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If you are a corporation in search of disaster recovery networking solutions, a first responder who may need connectivity from anywhere at any time, or you simply need broadband internet connectivity from remote locations you have probably considered that satellite may be your only reliable option. In the midst of a disaster many businesses and first responders may find themselves without communications of any kind due to the loss of terrestrial infrastructures, or the lack of it ever existing in the first place.

The problem is that most business professionals and emergency service workers do not have a complete understanding of the satellite business and the idiosyncrasies of communications via satellite, and why should they? Satellite communications is not their profession. In the quest for a satellite internet service provider there are certain questions you should be prepared to ask before you get locked into a contract for services that won’t satisfy your needs:

1) Do you have Non pre-emptible satellite space segment? Satellite operators such as SES Americom, Intelsat among others lease space segment to satellite service providers. There are different levels of protection available in varying price ranges. Many service providers will opt to contract for pre-emptible space segment because it’s much less expensive and they can make larger profit margins which they may or may not pass on to their end users. Pre-emptible space segment gives the satellite operator the ability to deny access to the satellite for the service provider in the event of an on board equipment failure, or to make room for a service provider who is willing to pay the Non pre-emptible premium. During large scale disasters such as the hurricanes in the Gulf States in 2005 many pre-emptible segments of satellite space were cleared to make room for government requests for satellite service leaving other service providers with no access. If you are considering contracting for service for disaster recovery applications it is highly recommended that you find service providers that guarantee that they have contracted for Non pre-emptible space segment. The service provider should be able to provide you with evidence of their service agreement with the operators if you ask. You may pay a little more each month for your non pre-emptible service, but at least it will be available when you most need it.

2) What is your “Over Subscription” or “Contention Ratio”? Most satellite service providers who are providing Internet services are operating systems that use TDMA (Time Division Multiple Access) based systems. A TDMA system is normally controlled by a central hub location which will command the remote units in the field to transmit their data when the hub is ready to receive it. This allows for many remote units to share the same slice of bandwidth improving the overall efficiency of the system. The transmissions from the remote units are sequenced at a very high rate, many times per second, which makes the service appear to be continuous. However, the more units that are added to the system, the slower the service will be. A true enterprise level operator will never allow their contention ratio to exceed 20:1 or essentially 20 terminals per segment of bandwidth. Many operators that offer lower grade services will over subscribe their systems as high as 40, 80, 120:1 or more. Some operators may not be willing disclose this information to their end users. If a service provider will not tell you their contention ratio, you might consider looking elsewhere as their ratios are likely to be high. This will directly affect the quality of the service you receive. Enterprise level operators with contention ratios of 20:1 or less will charge more for their services since they have fewer users for their contracted space segment. But, you get what you pay for.

3) What is your system Latency, and does your hardware or software include TCP/IP acceleration? Any IP transport platform will have a certain amount of latency that is inherent to the structure of the system. Latency is normally measured by how long it takes for a TCP/IP “Ping” to be sent to a server on the other side of the transport link and be returned back over the link to the point of origin. Satellite systems, due to the physics involved will have much higher latency figures that any terrestrial link. Data is transmitted to the satellite at the speed of light, or 186,000 miles per second. The satellite is located 22,223 miles above the equator. For a ping to make its round trip it must travel up to the satellite, back to earth to the server, up to the satellite again and back to the origination point. This is a round trip is approximately 88,892 miles. When calculated with the speed of light, in a perfect world the round trip will take about 448 milliseconds. When you add in coding delays and processing delays you can increase that figure by 100 to 250 milliseconds. On an efficient system, a round trip ping should take between 550 and 700 milliseconds (225 ms one way in each direction). Many lower grade systems on the market today will actually return ping times of 1200 milliseconds or greater which is too slow to allow for functionality of certain software applications. Some system operators have added TCP/IP acceleration products to their equipment. This can either be a hardware or software solution. Acceleration of TCP/IP does not speed up the actual transmission as it is already being transmitted at the highest speed possible, the speed of light. The acceleration is achieved by modifying the TCP protocol in ways that allow for more efficient transmission over high latency networks such as satellite. Acceleration can significantly improve the speed of loading web pages, so it is a highly desirable product to have. Most of the products are not capable of accelerating encapsulated data such as VPN’s, but the system should still pass that data, however more slowly. Be sure to ask whether or not the system has an acceleration product included.

4) Does your system support VoIP, VPN, and Streaming Video transmissions? If you have certain applications that you intend to operate, be sure to inquire whether or not these applications are supported on the system. VoIP (Voice over IP) for telephone connectivity is becoming a very common need in satellite communications. All types of users from emergency services to business continuity are asking for telephone connectivity. The biggest concern most prospective users of VoIP over satellite have is that the latency will be too high for effective voice communications. This has largely been proven to not be true. In fact, most cellular telephone systems will experience as much or more delay in their systems than VoIP over satellite. Most satellite providers will support these systems, but if the system latency is more that about 800 milliseconds, you may experience difficulty carrying on a conversation. Some service providers will also sell VoIP equipment. If you choose to purchase from them, or on your own you will want to make sure the equipment includes good voice compression. Most off the shelf VoIP systems that are not designed for use with satellite will occupy between 40 Kbps and 90 Kbps of bandwidth to complete each call. If you purchase 128K of satellite uplink bandwidth you may consume all of your bandwidth with one or two phone calls leaving none for internet access for your computers. There are compression VoIP systems available that have been designed for use over satellite that will use as little as 8 Kbps per phone call and the call is toll quality. There are even compression systems that will allow for a 1544 Kbps T1/PRI connection over less than 256 Kbps of satellite bandwidth. You will also want to inquire about connectivity to the PSTN (Public Switched Telephone Network). When the signal lands at the hub it will need to connect your VoIP traffic to a telephone line. Some service providers will provide this service for a fee; some will not provide it at all, so be sure to ask. If you need to operate a VPN over the system, keep in mind that it will likely not be accelerated over the satellite. Acceleration of VPNs can be achieved with external hardware; however it is normally up to the customer to provide that equipment. There are some systems, mostly consumer grade, that will not support VPN’s at…
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Ihab Salloum