FCC has “serious doubts” that SpaceX can deliver latencies under 100ms(arstechnica.com)
arstechnica.com
FCC has “serious doubts” that SpaceX can deliver latencies under 100ms
https://arstechnica.com/tech-policy/2020/06/fcc-has-serious-doubts-that-spacex-can-deliver-latencies-under-100ms/
91 comments
I would posit a theory that the source of the FCC's skepticism is a verizon board meeting.
These analyses are quite optimistic as they only consider propagation delay.
Moreover, the idea of using user-terminals/gateways as ground-relays to bounce signals up-and-down is quite impractical, since you would be greatly reducing the capacity available to satellites on those "intermediate" satellite.
Moreover, the idea of using user-terminals/gateways as ground-relays to bounce signals up-and-down is quite impractical, since you would be greatly reducing the capacity available to satellites on those "intermediate" satellite.
Using user terminals was as much of a thought experiment as anything. The graphs in the video show you can do pretty well just using a few well placed groundstations - you can shave another millisecond or three off with higher densities, but it's not a lot. The big advantage of higher densities is really that you can get better spatial reuse - with more possible choices you can use RF uplinks in places where the spectrum would otherwise go unused, whereas you've less freedom to choose if you've fewer groundstations.
Having said that, this kind of wide-area low-latency bounced routing is never going to be used for you or me to watch Netflix. It will be reserved for high paying customers who really really care about latency. For you and me, we'll be dumped into the terestrial network at the nearest possible location that isn't already saturated.
The second generation of satellites should have optical inter-satellite links, and then you would only use ground relays rarely.
Having said that, this kind of wide-area low-latency bounced routing is never going to be used for you or me to watch Netflix. It will be reserved for high paying customers who really really care about latency. For you and me, we'll be dumped into the terestrial network at the nearest possible location that isn't already saturated.
The second generation of satellites should have optical inter-satellite links, and then you would only use ground relays rarely.
Hi Mark,
Thanks for your reply. I agree with you, using user-terminals is extremely challenging, especially from a link-budget perspective. You cannot pump enough data to make it worth it. For the gateways, my main concern is that the Ka-band spectrum would have to be shared between user-data and "inter-satellite" data.
Finally, I think that the use-case your described for those latency-sensitive customers is going to be hard to pull off, mainly because of link-availability concerns. There are too many "passes" through the atmosphere to guarantee the availability numbers that a user of such a service requires (99.5%?). Rain in any of these links might cause an outage or a re-route (causing too high jitter). Plus, it would be extremely difficult to have signals traveling from one continent to another.
Thanks for your reply. I agree with you, using user-terminals is extremely challenging, especially from a link-budget perspective. You cannot pump enough data to make it worth it. For the gateways, my main concern is that the Ka-band spectrum would have to be shared between user-data and "inter-satellite" data.
Finally, I think that the use-case your described for those latency-sensitive customers is going to be hard to pull off, mainly because of link-availability concerns. There are too many "passes" through the atmosphere to guarantee the availability numbers that a user of such a service requires (99.5%?). Rain in any of these links might cause an outage or a re-route (causing too high jitter). Plus, it would be extremely difficult to have signals traveling from one continent to another.
On routing: the best path in this sort of network changes something like every ten seconds or so. To make it work, you need to consider all the links that can delivery good enough SNR, so you're already factoring in rain for example. You've got many many possible paths, and you're considering the best route constantly, but you're only factoring links with acceptable quality into the computation. If you do this (and can solve the queue avoidance issues too), turns out jitter isn't such a big problem. As one path gets longer, it eventually gets longer than the next path, and you switch to the new path as close to that moment as you can. If you do this, you minimize step changes in latency. It only works if you've got enough satellites, but it looks like SpaceX will have.
If you can't eliminate all queuing delays, you can't factor all delays into your decision of when to change routes, and so you will get some jitter and hence reordering. If so, you need a reorder queue in the final receiving groundstation, so as to avoid confusing TCP. This removes jitter at the expense of adding some latency. How much latency depends on the queuing delays you're trying to smooth out, so it all really comes down to avoiding queues in the satellites.
If you can't eliminate all queuing delays, you can't factor all delays into your decision of when to change routes, and so you will get some jitter and hence reordering. If so, you need a reorder queue in the final receiving groundstation, so as to avoid confusing TCP. This removes jitter at the expense of adding some latency. How much latency depends on the queuing delays you're trying to smooth out, so it all really comes down to avoiding queues in the satellites.
Completely agree. While the video is awesome (nice job!), the logistics of pulling something like this off is extremely difficult. It's different from the "you could have said that about landing a rocket", in that there are thousands of different routes taken for different customers per second, and each route has its own issues like portillo said. The minute one stops working, debugging that will be a huge challenge.
