Very small aperture terminal

VSAT is short for Very Small Aperture Terminal. This is a satellite ground station (dish) with a small antenna - typically between 0.8 to 2.4 meters in diameter, as opposed for 10 meters for other satellite dishes.

VSAT is an efficient method to distribute decent amounts of bandwidth (max of 20 Mbit/s, usually 512 kbit/s or even 256 kbit/s, depending on the provider) to a large area with low population density, or where wires do not exist (e.g. hilly areas, dense forest, etc). The return channel is usually much slower than the downlink, typically between 10 kbit/s to 76 kbit/s. With certain non-DVB VSAT systems, up to 8 Mbit/s uplink can presently be realised. In the near future, even higher speeds - up to 45 Mbit/s - will become attainable.

VSAT can be set up very fast, and finds applications in disaster areas where communication infrastructure has been extensively damaged. In connection with Wifi (and future WiMax) cells, large areas with an underdeveloped infrastructure can be supplied quickly with telephony and broadband Internet services.

VSAT is commonly used for point of sale transactions including credit cards and RFID applications such as Mobil Speedpass. There are over 100,000 gas stations and lotteries in the United States alone that use VSAT.

VSAT usually provides a bi-directional data-stream, using either DVB(DVB-RCS,DVB-RCS2,DVB-RCS MPEG2 - each is optimized for different applications), or non- DVB standards. High-end high data-rate VSAT equipment, as used by offshore-oil companies and some military units, is typically non-DVB. Typical applications include multicasting video-streams, radio and tv channels, as well as Internet in areas without proper internet services.

DVB Technology Digital Video Broadcast (DVB) is a satellite-based standard that was primarily designed to use in broadcast video applications. The standard has been widely adopted due to its simplicity, easily available chipsets, and cost. DVB based technology is widely deployed and understood by most network operators. DVB was primarily designed for one way broadcast of video and [[MPEG traffic. Recently a new standard DVB-RCS (Return Channel via Satellite) was completed to allow for a standard based return channel for two-way traffic. The intent of the open standard is to accelerate economies of scale, thereby generating lower-cost solutions and opening the market in a shorter timeframe than could be possible with competing proprietary solutions.

DVB standard for the forward or broadcast channel has the following technical characteristics, - MPEG frame for transporting video and data - RSV (Reed-Solomon Viterbi) based Forward Error Correction - Very high bandwidth on the outbound DVB-RCS standard has the following characteristics, - TDMA based inroutes - MPEG frame for transporting data - Also supports ATM cells for transporting data

DVB standard based systems interoperate well on the outbound channel between different vendor equipment. DVB-RCS for the return channel is another story. The standard only provides for the basic interoperability between different vendors. For any enhanced services, the interoperability is lacking to say the least.

The standard does not guarantee basic interoperability (e.g. TDMA slot sizes, # of inroutes, hopping vs. static frequencies, frame sizes, code rates are all variable). In theory two vendors could design infinitely adjustable implementations of the specification. In reality, they would have to actively engage each other and support a set of interoperable modes.

Advantages of DVB based system: - High bandwidth outbound or broadcast - Designed and built for Video Broadcast - Lower Cost of Remote Terminals Disadvantages of DVB based system: - Generally Power-Limited satellite requirement - Very inefficient when use of transponder capacity - Not designed for TCP/IP traffic. IP is encapsulated within MPEG - Very high Hub equipment cost Advantages of DVB-RCS based system: - Potential interoperability between multiple vendors - Potentially lower cost of modems Disadvantages of DVB-RCS based system: - Interoperability between multiple vendors limits functionality - Typically implemented with RSV FEC which is not very efficient - TDMA protocol used is typically slotted-aloha

One non DVB system has, e.g., the following technical characteristics, - TDM Based Broadcast - Up to 23 Mbit/s Channel Rate - Primarily Bandwidth Limited Implementation - Turbo Product Codes (TPC) FEC - Lower Eb/No for 10-9 BER when compared to RSV - Frame Format optimized for TCP/IP Inbound or Return Channel has the following technical characteristics, - Enhanced Dynamic TDMA Technology - Up to 5.75 Mbit/s Channel Rate - Primarily Bandwidth Limited Implementation - Turbo Product Codes (TPC) FEC - Lower Eb/No for 10-9 BER when compared to RSV - Frame Format optimized for TCP/IP - Dedicated bandwidth per VSAT - Extremely fast dynamic allocation algorithms Advantages of Technology - Primarily Bandwidth limited, thus much lower service costs - Extremely responsive TDMA channels - Queue depth checked 8 times/sec - All remotes have a minimum CIR - Multiple-inroutes Network Capability - Frequency Hopping Capability – Dynamically Assigned based on demand - Very scalable hub equipment, with multiple network support within a chassis Advantages of Hub Technology - Support for multiple satellite and networks within one chassis - Extremely scalable - Very compact (1/6th the size) of comparable technologies - Very cost competitive - Carrier Class – Fully Redundant with Hot-Swap capability Other Solutions Benefits - TCP and Web Acceleration in BOTH directions - Application QoS in the BOTH direction - Network QoS - Rate Limiting Capability in BOTH directions - Committed Information Rate (Dynamic and Static) in BOTH directions - Fast “First-Click” Response - DHCP/NAT/Local DNS Caching Capability - Built-in AES/3DES Link Encryption Capability

