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IP Packet charging for multimedia services( Télécharger le fichier original )par SAIDI SAIBA et KAYISINGA Jean de DIEU National University of Rwanda - Bachelor's degree 2007 |
II.5.1.2 CHARACTERISTICS OF MULTIMEDIAMultimedia can be as simple as a few images with some accompanying text to a multimedia presentation using video clips, sound, images animation and text. Multimedia files to use a lot of data when in a digital format. Video is the most demanding. A PAL signal when digitised can require a data rate of 170 Mbps. Audio is less demanding but still requires 1.3 MB for a 1 minute clip using a Sound Blaster Pro system at 22 kHz sampling rate. Still images require use more data proportional to their size. Synchronisation of sound and video is important. Sound is likely to break up if parts of it are lost or delayed in storage or transmission. Video is less vulnerable to loss (depending on the application), but still requires the entire picture to be on the screen at the same time and is also vulnerable to jitter. Jitter could be controlled in some applications if the sender of the isochronous video data time stamps each piece of data when it is generated, using a universal time source, and then sends the data to the receiver. The receiver reads a piece of data in as soon as it is received and store it. The receiver processes each piece of data only at the time equal to the data's time stamp plus the maximum transit delay. Thus isochronised of the video would be restored. II.5.1.2 COMPRESSION have this sort of network access compression is the only hope for the widespread deployment of digital video and multimedia. Compression techniques depend on algorithms implemented in software or hardware. The use of hardware is important still to enable rapid compression, and also speeds de- compression. At this time the cost of hardware is still high, from 200 to 350 for a MPEG video compression PC card. Sound cards can implement proprietary compression, and software only video compression is available in products like Microsoft Video for Windows, or for UNIX operating system workstations. While compression can ease the demands on networks and storage media there is several trades-offs. Since some compression techniques remove information considered to be less important a loss in resolution may result. Once material is compressed the algorithms may prevent access to single frames of video for viewing or editing. The cost of complex hardware and software and compression and decompression delay are other factors important to users. Different uses require different compression methods. Video conferencing must be done in real time so fast encoding and decoding is needed. This is the aim of the H.261 standard. Video film distribution via cable networks, radio or CD is essentially a playback process, so encoding is not time critical, and decoding should be easy to implement to reduce consumer costs. The MPEG standards address these applications. MIDI encoding of audio notes is not really a compression method, but almost another form of media. Inevitably, successful compression techniques encourage the design of applications which require higher bandwidths still, such as Super Definition TV which will also require appropriate compression. II.6 STREAMING PROCESS II.6.1 STREAMING A technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can start displaying the data before the entire file has been transmitted. For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer. If the data doesn't come quickly enough, however, the presentation ofthe data will not be smooth. There are a number of competing streaming technologies emerging. For audio data on the Internet, the de facto standard is Progressive Network's RealAudio. 17 II.6.2 UNICAST In computer networks, unicast is the sending of information packets to a single destination. "Unicast" is derived from the word broadcast, as unicast is the extreme opposite of broadcasting. In computer networking, multicasting is used to regain some of the efficiencies ofbroadcasting. These terms are also synonymous with streaming content providers' services. Unicast servers provide a stream to a single user at a time, while multicast servers can support a larger audience by serving content simultaneously to multiple users.18 17 www.webopedia.com/TERM/M/streaming.htm,friday,novembre 17,2006 18 http://en.wikipedia.org/wiki/Unicast,friday,novembre 17,2006 II.6.2.1 UNICAST ARCHITECTURE Unicasts transmits separate video, audio or text streams to each computer requesting data. Unicast video can flood the network.
STREAMING SERVER ROUTER SWITCH LEGEND
CLIENT 1CLIENT 2 CLIENT 3 Figure 12 : High Level Network diagram for UNICAST Source: Own drawing II.6.3 MULTICAST destinations simultaneously using the most efficient strategy to deliver the messages over each link ofthe network only once and only create copies when the links to the destinations split. The word "Multicast" is typically used to refer to IP Multicast, the implementation of the multicast concept on the IP routing level, where routers create optimal spanning tree distribution paths for diagrams sent to a multicast destination address in real-time. II.6.3.1 MULTICAST ARCHITECTURE
STREAMING SERVER ROUTER SWITCH Multicast conserves Network bandwidth by sending a single stream of data. LEGEND
CLIENTCLIENT CLIENT Figure 13 : High Level Network for MULTICAST II.6.4 BROADCAST To simultaneously send the same message to multiple recipients. Broadcasting is a useful feature in e-mail systems. It is also supported by some fax systems. In networking, a distinction is made between broadcasting and multicasting. Broadcasting sends a message to everyone on the network whereas multicasting sends a message to a select list ofrecipients. II.6.4.1 BROADCAST TECHNIQUE OF IP PACKET MODEL As known, broadcast is when a single device is transmitting a message to all other devices in a given address range. This broadcast could reach all hosts on the subnet, all subnets, or all hosts on all subnets. Broadcast packets have the host (and/or subnet) portion of the address set to all ones. By design, most modern routers will block IP broadcast traffic and restrict it to the local subnet. And multicast is a special protocol for use with IP. Multicast enables a single device to communicate with a specific set of hosts, not defined by any standard IP address and mask combination. This allows for communication that resembles a conference call. Anyone from anywhere can join the conference, and everyone at the conference hears what the speaker has to say. The speaker's message isn't broadcasted everywhere, but only to those in the conference call itself. A special set of addresses is used for multicast communication. In this case the IP that has been used for multicast and broadcast is the same, and it is 192.168.12.2 which can be reachable by all users inside the network.
Figure 14: Broadcasting process Source: Own drawing To decrease traffic inside the network, broadcast has been used as it is the way that can help during live video streaming. The above figure show the broadcast process, the colored in red arrow shown the request of packets to the server from the CLIENT 1 that got the reply shown with black arrow. The blue arrow shows the request of the CLIENT 2 to the CLIENT 1 which got packets before CLIENT 2 instead of getting packets from the server. Broadcast process could help to maintain the performance and the quick relay of multimedia services inside networks. II.6.5 HIGH LEVEL NETWORK ARCHITECTURE
Figure 15: High level Network Architecture of live video streaming Source: Own Drawing The figure above shows all requirements of a live video streaming that are follow:
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