System of guaranteed data delivery over satellite channel
By Alexander Anufriev

Company or big bank which has its own affiliate network over the country needs to provide all these affiliates with up-to-date information about central storage conditions or transmit in real time financial reports or another necessary documents. It is very inconvenient to deliver huge amounts of information via e-mail: everyone who even once upon time sent or received messages over 1 MB in volume by means of telephone modem will confirm this statement. Receiving the information in real time mode from the corporate server in the Internet is inconvenient too. Firstly, it will take a lot of time to receive data via telephone lines, and secondary, each affiliate will download information independently which results in server overflow. The excellent solution of the problem is satellite channel. But...

Intriduction

Several problems traditionally exist related to transmission of digital files and streams over satellite. One of them is that different types of noise and especially rain may cause short time falls of connection, which resulting in the lost or corruption of some fragments translated from satellite to terrestrial site. This has drove to impossibility of transmission of movies, music, software, financial information and other digital data over satellite system without return link. Traditional solutions include multitimes file sending (which is slow and non-effective) or require the terrestrial return channel for server to receive the information about transmission status. This is necessary to resend corrupted or lost packets. Unfortunately it is too hard to organize this kind of link for many thousands of reception points and even if this link exists the transmission will go much more slower, and less effectively than in case of one time delivery.

Today there are two main techniques for file transmission over the satellite channel: push and pull. When using push technique the user place a query to the system over terrestrial channel about what kind of data and at what time he wants to receive. Than the user is disconnected from provider and is waiting for data reception. Computer is not shut down. At the specified time UDP/IP channel from server to user is opened. Transmission is performed on high speed. And what if rain or power disconnection occurs at that time? This happens quite often today. The sufficient disadvantage of this technique is absence of return channel and server doesn't receive user's message about transmission status and it cannot resend lost data if necessary.

When working with pull technique user downloads data from server in on-line mode over TCP/IP protocol. In this case return channel is a rule. Disadvantage of this technique is low speed of transmission which is caused by specifics of TCP/IP protocol.

And what about disconnections of telephone line which is common cause too? Transfer will stop and user don't get necessary information even with return channel existence. Transmission of digital audio and video data streams without reliable and high speed channel is mostly impossible.

The system of guaranteed data delivery over satellite channel which is offered by Syrus System Company allows to solve all these problems and combines power technologies of world leading manufacturers of software and hardware for satellite transmission and reception such as Scopus Network Technologies, RadyneComstream, PentaMedia, KenCast. Systems is intended for any data delivery (single files of databases, video streams etc.) over satellite channel to remote receiving stations which don't have any link to transmission station, i.e. with no return channel. It is important that there is no limitation to file size and speed of transmission is limited to unoccupied bandwidth of satellite only. Return channel existence in the system is desirable but not necessary. In many cases the use of functionality of software allows to avoid return channel use for transmission either files or digital audio and video streams. The use of this system allows to get the reliable and speedy satellite channel even in bad environmental conditions.

This system has a number of unique capabilities which make it a system with really guaranteed delivery of multimedia content both to individual users and multiple users simultaneously. The system is oriented for use in corporate satellite networks and can be useful for providers of satellite Internet access for expanding of services range and increasing its quality.

Main technological solution and system specification

The system consists of two functional parts: software and hardware. Software part is presented by digital delivery application Fazzt Digital Delivery System of US KenCast Company. Powerful software tools integrated into the Fazzt application allow users to solve lot of tasks and problems which are traditionally related to data transmission over satellite channel.