DVB vs. Non- DVB – IP Efficiency Comparison DVB frame format uses MPEG for broadcasting video. IP over DVB has to encapsulated within an MPEG frame to be transported over DVB. IP packets must be segmented into MPEG 188 byte cells which further decreasing efficiency. This is a consequence of using a system optimized for digital video to transport IP packets. A maximum sized 1500-byte Ethernet packet has to be segmented into 8 or more MPEG cells. The non-DVB solution described here has no such constraint. Transport cells are sized variably depending on the size of the IP packet instead of having to conform to fixed sized cells. This provides a much better throughput efficiency over an Network. As an example, over a 500 kHz satellite capacity, with an solution one can get a TCP/IP throughput of 530 kbit/s. With the same satellite capacity over a DVB network, the TCP/IP throughput is 385 kbit/s.

Case Study: On 8 MHz of satellite capacity, using QPSK and some guard band and RSV Coding Rate ¾ , with DVB one will get a data rate of 7.7 Mbit/s, but the actual IP throughput of 90%, assuming MPE configuration. The IP throughput will be around 7.0 Mbit/s. Over the same satellite capacity the solution gives an IP throughput of 8.8 Mbit/s. This is an increase of 25% IP throughput.

DVB vs. – Satellite Transponder Capacity Usage DVB based systems use concatenated Reed Solomon and Viterbi for its FEC. uses Turbo Product Codes (TPC) FEC for its system. systems operate at Eb/No’s approximately 1.5 dB lower than DVB based competitors to deliver 10-9 BER performance. This reduced requirement allows an operator to use lower power on the satellite thus reducing overall cost of the system. This allows the network operator to provide a more cost-competitive solution that provides a better TCP/IP performance over satellite.

Case Study: BER performance of 4k TPC decoder is equivalent to the Reed Solomon / Viterbi 3/4 code. (TPC is actually slightly better by about 1/4 dB). In addition, an RSV based system requires about 1.5 dB more power to maintain a BER of 10-9 (This is critical when having TCP/IP over satellite).

Network Size: Channel Rate: 5 Mbit/s Encoding: QPSK (2 bits/symbol) RSV: RS/Viterbi ¾ Code Rate: 0.691 User Data: 5 Mbit/s * 0.691 = 3,455,000 bit/s Satellite Capacity: 2.5 Mhz Power Equiv. BW (+1.5 dB): 3.54 Mhz (To Provide Equivalent Quality as TPC) TPC: TPC Code Rate: 0.793 User Data: 5 Mbit/s * 0.793 = 3,965,000 bit/s Satellite Capacity: 2.5 Mhz If we consider a typical rate of $5.00 per kHz per month.

Comparison 1: Code Rate Efficiency and Usable Bit Rate The coding efficiency of an system is significantly better than the competitors RSV based systems. From the above calculations it can be clearly shown that the system has 14.76% higher data throughput than the competitors. 3,965,000 – 3,455,000 = 510,000 extra user bits for same transponder capacity (14.76% more) Comparison 2: Cost of satellite segment RSV based system requires about 1.5 dB more power, than an TPC system, to maintain a BER of 10-9. This BER performance is critical for a system with TCP/IP traffic. TCP/IP is very sensitive to BER performance, and throughputs will vary significantly if a low BER is not maintained. To achieve the same BER levels of a Non-DVB system, competitors RSV based systems need about 1.5 dB additional power. Thus the total additional bandwidth required by DVB based system is 1.04 Mhz. Additional cost per month for a DVB based system is $5,200.00 / Month or $62,400.00 / Year

Comparison 3: Data on equivalent bandwidth Another way of looking at this is, how much more data bits will one get when using the transponder capacity required by an RSV based system, by implementing an TPC system. From the above example if one had 3.54 MHz of satellite capacity, using the system one will get 5,600,000 bit/s of user data rate. This equals (5,600,000-3,455,000/3,455,000) = 2,145,000 bit/s or 62% more data.

Bandwidth: 2.5 MHz Channel Rate: 5 Mbit/s Data Rate: 3.965 Mbit/s DVB Bandwidth: 2.5 MHz Channel Rate: 5 Mbit/s Data Rate: 3.455 Mbit/s Power Equiv. BW(+1.5dB): 3.54

Bandwidth: 3.54 MHz Channel Rate: 7.08 Mbit/s Data Rate: 5.6 Mbit/s DVB Bandwidth: 2.5 MHz Channel Rate: 5 Mbit/s Data Rate: 3.455 Mbit/s Power Equiv. BW(+1.5dB): 3.54 MHz

Comparison 4: Actual IP Throughput on Equivalent Bandwidth IP throughputs over a DVB based system are typically about 80% of the user data rate. In the above example, the actual IP throughput over the DVB based system, with MPE enabled, is 3,455,000*0.90 = 3,109,500 bit/s. IP throughputs through the system are close to 95% of the data rate. For the above example, the IP throughput through an system would be 5,333,000. When compared to the DVB solution, the total increase in data through the systems is an additional 70% or a difference of 2,223,500 bit/s of IP data.

