UpnP in Digital Home Networking

Network Systems & Technologies (P) Ltd
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UPnP in Digital Home Networking
A White Paper
Network Systems and Technologies - NeST
Thiruvananthapuram
India
www.nestsoftware.com

UpnP in Digital Home Networking – A Whitepaper
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Copyright Information
Copyright 2004 NeST
NeST owns all title to the contents of this document and its copyright, which
are protected by copyright law and international treaty provisions. No part of
this document may be reproduced in any form or by any means without
written permission from the publisher.
It is against the law to copy the information described in every part of this
document.

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Abstract
This paper provides an overview of Universal Plug and Play (UPnP) and how
it works to build a digital home network. UPnP network technology allows
personal computer and consumer electronics devices to advertise and offer
their services to network clients. UPnP can be viewed as the technological
foundation of the digital home, enabling innovative usage models, higher
levels of automation, and easier integration of devices from different
manufacturers.
UPnP technology is all about making home networking simple and affordable
for users . UPnP architecture offers pervasive peer-to-peer network
connectivity of PCs of all form factors, intelligent appliances, and wireless
devices. UPnP architecture leverages TCP/IP and the Web to enable
seamless proximity networking in addition to control and data transfer among
networked devices in the home, office, and everywhere in between. UPnP
technology can be supported on essentially any operating system and works
with essentially any type of physical networking media - wired or wireless -
providing maximum user and developer choice and great economics.

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What is UPnP?
UPnP technology is a distributed, open networking architecture that employs
TCP/IP and other Internet technologies to enable seamless proximity
networking, in addition to control and data transfer among networked devices
in the home, office, and public spaces. UPnP technology enables developers
to create such products — products that free their customers from thinking
about network configurations, setup, maintenance, software or Internet
protocols. Universal Plug and Play (UPnP) extends this simplicity to include
the entire network, enabling discovery and control of devices, including
networked devices and services, such as network-attached printers, Internet
gateways, and consumer electronics equipment.
UPnP is more than just a simple extension of the Plug and Play peripheral
model. It is designed to support zero-configuration, "invisible" networking,
and automatic discovery for a breadth of device categories from a wide range
of vendors. With UPnP, a device can dynamically join a network, obtain an IP
address, convey its capabilities, and learn about the presence and
capabilities of other devices—all automatically; truly enabling zero
configuration networks. Devices can subsequently communicate with each
other directly; thereby further enabling peer to peer networking.

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UPnP uses standard TCP/IP and Internet protocols, enabling it to seamlessly
fit into existing networks. Using these standardized protocols allows UPnP to
benefit from a wealth of experience and knowledge, and makes
interoperability an inherent feature. Because UPnP is a distributed, open
network architecture, defined by the protocols used, it is independent of any
particular operating system, programming language, or physical medium (just
like the Internet).
The “Digital Home Platform”
UPnP is gaining momentum as the preferred device discovery and control
protocol for IP networks in the home and small office. There are many UPnP
SDKs (software development kits) and development tools available. Over
time, as more and more UPnP devices appear based on these SDKs, a new
digital home platform will emerge with UPnP technology as the foundation.
The digital home platform will span wired and wireless networks,
entertainment devices, telephone equipment, home control, and so on. It will
link the various networks in the home—entertainment, home control and
automation, communications, and the data network—into a single logical
network of programmable devices.
The resulting logical network will contain a multitude of UPnP devices that
will be able to interact with each other. Speakers, for example, could be
networked and used for a variety of purposes, not just for playing audio.
Control points on the network, such as the PC in the den, or the television
and remote in the entertainment area, will have programmatic access to all of
the devices on this network and will be able to run programs that aggregate
the devices into innovative applications.
The UPnP foundation of the digital home will enable a transition to new home
networking usage models. This transition will have great benefits for people
in the home, as the focus will shift from a specific user interaction model—
"the computer in the den"—to devices supporting user activities in the home
in their natural settings.
Eventually, entertainment devices will be networked and have UPnP device
capabilities built-in and won't need a proxy UPnP device. Devices will work
together to provide new usage models that support the various activities in
the home, providing new kinds of user interaction paradigms and new levels
of automation. The figure shows a sample home network with some of
today's UPnP devices.

