mesh connectivity 20040120 connectivity...these mesh vsat send unacknowledged traffic (like udp...

Ninh Le

Mesh Connectivity in an

iDirect VSAT Network

January 20, 2004

THIS PAPER AND THE INFORMATION HEREIN IS PROPRIETARY TO IDIRECT TECHNOLOGIES AND SHALL NOT BE PUBLISHED, COPIED, OR ELECTRONICALLY TRANSMITTED WITH INTENDED DISTRIBUTION OUTSIDE OF IDIRECT TECHNOLOGIES. IT IS SOLELY INTENDED AS AN INTERNAL DOCUMENT ONLY.

PROPRIETARY & CONFIDENTIAL

Use Pursuant to iDirect, Inc. Instructions

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Overview The iDirect VSAT system can provide mesh connectivity among the remote terminals in a satellite network. In a mesh topology network, iDirect’s Netmodem II+ VSAT sends unacknowledged traffic directly from one remote terminal to other remote terminals without going through the hub. This feature is designed to deliver UDP packets for voice and video conferencing applications with half the latency that a double hopped satellite transmission would. Relative to iDirect’s normal star topology, mesh connectivity saves half the time and half the bandwidth needed to ship real time data from one remote terminal direct to another remote terminal. The System Architecture

The components of an iDirect network with mesh VSAT are depicted in Figure 1.

Figure 1: An iDirect Satellite Network with Mesh VSAT

5IF (or 1IF) Hub Chassisor Private Hub

Star-MeshTDMACarrierDownstream

TDMCarrier

UpstreamTDMACarrier

UpstreamTDMACarrier

Protocol Processor

LAN 1 LAN n

…StarVSAT

Network Management System

UpstreamTDMACarrier

MeshVSAT

NetModem II+ IDUTDMA Demodulator

Packet Assembler & Router

Receive-TransmitAntenna forStar Traffic

AntennaReceivingStar-Mesh

Traffic

5IF (or 1IF) Hub Chassisor Private Hub

Star-MeshTDMACarrierDownstream

TDMCarrier

UpstreamTDMACarrier

UpstreamTDMACarrier

Protocol Processor

LAN 1 LAN n

…StarVSAT

Network Management System

UpstreamTDMACarrier

MeshVSAT

NetModem II+ IDUTDMA Demodulator

Packet Assembler & Router

Receive-TransmitAntenna forStar Traffic

AntennaReceivingStar-Mesh

Traffic



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Central Hub Equipment

At the central hub, a mesh system from iDirect has two dishes instead of the one antenna normally associated with any hub from iDirect. A large dish carries all the star topology traffic as in any ordinary star topology iDirect VSAT network. A small dish receives the star-mesh carrier. The star-mesh carrier carries traffic among mesh VSAT as well as traffic from those mesh VSAT back to the central hub. The small dish is the exact same size as the dishes deployed at the mesh VSAT. This small dish at the central hub only receives signals, but it is highly recommended that this small dish be a receive-transmit dish exactly like the antennae deployed at the mesh remotes. The small antenna at the central hub feeds the contents of the star-mesh carrier into one of iDirect’s Hub Chassis. Any iDirect Hub will work, be it a Private Hub, a 1IF Hub, or a 5IF Hub. However, the 5IF Hub is highly recommended for iDirect networks with mesh VSAT. At a 5IF Hub, the feed received from the small dish should not share an IF section with any other upstream carriers. Such a configuration avoids the need to add complex and expensive L-band combiners. In fact, it is highly recommended that the network operator set aside one IF section in the 5IF Hub Chassis for… 1. One Universal Line Card to project a large downstream TDM carrier, and 2. One Universal Line Card to demodulate each star-mesh TDMA carrier. Mesh VSAT (Remote Terminal) Equipment

At the remotes, iDirect’s mesh VSAT has an indoor unit (IDU) that consists of at least three boxes as opposed to the one box normally found in a NetModem II+ VSAT. Those 3 IDU boxes are as follows: 1. NetModem II+ IDU 2. TDMA Demodulator 3. COTS PC The NetModem II+ IDU communicates with the hub just like any normal star topology iDirect VSAT. In addition, the NetModem II+ uses its “Rx Out” port to send the star-mesh carrier at L-band to the TDMA Demodulator. Through an opening originally designed for voice ports, the Netmodem II+ also sends the “start-of-frame” and 10 MHz reference to the TDMA Demodulator. This demodulator is nothing more than iDirect’s Private Hub IDU deployed at a remote site. It demodulates all the traffic on the star-mesh carrier and sends the TDMA frames to the COTS PC (commercial-off-the-shelf personal computer) for reassembly into IP packets. The COTS PC (or possibly a set top box) runs Linux as its operating system. On this Linux box runs the software from iDirect’s Protocol Processor that assembles TDMA frames into IP



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packets. The Linux router then forwards to the LAN only the IP packets that are addressed to that LAN. A typical mesh VSAT from iDirect is depicted in Figure 2.



