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Support SkyVision is dedicated to providing unparalleled support to all of our customers. We have a Network Operations Center that operates 24 hours a day, 7 days a week to ensure that all of our customers' needs are met. If you are in need of support, please call one of our qualified professionals who expertly handle each inquiry we receive. Contact us anytime at +44 20 8387 1770 or email us at support@sky-vision.net. For every email sent to the Support dept, please indicate your phone number and your technician's phone number to facilitate the future contact to solve your technical request. TCP over Satellite Connections Throughput Testing Most of the Internet Protocol (IP) packets found on the network are either TCP or UDP packets. UDP is a connectionless protocol, which means that there is no establishment of a connection, and therefore no acknowledgement of successful data transmission. This makes it more susceptible to errors or link problems because it does not retransmit bad packets, but it also makes it much faster since the packet transmission does not need to be acknowledged. For this reason, UDP is used for real-time applications such as video and VoIP. TCP on the other hand, does involve the establishment of a connection between two computers. Since TCP also has mechanisms to re-order packets in sequence and re-transmit corrupted packets, it is necessary for the one side of a connection to acknowledge the successful transmission of packets from the other. After a certain amount of bytes are transmitted, the sending side will stop and wait until the receiving side has acknowledge the packets it has sent. The volume of data that is sent before stopping to wait for acknowledgement is known as the TCP Window. On a Windows-based computer, the default TCP Window is only 32 kilobytes. Since data is not transmitted while waiting for acknowledgement, the longer it takes to receive this acknowledgement, the lower the overall data transfer rate. Because of the higher latency of satellite links, there is a finite ceiling to which a single TCP session can reach in terms of throughput that is much lower than an identical download over LAN or fiber WAN links as a result of the acknowledgement process. One vendor published test results that showed with a 550ms Round Trip Time as is typical over satellite, a maximum throughput for a single TCP session of only 100-150kbps was measured. Therefore, when testing the throughput of a satellite link, it is not sufficient to make a single download. Depending on your link size, you probably will not be able to consume all of your bandwidth. That doesn't mean it's not available, a single download can't create enough traffic to utilize the bandwidth. Additional parallel downloads are required. A download accelerator is one method to create these parallel streams. This test can be performed using the following procedure:
If you wish to improve performance, one method available is to increase the TCP window size. This isn't very practical for an ISP to change each end-customer's PC settings, so it is usually done through the use of a proxy web server which is itself configured for a larger window. Alternatively, some companies have chosen to address the latency issue and install TCP acceleration devices on both sides of the link to eliminate the effect of latency on TCP sessions. A number of vendors such as Packeteer manufacture such products. These products change the packets passing over the satellite link, using a protocol that more resembles the connectionless nature of UDP. If you are interested in such a solution, please speak with your SkyVision Account Manager. Downloads DNS Look up http://www.ip-plus.ch/cgi-bin/dig.cgi Traceroute and Ping tools and sites http://www.traceroute.org/ IP Look up - RIPE DB http://www.ripe.net/perl/whois MTR Tool for Windows WinMTR is a Windows clone of popular Matt's tracerout (mtr) Linux program. It combines the functionality of the 'traceroute' and 'ping' programs in a single network diagnostic tool. download Exe/Zip file Looking Glass http://netmon.sky-vision.net/lg/ customers statistic |