A VSAT satellite service provider came to Isotropic Networks recently with a big issue “We are running out of TDMA time slots, but not bandwidth.” They added additional inbound carriers, which did not solve the problem. As you probably know, satellite bandwidth is the most expensive part of providing satellite service. Optimization of your space segment, particularly your iDirect upstream carriers, is extremely important and takes skills many satellite operators might not have on staff. Read on to find what we did, specifically, to fix the problem of running out of TDMA time slots, but not bandwidth.

Summary of Improvement

  • 110% – Increase in the number of TDMA Time Slots Available
  • 14% – Increase in available bandwidth for use by end users on the network.
  • 3sec – Decrease in latency during peak hour

iDirect Upstream MODCODS

Possible MODCODS on iDirect Upstream Carrier

Even with over 200 VSATs on their network, this iDirect virtual network operator (iDirect VNO) shouldn’t run out of TDMA time slots before running out of bandwidth. We couldn’t resist the opportunity to exercise our bandwidth optimization skills to engineer an optimized iDirect upstream carrier plan for this satellite service provider. Proper design and optimization of the iDirect upstream carriers produces a reliable, high-performance satellite network, enhancing the client experience.

Our investigation found that some of the assumptions made when the satellite service provider created the initial link budgets didn’t fully utilize the features of the iDirect platform to optimize the satellite network. As you can see from the chart to the left, possible iDirect MODCODS, there are a many options to chose from when designing your upstream carriers. We analyzed the satellite service provider’s goals for the network, current configuration, end user usage patterns, applications, and satellite link budgets. With this information we created a new upstream carrier configuration that prioritized “lowest cost per bit”, reliability and network performance.

Results from Satellite Network Analysis

Two network inefficiencies where found that dramatically impacted the overall performance of this satellite network:

  • FEC (Forward Error Correction) Selection
  • Block Size Specified

We are now ready to reconfigure the in-routes toward an optimized network.

Forward Error Correction Optimization (FEC)

Network efficiency is dramatically affected by the selection of the FEC rate on the iDirect upstream carriers. iDirect’s Adaptive-TDMA (A-TDMA) was employed to solve the issue of VSATs on the edge of the footprint from dragging down the performance of the entire network, while also providing additional network reliability.

Switching on A-TDMA allowed the creation of a small inbound carrier with lower FEC rate to handle small antennas near the beam edge and a inbound carrier with an more efficient FEC rate for the majority (over 95% of the sites) of the network. This increased the throughput of the main carriers by 30%. That is, the majority of the network had an increase in bandwidth of 30% for free!

iDirect Block Size Optimization

Next the TDMA block size was designed to fit the actual applications used by the end user. This network had been defined with the largest block size possible on the iDirect upstream carriers. This is fine if you have only a few sites transmitting very large files like geographical data or movies. However, most applications use small packets, which means, small blocks should be used. Voice over IP relies on small blocks to avoid choppy conversations (caused by jitter).

The bandwidth provider used large block sizes to maximize theoretical speeds and reduce the required uplink power. In this network the blocks were partially filled, because of the small packet sizes, which wasted bandwidth. The low number of TDMA time slots didn’t provide enough slots for the number of remotes on the network. Network latency was spiking at 2 seconds due to the remotes inability to find a free time slot creating a huge latency and packet loss.

The iDirect inbound carrier block size was optimized to match the actual user type, applications and traffic patterns on the network. The result is an increase in the total available TDMA time slots by 65% and a dramatic increase in the usable bandwidth due to the slot size matching the traffic pattern.

Summary of Bandwidth Optimization Benefits

The newly configured network optimized on the customers traffic profile, location, and applications resulted in a 110% increase in the number of TDMA time slots and an upstream throughput increase of 14%. Latency was dramatically reduce and there is no packet loss. Changing the FEC rate on a per upstream carrier basis to match the performance of the remote VSATs, refining the block size and minimum bandwidth requirements, and utilizing A-TDMA created a network that performs well, is reliable, and produces the best bit/Hz performance. The end customers’ experience on the network improved dramatically.

And, Isotropic has a new client under our “Guidance, Care and Protection”.

Secrets of a VSAT Satellite Service Provider

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