Definition

Universal multimedia access refers to access to multimedia content over wired and wireless networks on a range of devices with varying capabilities.

Recent technology advances have made possible access to digital multimedia content over wired and wireless networks on a range of devices with varying capabilities such as mobile phones, personal computers, and digital video recorders. This Universal Multimedia Access (UMA), enabled by new technologies and standards, poses new challenges and requires new solutions. Content delivery services to resource constrained devices such as mobile phones are limited due to the mismatch between the resources required to play the content and the device capabilities.

Figure 1 shows the key elements of a pervasive media delivery environment. The capabilities of the receivers in such an environment vary, requiring a server that can satisfy receivers with different capability sets. The capabilities of these devices would also change with the available battery, concurrently running applications, and available resources such as memory, bandwidth, and peripherals. As the available resources on a device change, the capability of the devices to process/playback content also changes. The resource variants shown in Fig. 1 represent the same device with changing capabilities. As the capabilities of a device change, the device cannot continue to play the same content. The content now has to be adapted to meet the resource requirements or the session has to be terminated. The content available at a sender may be adapted dynamically to meet the changing resource capabilities or a discrete number of content variants could be created offline to serve the receivers. The primary goal of content adaptation is to maximize the end users quality of experience given the resource constraints at the receiver and the sender.

Universal Multimedia Access. Figure 1.
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Pervasive media delivery environment.

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Content Adaptation

The mismatch between the content and resources required to play the contest is bridged using adaptation techniques. The adaptation techniques can either adapt the content to match the receiver capabilities or adapt the resources to match the content. Resource adaptation typically takes the form of resource acquisition. The content adaptation problem has two aspects (1) determining what information to send and (2) how to encode that information efficiently for transmission. Determining the right information to be sent based on user preferences and available resources uses summarization techniques that strive to maintain semantic equivalence with minimal amount of information [1]. Once the appropriate content has been determined, a suitable compression technique is selected and the content is transcoded to match the receiver capabilities [2].

Resource Adaptation

Another approach to UMA is through resource acquisition. A receiver acquires additional resources to bridge the mismatch with the content, primarily by collaborating with other devices in its environment and thus creating a virtual device. This virtual device approach to receiver adaptation was reported in [3]. The availability of Bluetooth and the upcoming short range ultra wideband communications make the virtual device a possibility. The virtual device concept works well in home and office environments with access to a number of peripherals. The key issue here is security: how can trust be established in a peripheral device.

Standardization

The UMA is also supported by the international standardization activities. The MPEG committee, under its MPEG-21 activity, has standardized tools for digital item adaptation (DIA) [4]. Digital item is a generic term for digital information that is exchanged between devices. The standard specifies tools for describing the digital items and adaptation alternatives when adaptation is necessary. The TV anytime forum has also released a series of specification to enable pervasive audio visual services (www.tv-anytime.org). The W3C has developed a standard to describe device capabilities and user preferences called Composite Capabilities/Preferences Profile (CC/PP) [5]. The CC/PP descriptions can be used during session setup to understand the receiver preferences and capabilities. These CC/PP descriptions can drive the content and resource adaptation necessary to make the content delivery possible.