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The UPnP Device Architecture
The key components of the UPnP architecture are as follows:
Devices
A UPnP device can contain a number of services and nested devices. For
identification purposes, the device must host an XML device description
document that lists specific properties about the device, the services
associated with the device, and the nested devices. The device description
document must also include a Uniform Resource Locator (URL) for the
service description. The service description is an XML document that lists the
actions and state variables that apply to a specific service offered by the
device.
Services
Services or functionalities are provided by a UPnP device for other devices to
use. A UPnP service consists of state variables that provide information

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about the service, and actions that can be invoked to take advantage of what
the service provides.
Control Points
A UPnP control point is a controller (which may be embedded in a UpnP
device but typically a PC) capable of discovering and controlling other
devices. A control point is able to retrieve descriptions of devices and the
services they offer, invoke the advertised actions to use the service and
subscribe to a service to receive event messages.
UPnP Networking Mechanisms
There are seven steps in the UPnP mechanism.
Step 0: Addressing
The device and control point search for a DHCP server to get an IP address.
If no DHCP server is available, automatic IP addressing (Auto IP) should be
used
to obtain an IP address.
Step 1 : Description
Description allows devices to list the functionality they provide. Descriptions
of devices and their services are contained in XML-based description
documents. The device description document contains device information
such as manufacturer, make, model, and serial number; a list of services
provided by the device; and a list of embedded devices. A service description
document contains detailed information about a device's service, the actions
that service provides, and the service's parameters and return value. Control
points in the device discovery process use description documents in order to
learn more about a device. The figure illustrates the device and service
description hierarchy.

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Step 2: Discovery
The device advertises its services to the control point on the network when it
is added to the network. The discovery process enables control points to find
devices and services of interest and retrieve information about them. UPnP
devices use the Simple Service Discovery Protocol (SSDP) for Discovery.
SSDP extends the HTTP (Hypertext Transfer Protocol) header to provide a
simple multicast-based discovery protocol.
Once a device has acquired an IP address, that device periodically
advertises itself and its services on the network. A device includes a URL of
its device description XML document in its advertisement and discovery
responses. That URL provides control points with the information those
control points need to retrieve the device and service descriptions

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Step 3: Control
The control point can invoke actions to manipulate the services on a device
by sending suitable control messages to the device using the Simple Object
Access Protocol (SOAP).
Step 5: Eventing
The control point can subscribe to a device's service for event messages.
Event messages are published when changes in device status occur. The
messages contain the name of one or more state variables and the current
value of those variables. Event messages are expressed in XML syntax and
formatted using the General Event Notification Architecture (GENA).
The figure shows how a control point communicates with a service to
subscribe to and receive notifications of state variable changes.

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Step 6: Presentation
The control point can display a user interface provided by the device. By
retrieving a page from the device URL into a browser, you can view the
device’s status and/or control the device.
Conclusion
UPnP is the foundation of other home networking standards such as the
Digital Living Network Alliance (formerly the Digital Home Working Group)
and Intel's Networked Media Products Requirements (NMPR) specifications.
These specifications add to the UPnP foundation, going beyond the basic
UPnP device architecture specification to include media formats and other
issues such as Digital Rights Management (DRM) to ensure a higher degree
of device interoperability
UPnP implementation is not rocket science, and there are excellent tools to
make the design of UpnP enabled devices even easier. User interface design
can be as simple as an HTML page. No additional hardware is required.
Once vendors and users see the power of UPnP, every network-enabled
device will also be UPnP enabled.

UpnP in Digital Home Networking

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