PDF of this tutorial| To be truly wired, you must be wireless. —Wired, October 1997. |
Wireless-Based Transport Element (Irda, Analog Cordless Phone)
The typical topology of these elements is demonstrated in Figure 6.
Figure 1. Worldwide Local-Loop Demand
Traditional wireless home-networking technology is used for line-of-sight, infrared, unidirectional, hand-held controller applications. Typical uses today are for VCRs, TVs, and some security and alarm applications. The other obvious wireless technology is the cordless phone. However, neither can be definitively classified as a robust home-network element. The cordless phone still requires the twisted copper pair and a jack as an access point, and today's infrared applications rarely leave the confines of the home.
Wireless-Based Transport Element (Radio Frequency)
Currently, there are several standards and working groups focused on wireless networking technology (radio frequency [RF]). These include the IEEE 802.11, HomeRF, Bluetooth, and standard wireless access protocol (SWAP). Wireless-based transport element technology can be used to distribute multiple types of information within the home. Some examples use a discrete controller device, some a PC as a controller device, and others no controller device at all (i.e., peer to peer). Wireless RF transmission is the recognized home-networking topology of choice for the emerging network-centric home as a result of its flexibility, mobility, and ability to network without wired connections.
The RF Transport Network Element
Most emerging home-networking wireless systems utilize spread-spectrum technology. This technology offers high bandwidth capacity and is used widely in the military, as it is secure and reliable. Two types of spread-spectrum radios are in common use today: frequency-hopping spread-spectrum (FHSS) and direct-sequence spread-spectrum (DSSS) radios. These radios will not interoperate, as a result of different frequency bands and vendor systems. System selection is critical, and once the user engages a supplier, it is difficult to transfer to another—even in those cases where industry standards are in effect. De facto or proprietary standards reign.
FHSS is a narrowband carrier with changing patterns of transmission that are recognized by both receivers and transmitters. When the two devices are in synch, they produce one logical communications channel.
DSSS produces bit patterns called chips or chipping codes. Reliability is based on the length of the chipping code or on how many bits of data it carries. Because an error-correcting function is built into radios, it is often not necessary to retransmit data, thus improving performance.
PC or Non–PC–Based Wireless Systems
System suppliers use several approaches, two of which are detailed in this tutorial: a PC–centric, data-only application and a data and voice home-networking application.
The PC–Centric, Data-Only Network
Some software and hardware suppliers provide home-networking solutions via a wireless LAN, using the home's PC as the central control element. Figure 7 reflects a wireless home LAN configuration in which one PC acts as a master to the network. It provides network addressing and routing between the home and the Internet.
Figure 7. PC–Based Wireless Home Networking System
This straightforward approach simply marries familiar PC technology to new home-networking technology. It also represents some consumer-marketplace challenges to ultimate mass-market success.
First, a home network built around a master PC implies that the PC will always be on and available for communications. It also implies that no other software or hardware application running on the PC can interfere with its ability to perform its communications tasks. Consumers are somewhat forgiving of PCs that have fatal errors and must be rebooted. They generally do not forgive their communications-network failures, because they expect the network to function smoothly at all times—as it historically has.
Second, a home network built around a master PC only addresses the PC–related network elements in the home such as file and printer sharing, multiuser game playing, and a single shared ISP account. It leaves the other elements such as voice communications and control and monitoring applications without a solution.
The Controller-Based Data and Voice Home Network
Figure 8 demonstrates the use of one integrated home-network system available on the market today.
Figure 8. Voice and Data Wireless Home Networking System
In this scenario, the microprocessor-based digital switch acts as the communications server, addressing and routing voice data traffic throughout the home. It also sends the home network–transport element through a powerful on-board RF transceiver. The transceiver is based on patented digital spread-spectrum technology and has an effective reach of several hundred feet from the home.
The controller shown in Figure 8 supplies a robust home network for voice and data with high bandwidth capacity. It is the bridge between the transport network element serving the home from the customer-selected service provider and the wireless home network. Networked devices require no wires or fixed wired jacks. This system also offers several hundred feet of accessibility within and outside the home. There are no relocation restrictions. Data and voice services, including internal device-to-device communications, are commonplace.
There are four distinct functional areas served by a controller-based, data and voice home-network system:
- home local-area network—Networking capabilities provide the home-network user an easy-to-install LAN between all PCs within the home. This allows sharing of computer files, printers, and disk drives and supports multiplayer PC games via a wireless Ethernet and a transmission control protocol (TCP)/Internet protocol (IP) LAN.
- Internet gateway—The controller provides an Internet gateway addressing and routing function for sharing a single ISP account and connection with all PCs. All surf the Internet at the same time on only one 56-kbps, 128-kbps, or faster account, with only one monthly charge.
- wireless voice networking—Each wireless handset can view and manage up to four plain old telephone service (POTS) lines while the PCs are simultaneously being used on the LAN. The handset displays allow users to access caller ID and voice-messaging status information and make decisions about call management in real time.
- traditional wireline POTS networking—All telephone lines serving a home terminate on the controller. They are then distributed to wireless handsets or to wireless RJ–11 phone jacks with built-in transceivers to which standard telephones, fax machines, or modem-equipped PCs can be connected.
The non–PC–based switching center (the controller in Figure 8) is software derived so that new networking requirements in the home can be met without wholesale changes. Future developments for home networking are outlined in the next module.
