C. Las etapas del proceso penal acusatorio y oral.
2. Etapa intermedia o de preparación del juicio oral.
Several data storage and distribution systems have been researched. These include the centralized system, the storage area network (SAN), the content distribution network (CDN), and the serverless or peer-to-peer (P2P) net- work.
The centralized system stores all the multimedia objects in one location. The storage area network stores the multimedia objects on several servers. These storage servers are connected over a local area network using optical
fibres. The content distribution network distributes the multimedia objects on servers that are spread over a wide area network. Client requests are sent to the nearest server that contains the object to serve the request.
The serverless systems or peer-to-peer networks do not permanently store the objects on the servers. The server containing the object will only serve the
first few requests for the object. Afterwards, the nodes that have the object
will become the seed and serve other clients (Jeon & Nahrstedt, 2002). Thus, the server can become free, and it can be disconnected from the network.
Delivery.Network.and.Scheduling
The data delivery network can be built by laying dedicated cables or by the Internet. The multimedia objects can be delivered via broadcasting or video- on-demand (VOD) systems. Depending on the delivery scheduling and the delivery network, at least four types of system architectures can be built. The interactive television (ITV) companies build their systems by broadcast- ing over dedicated cables (Figure 2.1). In the systems, the users subscribe to an ITV company. The ITV company broadcasts a number of channels of
TV TV
Cable network
STB
STB
STB: Set Top Box
Interactive TV Broadcasting Server
Hard
disk …
video content via a cable to a dedicated set-top box (STB). The STB is then connected to the television set. The user selects a channel to watch via a remote control unit of the STB (Furht, 1996).
The ITV companies may provide video-on-demand via dedicated cables (Figure 2.2). In the systems, the users subscribe to an ITV company. The ITV Company downloads a movie list to the Set Top box. User then selects a movie from the list using remote control of set top box. The ITV Company broadcasts the movie in a new channel to the user. Some user may join an existing channel to watch.
Figure.2.2..Video-on-demand.over.dedicated.cables TV TV Cable network STB STB
STB: Set Top Box
Interactive TV Video On Demand Server Hard disk … Figure.2.3..Broadcasting.over.the.Internet
Internet
Broadcast Streaming Server User computers Hard disk…
The content providers may deliver multimedia objects by broadcasting over
the Internet (Figure 2.3). Users first subscribe to a content provider on the
Internet. They are then allowed to join a live video/audio channel. The content provider then delivers the live multimedia objects from the streaming servers to all users. Users then use their browser to receive and play streams. The content providers may also provide video-on-demand services over the
Internet (Figure 2.4). Users first subscribe to a content provider on the Inter- net, and the user may select a multimedia object from the content provider’s Web site. The content provider then tests the streaming ability to the user’s computer. The streaming server delivers the low or high resolution object suitable for delivery to the user. The browser on the user’s computer receives and plays the streaming object.
Video-on-Demand.Systems
Four different types of video-on-demand systems have been investigated (Furht, 1996). These include the near video-on-demand (NVOD) systems, true video-on-demand (TVOD) systems, partitioned video-on-demand (PVOD) systems, and dynamically allocated video-on-demand (DAVOD) systems. In the true video-on-demand systems, the user has complete control of a multimedia program. The user can perform normal play, reverse play, fast forward, random positioning, pause, and resume. In this system, each user is allocated a unique channel during the total duration. It allows complete user interactivity. The number of concurrent users is however limited by the
Figure.2.4..Video-on-demand.over.the.Internet
Internet
Video On Demand (VOD) streaming server
Hard disk …
number of available channels. As a result, many potential viewers may not be able to access the system during the busy period of time.
The near video-on-demand system (Figure 2.5) provides video distribution at relatively low cost. This system however provides only limited user interactivity. A popular video is broadcast using several streams or channels. Each channel is
separated from the previous channel at a fixed interval. When the user requests for
this video, the user’s access will be delayed until the start of the next stream. The partitioned video-on-demand system (Figure 2.6) combines the advan- tages of both NVOD and TVOD systems. User interactivity is provided at the capacity of the system. Digital channels are partitioned into two groups: NVOD and TVOD services. NVOD channels broadcast the most popular
Figure.2.5..Near.video-on-demand.system Channel 1 Channel 2 Channel n
…
T Channel 3 Tstart end start again
Video length
start end
Consecutive channels start the same video with a time difference ofTsec. User waits for a time period up to T
seconds to watch a video from the beginning.
Figure.2.6..Partitioned.video-on-demand.systems 50 broadcast channels 450 interactive channels Near VOD 250 channels True VOD 200 channels
All channels are divided into broadcast channels and
interactive channels. The interactive channels are subdivided into Near Video On Demand channels and True Video On Demand channels.
video with limited user control. TVOD channels will provide complete user control functions. For example, the digital channels are divided into 50 broadcast channels and 450 interactive channels.
The dynamically allocated video-on-demand system is an extension of the PVOD scheme. The user, watching a video from the NVOD list of most popular videos, can request the interactivity with the video at any time. If a channel is available, the user will be switched to the TVOD group of chan- nels which allows complete control. The split-and-merge (SAM) protocol provides a mechanism to split user streams for interactive functions and merge streams when possible (Liao & Li, 1997).
Video.Conference.System
In video conference systems (Figure 2.7), computers are each installed with a video camera, microphone, and connected to the network. A user initiates and hosts a conference meeting. Other users then join the meeting. All of them send their own video and audio signals to all the other users. Users may speak, type, or draw on whiteboard.
In these systems, the network needs to deliver the video capture stream from every user to all other users. The number of video streams is equal to n(n- 1) for n concurrent users. Thus, the network needs to support a very large number of streams.