Chapter 12. Home Networking Protocols

When a user interacts with a Web server over the Internet using his PC connected through a home network to an ADSL line, IP packets are exchanged frequently across many different segments of a network connection. IP packets are encapsulated with Ethernet frames and again with ATM cells through the home network and the ADSL line and recovered by an Internet Service Provider (ISP). Many different formats of home networking physical layers discussed so far are designed to be used by communication applications mainly through a PC. Transmission physical layers usually provide only physical layer signaling and Media Access Control capabilities. Functions to utilize these physical layers such as Logic Link Control and Internet Protocols are usually implemented as a part of a computer operating system, such as Windows or Linux, or require dedicated hardware for the case of a home router. An integrated home network structure is better viewed through not only wiring configurations but also involved communication protocols. For practical purposes, many implementable home network configurations using different physical layers are described in this chapter along with the introduction of broadband internet access, peer-to-peer networking, network address translation, and MAC bridge. These functional components provide fundamental benefits to the home network utilizing those physical layers.

A broadband internet access involves a communication link between an ISP and an ADSL or a cable modem and a connection from the modem to a PC or PCs. An ADSL communication link is established and maintained via a Permanent Virtual Circuit (PVC) of ATM cells. A cable modem communication link relies on LLC or SNAP (SubNetwork Access Protocol). The connection from the modem is usually a twisted pair Ethernet cable. The connection from a modem can be extended to multiple PCs using an Ethernet hub and/or a home router. A peer-to-peer network for sharing files and printer among multiple PCs can be enabled by using an Ethernet hub and activating the NetBEUI protocol on connected PCs. NetBEUI consists of a group of communication protocols for name management, connectionless, and connection-oriented transmissions. A single IP address can be shared by multiple PCs and their users by using a home router with NAT (Network Address Translation) or NAPT (Network Address Port Translation) function. NAPT maps a single public IP address of different port numbers to a group of dynamically assigned internal IP addresses. Different physical transmission layers can be grouped together using the MAC bridge function. A MAC bridge relays packets among different physical networks based on MAC addresses it learned by monitoring the transmission traffic.