sky x technology
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15-02-2010, 06:28 PM

pls send me abstract and reports of the topic sky x technology with clear diagrams.pls send me soon

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 over come 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.


Satellites are an attractive option for carrying Internet and other IP traffic to many locations across the globe where terrestrial options are limited or [censored] 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.

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 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. This algorithm does not respond well over satellite networks where the round-trip time is long and error rates can be high. Further, this constant stream of acknowledgments wastes precious back channel bandwidth and if the back channel is small, the return of the acknowledgments to the sender can become the system bottleneck. The acknowledgements and error messages will always dominate the data transfer and the rate of flow reduces very much.

Congestion Avoidance

In order to avoid the possibility of congestive network meltdown, TCP usually assumes that all data loss is caused by congestion and responds to this by reducing the transmission rate. However, over satellite links, TCP misinterprets the long round-trip time and bit errors as congestion and responds inappropriately. Similarly, the TCP Slow Start algorithm, which over the terrestrial infrastructure prevents new connections from flooding an already congested network, forces an excessively long ramp-up period for each new connection over satellite. While these congestion avoidance mechanisms are vital in routed environments, they are ill-suited to single-path satellite links.

So the congestion avoidance mechanisms used by TCP is also not suited for the satellite link since it reduces the data flow through the network and thus reduces the overall rate of data transfer.


Sky X Technology Overcomes TCP Performance Limitations

Sky X products increase the performance of IP over satellite through a combination of protocol connection-splitting, data compression, and Web pre-fetching, while remaining entirely transparent to end users. The Sky X gateway works by transparently replacing TCP connections from the client and converting the data to Xpress Transport protocol (XTP) for the hop over the satellite link which is the protocol optimized for satellite conditions

The Sky X gateway works by intercepting the TCP connection from the client and converting the data to the Xpress Transport Protocol (XTP) for transmission over the satellite. The Sky X gateway on the opposite side of the satellite link translates the data back to TCP for communication with the server. This architecture offers vastly improved performance while remaining entirely transparent to the end user and fully compactable with the internet infrastructure. No changes are required to the client or server and all applications continue to function without modification. This architecture is also referred to as TCP Performance Enhancing Proxy (TCP-PEP) and is compactable with IETF RFC 3135.

Sky X Technology

The Sky X gateway splits the single TCP connection into three separate components. A TCP connection on the remote side between the client and Sky X gateway, an XTP connection involving Sky X protocol over the satellite between the two Sky X gateways and a TCP connection between the opposite Sky X gateway and server.

XTP is a reliable, transport-layer protocol specifically designed to operate efficiently over high-speed networks and offers a level of performance not possible with TCP on long latency, high loss satellite links. XTP is an open standard developed by the XTP Forum, a non-profit organization composed of networking protocol researchers, implementers, and user organizations.

By splitting the end-to-end TCP connection, the segment over the satellite can take advantage of the performance of XTP. TCP congestion avoidance mechanisms remain in place over the terrestrial connections to protect the stability of the routed network. The two Sky X gateways pass control data between each other, allowing the Sky X gateway on the opposite side of the satellite to appear to be the original source or destination device. This architecture maintains full TCP reliability and end-to-end flow control.

Sky X Technology

Web Pre-Fetch functionality further enhances the performance of HTTP transfers over the satellite link by pro-actively retrieving the many embedded objects on a Web page along with the requested HTML page. The Sky X system delivers the Web objects to the Sky X gateway on the client side of the satellite link where they can be served locally when requested by the browser, avoiding the satellite delay
The Sky X gateway XR10, XH45, and XH155 are available as ready-to-install hardware solutions which can be added to any satellite network. The Sky X Client software installs directly on the PCs of end-users and works in conjunction with a Sky X Server SS10 or SS45 hardware unit located at the network hub. Mentat also licenses the Sky X gateway technology in software source code form for integration with satellite modems, VSATs, routers, caching systems, or any other satellite connectivity equipment. The Sky X gateway can also be used in multilink configurations where a single Sky X gateway hub unit enhances the performance of multiple separate outbound links from a single uplink facility.

The Sky X Client / Server product operates similarly to the Sky X gateway except the Sky X Client software is installed directly onto the client PC. Connections from applications running on the PC are intercepted and sent over the satellite using Sky X protocol. At the network hub, a Sky X Server establishes a TCP connection with the destination server.

Sky X Client/Server

The Sky X Client / Server increases the throughput and efficiency of network access over satellites by transparently replacing TCP with the Xpress Transport Protocol (XTP) for the satellite segment of the connection. Combined with data compression and Web-specific enhancements, the Sky X system provides maximum performance under the long latency, high loss, and asymmetric bandwidth conditions typical of satellite communications.

The sky X client/server system enhances the performance of the internet and private network access over satellite links. The sky X client software installed on the PC™s of the end user, works in conjunction with a sky X server hardware unit located at the network hub. Through the use of a unique connection splitting and protocol “translation system, the sky X client/server system overcomes the deficiencies of TCP/IP in satellite “based networks while remaining entirely transparent to end-user applications. The sky X client is ideal for use with any satellite receiver card or set “top box

Sky X Client / Sky X Server Operation

The Sky X Client / Server increases the throughput and efficiency of network access over satellites by transparently replacing TCP with the Xpress Transport Protocol (XTP) for the satellite segment of the connection. Combined with data compression and Web-specific enhancements, the Sky X system provides maximum performance under the long latency, high loss, and asymmetric bandwidth conditions typical of satellite communications.