Conclusion: Based on the above case studies, the difference in cost for implementing a network using a non-DVB solution when compared to DVB based system is significant. This allows a Network Operator to lower their service costs and provide a more efficient system. An solution not only uses the transponder capacity more efficiently, it also increases the actual throughput of TCP/IP dramatically. More importantly, an network provides a much better performance, which increases customer satisfaction and customer retention. In addition, most TDMA systems use Slotted-Aloha protocol over the return channel. Throughput performance of slotted ALOHA is efficient until the channel utilization exceeds 36.8% at which point the number of collisions increases dramatically and there is a snowball effect where none of the users get good throughput on the channel. Most real implementations of slotted-aloha have an efficiency of about 25%, in the best case. The Deterministic-TDMA (D-TDMA) system provides guaranteed bandwidth to every user in the system according to the Quality of Service parameters allocated to the user. ’s advanced Demand Assignment algorithm ensures that data gets through with minimal latency even when the channel utilization is approaching 100%.

Bandwidth: 3.54 MHz Channel Rate: 7.08 Mbit/s Data Rate: 5.6 Mbit/s IP Throughput: 5.33 Mbit/s DVB Bandwidth: 2.5 MHz Channel Rate: 5 Mbit/s Data Rate: 3.455 Mbit/s Power Equiv. BW(+1.5dB): 3.54 MHz IP Throughput: 3.1 Mbit/s

Non-DVB standard system: The Multi-Star Alternative to Mesh

SOme bespoke VSAT systems target the high end of the broadband market. Small, private networks use all three VSAT solutions to deliver broadband services like…

• WAN Connectivity for Intranet Access • Web Surfing and Internet Access • Electronic Mail • Broadband Content Collection and Delivery • Real Time Applications like Voice and Video

The conventional wisdom in the VSAT industry is that star VSAT and mesh VSAT occupy orthogonal market niches. The reality is that the overwhelming majority of mesh VSAT systems are deployed in multi-star networks and small star topology networks where the cheap hubs of the mesh VSAT minimize the overall cost of the network.

Unlike the old star terminals whose hubs cost $250,000 or more, Non-DVB standard system is affordable in multi-star and small star networks because Non-DVB standard system offers hubs priced like high-end DVB System and remotes. Once it becomes affordable, a small star topology system more desirable than a mesh system because the star system is easier to implement and maintain. Mesh networks are notoriously difficult to configure due to their complex routing tables, which are labor intensive to define and to update. Furthermore, Non-DVB standard system is more bandwidth efficient than any mesh VSAT. For broadband applications where satellite bandwidth makes up more than half the total lifetime cost of ownership, Non-DVB standard system minimizes monthly operating costs.

The market has voted with its dollars overwhelmingly in favor of Non-DVB standard system. Thousands of Non-DVB standard system terminals are sold every year compared to only hundreds of DVB System or terminals. Whereas sales of DVB System and units have stabilized or declined in recent years, sales of Non-DVB standard system units have grown exponentially. Network operators trust in Non-DVB standard system’s many advantages over DVB System and , such as…

1. Less Expensive Remotes 2. Smaller Antennas 3. Faster Speeds 4. Greater Aggregate Network Capacity 5. Greater Bandwidth Efficiency 6. Superior Traffic Management and QoS

Non-DVB standard system will even adapt on short notice to accommodate uncommon needs like…

1. Mesh Connectivity 2. Plug and Play Voice Lines 3. Legacy Data Protocols

The System Architecture for Non-DVB standard system As shown in Figures 1 and 2, Non-DVB standard system offers a star topology TDM/TDMA VSAT network that offers frequency hopping among its reservation TDMA return channels.

Figure 1: A Typical Non-DVB standard system VSAT Network

Figure 2: An Example of Non-DVB standard system’s Carrier Assignments

Non-DVB standard system’s standard 5IF Hub Chassis and its standard 1IF Hub Chassis both hold up to 20 Universal Line Cards (ULC) apiece. Each ULC can act as a modem, a modulator, or a demodulator. The carriers generated by the line cards enable the Non-DVB standard system hub to talk to a variety of Non-DVB standard system remote terminals. As in all star topology systems, the remote terminals only talk back to the hub.

Each carrier in Non-DVB standard system’s forward channel transmits at speeds from 128 kbit/s up to 9.1 Mbit/s. So, one Non-DVB standard system Hub can deliver 128 kbit/s to 182 Mbit/s of forward channel capacity. In the return channel, Non-DVB standard system has demodulators that operate between 64 kbit/s and 4.2 Mbit/s. So the aggregate return channel capacity of a standard Non-DVB standard system hub can be as much as 84 Mbit/s. In reality, no network operator has ever needed the full 182 Mbit/s forward channel or the full 84 Mbit/s return channel that a standard Non-DVB standard system hub is capable of providing.

The backplane of Non-DVB standard system’s 1IF Hub Chassis combines the output of all line cards in that chassis onto one L-band intermediate frequency (IF) chain. All line cards in a 1IF Hub Chassis share a common frequency reference. The 1IF Hub Chassis is typically used to build networks with more than four return channels for each forward channel. Such networks tend to be very large and very asymmetric shared hubs.

The backplane of Non-DVB standard system’s 5IF Hub Chassis is split into 5 sections, each of which can hold up to 4 line cards. Each section resides in an independent L-band intermediate frequency (IF) chain. So Non-DVB standard system’s carriers can reside on as many as 20 different transponders on as many as 5 different satellites. The 5IF Hub is typically used to build a series of small, independent networks co-located at one teleport.

