Is your satellite link oscillating? Improving goodput using network coding
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Re: Is your satellite link oscillating? Improving goodput using network coding
#2Clever solution to a unique problem!
> So how does this help with queue oscillation? Simple: We generate a few extra "spare" combination packets, so that we now have more equations than variables. This means we can afford to lose a few combination packets in overflowing queues or elsewhere – and still get all of our original packets back.
If I understand correctly, this would also work with a more traditional coding scheme (block coding or convolutional coding). I'm curious if there are plans to take advantage of the properties of network codes in the future.
Re: Is your satellite link oscillating? Improving goodput using network coding
#3This is great, spent a lot of time reading about this kind of stuff (from books like this: http://www.amazon.com/Satellite-Technology-Principles-Applic... ) before I went to work on a ship with the task of maintaining the satellite connection. Turned out I didn't have much control over our traffic on the satellite side, but it was interesting nonetheless to think of what was happening to our traffic once it reached there.
Re: Is your satellite link oscillating? Improving goodput using network coding
#4Clever solution to a unique problem! > So how does this help with queue oscillation? Simple: We generate a few extra "spare" combination packets, so that we now have more equations than variables. This means we can afford to lose a few combination packets in overflowing queues or elsewhere – and still get all of our original packets back. If I understand correctly, this would also work with a more traditional coding…
"Network code" as described here isn't the academic definition, I think he's just describing colloquially "i'm using a code in my network". The technical definition is a Packet Erasure Channel [1], which any erasure code [2] can deal with. Network coding is a more unexplored technique where routers in the network combine packets in various ways that are better than regular routing: see the example at [3].
[1] http://en.wikipedia.org/wiki/Packet_erasure_channel
[2] http://en.wikipedia.org/wiki/Erasure_code
[3] http://en.wikipedia.org/wiki/Linear_network_coding#The_butte...
Re: Is your satellite link oscillating? Improving goodput using network coding
#5Clever solution to a unique problem! > So how does this help with queue oscillation? Simple: We generate a few extra "spare" combination packets, so that we now have more equations than variables. This means we can afford to lose a few combination packets in overflowing queues or elsewhere – and still get all of our original packets back. If I understand correctly, this would also work with a more traditional coding…
"Network code" as described here isn't the academic definition, I think he's just describing colloquially "i'm using a code in my network". The technical definition is a Packet Erasure Channel [1], which any erasure code [2] can deal with. Network coding is a more unexplored technique where routers in the network combine packets in various ways that are better than regular routing: see the example at [3]. [1] http://…
The vendor mentioned in the article, Steinwurf ApS, says on their website that "Our products are based on Random Linear Network Coding[...]" [1]. In this case, it looks like they're using it as an erasure code, though.
Re: Is your satellite link oscillating? Improving goodput using network coding
#6One thing I wish they had talked about, was about applying Random Early Detection (RED) to this problem. It seems to be, that RED, while an older technique, was created for exactly this purpose, and is supported in every IP router I've ever worked with. Perhaps there are challenges applying RED here, but I would suspect that if introduced it would also have considerable improvements to the internet performance for those islands.
Now, the solution presented, could be superior to RED, but based on what they've shown, I'm not entirely convinced. It is an intriguing solution though.
Also, an important takeaway they presented, that translates to other software tasks, is that increasing the buffer often makes the situation worse. One thing you can look into, is the research currently underway into buffer bloat, and the suspected impacts it is believed to be having on consumer internet service. My understanding is it appears to be caused by this exact phenomenon, where engineers from equipment manufactures and telecom operators reacted to the problem by drastically increasing buffer sizes.
*Please be aware, I work for a large telecom operator in Canada, but the views are my own and do not reflect any position of my employer.
Re: Is your satellite link oscillating? Improving goodput using network coding
#7One thing I wish they had talked about, was about applying Random Early Detection (RED) to this problem. It seems to be, that RED, while an older technique, was created for exactly this purpose, and is supported in every IP router I've ever worked with. Perhaps there are challenges applying RED here, but I would suspect that if introduced it would also have considerable improvements to the internet performance for th…
There are challenges to deploying RED anywhere. That's why we now have a new generation of queue management strategies stemming from CoDel. Still, even with the best queue management there's obviously a benefit to using extra forward error correction like this to further reduce packet drops if the latency is high enough, but I'm not sure it is in this case.
Re: Is your satellite link oscillating? Improving goodput using network coding
#8Reminds me of Forward Error Correction [1], a technique used by Satellite providers and even WAN optimization vendors like Silver Peak to "erase" packet loss events by injecting parity packets into the flow, which can be used to rebuild lost packets at the receiving end if needed. This prevents TCP synchronization, aka the throughput see-saw described in the article. This problem isn't limited to high latency / satellite links but exists on any path with packet loss, like your internet connection, or even MPLS.
Re: Is your satellite link oscillating? Improving goodput using network coding
#9From my experience (~10 years ago) sat links suffer high latency and VERY low packet throughout. At the time I played with one in Europe it was delivered with special sauce Windows proxy software that had one purpose - cut packets/s and keep retransmissions local.
I got the feeling installing traffic shaping routers with explicit packets/second limit would also do wonders for links mentioned in the article.
Re: Is your satellite link oscillating? Improving goodput using network coding
#10yes, it's really neat. then the more you dig into it the more you realize literally everything and the kitchen sink is patented to all hell and back.
best of luck using any of it without a large team of expensive lawyers.