ABOUT HOMEPNA
The HomePNA is a group of more than 130 companies seeking to develop specifications for interoperable, home-networked devices using existing phone wiring. The group was founded in June, 1998 by 11 companies (3Com, AMD, AT&T Wireless, Compaq, Conexant, Epigram, Hewlett-Packard, IBM, Intel, Lucent Technologies, and Tut Systems). Toward the end of 1998 the group created a de facto industry standard when it published an easy-to-use, cost-effective, and proven 1 Mbps home phone-line networking technology as its 1.0 specification. The technology allows computers, peripherals, and other information appliances to connect with each other and the Internet without interrupting standard telephone service. Utilizing existing telephone wiring, it requires no costly or disruptive rewiring of the home. HomePNA members began producing compliant products in December, 1998. In December of 1999, the organization announced the release of its much-anticipated second-generation home phone-line networking technology (HomePNA 2.0). The new specification brings a faster 10 Mbps to phone-line networking, while at the same time maintaining backward compatibility with existing 1 Mbps HomePNA technology. The new technology uses selective portions of the 2 to 30 MHz frequency band to achieve these data rates. The technology foundation for the 10 Mbps HomePNA 2.0 standard is currently based on chipsets from a U.S.-based company called Broadcom Corporation.
In addition to increasing data speeds within the home, HomePNA is working to incorporate their technologies into a range of electronic appliances including: PCs, ADSL modems, cable modems, digital televisions, set-top boxes, and IP-based Web phones. Let's examine each component of a HomePNA-based network and see how they work together.
HomePNA Technical Architecture
Network Transport Technologies
The Alliance has chosen to standardize on Ethernet-based technology, allowing consumers to link devices at speeds up to 10 Mbps over existing home telephone wires. Ethernet is a popular and internationally standardized networking technology (comprising both hardware and software) that enables computers to communicate with each other. Ethernet was developed by Xerox, Intel, and DEC. The Institute of Electrical and Electronics Engineers (IEEE) later standardized it as IEEE 802.3. As a result, people tend to use the terms Ethernet and IEEE 802.3 interchangeably. The fact that IEEE 802.3 has been chosen as a networking technology allows HomePNA to leverage the tremendous amount of Ethernet-compatible software, applications, and existing hardware in the market today. The IEEE 802.3 standard was designed to support the CSMA/CD access method. CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. Let's briefly explore what this means. On a home network that uses the CSMA/CD access method, the devices can send data at any time—so there's multiple access. When an electronic or PC device has data to send, it listens to the phone line to see if it is busy. The device is sensitive to any carrier on the line— that's why this access method is said to have carrier sense. If there's traffic on the line, the device waits—in other words, it enters waiting mode. If the line is free, the station transmits its data immediately. Let's say that another device in another part of the home decides to send data at the same time. In such a case, a collision may occur. Collision detection allows the two devices to detect this event and perform the required recovery. The devices back off for a period of time before retransmitting. Of course, it's essential that the two devices do not back off for the same length of time. If, for example, all appliances on the home network were set to back off and retry after half a second, the same two frames would collide again. To prevent continual collisions, each appliance on the network backs off for a random amount of time. Under the Ethernet standard, information is bundled into a package called a frame. Figure 4.1 shows the home phone-line networking data frame.
A standard Ethernet frame consists of the following six sections of information:
Frame Check Sequence (FCS)— This field is used to identify whether there are any errors in the received frame. The transmitting digital appliance performs a mathematical computation, known as a CRC (cyclic redundancy check) on the frame and stores the resulting value in the FCS field. Because the FCS field contains the frame's CRC value, it's often referred to as the CRC field. The same calculation is performed again by the receiving appliance when the frame is received. If any errors occur, a new frame has to be built and retransmitted. From Figure 4.1, we can see that the home phone-line networking data frame is based on Ethernet standards with a specialized header. Under the Ethernet standard each digital appliance on the home network receives, but does not necessarily process, each frame. First an appliance checks to make sure that the packet consists of at least 64 bytes. If the frame is too short, it is immediately discarded. If the frame is an appropriate length, then the appliance checks the destination address. If the appliance is itself the target address, it copies the rest of the frame into its buffer. Once the frame is in the buffer, the CRC value is calculated and the value is compared with the one stored in the frame's FCS field. If the two values don't match, the receiving appliance assumes that the frame was corrupted in transit, and discards it. If the receiving digital appliance is satisfied with a frame's CRC value, it examines the frame's length field to make sure it is not greater than 1518 bytes. If any errors are detected, the frame is discarded.
