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CHAPTER 3: NETWORKING
Communications
Data communication involves the flow of packets of data from one device to another. These devices include
personal computers, Ethernet, cable modems, digital routers and switches, and highly integrated devices that
combine functions, like the Wireless Cable Gateway.
The gateway integrates the functionality often found in two separate devices into one. It’s both a cable
modem and an intelligent wireless voice gateway networking device that can provide a host of networking
features, such as NAT and firewall. Fig.3-1 illustrates this concept, with the cable modem (CM)
functionality on the left, and networking functionality on the right. In this figure, the numbered arrows
represent communication based on source and destination, as follows:
Fig.3-1 Communication between your PCs and the network side
Type of Communication
1.
Communication between the Internet and your PCs
Example: The packets created by your request for a page stored at a web site, and the contents of that
page sent to your PC.
2.
Communication between your cable company and the cable modem side
Example: When your cable modem starts up, it must initialize with the cable company, which requires the
cable company to communicate directly with the cable modem itself.
3.
Communication between your PCs and the networking side
Example: The Wireless Cable Gateway offers a number of built-in web pages which you can use to
configure its networking side; when you communicate with the networking side, your communication is
following this path. Each packet on the Internet addressed to a PC in your home travels from the Internet
down- stream on the cable company’s system to the WAN side of your Wireless Cable Gateway. There it
enters the Cable Modem section, which inspects the packet, and based on the results, proceeds to either
forward or block the packet from proceeding on to the Networking section. Similarly, the Networking
section then decides whether to forward or block the packet from proceeding on to your PC. Communication
from your home device to an Internet device works similarly, but in reverse, with the packet traveling
upstream on the cable system.