For small, truly independent, private networks, Non-DVB standard system offers its Private Hub and its Mini Hub. These smaller hubs contain one and only one modem. The satellite networks built upon these smaller hubs have only one TDM carrier for downstream traffic and one TDMA carrier for upstream traffic. The appeal of these smaller hubs is that they can be as much as an order of magnitude less expensive than Non-DVB standard system’s 5IF Hub. The difference between the Private Hub and the Mini Hub is that the Private Hub supports an unlimited number of remotes whereas hardware limitations in the Mini Hub restrict it to networks with no more than 15 to 30 remotes.

The System Architecture for DVB System and The DVB System VSAT from ND SatCom and the VSAT from ViaSat are remarkably similar products. The DVB System and systems are mesh topology, packet switched, reservation TDMA VSAT networks. As shown in Figure 3, DVB System and networks can be configured in mesh, star, or hybrid topologies. These systems have no hub per se. However, there is a Network Management System (NMS) that assigns bandwidth among the remote terminals.

Figure 3: Available DVB System and Network Topologies

DVB System and employ a reservation TDMA carrier that is very different from the reservation SCPC carriers typically found in full mesh DAMA VSAT. Most of the strengths and weaknesses of DVB System and emanate from the unique way these terminals can use one carrier to both transmit and receive information at a remote terminal. This operating paradigm is depicted in Figure 4.

Figure 4: An Example of a DVB System or Carrier

In theory, each DVB System or terminal talks into dynamically assigned time slots in a TDMA carrier while listening to other terminals on different time slots in the same carrier. A DVB System or terminal hears all the traffic on a carrier, but it only keeps the packets that are addressed to it. DVB System carriers range in size from 64 kbit/s to 8 Mbit/s. carriers range in size from 130 kbit/s to 6 Mbit/s.

In practice, each DVB System or terminal can dynamically hop among many different carriers as long as its radio transmitter has enough power to match the speed of the carrier to which it wants to hop. Frequency hopping on the transmit side is coupled to frequency hopping on the receive side because the transmitter gets its timing information from the receiver. To burst information into any carrier, a DVB System or VSAT has to first listen to that carrier. While the VSAT is listening to one TDMA carrier, it cannot be bursting information into another TDMA carrier because each VSAT modem comes with only one TDMA demodulator.

What Makes Non-DVB standard system, DVB System, and Stand Out Among VSAT: Similarities that Define a Unique Niche in the VSAT Industry Small Minimum Scale Non-DVB standard system is unique among star topology VSAT in that it has a very small minimum scale in terms of start-up equipment and initial bandwidth commitments. Hub equipment from Non-DVB standard system can be purchased for tens of thousands of dollars instead of hundreds of thousands of dollars. Non-DVB standard system can also operate with as little as 150 kHz of satellite bandwidth as opposed to the MegaHertz of bandwidth needed by most star topology VSAT. Such a small minimum scale has heretofore been the exclusive purview of mesh VSAT systems like DVB System and .

Non-DVB standard system, DVB System, and all feature small minimum scales in terms of initial hub infrastructure. At the center of each subnet in a multi-star network, Non-DVB standard system places its $35,000 Mini Hub. For small star topology networks, Non-DVB standard system offers a $125,000 Private Hub that comes with installation, training, software upgrades, and a year of technical support – not just baseband equipment. Neither DVB System nor have a hub per se, but each does have a Network Management System (NMS) priced near $50,000. ND SatCom and ViaSat charge additional fees for installation, training, and technical support. Altogether, there is little difference between the costs of Non-DVB standard system versus DVB System or hub infrastructure.

All three systems also have a small minimum scale in terms of initial bandwidth commitments. Non-DVB standard system needs at least 150 kHz to support two carriers: a 128 kbit/s forward channel carrier and a 64 kbit/s return channel carrier. DVB System needs at least 100 kHz for its smallest carrier - a 64 kBaud signal that it uses for both incoming and outgoing transmissions. requires at least 250 kHz for one carrier that remote terminals both transmit to and receive information from.

Their small minimum scales enable these three systems to expand geographic coverage and frequency range with little incremental investment. The least expensive way for Non-DVB standard system to expand its 5IF Hub or its 1IF Hub is to add a Universal Line Card (ULC) for less than $30,000. The line card can act as a modem, a modulator, or a demodulator. Acting as a modem, the line card can add to an existing hub a new network on a different transponder or a different satellite. It costs less than $30,000 to expand the coverage of a 5IF Hub from Ku-band to C-band or from a transponder that covers Africa to one that covers Asia using a different bird.

Both DVB System and can expand to new geographic areas, different frequency bands, and different satellites just as elegantly as Non-DVB standard system can. DVB System and need only add a $50,000 NMS for each new transponder they light up. There are also additional fees for installation. But, overall, it is relatively inexpensive to expand a DVB System network or a system to accommodate more transponders on different satellites. In this regard, DVB System and are very similar to traditional mesh DAMA VSAT systems.