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Figure 2: A Typical Mesh VSAT from iDirect

Operating Paradigm

These mesh VSAT send unacknowledged traffic (like UDP packets) directly to each other via a mesh reservation TDMA carrier. Conceptually, the operating paradigm is very simple. The Protocol Processor at the central hub assigns time slots on the star-mesh carrier for each mesh VSAT to burst into. Every mesh terminal listens to the entire star-mesh carrier using its TDMA Demodulator. Routers then filter the traffic at the network layer. This filtering process consists mostly of dropping packets that appear in places where they do not belong. In doing so, the system routes unacknowledged packets over one hop directly to the places where they are supposed to go. Figure 3 illustrates the net effect experienced by the end user.

TDMADemodulator LAN

NetModem II+

TDMA Tx TDM Rx

COTS PC with at least 4 Ethernet PortsRunning Linux OS plus a Private Hub’sPacket Assembly Software

EthernetConnection

Mesh Carrier at L-band

TDMA Rx

Start-of-frame and10 MHz reference

TDMADemodulator LAN

NetModem II+

TDMA Tx TDM Rx

COTS PC with at least 4 Ethernet PortsRunning Linux OS plus a Private Hub’sPacket Assembly Software

EthernetConnection

Mesh Carrier at L-band

TDMA Rx

Start-of-frame and10 MHz reference



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Figure 3: A Typical Mesh “Connection” Between Two iDirect VSAT

In reality, the mesh “connection” depicted in Figure 3 is a not a connection at all. The Protocol Processor and the NMS at the central hub know little about the mesh connections in this VSAT network. From their perspective, the star-mesh carrier is just another upstream carrier. The central hub prioritizes traffic as it always does, normally giving the highest priority to real time traffic. If desired, the network operator can configure the central hub to give the highest priority across the entire network to real time traffic flowing from one VSAT to another VSAT in that network. As far as the hub’s physical and link layers are concerned, all transmissions from the remotes flow only to the central hub. The TDMA demodulator connected to the small antenna at the central hub provides all the physical layer and link layer feedback required by the system. This demodulator receives and processes all acknowledged traffic from the mesh carrier as if nothing unusual is happening. That is, all acknowledged traffic from one remote to another must still be double hopped. The only unusual event at the central hub is that, at the network layer, the hub’s upstream router will be configured to drop all packets that meet two criteria: 1. The packets contain real time traffic like voice or video conferences, and

VSAT 1Bursting

at1 Mbps

1 Mbps Common TDMA Carrierwith MultipleTime Slots

VSAT nBursting

at1 Mbps

VSAT 1Bursting

at1 Mbps

1 Mbps Common TDMA Carrierwith MultipleTime Slots

VSAT nBursting

at1 Mbps



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2. They are addressed from a remote to one other specific remote in the network. In the downstream router immediately before the TDM modulator at the hub, multicast packets must also be dropped if they originate from a remote terminal in the network. The central hub drops those packets because they are unwanted duplicates. The real packets are received by the TDMA Demodulators at the remotes eavesdropping on the star-mesh carrier. The TDMA Demodulators at the mesh VSAT listen to the star-mesh carrier without providing any feedback to the terminals that are transmitting into the star-mesh carrier. To maintain the link, the line card attached to the small antenna at the hub provides all necessary feedback. The actual health of each mesh link is reported to the Protocol Processor and the NMS at the hub via the mesh terminal’s NetModem II+ IDU. However, any adjustments required to keep the mesh link healthy will be sent as commands to the receiving line card at the hub instead of to the TDMA Demodulator at the mesh VSAT. For instance, if a TDMA Demodulator requests more power during a rain storm, the receiving line card at the hub will be told to increase the rain margin in its link budget beyond what it needs for itself when it sits at a hub under clear skies. Each TDMA Demodulator at a mesh VSAT will demodulate and reassemble all the traffic that it can from the star-mesh carrier. Any packets that cannot be reassembled will be dropped. The packets recovered from the star-mesh carrier will then be passed to the Linux router at the remote. That router will inspect traffic from the TDM demodulator and the TDMA demodulator separately. The router will treat traffic from the TDM demodulator like it normally would, sending those packets wherever it is appropriate. However, the Linux router will give special treatment to packets that come from the TDMA demodulator. (The router can tell where the traffic comes from because the traffic arrives at physically different ports, possibly even on different NIC cards.) The Linux router will only pass traffic to the LAN from the TDMA demodulator when that traffic meets two criteria: 1. The packets contain real time traffic like voice or video conferences, and 2. The packets are addressed to a device or devices on that specific LAN. In effect, unacknowledged packets can take a short cut through the TDMA Demodulator at a mesh terminal to get from one VSAT to directly to another without first going through the central hub. The central hub does not mind because, as far as it is concerned, it has done its job - receiving packets from the star-mesh carrier and passing those packets up to the network layer. Expansion Beyond One Star-Mesh Carrier