The user terminal as a gateway idea is also not practical due to link budget (EIRP and G/T), but also the much lower availability they'll be dealing with.
The user terminal as a gateway idea is also not practical due to link budget (EIRP and G/T), but also the much lower availability they'll be dealing with.
Computationally, it's difficult, but I don't think it's intractable. Bear in mind this this is not an animation, but a real-time simulation:
https://youtu.be/m05abdGSOxY?t=428
I'm running Dijkstra across this mesh at 30fps in real-time on my laptop while also doing the 3d animation. My laptop fan does spin a bit, but it's not crazily optimized code, and for the video I was also recording to H.264 simultaneously. Doing routing for all customers simultaneously is certainly feasible if their groundstations do the computation, based on routing state supplied in real-time by the constellation. Other solutions are probably possible too, but this seems simplest to me, and scales linearly with customers.
https://youtu.be/m05abdGSOxY?t=428
I'm running Dijkstra across this mesh at 30fps in real-time on my laptop while also doing the 3d animation. My laptop fan does spin a bit, but it's not crazily optimized code, and for the video I was also recording to H.264 simultaneously. Doing routing for all customers simultaneously is certainly feasible if their groundstations do the computation, based on routing state supplied in real-time by the constellation. Other solutions are probably possible too, but this seems simplest to me, and scales linearly with customers.
While that's true for a first approximation, weather, gateway outages (very common as you increase the number of them), total satellite capacity (making sure you aren't overloading a single link), and just non-working paths are commonplace. Just making sure that you aren't overloading a particular satellite is an extremely difficult problem. That would be really neat if you could work that into your simulation, where it would bypass certain satellites if there's just no more bandwidth available.
I just want to say thanks for those fantastic videos. I think visualizations like this are an incredible tool in lay people understanding research, or simply explaining yourself better.
[deleted]
If my math is right geostationary satellites have a round-trip time (just at speed of light in a vacuum) of ~240 mS whie LEO satellites have a round-trip time of ~13 mS.
Current observed latency on geostationary satellite uplinks is 550 mS, presuming delays scale linearly with the travel time in vacuum that puts us at ~30 mS round-trip for LEO satellites.
Sub-100 mS seems physically possible to me but from an engineering and volume perspective there may be a real challenge.
Anyone with more knowledge care to chime in?
Current observed latency on geostationary satellite uplinks is 550 mS, presuming delays scale linearly with the travel time in vacuum that puts us at ~30 mS round-trip for LEO satellites.
Sub-100 mS seems physically possible to me but from an engineering and volume perspective there may be a real challenge.
Anyone with more knowledge care to chime in?
>> Anyone with more knowledge care to chime in?
It isn't just a matter of altitude. The geostationary satellite is a simple bent pipe hanging in space. It returns signals to a fixed ground station that it remains in contact with 24/7. The low-orbit satellite isn't hanging off in space. It is moving, constantly connecting and disconnecting with multiple ground stations every couple minutes. The route between customer and internet is therefore unstable, akin to a cellphone on a speeding car having to negotiation with multiple cell towers. But in this case the cell towers are also each moving on different highways too.
Sometimes there is no up-and-down connection. Sometimes the satellite over the customer cannot 'see' a downlink station. Then it has to bounce your connection along a chain of multiple satellites. Theoretically this should all work, but you don't need to be a physicist to understand the complexity of chaining together so many wireless connections. Ping times will suffer.
AND... there are a bunch of issues regarding the relative speeds of these satellites. They move fast enough that Doppler shifts between them become significant. Satellites have to modulate signals depending on where they are going. That means processing times, buffering ... latency.
It isn't just a matter of altitude. The geostationary satellite is a simple bent pipe hanging in space. It returns signals to a fixed ground station that it remains in contact with 24/7. The low-orbit satellite isn't hanging off in space. It is moving, constantly connecting and disconnecting with multiple ground stations every couple minutes. The route between customer and internet is therefore unstable, akin to a cellphone on a speeding car having to negotiation with multiple cell towers. But in this case the cell towers are also each moving on different highways too.
Sometimes there is no up-and-down connection. Sometimes the satellite over the customer cannot 'see' a downlink station. Then it has to bounce your connection along a chain of multiple satellites. Theoretically this should all work, but you don't need to be a physicist to understand the complexity of chaining together so many wireless connections. Ping times will suffer.
AND... there are a bunch of issues regarding the relative speeds of these satellites. They move fast enough that Doppler shifts between them become significant. Satellites have to modulate signals depending on where they are going. That means processing times, buffering ... latency.