Broadband Speeds Like most mesh DAMA VSAT systems, Non-DVB standard system, DVB System, and have evolved into platforms that deliver true broadband services. Such services are the mainstream telecommunications applications typically found on terrestrial WAN’s – not the narrowband niche applications that HNS has made synonymous with the VSAT industry. In the VSAT industry, the term “broadband” refers to IP throughputs in excess of 256 kbit/s. Almost all VSAT can receive more than 256 kbit/s. What separates true “broadband” VSAT from mere “Internet access” terminals is the ability to transmit data – not just to receive data – at speeds beyond 256 kbit/s.

Non-DVB standard system, DVB System, and all offer transmit and receive speeds that qualify them as true broadband VSAT. An Non-DVB standard system VSAT receives information at speeds up to 9.1 Mbit/s and transmits information at rates up to 4.2 Mbit/s. DVB System transmits and receives information at speeds up to 8 Mbit/s. transmits and receives information at speeds up to 6 Mbit/s. Non-DVB standard system, DVB System, and are the first generation of VSAT to truly push the VSAT industry out of its narrowband niche into more mainstream applications like broadband data and high quality voice services.

Adequate Bandwidth Efficiency for All Traffic Patterns Mainstream telecommunications applications demand more than just high speeds from VSAT. VSAT’s need to be very bandwidth efficient to economically carry the heavy traffic loads in mainstream WAN’s. Non-DVB standard system, DVB System, and are unique in their ability to use reservation TDMA algorithms to efficiently transport the constantly changing mix of bursty and continuous traffic commonly found in WAN’s.

A broadband network seldom carries just broadband traffic. Most broadband networks carry a mix of traffic. Real time traffic like voice and video tends to be continuous streams – each operating at a different (but predictable) speed. Machine to machine traffic (as for enterprise resource planning and inventory management systems) tends to come in very short, high-speed bursts. Internet access creates self-similar traffic patterns where the variance in the flow of traffic is on the same order of magnitude as the average flow of traffic. Non-DVB standard system, DVB System, and carry all these different types of traffic with equal efficiency.

Non-DVB standard system, DVB System, and use reservation TDMA to efficiently share a carrier (or a set of carriers to be more precise) among a large mix of traffic. A reservation protocol is five times more bandwidth efficient than any contention algorithm like slotted Aloha for accessing a shared carrier. The problem with traditional reservation algorithms is that, over a latency-plagued satellite link, these algorithms react too slowly to efficiently allocate bandwidth for traffic demands that change from one millisecond to the next. Heretofore, only contention access reacts quickly enough through a 250 millisecond satellite delay to efficiently carry bursty data. Non-DVB standard system, DVB System, and have changed this paradigm by adding buffers to very fast bandwidth allocation algorithms. These VSAT are unique in their ability to efficiently carry large amounts of rapidly fluctuating traffic on a shared carrier.

The Advantages of the Non-DVB standard system VSAT System Less Expensive Remotes

Although Non-DVB standard system, DVB System, and are used for similar applications, they differ from each other in terms of price. DVB System terminals are priced from $12,500 to $25,000. terminals sell for $7,500 to $15,000 apiece. Non-DVB standard system’s remote terminals range in price from $1,500 to $6,000. Even large networks with thousands of sites are affordable at Non-DVB standard system’s prices. More importantly, small networks can significantly improve their chances of growing to become large networks by adopting Non-DVB standard system’s less expensive remotes. The price of remote terminals is critical because it is the single largest barrier to entry for new subscribers.

Smaller Antennas

One of the major reasons why DVB System and remotes are so much more expensive than Non-DVB standard system remotes is that DVB System and almost always have to use bigger antennas and more powerful transmitters than Non-DVB standard system would need at the same sites. Non-DVB standard system only needs a big antenna at the hub because it settles for a star topology that tolerates small antennas at the remotes. The price that DVB System and pay for mesh connectivity is their need for bigger antennas at all remotes.

Traditional mesh VSAT do not necessarily need bigger antennas and transceivers (so called outdoor units or ODU) than star VSAT. However, the unique way in which DVB System and have implemented mesh connectivity does necessarily dictate larger ODU than star VSAT would need under similar circumstances. DVB System and achieve an indefinitely large number of simultaneous mesh channels using only one modem in each remote by forcing a single reservation TDMA carrier to both transmit and receive information at the same time. In the network architecture employed by DVB System and , the transmit carrier is the receive carrier for a remote. For DVB System and , a VSAT’s transmitter bursts data out at the exact same speed that the VSAT receives data in.

ODU at every DVB System or site is sized for the combined transmit and receive speeds of the most heavily trafficked site in the network. The most heavily trafficked site is usually the hub. So every site in a DVB System or network has its ODU sized as if it were a hub with sufficient power to support on one carrier the aggregate forward and return channel traffic going through the entire hub!

In contrast, the ODU of Non-DVB standard system remotes are sized to support only the maximum upstream speed of the one VSAT that needs the fastest return channel. Supporting one remote’s upstream traffic requires far less ODU gain than supporting the aggregate throughput at the hub. The only time when a DVB System or remote antenna is equal in size to its Non-DVB standard system counterpart is when there is an equal amount of traffic going to and coming from every site – as in voice trunks among cellular base stations. In normal networks where the remotes experience less traffic than the hub does, DVB System and remotes are burdened with unnecessarily large ODU just because they need to access the exact same transmit/receive carrier as the hub. In other words, any DVB System or terminal that receives more information than it transmits is burdened with an unnecessarily large ODU.