If one star-mesh carrier is not enough to accommodate all the traffic from all the mesh VSAT in an iDirect network, then more carriers can be added. Such expansion means adding Universal Line Cards to 1IF or 5IF Hub Chassis to serve



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as TDMA demodulators. To the Protocol Processor and NMS at the central hub, the additional star-mesh carriers look like any other upstream carriers in a star topology iDirect VSAT network. The only special feature in these carriers is that, when a 5IF Hub is being used, the star-mesh demodulators are grouped together in one IF section of the 5IF Hub Chassis. It is highly recommended that all star-mesh carriers be assigned to a unique frequency hopping group – one that excludes any normal star topology upstream carriers. Frequency hopping is highly recommended. It increases bandwidth efficiency and decreases blocked calls, especially when end users run real time broadband applications like video conferencing over the network. The only problem with adding more star-mesh carriers to the network is that there must be one TDMA Demodulator at every mesh VSAT for each star-mesh carrier. At the remotes, TDMA Demodulators can be daisy chained together using the “Rx Out” port. Additional TDMA Demodulators can be added just like the first TDMA Demodulator was daisy chained to the NetModem II+ IDU at the remote. There are practical limitations to the number of TDMA Demodulators that can be added. First, the COTS PC that runs packet reassembly software and Linux router may run out of processing power and/or memory. A more expensive COTS PC is needed to process greater throughput. Money can be saved at the remotes by minimizing the throughput. Second, noise is added to the L-band signal from the antenna each time that it is passed through an IDU box. After some unknown number of iterations, the signal to noise ratio will degrade to the point where the information content cannot be recovered. To mitigate this problem, iDirect’s MUSiC Box can be used as an external IF splitter-combiner when there are many star-mesh carriers. The MUSiC Box introduces relatively little noise. Third, care must be taken to maintain the integrity of the “start-of-frame” and 10 MHz reference as that information is distributed to many TDMA Demodulators. The information can be preserved by digitally regenerating it as it is passed in a daisy chain from one IDU to the next. In the end, the maximum number of star-mesh carriers in an iDirect network is difficult to predict. That limit will depend on a large number of variables, including but not limited to… 1. The size and speed of the carriers. 2. The way the network is configured and operated. 3. The satellite on which the network is operating. 4. The performance of iDirect’s TDMA demodulators. 5. The size of the antennae at the mesh VSAT. 6. The weather. Only trial and error will reveal how many star-mesh carriers an iDirect network can support under a given set of circumstances.



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The Benefits of this Architecture

Using TDMA to implement mesh DAMA creates a large number of mesh “connections” directly among remote terminals for real time traffic. The only limit to the number of simultaneous “connections” at each site is the capacity of the star-mesh carriers. For example, each full duplex VoIP call requires 48 kbps without header compression. So each 384 kbps carrier can support up to 8 simultaneous full mesh calls. (The actual information rate of the star-mesh carrier needs to be about 25% higher than 384 kbps to account for TDMA overhead.) When necessary, one site can support all the simultaneous mesh “connections” available in the entire network. Such connectivity is ideal for making many simultaneous voice calls to or from any remote terminal. E.g., this technology can be used to trunk toll quality full mesh phone calls among isolated GSM base stations or among remote oil rigs. Incidentally, a mesh capability means that iDirect networks can now be configured in a multi-star topology. Phone calls do not necessarily have to access the PSTN through any one particular gateway. Instead, they can be landed where it is least expensive or where they are easiest to switch. Better yet, these mesh terminals from iDirect are affordable. The ODU for all mesh TDMA DAMA VSAT are about the same. The salient price differences come at the IDU. Even with two extra boxes of hardware at every remote, iDirect’s indoor units still cost half as much as IDU from competing full mesh TDMA DAMA VSAT. ViaSat’s Linkway and ND Satcom’s SkyWAN sell at prices between $10,000 and $30,000. iDirect’s mesh TDMA DAMA VSAT are offered at half that price. iDirect’s mesh TDMA DAMA VSAT are priced like full mesh SCPC DAMA VSAT with only one modem. Compared to these terminals, iDirect’s mesh VSAT are a bargain. iDirect only adds one TDMA Demodulator at every remote site for each allocated star-mesh carrier. Any SCPC DAMA VSAT adds one modem at each remote for each simultaneous connection at that site. So mesh VSAT from iDirect have a hardware advantage over SCPC DAMA VSAT. This advantage grows with the number of simultaneous mesh connections required at each site. For iDirect’s installed base, this approach constitutes an elegant upgrade that preserves and enhances the value of prior investments in iDirect equipment. All existing hub equipment stays in place. Except for some software upgrades, equipment installed at the hub is left intact. New indoor unit boxes need to be added to each remote site where mesh connectivity is desired. Fortunately, the new IDU boxes are easy to plug in and configure. Better yet, existing VSAT ODU need not be touched during an upgrade. And, all star topology remotes can be left alone if they do not need the mesh upgrade. Most important of all, this approach to mesh connectivity is available in only four months. This approach requires only a modest amount of non-recurring engineering.



