Chapter 1. Introduction

Using a PC at home to finish a little bit of work or to access the Internet has become a common practice. You might use a dial-up connection, a cable modem, or a DSL (Digital Subscriber Line) for your access. A broadband access service, such as a cable modem or a DSL, usually costs twice as much as that of the dial-up service. However, it is a much better option than installing a second phone line to keep the primary line open for in-coming calls, especially during prime hours. Used with a wired or wireless home network, multiple PCs and their users can share broadband access service at home simultaneously without noticeable access time degradation. Because of the popularity of broadband access services, the number of PCs at home, and the affordability of transmission devices, home networks are turning up in a growing number of households. With so many different households having network connections and a wide range of electronic devices, you might wonder at one time what is really going on when a Web page from a remote corner of the Earth is being displayed on your PC screen.

Information such as a text document, picture, or piece of recorded music is encoded as binary digits, or bits, of 1s and 0s. When interacting with a computer or a Web site, your commanding or responding key strokes are also coded into bits. Information and command bits are converted into electrical or light signals when relaying over a copper or optical communication link. To achieve high efficiency and reliability, a different protocol, including the definition of the electrical or optical signal, the encapsulation of information bits, and the set-up procedure, is usually specified for each individual communication link according to its unique throughput requirements and transmission media characteristics. An Internet access from a home PC consists of many communication links, which could include an Ethernet from a PC to a DSL modem at home, a DSL connecting a home to a CO (Central Office), an OC-3 (Optical Carrier 3) from a CO to a regional Internet access point. From the Web site regional Internet access point, there might be another OC-3 to a local CO, and a T3 from a CO to the Web site host location. SONET (Synchronous Optical NETwork) rings might be involved from one Internet access point to another.

After you gain access to the Internet, end-to-end application connections can be established for useful services such as e-mail, Web browsing, and instant messaging for known destinations based on the Internet Protocol (IP). Internet destination addresses of particular interests can also be identified through portals such as Yahoo. The information exchange between remote Internet destinations is accomplished by transmitting a different type of packet. A packet usually consists of a header and a body. The header normally contains source and destination addresses as well as some kind of identification that explains the purpose of the packet. The body can carry a command/response or an encoded text/picture. The IP is defined based on a set of packet formats and their exchanging procedures. The operation to detect and interpret these IP conforming packets has been embedded into e-mail and Web browser software such as Outlook and Netscape.

An original command or encoded text can be encapsulated many times before being relayed over a transmission link as an electrical or optical signal. For example, an e-mail message is first encapsulated into an IP packet, which in turn is encapsulated into an Ethernet packet for transmission to a DSL modem over a Category 5 twisted pair or a home network, and the Ethernet packet is encapsulated again into ATM (Asynchronous Transfer Mode) cells to be carried to a CO over DSL. There are always peer-to-peer connections to encapsulate and to recover the original packet. When you send an e-mail, a few ATM cells carrying the Ethernet packet, which carries the IP e-mail packet, are sent to a CO via Ethernet and then DSL. These ATM cells are then sent to a regional Internet access point also known as an ISP (Internet Service Provider) where the original IP e-mail packet is recovered and sent to the destination e-mail server over the Internet. The e-mail server sends back an IP packet to acknowledge the reception of the e-mail.

A home network can thus be used to share a broadband Internet access among multiple PCs. PCs connected to a home network can also share files on their hard disk drives and such peripheral devices as printers via the NetBEUI (NetBIOS Extended User Interface) protocol, which is supplied with every Windows operating system. Home networking has also been associated earlier on with home automation where household lighting and appliances were controlled automatically and remotely. One objective for implementing a hassle-free home network has been "no-new-wiring." In fact, some wiring infrastructures already exist in a typical home environment. There is usually at least one power plug on each wall of a living quarter; multiple telephone outlets and cable TV plugs can be found within a house. Wiring for the HVAC (Heating, Ventilation, and Air Conditioning) system and networked smoke detection devices is less accessible but still available. Wireless communication devices that use either Radio Frequency (RF) or Infrared also meet the "no-new-wiring" requirement very well. PC application-based home networks have increased in popularity recently and can be further expanded to distribute multimedia contents such as HDTV (High-Definition TV) signals. A high-throughput minimum latency home network can also be easily adjusted to accommodate other home networking needs such as home automation.