In normal broadband networks, most remote terminals receive far more information than they transmit. For common broadband applications like Internet access, the asymmetry can be as much as 10 bits for information received for every 1 bit of information transmitted. In asymmetric networks with high data rate downloads, DVB System and VSAT need antennas and transceivers that are several times the size of ODU required by Non-DVB standard system to do the same job because the receive carrier is the transmit carrier for all DVB System and remotes.

Faster Speeds

The need to contain remote terminal costs and ODU sizes forces DVB System and to implement much slower networks than their indoor units (IDU) are capable of supporting. DVB System modems support carriers as big as 8 Mbit/s and modems support carriers up to 6 Mbit/s. However, there are practical limitations that make carriers beyond 2 Mbit/s inordinately expensive to implement.

On most satellites, the largest carrier that an affordable 1.8m antenna and 4W Ku-band ODU can support is 2 Mbit/s. Beyond 2 Mbit/s, DVB System and require 8W+ Ku-band transmitters that cost tens of thousands of dollars. They may also need 2.4m+ antennas that cost tens of thousands of dollars in civil engineering works to install. Worst yet, the expensive ODU have to be replicated at every site in a DVB System or network because all sites in that network transmit into and get information from the same carrier. So carriers beyond 2 Mbit/s are cost prohibitive to implement using DVB System or equipment.

Non-DVB standard system remotes face the same economic constraints on the transmit side, but not on the receive side. Non-DVB standard system networks have one carrier for downstream traffic and a separate carrier for upstream traffic. The cost of Non-DVB standard system’s receive side decreases as receive speed increases. At higher speeds, less expensive DRO LNB can replace expensive PLL LNB whose better phase noise is only needed to lock onto smaller carriers. On the other half of the modem, the cost of Non-DVB standard system’s transmit side increases with transmit speed because transmit speed drives transmit radio power.

Thus, the price of an Non-DVB standard system remote increases as the speed of its transmissions increases, but the price of an Non-DVB standard system remote actually decreases as its receive speed increases. With 1.8m/4W Ku-band ODU as the threshold of affordability, Non-DVB standard system systems can be trusted to deliver 9.1 Mbit/s downloads and 2 Mbit/s uplinks. Meanwhile, because they use the same carrier to both transmit and receive traffic, neither DVB System nor remotes can offer more than 2 Mbit/s of transmit speed and receive speed combined when staying within any reasonable budget.

Greater Aggregate Network Capacity

For normal networks where most of the traffic flows in a logical star, Non-DVB standard system offers far greater aggregate network capacity than DVB System or . Non-DVB standard system’s forward channel capacity is limited to 9.1 Mbit/s by the maximum speed of one downstream carrier. The practical aggregate return channel capacity for an Non-DVB standard system network is at least 10 Mbit/s, assuming 20 TDMA carriers each operating at 512 kbit/s.

In networks where most or all of the traffic travels through a de facto hub, the aggregate forward and return channel capacity of a DVB System or network is limited in theory by the maximum carrier sizes to 8 Mbit/s for DVB System and 6 Mbit/s for . In practice, the real limit is about 2 Mbit/s of forward and return channel capacity combined! Recall that the ODU at every remote has to be sized for the combined transmit and receive throughput of the most heavily trafficked site in a DVB System or network. This most heavily trafficked site is the hub when traffic flows mostly in a star topology. In this case, the ODU of all the remotes have to be sized like the ODU of the hub. The hub cannot be allowed to carry more than 2 Mbit/s of total traffic if the size of ODU at the remotes is to remain reasonable.

DVB System and address their antenna size concerns, speed limitations, and aggregate network capacity constraints by offering an optional DVB overlay. The DVB carrier provides a 2 Mbit/s to 45 Mbit/s forward channel for economically shipping large volumes of traffic downstream from a hub. The DVB overlay frees the reservation TDMA carrier in a DVB System or network to carry mesh traffic and return channel traffic exclusively. With its responsibilities significantly reduced in scope, the TDMA carrier can be shrunk to the point where the ODU of remote terminals become reasonably priced. In effect, the DVB overlay creates very expensive versions of the SkyARCS and LinkStar DVB-RCS systems offered by ND SatCom and ViaSat respectively.

The DVB overlay will not solve the terminal price problems that haunt DVB System and . A DVB overlay noticeably increases the price of hub infrastructure. Each DVB overlay costs about as much as the NMS for DVB System or . Adding just one DVB overlay effectively doubles the price of a DVB System or hub. For the small 5-10 site networks that DVB System and target, the DVB overlay shifts some costs from the remotes to the hub. However, it will not reduce the overall cost of the network greatly with so few remotes over which to amortize the extra hub costs. For bigger networks with more than 10 sites, the $10,000 - $15,000 DVB System and indoor units (IDU) cannot compete against complete Non-DVB standard system VSAT that sell for as little as $2500 in small quantities.

