20-12-2012, 06:21 PM
SKY X TECHNOLOGY
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MOTIVATION
Expressing gratitute in words, is one thing which can never be done in adequate manner, as writing this we have found ourselves utterly at sea and we are afraid, however we may fail to express abounding gratitude but even then with few words from bottom of hearts and conclude an acknowledge for all that provided to us.
We are greatly indebted and express profound gratitude towards our honourable guide Prof. P. D. Kale who has given us her valuable time, motivations, suggestions and help throughout the project work right from selection to topic towards completing the seminar. At several occasions her magnanimous and affectionate attitude to help us tremendously to overcome shortcomings in our seminar and prove to be source of unending inspiration. We are extremely thankful to her. It gives greater pleasure in expressing our sincere thanks to our H.O.D Prof. S. R. Patil for his kind help.
I would like to thank our princpal Prof. D. S. Bilgi for providing all necessary facilities to complete my seminar report. We thank also all the teaching staff and non-teaching staff members who directly or indirectly contributed to our seminar.
INTRODUCTION
Satellites are ideal for providing internet and private network access over long distance and to remote locations. However the internet protocols are not optimized for satellite conditions and consequently the throughput over the satellite networks is restricted to only a fraction of available bandwidth. We can overcome these restrictions by using the Sky X protocol.
The Sky X Gateway and Sky X Client/Servers systems replaces TCP over satellite link with a protocol optimized for the long latency, high loss and asymmetric bandwidth conditions of the typical satellite communication. Adding the Sky X system to a satellite network allows users to take full advantage of the available bandwidth.
The Sky X Gateway transparently enhances the performance of all users on a satellite network without any modifications to the end clients and servers. The Sky X Client and the Sky X Server enhance the performance of data transmissions over satellites directly to end user PC’s, thereby increasing Web performance by 3 times or more and file transfer speeds by 10 to 100 times. The Sky X solution is entirely transparent to end users, works with all TCP applications and does not require any modifications to end client and servers
Sky X products are the leading implementation of a class of products known variously as protocol gateway TCP Performance Enhancing Proxy (TCP/PEP) , or satellite spoofer.The Sky X gateways are available as ready to install hardware solutions which can be added to any satellite network.
The Sky X family consists of the Sky X Gateway, Sky x Client/Server and the sky X OEM products. The Sky X Gateway is a hardware solution designed for easy installation into any satellite network and provides performance enhancement for all devices on the network. The Sky X Client/Server provides performance enhancement to individual PC’s.
OVERVIEW
Satellites are an attractive option for carrying Internet and other IP traffic to many locations across the globe where terrestrial options are limited or price prohibitive. However data networking over satellites is faced with overcoming the latency and high bit error rates typical of satellite communications, as well as the asymmetric bandwidth of most satellite networks
PERFORMANCE OF TCP OVER SATELLITE :-
• Communication over geosynchronous satellites, orbiting at an altitude of 22,300 miles has round trip times of approximately 540 m/s, an order of magnitude larger than terrestrial networks. The journey through the atmosphere can also introduce bit errors into the data stream.
• These factors, combined with backchannel bandwidth typically much smaller than that available on the forward channel, reduce the effectiveness of TCP which is optimized for short hops over low-loss cables or fiber.Eventhough the TCP is very effective in the local network connected by using cables or optical fibers by using its many features such as LPV6, LPsec and other leading-edge functionality.
• Also it will work with real time operating systems.TCP is designed for efficiency and high performance ,and optimized for maximum throughput and the highest transaction speeds in local networks.
• But the satellite conditions adversely interact with a number of elements of the TCP architecture, including it s window sizing, congestion avoidance algorithms, and data acknowledgment mechanisms, which contribute to severely constrict the data throughput that can be achieved over satellite links.
• Thus the advantages achieved by TCP in LAN’s are no longer effective in the satellite link. So it is desirable to design a separate protocol for communication through the satellite to eliminate the disadvantages of using TCP over the satellite link. The adverse effects of using TCP over satellite link in its various features are as follows:
Window size :-
TCP utilizes a sliding window mechanism to limit the amount of data in flight. When the window becomes full, the sender stops transmitting until it receives new acknowledgement. Over satellite networks, where acknowledgements are slow to return, the TCP window size gradually sets a hard limit on the maximum throughput rate.
The minimum window size needed to fully utilize an error-free link known as the “bandwidth-delay product” is 100 KB for a T1 satellite link and 675 KB for a 10 Mbps link.
Bandwidth Utilization :-
• However many implementations of TCP are limited to maximum window size of 64 KB and most operating systems use a default window size of only 8 KB , imposing a maximum throughput rate over a satellite link of only 128 Kbps per connection , regardless of the bandwidth available.
• So the high bandwidth available in the network is no longer effective, thus the data availability in a client is restricted to a small fraction of the available bandwidth. Thus the window sizing mechanism of the TCP limits the rate of flow of data through satellite link.
• The simple, heuristic data acknowledgment scheme used by TCP does not adapt well to long latency or highly asymmetric bandwidth conditions. To provide reliable data transmission, the TCP receiver constantly sends acknowledgments back to the sender. The sender does not assume that any data is lost or corrupted until a multiple of the round-trip time has passed without receiving an acknowledgment.