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It can be implemented quickly with minor modifications to existing hardware. Most of the work lies in reconfiguring existing software. Since this technology costs a relatively small amount of money to develop, the license for it can be sold at a relatively low price. Mesh NMS alone typically sell for $50,000 to $100,000. So it is reasonable to ask for a fee of $25,000 to add mesh connectivity to central hub equipment from iDirect. Limitations

There will be certain limitations to mesh connectivity on satellite networks from iDirect. The top ten limitations are itemized below. 1. Only unacknowledged traffic like UDP packets for voice and video conferencing

can be sent over the mesh links. Since the TDMA Demodulators at the mesh VSAT are only eavesdropping on the star-mesh carrier, the TDMA Demodulators cannot provide real-time feedback to the transmitters to create reliable links.

2. There can be no cRTP header compression for voice or video conferencing in this implementation of mesh connectivity. At this point in time, header compression in the iDirect system can only be implemented between the hub and a remote terminal.

3. The three boxes that make up the IDU of a mesh VSAT from iDirect are bulky and cumbersome. Competing mesh TDMA products from ViaSat, ND Satcom, and Gilat all have only one box for their VSAT IDU. Three boxes may take up more space, consume more electricity, and cost more to build than one box.

4. The central hub provides the only feedback to maintain the integrity of all mesh links. The small antenna at the central hub acts as a proxy for every receiving dish in the mesh network. However, local conditions (like rain) at any point in time are likely to differ between the central hub and each remote.

5. To compensate for transient differences between weather conditions at the hub and the most disadvantaged remote, this architecture consumes more satellite power than it theoretically needs to. This implementation assumes that it is always raining at the remotes. Extra power is always left in the link budget as a buffer against the rain at the most disadvantaged remote exceeding the rain at the hub. This extra power consumption is somewhat mitigated by iDirect’s use of Turbo Codes. iDirect’s Turbo Codes add 1.5 dB of power to the link budget relative to conventional Reed-Solomon Viterbi coding. This architecture becomes less bandwidth efficient than competing mesh VSAT only when more than 1.5 dB of satellite power is left as extra margin to combat temporary rain fade differences between the hub and the most disadvantaged remote.



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6. To support each incremental star-mesh carrier, an additional TDMA Demodulator must be added to each and every mesh VSAT in the network. To support a small number of star-mesh carriers in a small network, the incremental hardware cost is manageable. As the number of star-mesh carriers increases, the incremental hardware costs grow rapidly because all existing mesh sites have to be retrofitted with an additional TDMA Demodulator for each new star-mesh carrier.

7. There is no frequency hopping between star-mesh carriers and normal upstream carriers that bear only star topology traffic. Only one frequency hopping group is possible for each set of remotes that need mesh connectivity among each other.

8. A second antenna is required at the central hub. This second antenna increases the amount of time and money required to install a central hub from iDirect.

9. Only the 5IF Hub is recommended for mesh networks from iDirect. In theory, a 1IF Hub can support mesh topology VSAT. But a 1IF Hub needs external L-band combiners that add to the cost and complexity of the central hub. A good alternative for price sensitive customers is to use an inexpensive Private Hub as the central hub in a mesh network from iDirect. A mesh network built around a Private Hub would be limited to only one star-mesh carrier. But one star-mesh carrier is sometimes all that is needed, especially in a small network where the customer can afford expensive ODU to implement one large star-mesh carrier.