Furthermore, the DVB overlay introduces a few complications to DVB System and networks. First, the DVB overlay greatly increases the minimum scale of any network. Each DVB carrier operates at no less than 2 Msps. It consumes at least 2.5 MHz to deliver about 2 Mbit/s. So a fairly sizable anchor tenant is needed to alleviate market risks when a network operator expands into a new geographic area or a new frequency band using a DVB overlay. Second, instead of having a private network with dedicated bandwidth and dedicated equipment, end users will now likely have to time share portions of their network with other subscribers on the DVB forward channel. The risk of security breaches and other mishaps increases greatly in migrating from a truly private network to a shared public network. Finally, routing issues become more complex with multiple paths for getting from one site to another. External routers will probably have to be added to every site in the network because the native routing capabilities of DVB System and are primitive. The additional labor to configure and maintain these external routers may also add to the recurring cost of operating a DVB System or network.

Greater Bandwidth Efficiency

Relative to Non-DVB standard system, the recurring costs of operating DVB System and networks are bad enough without additional complications. In a star topology network, Non-DVB standard system’s forward channel is two to three times as bandwidth efficient as the receive side of a DVB System or VSAT. Non-DVB standard system’s forward channel uses Time Division Multiplexing (TDM) to combine together traffic destined for many different remotes. For downstream traffic in a normal star topology network, the Non-DVB standard system VSAT is not burdened by the time and frequency guard bands inherent in the Time Division Multiple Access (TDMA) algorithm that DVB System and employ to achieve mesh connectivity. Furthermore, Non-DVB standard system employs Turbo Codes that are far more bandwidth efficient than the Reed-Solomon Viterbi codes found in standard DVB System and VSAT. For broadband applications where satellite bandwidth constitutes more than half of the lifetime cost of ownership, Non-DVB standard system offers a 50% to 65% reduction in forward channel bandwidth costs relative to standard DVB System and VSAT. (DVB System now offers an optional Turbo Code upgrade. Even with Turbo Codes, DVB System is still 10% to 25% less efficient than Non-DVB standard system in star topology networks because DVB System uses TDMA instead of TDM to send traffic downstream.)

Not only does Non-DVB standard system have a more efficient forward channel, but Non-DVB standard system also has a more efficient return channel than DVB System or . As with the forward channel, the Turbo Codes in Non-DVB standard system’s return channel are 40% more bandwidth efficient than the Reed-Solomon Viterbi codes used by DVB System and . Its more efficient return channel enables Non-DVB standard system to collect information from a set of remote terminals into a central site at a much lower cost than DVB System or can offer.

Incidentally, the extra coding gain in Non-DVB standard system’s Turbo Codes need not necessarily be used to improve Non-DVB standard system’s bandwidth efficiency. Instead, the extra gain can be used to support smaller, less expensive radio transmitters and antennas than those required by DVB System or at any equal return channel speed. Where desired, an Non-DVB standard system VSAT can use a 30% smaller antenna than DVB System or can to support the same transmit rate. Non-DVB standard system remote terminals are thus easier to carry into the field for use as data collection devices.

Superior Traffic Management and QoS

Above the physical layer, the Non-DVB standard system system includes a set of advanced traffic management features that its competitors cannot match. Non-DVB standard system and come with network level software to route traffic and to prioritize packets for the purpose of ensuring Quality of Service (QoS). An Non-DVB standard system system behaves as if it is one router with a port located at each site. A system behaves in a similar manner. All traffic in the system is placed into one pool, sorted by priority, queued up, and then routed appropriately. The data rate of every path in the system changes dynamically in real time to accommodate constantly changing traffic patterns.

The DVB System system, on the other hand, is utterly lacking in any routing capability. A DVB System network is conceptually nothing more than a fixed set of fixed data rate circuits. Customers have complained that only a DVB System engineer can add a new site to an existing DVB System network. DVB System’s routing tables are so complex and unwieldy that making even small changes to a DVB System network is extremely labor intensive. DVB System depends on external routers at every site to perform layer 3 networking functions that are built into Non-DVB standard system and systems. DVB System manages traffic only at the edges of its wide area network (WAN). Once a packet enters a DVB System circuit, the packet is statically routed along predefined paths that run at predefined speeds. In contrast, Non-DVB standard system and shape the traffic flows before and after the traffic enters their wide area networks.

Despite many similarities in the way Non-DVB standard system and manage traffic, there is still one big difference between Non-DVB standard system and at the networking layer. Non-DVB standard system terminals include software to compensate for the harmful effects of sending acknowledged TCP traffic through long latency satellite links. lacks the TCP acceleration software to compensate for the 250 milliseconds of latency in satellite communications. Without TCP acceleration, data rates are limited to less than 100 kbit/s for each and every TCP session. File transfers, downloads from the Internet, and emails move slowly through a system when compared to an Non-DVB standard system system that comes with built-in TCP acceleration.

One DVB VSAT system uses external TCP acceleration software to compensate for its inadequacies. However, external acceleration software is only half as efficient as internal TCP acceleration software in networks where the size of each WAN pipe is constantly changing. Non-DVB standard system’s internal acceleration software can accelerate TCP sessions back up to line rates because Non-DVB standard system’s NMS explicitly tells its acceleration software what the line rate is at any moment in time. The NMS does not tell any external accelerator what the line rate is at any moment in time. On ’s shared TDMA carrier where the line rate allocated to any site is constantly changing, the external TCP accelerator pushes packets out at the average network capacity that it senses. However, external acceleration software cannot sense changes in capacity assignments fast enough to take full advantage of all the capacity assigned to a site. Any external TCP accelerator will also drop and have to retransmit packets when it tries to send too much data into a pipe that has collapsed before the accelerator detects the reduction in assigned capacity. Although they can push TCP sessions beyond 100 kbit/s through a satellite link, external TCP accelerators top out at a small fraction of the line rate.

