Hello All,
This is a new protocol proposed for the purpose of facilitating fast Linux CD/DVD ISO downloads through the DTH type satellite medium. A Linux satellite having a footprint over Asia and Africa will help in providing the latest Linux distributions to even the remotest areas of these regions. The broadcasts will be sequential and timed for every .iso file, just like regular television programmes with their respective timings. The number of transponders, frequency etc. is not discussed here. The main purpose of this writeup is to create a transmission protocol for error free unidirectional file downloads via satellite. A single broadcast should be received by un-limited number of receivers anywhere in Asia and Africa.
As satellite transmission is prone to disturbances, any error in the ISO file being downloaded will render the entire process useless. Since it is going to be a unidirectional broadcast that cannot receive feedback from the receiving units, certain correction features need to be added to the broadcast.
The proposed protocol will be called Unidirectional File Broadcast ( UFB-15 ) Protocol. The number 15 denotes the 15 second delay feature added for correction. This can vary from 1 second to 60 seconds or more as per the users' choice.
The UFBP-15 will broadcast data packets in groups of 1 second each. These packets will contain their parity check sequence interlaced to check downloaded packet integrity. After the first 15 packet groups of one second each are broadcast, the next one second will contain the first packet group re-broadcast. The next second will have the 16th packet group. The next one to follow will be the 2nd packet group re-broadcast. So every second a new packet group and its 15 second earlier packet group is alternately broadcast. This provides the receiver a 15 second delay to re-load the packets if they got corrupted in the first attempt. An illustration is placed below. 'P' denotes the packet group per second and its timing sequence. They are broadcast every second.
P1 --> P15 --> P1 --> P16 --> P2 --> P17 --> P3 --> P18 --> P4 --> P19 --> P5 --> P20 --> P6 --> P21 --> P7 --> P22 --> P8 --> P23 --> P9 --> P24 --> P10 --> P25 --> P11 --> P26 --> P12 --> P27 --> P13 --> P28 --> P14 --> P29 --> P15 --> P30
As you can see, after every 15 seconds a re-broadcast of old packets takes place to help the receiver catch up with broken packets. The delay time can be chosen after experimenting with different time delays. This will reduce the bandwidth by half but offer a self correction for unidirectional broadcasts. To increase bandwidth, a higher transmission frequency can be chosen. The proposed UFB-15 Protocol is free to anyone to modify and correct for better transmission quality. The only condition is that it should be released under the GPL license so that anyone can make use of it freely.
Another method of reducing reception errors is to avoid transmitting an ISO file as a whole. Instead, it can be transmitted as a set of files just as they exist on the CD/DVD. Individual files being smaller, can be corrected easily and will not disturb the entire ISO file block. An executable script file transmitted along with the download assembles all the components back into an single ISO file in the receiving unit.