Specifications

W
hether it’s to share files or In-
ternet connections or to play
digital content throughout
the house, networking has become part of
everyday life for many home and small-
business users. Despite this, networks
haven’t gotten a whole lot easier to set up
and configure. But a technology called
Universal Plug and Play (
UPnP) is starting
to make networking-configuration hassles
a thing of the past.
Just as Plug and Play (PnP) technology
changed the way we integrate hardware
with our
PCs, UPnP will ease the way we
add devices to a network. With PnP, you
no longer need to configure resources for
each device manually, hoping there are
no conflicts. Instead, each device identi-
fies itself to the operating system, loads
the appropriate drivers, and starts oper-
ating with minimal fuss.
PC-based net-
works, however, still require a cumber-
some setup and configuration process,
and devices such as printers,
VCRs, PDAs,
and cell phones are still difficult or im-
possible to network.
With
UPnP, adding devices to your
network can be as easy as turning them
on. A device can automatically join your
network, get an
IP address, inform other
devices on your network about its exis-
tence and capabilities, and learn about
other network devices. When such a de-
vice has exchanged its data or goes out-
side the network area, it can leave the
network cleanly without interrupting any
of the other devices.
The ultimate goal is to allow data com-
munication among all
UPnP devices re-
gardless of media, operating system, pro-
gramming language, and wired/wireless
connection. To foster such interoperability,
UPnP relies on network-related technolo-
gies built upon industry-standard proto-
cols such as
HTTP, IP, TCP, UDP, and XML.
Let’s take a closer look.
UPn
P is an open networking architec-
ture that consists of services, devices,
and control points. Services are groups
of states and actions. For example, a
light switch in your home has a state
(either on or off) and an action that
allows the network to get or change the
state of the switch. Services typically
reside in devices. A
UPnP-compliant
VCR might, for example, include tape
handling, tuning, and clock services—all
managed by a series of specific actions
defined by the developer. Devices may
also include (or nest) other devices.
Because devices and their correspond-
ing services can vary so dramatically,
there are numerous industry groups
actively working to standardize the
services supported by each device class.
Today, there are four standards: Inter-
net Gateway Device (
IGD) V 1.0; Media-
Server V 1.0 and MediaRenderer V 1.0;
Printer Device V 1.0 and Printer Basic
Service V 1.0; and Scanner (External Ac-
tivity V 1.0, Scan V 1.0, Feeder V 1.0, and
Scanner V 1.0). Industry groups will pro-
duce
XML templates for individual de-
vice types, which vendors will fill with
specific information such as device
names, model numbers, and descriptions
of services.
The various
UPnP devices will be
identified and managed by one or more
control points (a controller, such as an
application) on the network. In practice,
many devices may include control
points in order to facilitate true peer-to-
peer networking.
When a device is added to a
UPnP net-
work, its first step is to obtain an
IP ad-
dress. Once this is accomplished via its
internal
DHCP client, the device adver-
tises its presence, providing a descrip-
tion of itself and its services. A control
point receives the description, which in-
cludes a list of actions related to each
service and the variables that define the
possible states for the device, and then
sends action requests to the device. Re-
sults of the requests are published via
event messages sent by the particular
service and include the values of state
variables. If appropriate, the control
point presents a page in a user’s browser
that lets the user manage the device or
monitor its status.
This isn’t just theory. Both Microsoft
Windows Me and
XP support UPnP, and
many manufacturers are now producing
UPnP-compliant network devices. For
example, a variety of products, such as
the
D-Link DFE-530TX+ 10/100
Ethernet network adapter
(www.dlink.com) and the Linksys
EtherFast
BEFSR41W four-port
cable/
DSL router (www.linksys
.com), now fully support
UPnP.
And the new MusicMatch Juke-
box 8.0 media player supports
UPnP home-networking devices.
Industry groups will continue to
define new services not only for
PCs and related peripherals but
for home appliances, automo-
biles, and entertainment/media
devices—adding more flexibility
and features for home and small-
office users.
There is one caveat with regard
to
UPnP: security. Certain vulnerabilities
have been discovered in components of
Microsoft’s implementation of
UPnP,
which can let an attacker gain control of a
target system or exploit vulnerable sys-
tems to cause a distributed denial-of-ser-
vice attack (
DDoS). It is therefore impor-
tant to download and apply the patch
found at the Microsoft Security Bulletin
MS01-059 (www.microsoft.com/technet/
treeview/default.asp?url=/technet/security/
bulletin/ms01-059.asp) even if you’re not
yet using
UP
nP.
Stephen J. Bigelow is the author of Trouble-
shooting, Maintaining, & Repairing Per-
sonal Computers (5th edition).
PC MAGAZINE SEPTEMBER 16, 2003 www.pcmag.com
62
SOLUTIONS | HARDWARE
Universal Plug and Play:
Networking Made Easy
Imagine adding devices—from PCs to consumer electronics—
to your network, with zero configuration!
By Stephen J. Bigelow
UPnP DEVICE DEVELOPERS use standards, such
as GENA (General Event Notification Architecture)
and SSDP (Simple Device Discovery Protocol), to
enable automatic discovery and description.
DIAGRAM COURTESY OF THE UPnP FORUM