this case you will get more noise and pickups, that is why the decision of whether to enable it or not depends on a definite topology of the network. You can, however, adjust power of a signal separately on each port. Sometimes it should be done because of a growing number of collision (with large signals and at small distances), which affect a data rate. For example, when computers were directly connected to the ports of a commutator, the data rate achieved 576 Kbit/s, and the ports had a lot of collisions (at default settings). The distance between the port of the commutator and the computer was only 20 m. But the maximum data rate we fixed was 960 Kbit/s, which is very close to the theoretical value of 1 Mbit/s. Once again it should be noted that in case of the HomePNA 1.0 (or HomePNA 1.1) the data rate drops and is defined by the number of lost packets. Besides, we checked that a telephone signal and one of the HomePNA 1.0 do not hamper each other. In principle, this standard can be used not only for networks of "star" type but also of "bus" one. And then you can connect up to 25 devices to each commutator port, or even do without commutators just joining all network cards. But it should be noted that the speed of 1 Mbit/s will be divided among all these devices.

Drivers for the HomePNA 1.0 network cards can be found for the following operating systems: Windows 9x/ME/NT/2000, Linux and FreeBSD. Their installation and configuring do not differ from those of usual Ethernet cards.

Now let's take a gander at the second newer standard -

HomePNA 2.0

The specifications are 10 Mbit/s speed, a range of 350 m, the number of devices up to 32. These data are taken from Broadcom corporation (iLine 10 series). There are also Intel's solutions, but they yield much to Broadcom. As a result, all top manufacturers of HomePNA 2.0 cards such as D-Link, 3COM, NetGear, Linksys produce its cards only according to the reference design from Broadcom. They differ only in price and in some peculiarities in drivers (for example, drivers from D-Link can count received/sent packets). The range of equipment produced by these manufacturers is also the same - PCI and USB cards and HomePNA 2.0 <-> Ethernet convertor (fig. 4).

Fig.4A D-Link HomePNA 2.0 PCI Card DHN 520;

Fig.4b D-Link HomePNA 2.0 PCI Card DHN 120;

Fig.4c D-Link HomePNA 2.0 <-> Ethernet Converter DHN 1000;

Commutators are unfortunately absent. The manufacturers have encountered a problem of mutual inducing of ports during their operation. 3COM, for example, started delivering HomePNA 2.0 hubs, but then stopped this enterprise very quickly. That is why bus is a typical topology for the HomePNA 2.0. And realization of this bus can differ - various branches etc. On the whole, although the HomePNA 1 and 2 standards are compatible, the HomePNA 2.0 is based on different principles. It can adapt a data rate! And, as our experiments showed, the communication medium can be almost whatever you want. Our HomePNA 2.0 network operated flawlessly in such media as UTP 3 and 5, telephone cables, laminated metals, coaxial cables etc. The HomePNA 2.0 worked also good when we applied native signals to these cables - broadcasting, television, telephone etc. And within 350 m stipulated in the documents the speed didn't depends on a type of cable. Besides, the network had no problems when the cable consisted of smaller cables twisted together on their ends. Twisted joints didn't affect a data rate, at least in our experiments. Moreover, no problems occurred when we connected cables made of different materials, e.g. copper, UTP 3 and steel.

The data rate is severely affected by different pickups. Try to coil a cable, and the signal may be lost. Everything depends on the equipment, especially when a signal goes via main telephone lines. In case of a coaxial cable the distance range is about 2.5-3 km. On fig.5 you can see a graph of dependence of data rate on distance.

Fig. 5. Dependence of data rate on distance for HomePNA 2.0, with a communication medium being a telephone cable.

Conclusion

The HomePNA has won a firm foothold on the market. First, the HomePNA 1.0 is used successfully in office buildings - practically all of them have their own telephone network, which can be used for the Internet as well. It is very convenient both for clients and providers. HomePNA networks can be built in those buildings which have phone jacks. I.e. you don't need hubs and switches, but only HomePNA cards. Theoretically, the HomePNA 2.0 standard has every chance to reach 100 Mbit/s speed! Broadcom is now testing the equipment which can work at 32 Mbit/s up to 2.5 km...

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