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Document Contents Abstract Executive Summary Background Conclusion Appendix: How MOREnet Delivers Services Statewide Endnotes Illustrations Figure 1: Satellite Uplink, Satellite Downlink

Satellite Data Service: An Introduction to Satellite-based Data Services

Abstract

With the increasing need for bandwidth in locations where traditional wireline services are expensive or unavailable, satellite-based services offer an alternative connectivity solution. Since these services are not tied to cables, the deployment costs are minimal, bandwidth is plentiful and systems are relatively cheap to buy and maintain.

In this paper, the general nature of satellite-based systems is explained, along with the issues presented by satellite delivery of IP-based services, followed by the technical information regarding the results and conclusions of MOREnet's testing.

Executive Summary

Internet and network access to organizational network resources continues to grow, both in the number of organizations that are building out wide area networks as well as the bandwidth required to support them. Traditional dedicated circuits such as 56K, fractional T-1s and T-1s are being challenged by a variety of alternative access solutions, such as DSL¹ and EtherLoop², to deliver high bandwidth at low costs. However, Missouri is a predominantly rural state, and delivery of these technologies is problematic in both technological and financial aspects in areas where there are long distances between subscribers and/or low population densities. Satellite providers have been working to develop a low-cost system to meet this bandwidth need in areas where traditional circuits are either unavailable or cost prohibitive.

Satellite delivery of network access has some disadvantages over traditional circuits, such as antenna placement and cable runs, which can be problematic, especially on older or historic buildings. More important, however, is the nature of the transmission path-22,000 miles up to a satellite and 22,000 miles back. This distance creates a signal delay, which can be problematic for certain types of network applications. Non-real time applications such as the World Wide Web and FTP can sustain a certain amount of latency with little difficulty, as can one-way streaming audio and video. Time-sensitive applications, however, such as access to file servers, some e-mail systems, printing, and interactive real-time applications such as voice over IP and H.323 videoconferencing, may experience problems.

Satellite-based systems do offer a solution for locations needing general Web browsing and e-mail, where the additional delay is an acceptable tradeoff for low-cost, high-speed access. However, MOREnet's field-testing of a satellite-based network system demonstrated that these problems can be significant for our customers and their applications³. For MOREnet's customers looking to deploy interactive applications such as videoconferencing, VoIP and other real-time applications, the delays in the satellite transmission make it unworkable, regardless of cost.

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Background

How Satellite Data Services Work

Satellite data services use geosynchronous⁴ satellites, which are 22,000 miles above the earth's surface at the equator. These satellites perform many tasks, from providing video distribution feeds for the TV networks to credit card validation for major retailers. As more satellites were launched into orbit, their use for data transmission has increased, as the increased capacity has driven prices down. This price drop is most notable in the consumer market, where there are several satellite providers offering high-speed Internet services to home users⁵. The increased demand for bandwidth has not been well met by traditional wire line providers, as ATM, Frame Relay and DSL services are not ubiquitously available, nor are they cheap outside metropolitan areas⁶. Rural areas are highly underserved with low-cost broadband data services, and this situation has created a market for satellite providers to fill.

By using a single satellite in a "fixed" location in the sky, the ground antenna does not need to move⁷. The satellite has a number of transponders, which take the incoming signal (beamed up from Earth) and rebroadcast it down to the receiver(s) back on Earth. For example, the TV signals on a DSS system originate at an uplink facility, where large dish antennas beam the digitized TV signals up to the satellite for rebroadcast. The satellite then rebroadcasts the signals down to Earth, where an antenna receives the signals and sends them to the receiver, which selects a channel and decodes the digital signals and outputs them to a TV or VCR.

Figure 1: Satellite Uplink, Satellite Downlink

For data services, this process needs to be two-way: receive data from the uplink facility, and send data to the uplink facility [Fig. 1]. By slightly modifying the DSS dish, adapting the receiver to output digital data, and adding a transmitter, satellite companies created a two-way satellite system for high-speed data⁸. This two-way system can then provide high-speed access in both directions in any location.