Digital data delivery application Fazzt Digital Delivery System includes:

• Fazzt FEC. KenCast patented algorithm for forming of additional packets is used by the application for protection of data and video streams transmitted from loosing and corruption which may occur during transmission over noisy connection lines;
• mechanism for forming of queues for priority control and planning. It is used for time and priority planning control, which gives system administrator more possibilities of control and more flexibility for adaptation to changes being happened in the network. Queues are used for establishing of consequences and planning of new transmissions and insertion of new data for pre-processing;
• integrated web server. New interface which is using integrated web server allows administrator to configure and control system's functioning even from remote computer;
• connection lines support with unicast delivery. Fazzt provides specific line configuration tools for support of unicast UDP delivery;
• additional tools for scripts writing. Application has wide set of scripts which allows sufficiently broaden the functions of standard application set. Editing mechanism allows creation of the news scripts for user's tasks;
• enhanced capture and transportation of video streams. Fazzt can capture video stream translated from remote site with use of any standard streaming server (RealServer, Cisco IPTV, Windows Media Encoder and etc.), and transmit it over Fazzt, and manipulate it by means of all Fazzt's instruments for registration, filtering, recovering with Fazzt FEC and others;
• administrator's web interface for system control. Graphics web interface of Fazzt provides administrator with simple manual tools for translation functions control;
• increased precision of bandwidth . Fazzt provides the satellite transmission with more precise and uniform bandwidth which is used for translations over channels.

Fazzt application itself consists of three basic parts: Fazzt Host, Fazzt Publisher and Fazzt Client.

Fazzt Host is being installed on system's central server, and serves for outgoing data stream forming in conform with scripts written, and controls processes of files encoding before sending, queues creation, hot folders and carousel transmissions of files and streams.

Fazzt Client is being installed on remote client computer and makes the decoding and recovering of received files, records received data onto computer's hard disk accordingly to specified path. Client application performs all these tasks automatically and with minimum user intrusion. Each client application has a unique license key.

Fazzt Publisher is used on remote sending computers which have the connection with central server over terrestrial lines and are sending to it files for further delivery over the satellite.

One of the elements of the system's software part may be considered a driver of computer satellite card Pent@NET which is being installed into the client computer together with card itself.

Hardware part of the system consists of the following main components: central server, IP/DVB encapsulator with control computer, QPSK modulator, Pent@NET computer DVB PC card.

Central server with licensed OS and Fazzt Host installed serves for preparation and generation of initial IP stream of digital data. It can be multimedia server connected to central Fazzt server, which generates (streaming) continuous digital video or audio stream into local network. In this case captures this stream, then protects it with FEC encoding and forms new streams with loss protection. Such scheme can be used for example for video-on-demand service with receiving of video to the computer over satellite channel. Besides, central server is accessed by publishing computers (Fazzt Publisher) via terrestrial lines over Internet. These computers transmit to central server signals dedicated for satellite channel transmission. Fazzt Host processes these received files and digital streams and outputs IP stream onto the input of IP gateway. As a rule system's central server is placed in the central satellite control room of the corporate network or not far from it. It is caused by the fact that for security reason server is connected to encapsulator directly. Server and IP gateway interconnect over network Ethernet cards via RS-422 interface.

General system scheme

Gateway's tasks are: encapsulation of input IP packets into MPEG-2/DVB compatible transport stream; providing of necessary QoS level for registered statistic users and groups of users. Each group of users has its own personal identification number (PID) in the stream, and each user and each group has its own minimum (CIR) and maximum speed.

Encapsulator allows to organize up to 8,000 groups of users and each of group can encounter hundreds of users. Maximum output gateway speed is up to 53 Mbit per second. While functioning gateway forms dynamic and statistic users tables. These tables represent IP user's address, its MAC address, maximum and minimum speed given to it at the present moment of time. The tables displays both registered and non-registered users.

Transport DVB stream formed by encapsulator is transferred over ASI interface to QPSK modulator from where modulated carrier via IF 70 MHz feeds to satellite transmitter.

As it was mentioned above the system of guaranteed delivery allows to organize both multicast and unicast data delivery. Both multicast and unicast channels can function simultaneously and independently form each other. Remote user on its side can simultaneously receive both multicast and unicast translation.

On the receiving side the remote user computer has Pent@NET DVB PC card installed along with driver appropriate for particular OS. Signal form the satellite antenna goes to the card's input. This satellite card plays a role of satellite receiver-decoder and serves for data reception only and cannot be used for reception of satellite digital TV channels. However if one will use Pent@VALUE card then using supplied with card software decoder MPEG-2 it is possible to view TV programs as well. Pent@VALUE has better characteristics and lower price.

