Fiber optical system must have transmitter, receiver and information channel. Block transmitter had information, before this information will to send must recognized match with channel information. And this information delivered to receiver used information channel.
Information channel have two part : Unguided channel and Guided channel. Example from unguided channel that is atmosphere where this system was use for radio, television and microwave relay links. Scope guided channels included few structure variant conduction transmission, like two wire line, coaxial cable and twisted pair
Message origin
Message origin there is information like non-electrical physical (audio and video), so that needed transducer (sensor) can change from non electrical to electrical, example : Microphone change sound become electrics, and video camera (CCD) change picture become electrics.
Modulator and carrier source
- Have two function, First change electrical message into appropriate form, Second joining this signal with others waving awakened by source carrier.
- Modulation can be different that is analog modulation and digital modulation.
- Modulation digital to joining with other signal and digital data in wave carrier, modulator must on or switch off carrier source match with data signaling.
Optical communication systems date back two centuries, that was begin from "optical telegraph" that French engineer Claude Chappe invented in the 1790s. His system was a series of semaphores mounted on towers, where human operators relayed messages from one tower to the next. It beat hand-carried messages hands down, but by the mid-19th century was replaced by the electric telegraph, leaving a scattering of "Telegraph Hills" as its most visible legacy. And Alexander Graham Bell patented an optical telephone system, which he called the Photophone, in 1880, but his earlier invention, the telephone, proved far more practical. He dreamed of sending signals through the air, but the atmosphere didn't transmit light as reliably as wires carried electricity. In the decades that followed, light was used for a few special applications, such as signalling between ships, but otherwise optical communications, like the experimental Photophone Bell donated to the Smithsonian Institution, languished on the shelf.
Fiber optic are essentially transparent rods of glass or plastic and it not flexible like metal cable. Diameter core optic not more 1 mm, it can transmission many information and not low loss information.
Core optical had protect by coating and cladding. Function core optical there is transmission for light wave, and core optical have refractive more better than coating and cladding because material it from transparent rods of glasses or plastic, diameter it about 2-125 μm (depend on optic type). Function cladding as fiber bodywork packer encircling core and refractive is low. Refractive at cladding low more than core, that is to make light in core keep focus until light receiver. Material of cladding that same with core but diameter more bigger than core between 5-250 μm (depend on optic type). Coating function is protect core and cladding, made from elastic plastic.
Difference of refractive of materials core and cladding, also damping or loss become important attention an optical fiber transmission system. Refractive useful in determining light coupling from optical source and useful in determining crept path of light variation of optical fiber. For the delivery light wave used infra-red area with wavelength 850-1600 μm. Damping of loss will have an in with determination apart maximum before repair of signal, smaller generated damping hence progressively the optical transmission the system is goodness.
Streaming video is content sent in compressed form over the Internet and displayed by the viewer in real time. 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. With streaming video or streaming media, a Web user does not have to wait to download a file to play it. Instead, the media is sent in a continuous stream of data and is played as it arrives. The user needs a player, which is a special program that uncompresses and sends video data to the display and audio data to speakers. A player can be either an integral part of a browser or downloaded from the software maker's Web site.
A leader in streaming that is RealMedia and Microsoft Windows Media. Major streaming video and streaming media technologies include RealSystem G2 from RealNetwork, Microsoft Windows Media Technologies (including its NetShow Services and Theater Server), and VDO. Microsoft's approach uses the standard MPEG compression algorithm for video. The other approaches use proprietary algorithms. The program that does the compression and decompression is sometimes called the codec. Microsoft's technology offers streaming audio at up to 96 Kbps and streaming video at up to 8 Mbps, for the NetShow Theater Server. However, for most Web users, the streaming video will be limited to the data rates of the connection (for example, up to 128 Kbps with an ISDN connection). Microsoft's streaming media files are in its Advanced Streaming Format (ASF).
Streaming video is usually sent from prerecorded video files, but can be distributed as part of a live broadcast "feed." In a live broadcast, the video signal is converted into a compressed digital signal and transmitted from a special Web server that is able to do multicast, sending the same file to multiple users at the same time.
Streaming involves sending movies (included audio and video) from a server to a client over a network such as the Internet. The server breaks the movie into packets that can be sent over the network. At the receiving end, the packets are reassembled by the client and the movie is played as it comes in. Aseries of related packets is called a stream.
Streaming is different from simple file transfer, in that the client plays the movie as it comes in over the network, rather than waiting for the entire movie to download before it can be played. In fact, a streaming client may never actually download a streaming movie; it may simply play the movie’s packets as they come in, then discard them.
Quick Time the best in multimedia system included (video or audio). QuickTime Streaming extends the QuickTime software architecture to support the creation, transmission, and reception of multimedia streams. QuickTime programmers to create applications that receive multimedia in real time, and to create authoring and editing tools that work with streaming content. Existing applications that play QuickTime movies can play real-time streaming movies with little or no code change.