It's not quite as bad as the cell phone case, since the exact visibility of users to satellites and ground stations to satellites is completely predictable, since the ground stations don't move, and the satellites move in fairly stable orbits.
In the cell phone case, you really have no idea when someone is about to go behind a building or something and have to switch cells.
All of the relative dopplers are also known ahead of time, so the transmitter should be able to change frequencies on a preplanned schedule without needing much time for resynchronization.
In the cell phone case, you really have no idea when someone is about to go behind a building or something and have to switch cells.
All of the relative dopplers are also known ahead of time, so the transmitter should be able to change frequencies on a preplanned schedule without needing much time for resynchronization.
Just nitpicking, but uppercase S is symbol for Siemens, the unit of electrical conductance: https://en.wikipedia.org/wiki/Siemens_(unit)
The symbol for second is lowercase s. The SI is funny like that.
Other than that, I fully agree with your post.
The symbol for second is lowercase s. The SI is funny like that.
Other than that, I fully agree with your post.
Man, product placement has really gone overboard this time.
Not really just nitpicking. I actually was thinking Siemens when I first saw the post. After reading it I did quickly realize it was milliseconds.
From the FCC quote in the article: "Propagation delay in a satellite network does not alone account for latency in other parts of the network such as processing, routing, and transporting traffic to its destination."
In other words, client and server are not both sitting right under the same satellite. The trip to and from LEO is just part of the full route; you also have server to ground station and (in future) uplink satellite to downlink satellite (AFAIK Starlink currently doesn't do that).
In other words, client and server are not both sitting right under the same satellite. The trip to and from LEO is just part of the full route; you also have server to ground station and (in future) uplink satellite to downlink satellite (AFAIK Starlink currently doesn't do that).
I mean- sure? But that's also true of terrestrial internet. It's 22 hops between my laptop and www.google.com, and it pings at 5-10ms. Certainly Starlink isn't do any fancy routing that my internet isn't already doing?
Switches and fiber are well known proven technology. Satellite laser interlinks are R&D dreams at the moment.
There are satellite laser interlinks in orbit right now.
I thought the current starlink generation wasn’t using laser links yet
I believe both your comment and the parent comment are true. Laser comm has been done at fairly high speeds (both sat to sat and sat to ground station), but it's relatively cutting edge and Starlink isn't currently doing it
Sure, operated manually by a bunch of people with PhDs.
Is there any public documentation on how much of the round-trip time the processing and routing takes up? It has had the shit optimized out of it every else, so I can't imagine it would get significantly worse for a satellite, especially one of SpaceX's which attempt to use commodity hardware as much as possible.
Satellites have to operate in a very different thermal and radiation environment than most networking hardware.
Cooling is very difficult when you're surrounded by a vacuum. Also, without the planet acting as a heat sink, the difference between daytime and nighttime temperatures is staggering.
I don't actually know to what extent radiation hardening is a concern for these satellites. They're well below the Van Allen Belt, so the background radiation is nothing like deep space. Still, it's something you need to consider for systems that are expected to have years of continuous uptime.
(The Russians use commodity PC hardware on the ISS for systems not involved in navigation or life support. But that's a situation where there are people around to hit the power button.)
Not to mention that replacing hardware is expensive, and repair is basically impossible, so there are incentives to prioritize reliability over performance.
Cooling is very difficult when you're surrounded by a vacuum. Also, without the planet acting as a heat sink, the difference between daytime and nighttime temperatures is staggering.
I don't actually know to what extent radiation hardening is a concern for these satellites. They're well below the Van Allen Belt, so the background radiation is nothing like deep space. Still, it's something you need to consider for systems that are expected to have years of continuous uptime.
(The Russians use commodity PC hardware on the ISS for systems not involved in navigation or life support. But that's a situation where there are people around to hit the power button.)
Not to mention that replacing hardware is expensive, and repair is basically impossible, so there are incentives to prioritize reliability over performance.
> Not to mention that replacing hardware is expensive, and repair is basically impossible, so there are incentives to prioritize reliability over performance.
SpaceX is actually changing this equation quite a bit in case of Starlink - mass-produced satellites + much cheaper and more frequent launches = replacing hardware gets much cheaper, which means they can prioritize performance over reliability more than it's customary in the industry.
SpaceX is actually changing this equation quite a bit in case of Starlink - mass-produced satellites + much cheaper and more frequent launches = replacing hardware gets much cheaper, which means they can prioritize performance over reliability more than it's customary in the industry.
> Not to mention that replacing hardware is expensive, and repair is basically impossible, so there are incentives to prioritize reliability over performance.
I'm well aware. But SpaceX is heading in the direction of quantity over quality, and banking on the sheer volume of satellites being launched cheaply outweighing any one failure.