10. Configuring a mesh network from iDirect may be labor intensive. The NMS will be modified to monitor and control the mesh links. The network operator will be able to configure all the mesh remotes from the central hub. However, mesh routes are implemented as “short cuts” around the central hub. So the advertisement of new mesh routes may be more manual than automatic.

The Price of Mesh Connectivity

Mesh connectivity requires upgrades above and beyond the equipment that constitute a normal star topology VSAT network from iDirect. The upgrades include: 1. Mesh Software at Each Hub 2. TDMA Demodulator(s) for Mesh VSAT 3. COTS PC for Mesh VSAT The license for Mesh Software at each hub is priced at $25,000. It includes software upgrades to both the Protocol Processor and the NMS. The $25,000 fee actually pays for two copies of the software: one for the primary hub equipment and one for the spare hub equipment.

A standard mesh indoor unit from iDirect consists of three boxes:



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1. NetModem 4200 IDU 2. TDMA Demodulator 3. COTS PC This set of three boxes constitutes one Mesh NetModem indoor unit. The price of the Mesh NetModem is given in Table 1: Prices for Mesh NetModem IDU.



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Table 1: Prices for Mesh NetModem IDU

One TDMA Demodulator is needed at each mesh VSAT for each star-mesh carrier in that VSAT’s frequency hopping group. In most networks, only one TDMA Demodulator is needed at each remote because the amount of mesh traffic is small. That price of that first TDMA Demodulator is included in the price of the Mesh NetModem IDU. However, there may be occasions where more than one TDMA Demodulator is needed at each mesh VSAT. For those occasions, additional TDMA Demodulators can be purchased a la carte. The a la carte price of TDMA Demodulators is given in Table 2: Prices for TDMA Demodulator.

Table 2: Prices for TDMA Demodulator

Only one COTS PC is ever needed at each mesh VSAT regardless of how many TDMA Demodulators are daisy chained together at that mesh terminal. Each COTS PC comes complete with all the appropriate software to reassemble and route IP packets. The price of the COTS PC for each mesh VSAT is included in the price of the Mesh NetModem IDU.

Special Promotion: How a Customer Can Get a Mesh Software for Free

iDirect needs four months and $150,000 of NRE funding to develop mesh equipment for its VSAT networks. That is, iDirect needs to sell at least six Mesh Software licenses at $25,000 apiece to make sure that the value of mesh connectivity is greater than the cost of mesh connectivity in iDirect’s customer base. To encourage early adopters, iDirect offers to refund the $25,000 cost of the Mesh Software at the hub to the customers who buy the first 6 Mesh Software licenses.

Discount Plan Model(s): Mesh NetModemVolume Level Discount Price

List Price 0% $ 9,375.00 10-99 25% $ 7,035.00

100-249 35% $ 6,090.00 250-499 40% $ 5,625.00 500-999 45% $ 5,250.00 1000+ 48% $ 4,800.00

Discount Plan applies to NetModem Router Only

Discount Plan Model(s): TDMA DemodulatorVolume Level Discount Price

List Price 0% $ 6,250.00 10-99 25% $ 4,690.00

100-249 35% $ 4,060.00 250-499 40% $ 3,750.00 500-999 45% $ 3,500.00 1000+ 48% $ 3,200.00

Discount Plan applies to TDMA Demodulator Only



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The refunds will be made when iDirect sells its 7th through 12th Mesh Software licenses. The proceeds from the sale of the 7th license goes to the customer who buys the first license, the proceeds from the sale of the 8th license goes to the customer who buys the second license, and so on and so forth. No refunds will be offered to customers who buy the 7th license and beyond. If iDirect sells less than 12 Mesh Software licenses, then some of the first six customers will not get a refund. Customers who buy their Mesh Software licenses sooner rather than later increase their probability of getting refunds while decreasing the amount of time between the purchase and the refund.

iDirect will deliver the Mesh Software and the mesh VSAT four months after the 6th license is ordered. A customer can buy more than one Mesh Software license if he wants iDirect to get started on mesh connectivity sooner rather than later. Mesh Software licenses are 100% transferable. So a customer who wants iDirect to get started on mesh connectivity immediately can conceivably order six Mesh Software licenses and hold them in inventory for resale at a later date to other operators who own iDirect networks. A customer need not necessarily own an iDirect hub to place an order for a Mesh Software license. However, a Mesh Software license cannot be delivered until the customer specifies the exact hub on which the software should be installed. Each customer pays for his Mesh Software only after it has been delivered and accepted in accordance with iDirect’s normal acceptance procedures.

mesh connectivity 20040120 connectivity...these mesh vsat send unacknowledged traffic (like udp...

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