Incidentally, DVB System does not suffer any of ’s problems with external TCP accelerators because the size of DVB System circuits are fixed. However, any external appliance – be it a TCP accelerator for or a router for DVB System – is labor intensive to manage. Non-DVB standard system has integrated control of all its routing software and all its TCP acceleration software into its Network Management System. All aspects of an Non-DVB standard system network can be managed centrally. Centralized configuration and management of network policies make Non-DVB standard system networks far simpler to operate than DVB System and networks performing the same functions.

How Non-DVB standard system Satisfies Uncommon Needs Mesh Connectivity

There are a few features in the DVB System and systems which are not available in the Non-DVB standard system system today. One such feature is mesh connectivity. Non-DVB standard system is currently developing mesh connectivity. The Non-DVB standard system hardware to enable mesh connectivity will be available in March of 2005. The software to implement mesh connectivity will be released in July of 2005. If true mesh connectivity is really needed instead of just a multi-star network, a network operator can begin to roll out an Non-DVB standard system network in March of 2005 knowing that the Non-DVB standard system hardware by that time will only need a software upgrade to become a full mesh network. By the middle of 2005, Non-DVB standard system will field a mesh solution that is far less expensive to implement and to operate than either DVB System or can offer.

For at least a few more months though, one advantage of DVB System and terminals over an Non-DVB standard system VSAT is that the former can talk directly with any other terminals in the same network without going through a hub. For traffic from one remote to another, mesh connectivity halves the latency of satellite communications down to about 250 milliseconds. This quarter second of delay is virtually undetectable in voice calls and videoconferences, whereas the 500 millisecond latency of a double hopped voice call is easier for end users to notice.

Fortunately for Non-DVB standard system, end users experience degraded call quality only 5% of the time without mesh connectivity. Traffic studies show that phone calls in mesh networks are routed through the hub 95% of the time. Only 5% of the time does one end user directly call another remote terminal. So the bandwidth cost savings associated with mesh connectivity are negligible. Given the small number of mesh calls, a network operator will save less than 2.5% on bandwidth by using mesh VSAT instead of star topology VSAT. Mesh connectivity only has value if a service provider can get subscribers to pay more money for 250 milliseconds’ less latency in the 5% of voice calls that occur between two remotes. If end users will not pay extra for slightly better call quality in 1 out of 20 voice calls, the financial value of mesh connectivity may not justify its extra hardware and maintenance costs.

The unique mesh architecture of DVB System and make these systems less expensive than star topology systems for bandwidth intensive data communications among peer LAN. For DVB System or to cost less than Non-DVB standard system, these LAN have to be true peers. No one central LAN should be sending or receiving significantly more information than the others. In such a scenario, DVB System and would be executing single hops where Non-DVB standard system would have to execute mostly double hops that consume twice as much bandwidth. Fortunately for Non-DVB standard system, it is very rare for the endpoints of a WAN to consist of peer LAN. The only time this happens is when large corporations tie large campuses together in a WAN. Since large campuses tend to sit near fiber optic cables, there is limited demand for WAN connectivity via satellite among peer LAN – the forte of DVB System and .

Plug and Play Voice Lines

DVB System and feature built-in voice services that Non-DVB standard system must add external appliances to support. Individual telephones and telephone trunk lines can be plugged directly into the remote terminals of DVB System and networks. These products support voice, fax, and data services with a variety of analog and digital interfaces. They also offer several voice compression options and fax data rates.

One Non-DVB standard system IDU has no voice interfaces, and is strictly an IP platform. One Non-DVB standard system adds external Voice over IP (VoIP) equipment at every site where voice is needed. The Non-DVB standard system remotes get VoIP phones or VoIP adapters. Each Non-DVB standard system hub needs a VoIP gateway to access the PSTN. Nonetheless, the Non-DVB standard system does come with many built-in features to improve the quality of VoIP calls on the network. Furthermore, one Non-DVB standard system prioritizes voice calls over data traffic at a network level to complete 3 times as many phone calls in the busy hour as DVB System or can with the same bandwidth.

Legacy Data Protocols

The more expensive versions of include integrated support for IP, ISDN, Frame Relay, and ATM. Most DVB System IDU internally support Frame Relay and IP. Non-DVB standard systems need an external protocol converter at every site to support any protocol beyond IP. External protocol converters sell for $500 to $1500, depending on quantities and features.

Despite their ability to interface with some legacy protocols, DVB Systems will also use external protocol converters from time to time. There are so many legacy protocols that it is impossible for any single appliance to support them all. Every VSAT system needs external protocol converters occasionally. and DVB Systems simply need external protocol converters less frequently than a Non-DVB standard system does.

See also

• satmodem

External links

• VSAT Satellite Internet (http://www.lamit.ro/two-way-satellite-internet-services.htm)

• Setting up a VSAT in Iraq (http://www.livejournal.com/users/ioerror/179521.html?nc=8)

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