QuickTime movies can be streamed using a variety of protocols, including :
■ HTTP (Hyper Text Transport Protocol)
■ FTP (File Transfer Protocol)
■ RTP (Realtime Transport Protocol).
HTTP and FTP are essentially file transfer protocols. Any QuickTime movie saved using the QuickStart option can be streamed using these protocols because the QuickTime client software is able to start playing the movie before the entire file has arrived.
RTP is used for real time streaming. The movie packets are sent in real time, so that a one-minute movie is sent over the network in one minute. The packets are time-stamped, so they can be displayed in time-synchronized order. Because packets are sent in real time, RTP streaming works with live content in addition to previously-recorded movies. It can even carry a mixture of the two. Real-time streams can be sent one-to-one (unicast) or one-to-many (multicast).
Unicast streaming
In a unicast, the client contacts the server to request a movie using RTSP (Real Time Streaming Protocol). The server then replies to the client over RTSP with information describing the movie as a streaming session. A streaming session consists of one or more streams of data, such as a video stream and an audio stream. The server tells the client how many streams to expect and gives details on each stream, such as the media type and codec. The actual streams are then sent to the client over RTP. When a QuickTime movie is streamed over RTP.
A stream can contain live content, such as a stock ticker or a radio broadcast, or stored content, such as a video track from a QuickTime movie. When a client is receiving unicast streams from stored content, the client’s movie controller includes a “thumb” that allows the user to jump to any point in the movie. This gives the client random access to long movies without having to download an entire movie or store it locally.
Multicast streaming
In a multicast, one copy of each stream is sent over each branch of a network. This reduces the amount of network traffic required to send the streams to large numbers of clients.Aclient receives the streams by “joining” the multicast.
The client finds out how to join the multicast by opening an SDP (Session Description Protocol) file. The SDP file contains the information needed to join the multicast, such as group address and port number, as well as the stream description information that would come over RTSP for a unicast. See Figure, SDP files are commonly posted on web servers to announce upcoming multicasts.
Introduced and installing Darwin Streaming Server for Windows
Darwin Streaming Server, this server made by Apple's open source version of the QuickTime Streaming Server technology allowing you to send streaming media across the Internet using the industry standard RTP and RTSP protocols. Based on the same code base as QuickTime Streaming Server, Darwin Streaming Server provides a high level of customizability and runs on a variety of platforms allowing you to manipulate the code to fit your needs (included Mac OS X, Linux, Solaris and windows).
Darwin Streaming Server includes:
- Latest security update changes
- Latest 3GPP release 5 client support
- High definition H.264 streaming
Darwin Streaming Server :
- Enhanced multithread support
- Home directory streaming (UNIX-based platforms only)
- Broadcast directory streaming
- HTTP to RTSP url redirection using QuickTime HREF support.
- Improved security through non-root user execution (UNIX-based platforms only)
- 3GPP streaming enhancements - As we constantly improve our support for streaming the latest digital media standards, DSS 5 includes a number of enhancements for 3GPP streaming
Darwin Streaming Server is compatible with QuickTime 4 or later client software. Digest mode Authentication and Skip Protection (first introduced in QuickTime Streaming Server 3.0) require QuickTime 5 or later client software.
Installing Darwin Streaming Server (Windows 2000/2003 Server)
The Streaming Admin requires ActivePerl 5.8 (or later) to be running on the server machine. You must install a Perl interpreter in order to use the web-based administration software. ActivePerl 5.8 is a free ware software.
To install Darwin Streaming Server software, follow these steps on the server computer:
Stop any Darwin Streaming Server related processes.
When the Server package is unzipped, a folder with Darwin Streaming Server and associated files will be created. Inside this folder is an Install script, named "Install.bat". Double-click this file to install the server and its components on the server machine. The installer also starts up the Streaming Server Admin, so keep the command prompt window open.
The Install script will create the following directory:
AdminHtml\ - Folder containing the CGIs and the HTMl files required by the Admin Server
Documentation\ - Documentation folder
The Install script also installs Darwin Streaming Server as a service in the Service Manager. It is possible to start, stop, and check server status from the Service control panel.
The Install script will attempt to launch the Admin Server. Make sure that the Perl interpreter installed on your machine is in the system PATH.
The Admin Server can be launched from the command prompt by typing:
where perlpath is the path to the Perl interpreter on your machine.
If you are installing for the first time,you will be asked to create a user name and password for administering the server.You must complete this step to administer the server from a remote system using a web browser.
Set Up (Windows 2000/2003 Server)
After creating an administrator user name and password,you can connect to the Darwin Streaming Server from your web browser.
Enter the URL for your Darwin Streaming Server:
http://localhost:1220 on the same local system or
http://myserver.com:1220 from a remote system
Replace "myserver.com" with the name of your Darwin Streaming Server computer.
1220 is the port number.
For help on using Streaming Server Admin, setting up secure administration (SSL), and setting up your server to stream hinted media, refer to the online Help by selecting the Question Mark button from the Streaming Server Admin.