The end user is generally provided with an Ethernet connection from the satellite transmitter/receiver (or satellite modem) and connects his/her PC or home network into the satellite modem. Some providers use NAT⁹ to address end user machines, while others may provide one or more public addresses for the end user's network. The satellite modem acts as a router or gateway and may offer other functions, such as web caching, to the user.

With this setup, high-speed connectivity can be provided to most locations without pulling cable (electrical or fiber). The satellite system is transparent to the Internet protocols used for the WWW, e-mail and other applications, appearing to be a circuit, just like a DSL or T-1 circuit would, to the PC. However, this transparency is only at layers one and two¹⁰, and although the TCP/IP traffic will pass over the link, issues unique to satellite transmission affect the application traffic and its performance over the network.

Advantages of Satellite Data Systems

Location

Location is the primary advantage of a satellite-based system. By not depending on wired connectivity, a satellite system can be deployed anywhere -- from downtown St. Louis to the middle of a wheat field, as long as there is a clear line of sight to the satellite. (Satellite signals cannot travel through solid objects, so the dish-shaped antenna must have a clear view of the southern sky in the direction of the satellite.) This ability allows a system to be installed just about anywhere, providing the opportunity for broadband connectivity regardless of location.

Inexpensive to install

Since the only cost involved with adding a location is the cost of the hardware at a location plus installation fees, new locations can be added at a fixed, per-site cost. No lengthy wait for copper or fiber to be installed, with expensive installation fees, followed by long duration contracts to ensure the provider recoups the investment is required. Two-way satellite systems cost less than $1,000 installed (sometimes free, as the install charges and equipment costs can be included in the monthly fee).

Inexpensive to operate

The monthly charges for satellite services are generally $80 to $500, depending on the company, the speed of the connection and the services offered (such as lease/purchase of the equipment, maintenance, guaranteed bandwidth, etc.). The system MOREnet tested has a 36-month rate of $250 for the equipment, installation, maintenance and bandwidth, dropping to $125/month for bandwidth only after the 36-month contract is up. For comparison, a typical T-1 circuit costs $400 to $2,500 per month (depending on the location and type), with MOREnet paying around $500 for a typical circuit.

Fewer outages

With no underground cables to cut with a backhoe, no aerial cables to knock down with ice or tree branches and no intermediate switches and handoff points between providers, satellite systems have excellent availability (uptime). With fewer outages, especially unplanned outages, productivity rises and the users' confidence in the network remains high.

Scalability

By changing the equipment at a location, a site can move from 384K to 512K to T-1 (1.5Mbps)¹¹ speeds, providing a scalable method to upgrade bandwidth without requiring an upfront investment in the fastest connection needed (fiber), while only needing a fractional T-1 (copper) at the moment. Some upgrades can even be done via software, providing additional functionality using the same equipment.

Potential Disadvantages of Satellite Data Systems

There are drawbacks and issues associated with satellite technology. Some of the limitations can be accepted, while others will require a change in the way applications are used or operated and, in some cases, which application is used. The limitations may make satellite systems unsuitable for a limited set of applications.

Delays

Satellite systems have inherent delays due to distance. The satellite is in geosynchronous orbit, approximately 22,000 miles from the Earth's surface. Therefore, any signal has to travel up and back, for a total round trip of 44,000 miles, which causes a noticeable delay, or latency. This delay is about 250 milliseconds, or a quarter of a second, one way (i.e., from the user ground station to the uplink facility). To send a request and receive a response, the user will experience a minimum of about one half second of latency.

While the delay is not noticeable when receiving a data download (such as a file transfer) or watching a video stream, any interactive service (such as videoconferencing or voice over IP) will be adversely affected. With the round-trip time taking at least one half of a second, the video or audio interactivity is severely degraded as compared to wireline circuits (such as a T-1), whose latency is on the order of 1ms per 100 physical circuit miles.