Figure 4.1. HomePNA data frame. (Courtesy of Intel Corporation)
An additional requirement of home phone-line networking is the coexistence of multiple services on a single piece of telephone wire. For example, members of the household may need to make telephone calls while other members of the family use the home network for data transfer purposes. One of the most common methods of simultaneously operating multiple data and voice services over a single pair of wires is Frequency Division Multiplexing (FDM). This is a multiplexing technique that assigns each communications service a frequency spectrum that is different from all others. Through the use of frequency-selective filters, devices using one type of service can exchange information without interference from other services that communicate in another frequency band. The home network operates in the frequency range between 5.5 MHz and 9.5 MHz. Passband filters attenuate frequencies below 5.5 MHz very rapidly to eliminate interference with other potential services sharing the wire, such as standard voice communications (which operate in the 20 Hz to 3.4 kHz range in the United States, slightly higher internationally) and UADSL services (which occupy the frequency range of 25 kHz to 1.1 MHz). The chart in Figure 4.2 depicts the spectral usage of three services that can share home phone wiring. POTS, UADSL Internet connectivity, and home phone-line networking share the same line by operating at different frequencies.
Figure 4.2. HomePNA spectral usage. (Courtesy of Intel Corporation)
Wiring
The Ethernet technology found in corporate office environments was originally designed to support four types of wiring systems:
Thick coaxial cable
Thin coaxial cable
Unshielded twisted pair
Fiber-optic cable
These types of expensive cabling systems are not available in most residences. Consequently, HomePNA decided to leverage the existing infrastructure provided by phone wire inside the home. The use of the phone wiring system means that every RJ-11 modular jack in the house becomes a port on the home network, as well as a phone extension. RJ-11 is a standard telephone line connector.
The first HomePNA specification operates at maximum distances of at least 500 feet between nodes on the network and is capable of achieving data rates of 10 Mbps. Each appliance that forms part of the home network is known as a node.
Network Interface Cards
All the appliances on a HomePNA-based network need an adapter to control the I/O to the network. The network interface card (NIC) acts as the physical interface between the appliance and the telephone cable. Without the card, digital appliances would be unable to connect to the network or each other. Network cards are typically connected to each computer or A/V device via an interface slot.
After the card has been installed, the telephone cable is attached to the card's port. Once this connection is made, the computer is physically linked to the home network. All network cards are equipped with onboard microprocessors. The microprocessor is like the card's brain—it is the central point from which the card's various functions are coordinated. The roles of the network card are to:
Prepare data for transmission
Send data across the in-home network
Store data prior to transmission
Control the flow of data between the digital appliance and the transmission medium
The NIC also acts as a translator. When receiving data, it translates electrical signals from the telephone cable into bytes that the processor in the digital appliance can understand. And when transmitting data, it translates the computer's digital signals into electrical pulses that the telephone cable can carry. A typical HomePNA card will cost you around $100. This card contains the necessary hardware and software routines that are stored in read-only memory that allow you to create a home network using the existing in-home phone wiring system. Some HomePNA certified adapters come with connectors known as RJ-45. These interfaces are slightly wider than RJ-11 connectors and can be used to connect into a sophisticated data wiring system.
Software
As mentioned previously, every device on a home network needs an OS with networking capabilities. Once a NIC is installed in a PC, a driver is required to communicate with other appliances on the network. It is also very important that the driver is configured correctly. If the driver communicates commands to the network card quickly and clearly, the card will operate efficiently. If the card is not configured correctly by the driver, the card will perform less effectively. This will slow up network performance as a whole. HomePNA has decided to use the NDIS driver model that is integrated with most of the Microsoft Windows Operating Systems. NDIS is short for the "Network Driver Interface Specification."
As shown in Figure 4.3, NDIS provides a simplified plug-in driver architecture. At the lowest boundary layer, NDIS contains a driver that is specific to the telephone wiring transmission medium. The layer above this contains a platform-independent driver called a miniport. This layer interfaces through a standard Application Programming Interface (API) to the NDIS layer and this layer in turn communicates with the transport protocols that are running across the home network. A major advantage of the NDIS software model is that network cards can be installed in a telephone-based home network without requiring a truck roll from the local service provider.
