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Networking service systems and related standards
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1. Network services |
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| The main issue in multimedia delivery is the transfer speed and the reliability of transmission. First, the physical media service and its related protocols and standards determine the network transfer speed. The investment in devices, existing network systems, the scope of the users, the contents of the payloads and the transfer speed demanded are the main factors when selecting a suitable network. |
For multimedia delivery, the most commonly used network media services are POTS, ISDN and LAN. They all have strengths and weakness that should be considered carefully before deciding which one to use. The following are some simple descriptions of each network service. |
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POTS refers to the international telephone system based, at the user end, on copper wires carrying voice data. It is a basic telephone service that provides access to the public switched telephone network (PSTN) that most homes use. It uses modems to connect each computer for their communications. The maximum throughput on this network is limited to 56 Kbps, which is the speed of the fastest modem (without compression). The ITU (International Telecommunication Union) standard for conferencing over this network is H.324 which includes H.263 video, G.723.1 audio and T.120 data [14]. |
These standards were set by International Telecommunications Union (ITU) and the Internet Engineering Task Force and allow users to participate in a conference, regardless of their platform [14]. Here is a brief introduction to these standards. T.120 is an ITU recommondation that specifies the document conferencing and application as a part of a multimedia teleconference. It describes the method to distribute files and graphical information in real-time efficiently and reliably during a multipoint multimedia meeting. |
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ISDN is a system of digital phone connections, which allow data to be transmitted simultaneously across the world using end-to-end digital connectivity. [28] This is a digital service that defines a 64 Kbps (B-channel) for voice and data, and a 16 Kbps or 64 Kbps (D-channel), depending on the service type, for control transmission. There are two basic types of ISDN service: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI specifies two 64 Kbps B channels and one 16 Kbps D channel for a total of 144 Kbps whereas PRI defines 23 B channels plus one 64 Kbps D channel for a total of 1536 Kbps. BRI is designed for most individual users and PRI is intended for users with greater capacity requirements. |
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Feathers: [28] High speed: Multiple digital channels can be operated simultaneously through the same regular phone line used for analogue lines as long as the telephone company's switches can support digital connections. This digital transfer rate is much faster than for analogue signals. For example, BRI ISDN, uses a channel aggregation protocol, such as BONDING or Multilink-PPP, that supports an uncompressed data transfer speed of 128 Kbps. Furthermore, the latency is typically half that of an analogue line. One line for Multiple Devices: Because of its digital signal, many different data sources such as telephone, fax, computer, bridge/router and live videoconference system can be combined and routed to the proper destination. Also, the noise and interference can be easily eliminated while combining these signals. Signaling: ISDN sends a digital packet on a separate channel, Out-of-Band signal, rather than a ring voltage signal sent by the phone company ("In-Band signal"). This digital signal does not disturb any established connections, its calling set-up time is very fast, usually 15-30 times faster than a V.34 modem. This digital signal contains more details, such as who is calling, what is the type of the call (data/voice) and what number was dialled. |
| The ITU standard for ISDN is H.320, which includes H.261 video, G.711, G722, G728 audio and T.120 data[14]. |
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Designed by Yong Qiu Liu.
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