The Sky X Client, installed on Microsoft Windows-based computers, transparently intercepts TCP connections from applications running on the PC and transmits the data over the satellite link using XTP. The Sky X Server, installed at the hub of the satellite network, establishes a new TCP connection for communication with any device on the local network or over the Internet. Through this unique, patented architecture, the Sky X Client / Server system requires no proxy settings while providing performance enhancement for all TCP applications.

The Sky X Server is available in two models namely the SS10 and SS45. The SS10 provides Sky X enhancement for links of up to 10 Mbps while the SS45 provides Sky X enhancement for links of up to 45 Mbps.

Sky X Multicast Fan-Out

Computer networking traditionally relies on unicast data transfers which establish point-to-point connections between devices. In situations where the same data is transferred to multiple users, the server must send a copy of the file to each recipient independently. This process is both time consuming and wastes much of the bandwidth resources.

In contrast, multicast technology makes it possible for multiple recipients to receive a single data stream. This can be an especially powerful tool for satellite networks or similar architectures where the multicast transfer can take advantage of an underlying link layer broadcast media. Unfortunately, the only multicast capability built into the Internet Protocol is a UDP-based, unreliable, best-effort service that is only appropriate for real-time streaming applications such as event broadcasting. Because UDP-based IP multicast does not include any mechanisms for detection and retransmission of lost or corrupted data and does not resequence any packets that arrive out of order, IP multicast is not suitable for file downloads and other data transfer applications. Sky X Multicast Fan-Out offers a simple and convenient solution for reliable multicast over wide area networks. By taking advantage of reliable multicast functionality built directly into XTP, the open-standard transport-layer protocol used by the Sky X Gateway to transfer data over the WAN link, the Sky X Gateway provides fast, efficient, fully reliable multicast file transfers. Any data that is lost or corrupted is retransmitted, providing transfer reliability and rendering special FEC software unnecessary
The Sky X multicast fanout, an integral component of the Sky X gateway, transparently converts TCP unicast connections into reliable multicast transfers. Through the use of common TCP based applications such as FTP, the Sky X gateway can deliver a file to every remote location across a wide area network with only a single multicast transfer. Sky X multicast fanout is built on the industry leading Sky X gateway IP over satellite performance enhancement system. Because the Sky X multicast fanout process is transparent to the end devices , any machine can originate or receive the multicast transfer regardless of operating system and without requiring the installation of any specialized multicast software.

By combining this reliable multicast transmission technology with a transparent fanout functionality which allows any TCP connection to be converted into a multicast transfer, the Sky X gateway marries the power of multicasting with the convenience of using FTP or any other TCP-based application. In addition to the multicast benefits themselves, the Sky X gateway includes on-the-fly data compression which further increases transfer speeds for compressible data by up to 5 times. Sky X multicast fanout functionality is ideal for file transfers, cache replication, video file distribution, content delivery networks, database replication, and any other distribution of data or files to multiple users over a satellite link or other wide area network.

Sky X Performance

The performance benefits of the sky X gateway depend on many factors including the bandwidth, delay, asymmetry and bit error rate of the link, the number of simultaneous connections, the compressibility of the data and the behavior of the application itself. Below are data for two typical applications across a range of conditions

File Transfers

The following file transfer tests illustrate the benefits of Sky X performance enhancement for different windows sizes, link band-widths, round-trip times, and bit error rates. Users should expect similar results for any large, single-connection data transfer. Each graph shows Sky X enhancement for three cases: no compression, highly compressible text, and Corpus benchmark compressibility.

Window Size and Link Speed vs. Throughput
Without performance enhancement, a default window size of 8 KB limits TCP throughput to less than 100 Kbps over satellite. As the graph on the left illustrates, even on server operating systems using a 32 KB window, TCP is only able to reach a through-put of 440 Kbps. Sky X gateway overcomes this limitation, taking full advantage of the available bandwidth regardless of the window size of the client or server. For compressible data, Sky X can provide throughput rates far greater than the link bandwidth.

Sky X Technology

Round-Trip Delay vs. Throughput

The Sky X gateway system removes the dependency of TCP on the round-trip time of the link. The figure below shows the measured throughput on an error-free, 10 Mbps link. These results illustrate that TCP throughput drops rapidly as the round-trip time increases. In contrast, Sky X is able to maintain full usage of the link regardless of the round-trip time. For compressible text, Sky X consistently delivers throughput rates greater than the actual bandwidth.

Sky X Technology

Bit Error Rate vs. Throughput

The Sky X system overcomes the high sensitivity of TCP to the bit error rate of the link. The graph given below shows the throughput as a function of the bit error rate for a 10 Mbps satellite link using a 1 MB TCP window. Even at low error rates, TCP is able to deliver only 1.5 Mbps, while at an error rate of 1×10-5, TCP™s throughput drops to less than 0.03 Mbps. Sky X fully saturates the link at low error rates and even at an error rate of 1×10-5, achieves 5.1 Mbps without compression and up to 15.8 Mbps for compressible data

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04-09-2010, 08:31 PM


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