Shared bandwidth

Satellite systems are shared networks. Like unswitched Ethernet, every use of the system consumes bandwidth; the more users there are, the less bandwidth there is for any single user. Unlike cable systems, though, where the competition is generally limited to a single "drop" area or neighborhood, the competition for satellite bandwidth is nationwide. So, as more users begin using the satellite service and more high-bandwidth streams for audio and video are transmitted, overall per user capacity will drop. Some providers offer guaranteed bandwidth, and private networks can be built with guaranteed bandwidth allocations, however, these options will increase the cost of the system.

To an end user, this means that although the downlink bandwidth is configured for one Mbps (for example), the actual speed of data coming to the user from the satellite depends on the total amount of bandwidth the satellite is handling at that moment and how much it can dedicate to the user. The same is true of uplink bandwidth; how many other users are transmitting at the same time affects the upload speed. As in any shared system, the economies of sharing at some ratio (or oversubscribing) keep the costs down, as users are not paying for dedicated bandwidth; however, if the sharing arrangement is not carefully monitored and designed for peak demand (not average demand), end user performance will suffer for all users.

Security

Satellite systems can be insecure as user data is beamed down to earth in a wide broadcast. Anyone within view of the satellite can potentially eavesdrop on any transmission. To address this problem, some satellite vendors have implemented encryption and other security technologies to protect the data stream from the remote location to the satellite hub. This practice ensures that anyone eavesdropping on the transmission will be unlikely to be able to reconstruct your data transmission.

Encrypting the satellite data stream is not and end-to-end solution, and any organization that comply with HIPPA or desires encrypted transmission from end-to-end must use an encrypted VPN solution. These systems ensure that the data is encrypted before being sent to the satellite and remains encrypted until it arrives at the "home office". Note that encrypted VPN technology cannot be accelerated by most VSAT providers; organizations must test the VPN solution over the satellite prior to purchase to ensure that it will function appropriately.

Quality of Service

Satellite systems cannot provide full quality of service (QoS) or bandwidth controls. In wireline systems, QoS can be finely controlled since each user has a separate entry point into the network, providing a control point for flow management. With a satellite system, all users beam their data to the satellite, which relays the data to the ground to be routed. Since there is no control on the amount of traffic a single user can send based on the traffic already being sent by other users, several simultaneous high-bandwidth users can consume the satellite and effectively block other users. There are some rudimentary controls in place to provide some limits, and some vendors have proprietary solutions (e.g., SkyCasters)¹² to provide some QoS, but these solutions are not as good as what today's wire line systems can offer and improvements may be difficult to achieve due to the nature of the satellite system.

Location

Satellite systems require a clear line of sight to the satellite. Although it seems unlikely, there are areas where a clear view of the sky and the satellite is not available. Urban areas with tall buildings are a problem, as are rural areas close to mountains, bluffs, in valleys and near other natural formations that may block the sky. In any location, other buildings, trees and a myriad of other obstacles may block enough of the sky to prevent the system from functioning. Items such as trees and other buildings may obstruct the view, which will require the location to be changed (if possible) until a clear view is obtained.

Applications

TCP/IP applications were designed for low-latency, high-reliability networks. An increasing number of real-time, interactive applications are being used on the network. Although some applications can be tuned to allow for increased latency, many of the applications MOREnet tested cannot be easily adjusted (or cannot be adjusted at all), making the use of the application problematic.

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Conclusion

The viability of delivering data over a satellite depends on the applications that are commonly used over the network. Applications like web browsing are excellent candidates for satellite delivery, but highly interactive applications like video conferencing may suffer from performance issues.

DSL services are available to many locations and offer similar speeds while avoiding the latency issues that cause TCP/IP applications to struggle or fail.

Considering the number of satellite providers offering services, at some point TCP/IP applications may be tunable to adjust for the significant delays imposed by the satellite transmission. Some applications, especially real-time, such as VoIP and H.323 video, may never function well over the system. MOREnet's customers have clearly stated that quality video is of prime importance.