Figure 4.3. NDIS architecture
HomePNA Products
The new HomePNA networking standard has caught the attention of a number of companies and has sparked the launch and deployment of several new products. The following subsections provide specific details about implementations based on the HomePNA standard. Please note that these specifications are subject to continual improvement and hence may have changed since the writing of this book. There is also a high probability that by the time you read this book, many more HomePNA products will have hit retail stores.
HomeRun Products from Tut Systems
Tut Systems is shipping HomeRun products that fulfill the promise of a home networking solution that is easy to install, easy to use, and inexpensive. These products use the telephone wires that already exist inside a home and eliminate the time, costs, and headaches associated with installing new wires. Simply plug any HomeRun-enabled device into an RJ-11 jack to allow it to share a 1 Mbps Ethernet-compatible network with other devices. A HomeRun network supports up to 25 PCs, peripherals, or network devices and connects them across distances of up to 500 feet. With Tut's HomeRun technology, telephones share the same physical wire with the network devices. Voice and data operate simultaneously on the same pair of wires without compromising the voice quality in any way.
HomeRun's 1 Mbps data rate provides the bandwidth necessary for today's home networking applications, such as file sharing, application sharing, and peripheral sharing. HomeRun allows users to share high-speed Internet access devices such as xDSL, wireless, ISDN, and cable modems. With simultaneous Internet access, it is no longer necessary for one person to wait while another finishes accessing the Internet.
Current HomeRun products include:
HR1000T HomeRun Ethernet Adapter—A stand-alone external adapter that connects any Ethernet device to a HomeRun network.
HR1000PCI NIC—A network interface card for desktop PCs. The network driver supports Windows 95, Windows 98, Windows NT 3.5.1, and Windows NT 4.0.
In addition to the products listed above, Tut is working with other industry leaders to license HomeRun technology for compatible networking products such as PCs, printers, TV-based browsers, IP telephones, IP cameras, and residential gateways.
3Com HomeConnect Networking Kit
At the beginning of 1999, 3Com teamed up with Microsoft to develop easy-to-use home networking kits based on Ethernet technologies. The 3Com HomeConnect kit includes the hardware and software you need to get your home network up and running. The cables and adapters that are included in the kit are simple to install and plug in. 3Com recommends the following PC hardware and software configuration for installing the kit:
486DX/66 Mhz or higher processor
CD-ROM drive
Available PCI slot
Windows 95, 98, or 2000
16 MB RAM
5 MB of hard disk space
Modem
HomeConnect home networking kits provide all the necessary hardware and software needed to set up a home network for high-speed Internet access, peripheral processing, and personal file sharing. A HomeConnect kit includes two 10/100 Mbps internal Ethernet network adapters, one five-port 10/100 Mbps dual-speed Ethernet hub, cables, HomeClick software, a Windows 98 Second Edition update, and a collection of Microsoft games.
3Com uses Microsoft HomeClick network software to simplify network setup. HomeClick network software features a step-by-step setup wizard and network center application. With HomeClick software, complex network configuration functions are transparent to consumers, since they are completed behind the scenes. You need only complete a simple series of steps to install a new home network. If necessary, HomeClick network software provides equally intuitive troubleshooting, helping you to pinpoint and correct any errors on your network.
Intel AnyPoint
In September 1998, Intel announced the Intel 21145 Phoneline/Ethernet LAN controller, a single-chip, low-cost silicon solution that enables home networking over existing telephone lines. Using this chip, PC and peripheral manufacturers can develop home-networking-capable devices.
On April 6, 1999, Intel announced the AnyPoint suite of phone-line–based home networking products. The AnyPoint network uses regular phone lines within your home to send data between your home PCs. From Figure 4.4 we can see that there is no network wiring to string, no complicated network configurations to tangle with, and you can use your phone normally. PCs on the home network can send and receive data at up to 1 Mbps—fast enough to share most PC resources with ease. At this speed, you can experience the Internet on all connected PCs, without bottlenecks. Because most Internet traffic is intermittent, the speed of your Internet connection is easily shared with all PCs. The 1 Mbps AnyPoint models will support up to 10 PCs, and the 10 Mbps products will support up to 25 PCs. The AnyPoint home network lets you simultaneously share access to the Internet across multiple PCs, even if only one connected PC has a broadband Internet connection, like a DSL or cable modem.
In addition to the products described above, large IT companies like Compaq, Linksys, and IBM have also started to ship families of products that are based on HomePNA.
Figure 4.4. Intel's AnyPoint network. (Courtesy of Intel Corporation)
