Very well. It is proved by ever-increasing demand from ISPs for geostationary satellites to support their growing need for Internet capacity. Satellite links provide Internet service to end users and ISPs all over the world at rates from 64 kbps to 52 Mbps.

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Independent tests have demonstrated that users do not notice when there is a satellite link in their TCP session; however, it is true that TCP/IP throughput is affected by the round-trip time of a communications channel. The maximum throughput is estimated by taking the window size and dividing it by the round- trip time. The window size is the amount of data that can be sent before receiving an acknowledgment from the receiver. For a typical application, the throughput is 874 kbps, which is calculated as follows: 65,535 (64 K byte window size) multiplied by 8 (there are 8 bits per byte) divided by 0.6 (satellite delay round-trip time).

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For most users, 874 kbps does not limit their Internet connection because most access the Internet from a dial-up phone line and are limited by the speed of the modem, typically 56 kbps or lower. Users who access the Internet via a corporate LAN generally achieve higher throughput levels than 56 kbps, but generally well below 874 kbps. Therefore, neither typical home users nor office LAN users would normally notice a satellite connection within an Internet transmission path.

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While most PCs use a default window size of 8 kbytes (which yields effective download rates around 100kbps), users can reconfigure this to the maximum window size for TCP today, which is 65,535 bytes. There is a proposed standard to increase the maximum window size even further to 1 Gbyte or 1.07*109 bytes (RFC 1323).

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Slow-start is a part of TCP/IP protocol that controls the rate at which a session can send data. An algorithm is used to limit the increase in the data transmission rate to the same rate that acknowledgments are received. Slow-start was added to TCP to protect the Internet from sudden bursts of traffic, which could overload the network. The individual user's throughput is, therefore, limited to improve overall network stability. Slow-start does increase the time required to reach the maximum throughput, both at the beginning of a TCP session and whenever a segment is lost or received in error. To account for any lost segments during a TCP session, two algorithms have been incorporated as part of the TCP standard to improve throughput. These are Fast Retransmit and Fast Recovery (RFC 2001).

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Forward-Error Correction (FEC) should be employed on satellite links to improve the bit-error-rate. The types of FEC generally used today are Viterbi and Reed-Solomon. These are often used together to get the maximum benefit of both codes.
Avoiding traffic overload (timely upgrade of satellite link capacity) is crucial for good throughput over satellite links. This is because congested satellite link causes random packet discard on transmit side, which in turn activates slow-start mechanism in active TCP sessions.

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RFC 1323 (TCP Extensions for High Performance) introduces a larger window size, improved round-trip-time measurement, and protection against wrapped sequences. These proposed enhancements to TCP provide for improved efficiency over large bandwidth paths, and are designed to be compatible with existing TCP implementations.

RFC 2018 (TCP Selective Acknowledgment Options) is another proposed standard that further improves performance of TCP sessions with large windows; it allows for selective retransmission of only those packets not received.

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Most links serve as a connection for a community of users (many people sharing the same path). Even though the window-size limits throughput on a single TCP session, that limit is not noticeable on multiple sessions. For example, 9 users each could simultaneously achieve up to 874 kbps throughput each on an 8 Mbps link, or 140 users could achieve 56 kbps throughput each (a more typical situation) on an 8 Mbps link. It is important to note that non-TCP applications such as voice and multicasting are not limited to 874 kbps. Delay does not affect the UDP protocol; and as a result, there is no decrease in throughput.

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In 1999 the transponder availability in the INTELSAT system was better than 99.99 percent. That's true reliability.
Why use satellites for voice and data networks?
Satellites provide excellent network facilities in areas where existing communications infrastructure is patchy, unreliable, very expensive etc. Satellites also come into play when connecting up a number of sites spread across a wide area where the bandwidth can be shared across the network.

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The speed of light means that a round trip time over a satellite link is around 0.5 secs. For most data applications this is not a problem. If you are downloading large files then there are settings on the PC you are using which can speed things up and have you downloading at broadband speeds.

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Not at all. The delay is often less than making GSM to GSM calls between certain GSM networks. More importantly the actual voice quality is usually much better and more consistent. So you don't keep repeating yourself to make yourself heard.

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No. Many of our customers run star type networks which we hub in the UK. Double hop voice calls with good quality voice are much better than calls on some of the telephone networks in the locations we serve. At least you don't have to redial 10 times to get the call through.

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Quality of service or QOS is obtained on the DVB interface by using what is known as "Bandwidth Managers". SpiderSAT uses "Netenforcer's" from Allot (www.allot.com) for all their QOS requirements / implementations. With the "Netenforcer" SpiderSAT is able to dedicate bandwidth on the DVB/ Ethernet interfaces and also able to prioritize types of traffic, thus allowing applications like voice to have a higher priority over Peer 2 peer music downloads, and allowing networks to maximize the use of their bandwidth.

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SpiderSAT provides a graph to all customers, showing them their bandwidth consumption, which is updated every 5 minutes. The graph then logs daily, weekly, monthly and yearly usage, and is accessible to the customer 24/7.

The graphs can also be used to see when the customer has high traffic times, and the need to increase bandwidth, etc.

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A 4. Upgrading bandwidth with SpiderSAT is relatively easy, all you have to do is send an e-mail to sales@spidersat.net with your site identification (which will be provided to you on install) requesting the amount of additional bandwidth you require, a sales representative will send you an e-mail with the additional costs, and then forward the request to the Network operations center (NOC). Depending on the amount of bandwidth you require, the NOC might allocate a different frequency to you, with the higher data-rate. All IP address settings stay the same, and the change will be implemented within 4 weeks from the date of application.

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SpiderSAT guarantee's 99.98% uptime and all connections are monitored in real time via our NOC's Network monitoring software (NMS), In the event of downtime SpiderSAT's engineers will contact the client, and will run through an escalation process eliminating possible causes of the downtime. The Intersky indoor unit also has remote control software pre-installed that can be accessed via a telephone line. Our NOC engineers would ask you to connect a phone line in the worst case scenario and dial into the unit, to reconfirm all parameters, and check all components. This is also how we offer backup services, without jumping onto a plane every time a problem arises.

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You get a set of 8 public IP's on a standard installation, but can get more on request, IP's are then routed to your device directly from our NOC, and a small change made to your Indoor unit, that's done directly by our NOC, without disruption of service.

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All spiderSAT installations are global, and have webmail interfaces, where the customer can receive their mail from any connection, any where in the world. However clients can choose to POP their mail as well as Web mail access.

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SpiderSAT uses VOIP devices from Multitech (www.multitech.com) that use a standard Ethernet interface, and have FXO / FXS and E&M interfaces on. The multiVOIP comes in multiple configurations, 1 line, 2 line, 8 line, and 30 line models.

The units have been tested on the SpiderSAT system extensively, and have passed all tests with excellent voice quality on dual hops and between site of up to 30 hops away, on a variety of bandwidth settings, including shared bandwidth.

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