The use of VSAT systems for disaster recovery is a reasonable tradeoff between access, speed, and cost. In cases where no alternative is available, or traditional services are unavailable due to disaster, a VSAT system, providing IP-based services (data as well as voice and video) is a very attractive short-term solution.

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Appendix: How MOREnet Delivers Services Statewide

MOREnet delivers equitable service statewide using a patchwork of Frame Relay, ATM and Point-to-Point circuits, as few local providers have the service offerings needed to deliver data services.

MOREnet uses Frame Relay as the predominant customer connection type, with ATM a distant second. Circuits delivered within SBC, Sprint, and Century Tel territories are generally single circuits, meaning that only one carrier is involved with providing the circuit. Locations outside these three territories are delivered by a combination of circuits-a Frame Relay or ATM circuit from SBC, connected to a Point-to-Point circuit from the local provider. This arrangement allows MOREnet to deliver ATM or Frame Relay services to customers in areas where these services are not locally available. The disadvantage of this approach is the mileage-sensitive pricing and meet-point fees (where the local telephone company hands the connection to SBC), which can add up quickly.

This system allows MOREnet to provide any school district, library or college bandwidth, although at times the cost can be quite high. This does provide an opportunity for alternative providers to expand into these areas (such as Sho-Me Fiber) and provide high-speed bandwidth and services that are not being currently offered, at a lower price. When other providers enter a market and drive down the price, it lowers MOREnet's costs and provides services to others in the community who may not have been able to afford the incumbent's pricing. In addition, the incumbent provider often begins to evaluate offering the services as competition arrives and more sites are connected within their operating territory, which makes Frame Relay and/or ATM widely available.¹³

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Endnotes

1. DSL, or Digital Subscriber Line, is used to refer to a set of xDSL technologies, including Asymmetric DSL (ADSL). See http://www.dslforum.org for more information.
2. Etherloop is a technology to deliver Ethernet over phone lines - see http://www.paradyne.com/technology/etherloop.html for more information.
3. Applications known to be used by customers include Microsoft SMS, Outlook/Exchange, H.323 video, remote printer and file shares, Novell ZENworks, & remote control systems such as VNC and PC Anywhere.
4. A geosynchronous orbit is where an object remains fixed over a point on the Earth. See http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.html for a detailed explanation of geosynchronous orbits and how they are calculated.
5. DirecTV and Dish Network are the two largest, and sell direct as well as through resellers. Both also offer business data service over the same satellite network.
6. See Appendix B.
7. Fixed dishes, such as the fixed DSS dishes used by DirecTV and Dish Networks, are focused on a single point in the sky. Movable dishes, such as the larger C-band and Ku-band dishes on older satellite TV systems, move to select different transponders and satellites in geosynchronous orbit, but not to 'track' satellites.
8. Original implementations continued to use the phone line and standard modem for the 'uplink' part, and the satellite was used only for the high-speed download of the requested data.
9. Network Address Translation-Used to remap private network address to a public, routable address(es) to reduce the number of public IP addresses used in a network.
10. The seven-layer ISO model of networking defines the Physical, Data Link, Network, Transport, Session, Presentation, and Application layers (1-7 in order) . Each layer allows for independent control of portiions of a network connection. TCP/IP operates at layer 3, which would be unaware of the satellite connection at layer 1. See http://www.webopedia.com/quick_ref/OSI_Layers.asp for more information.
11. Speeds of DS-3, OC-3, and higher are available from some providers-see http://www.convergedigest.com/satellite/satresources.htm.
12. http://www.skycasters.com/super-vpn.htm
13. Over the ten years MOREnet has been in operation, this scenario has repeatedly occurred in Missouri. MOREnet works with a provider to deliver services on a Individual Case Basis tariff (ICB) to solve a need, and the carrier will later file a public tariff for the services and make them available to everyone in their operating territory.

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