Hardware Reference
In-Depth Information
is 10 seconds, but longer amounts of time (up to unlimited!) are also supported by this feature.
Modem-on-Hold also allows you to make an outgoing call without hanging up the modem
connection. Modem-on-Hold, similar to previous proprietary solutions, requires that you have
the call-waiting feature enabled on your telephone line and that your ISP supports this feature of
V.92.
Note
Although Modem-on-Hold is good for the Internet user with only one phone line (because it
allows a single line to handle incoming as well as outgoing calls), it's not as good for ISPs
because when you place your Internet connection on hold, the ISP's modem is not capable of
taking other calls. ISPs that support Modem-on-Hold might need to add more modems to
maintain their quality of service if this feature is enabled. More modems are necessary because
the ISP won't be able to count on users dropping their Internet connections to make or receive
voice calls when Modem-on-Hold is available.
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PCM Upstream
—PCM Upstream breaks the 33.6Kbps upload barrier, boosting upload speed
to a maximum of 48Kbps. Unfortunately, because of power issues, enabling PCM Upstream can
reduce your downstream (download) speed by 1.3Kbps-2.7Kbps or more. PCM Upstream is an
optional feature of V.92, and ISPs who support V.92 connections might not support this feature.
Modems that support V.92 typically also support the V.44 data-compression standard. V.44, which
replaces V.42bis, provides for compression of data at rates up to 6:1—that's more than 25% better
than V.42bis. This enables V.92/V.44 modems to download pages significantly faster than
V.90/V.42bis modems can at the same connection speed.
Internet Connection Security
Virtually all forms of Internet connections use some type of external modem, which acts as a bridge
between the Internet and your PC or your local network. Many, if not most, of these modems are just
modems, and they do not include other functionality such as a router or a switch. Some modems
include a built-in router, and others include both a router and a switch. There is an important
distinction between them, and you need to know the ramifications before you use them.
The most important thing you can do for security when using a broadband Internet connection is to
ensure that you are connected though a router, which acts as a gateway with a hardware firewall
between your local network and the Internet. A router includes a DHCP (Dynamic Host Configuration
Protocol) server, which allows it to automatically assign private IP (Internet Protocol) addresses to
systems on your network. Then, once the addresses are assigned, the router uses Network Address
Translation (NAT) to translate packets moving between the private IP addresses on your network and
the publicly visible IP address assigned to the router itself. Using NAT, only the router is publicly
visible on the Internet; all of the systems behind it are effectively hidden. This provides a hardware
firewall to protect the PCs on your network.
If your modem includes multiple Ethernet ports for connecting PCs, most likely it has both a router
and a switch built in. In that case, you can connect PCs to the modem/router safely, and the built-in
router will protect your systems. If your modem has only a single port, that means it definitely doesn't
include a switch and may or may not include a router. If it does include a router, and you only want to