All components of software and hardware parts of this system are checked by the time and reliably work within different applications, they are easy to install, maintain and control.

As the heart if the system is Fazzt digital delivery application anyway, let talk briefly about its main features and functions.

Fazzt application

Integration of the system into digital TV and radio broadcasting network

Fazzt Digital Delivery System application uses totally new patented algorithm for error correction while transmitting - Fazzt Forward Error Correction (Fazzt FEC) which provides additional protection from errors of information being transmitted. This algorithm allows users to define maximum percentage of packet losses by itself. File is being coded before transmitting by means of adding of especially created protection packets. Decoder on the receiving side can than recover initial file if the deal of lost packets is lower then pre-defined. And all lost information can be recovered so that received will be identical to transmitted. On practice 4...6% of additional information is usually enough to guarantee files delivery from the first attempt and without return channel. The same protection can be performed to video data streams which are transmitted from the translation site.

Fazzt has also confirmation routine which is an analyze of data received consist of data file and additional data. This routine can prove that received and recovered file is identical to transmitted initial one. While traditional error correction algorithms with use of control with redundant cycle code (CRC) are providing limited capability of error detection, realized in Fazzt confirmation is many times more powerful tool because it confirms whole file but not only packets/bits file consists of.

Moreover, Fazzt has many tools for wide range of tasks. First of all it is necessary to mark the following:

• system supports multicast channels for files and streams translated from the event place and can create multiplexed file streams, i.e. can transmit several files or streams simultaneously over single channel chosen. Level of protection in this case is being increased. It is possible also to realize unicast delivery. Both channels can be created and deleted dynamically;
• Queue Management mechanism supports pre-processing of files and allows to set the priorities of transmission as well as its start time. This mechanism allows to plan the date and time of selected data transmission;
• Fazzt has built-in web server which allows user to learn the system very fast and what is the main it gives the possibility of remote control over system functioning and configuration from any computer;
• Carousel function allows user on the reception side to select the most interesting upcoming translations and filter them from ones which must be ignored. Carousels can rotate in the channel for a long time during which user will be able to receive file he needs. This functions allows user to be independent from voltage falls or bad weather;
• Fazzt has its own Fazzt Packager which allows user to combine several quite small files into the big one or splice big file onto several small items. Packager includes compression option which reduces files size prior to sending so that they are transmitted faster and more effectively. In the most cases the economy reached by means of compression successfully compensates packet number increasing caused by Fazzt FEC encoding;
• using Scripting Engine, Fazzt simplifies realization mostly of any tasks. With the help of script editor it is possible to write scripts in simple format for: files and streams transfer over satellite or terrestrial networks with FTP; assembling and disassembling files into/from packets; encoding and decoding of files and packets; automatic script launch on the remote stations; control of files and dialog windows; control after the systems over the database via Fazzt ODBC interface and co-operation with other systems.

For automation of the wide range of tasks system contains script templates and samples which can be used immediatly after system installation.

There is no possibility to give a detail description of the application capabilities in a single article. But some of them should be marked.

The use of the system

Variants of system use are mostly unlimited. The system is capable to provide reliable, effective and budget delivery of digital data and files of any type and formats over different satellite network. Build on the base of open standards this system can be easily integrated with transmitting equipment of terrestrial station from main world manufacturers. At the end of the article it makes sense to give an estimate list of system implementations:

• corporate networks;
• multicast data delivery;
• digital sound transmission;
• distant education;
• file on demand delivery;
• financial information distribution;
• interactive Internet applications;
• multimedia files distribution;
• software distribution;
• webcasting .

Integration of the system

In the configuration described above the system is already used successfully in the one of non-government educational organization of Russia - Modern Humanitarian University . University has its own teleport and about 400 remote affiliates all over the Russia and surrounding countries. The system is used by the University for transmission to its affiliates of an educational materials, electronic version of books, software, slide lections.

Specific feature of this system is its ability to be scaled and easily integrated with existed satellite station equipment. For instance the system can be easily integrated into the digital TV and radio broadcasting network. Encapsulator's output is being connected to existing multiplexor, and IP/DVB stream is being included into general packet.

Syrus Systems Company.