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Chapter 2: Networking
Chapter 2 19
Illustrations contained in this document are for representation only.
Communications
Data communication involves the fl ow of packets of data from one device to another. These
devices include personal computers, Ethernet and USB hubs, 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 gateway networking device that can provide a host
of networking features, such as NAT and fi rewall. Figure 2 illustrates this concept, with the cable
modem (CM) functionality on the left, and networking functionality on the right. In this fi gure,
the numbered arrows represent communication based on source and destination, as follows:
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
CM
CM IP
IP Stack 1
CPE IP
IP Stack 2
WAN
LAN
Networking
Cable Modem Section
Networking Section
Cable service
Connected to your PC via:
• Ethernet
• 802.11b/g
• USB
1
2
3
1
Fig. 11
DCW725 book file.indb 19 DCW725 book file.indb 19 10/6/04 11:17:22 AM10/6/04 11:17:22 AM