I'm well aware. But SpaceX is heading in the direction of quantity over quality, and banking on the sheer volume of satellites being launched cheaply outweighing any one failure.
I don't see why the delays would scale linearly with travel time. I would naively expect them to be a constant. So geosynchronous satellites have 240 ms of travel time and 310 ms of delay, in which case we might expect LEO satellites to have 13 ms of travel time and 310 ms of delay.
Maybe it's not that bad. Maybe you have to use more robust coding with geosynchronous satellites, and that drives up latency. But i can't see a reason why it would scale linearly with distance.
Maybe it's not that bad. Maybe you have to use more robust coding with geosynchronous satellites, and that drives up latency. But i can't see a reason why it would scale linearly with distance.
It's not a linear change with distance, it's based on different technologies. Just as your wifi router doesn't add 100ms satellites don't inherently need to have that kind of latency.
However, one change that is based on distance is ground stations. With starlink they want a ground station under every satellite to minimize the number of hops required. Satellite internet however has minimal ground stations because they gain little from adding more. Similarly, less physical distance let's them more efficiently manage bandwidth reducing queuing delays.
PS: Also, it's a round trip so you subtract latency twice from the total delay. Further, it’s not just altitude GEO is above the equator at a specific point which can be significantly east or west of you. Giving Ohio worse latency than Florida etc.
However, one change that is based on distance is ground stations. With starlink they want a ground station under every satellite to minimize the number of hops required. Satellite internet however has minimal ground stations because they gain little from adding more. Similarly, less physical distance let's them more efficiently manage bandwidth reducing queuing delays.
PS: Also, it's a round trip so you subtract latency twice from the total delay. Further, it’s not just altitude GEO is above the equator at a specific point which can be significantly east or west of you. Giving Ohio worse latency than Florida etc.
Round trip latency includes two trips to the sattelite and back. So geostationary sattelites have ~480 ms of travel time and ~70ms of delay
[deleted]
Do you have any justification for assuming the delays scale linearly?
I'd expect them to be mostly decoupled from the uplink/downlink time (not for any particularly sophisticated reason, just because the parts of the link that aren't uplink/downlink can be optimized and the speed of light can't). So that's 70 ms.
I'd expect them to be mostly decoupled from the uplink/downlink time (not for any particularly sophisticated reason, just because the parts of the link that aren't uplink/downlink can be optimized and the speed of light can't). So that's 70 ms.
Starlink isn't supposed to be geostationary, to my knowledge.
According to the Wikipedia page, they requested the height be ~550km as of April 17th of this year.[1]
On 17 April 2020, in documentation to the FCC, SpaceX said lower altitude will put the satellites closer to Starlink consumers and allow the network "to provide low-latency broadband to unserved and underserved Americans that is on par with service previously only available in urban areas". The change will also improve service for U.S. government users in polar regions and allow for more rapid deployment of the network, SpaceX said. The lower orbits will help ensure the satellites re-enter the atmosphere in a shorter time in case of failure, and will enable them to broadcast signals at reduced power levels, because they are closer to Earth, which SpaceX said will allow the fleet to be compliant with limits to reduce radio interference with other satellite and terrestrial wireless networks.
The specific info on height is below that paragraph in the Wikipedia article. Whether that means it's achievable in practice or not I don't know, but geostationary orbit is 35,786 km, so that puts it at 1/65th the distance.
1: https://en.wikipedia.org/wiki/Starlink
According to the Wikipedia page, they requested the height be ~550km as of April 17th of this year.[1]
On 17 April 2020, in documentation to the FCC, SpaceX said lower altitude will put the satellites closer to Starlink consumers and allow the network "to provide low-latency broadband to unserved and underserved Americans that is on par with service previously only available in urban areas". The change will also improve service for U.S. government users in polar regions and allow for more rapid deployment of the network, SpaceX said. The lower orbits will help ensure the satellites re-enter the atmosphere in a shorter time in case of failure, and will enable them to broadcast signals at reduced power levels, because they are closer to Earth, which SpaceX said will allow the fleet to be compliant with limits to reduce radio interference with other satellite and terrestrial wireless networks.
The specific info on height is below that paragraph in the Wikipedia article. Whether that means it's achievable in practice or not I don't know, but geostationary orbit is 35,786 km, so that puts it at 1/65th the distance.
1: https://en.wikipedia.org/wiki/Starlink
That is not the round trip time, it's the one-way delay. Also, processing time can be significant in satellite networks. Finally, given the current architecture of SpaceX without crosslinks, the total RTT will be ~30 ms + processing time + whatever is the RTT of the backbone network they deliver the traffic to.
I think the processing time might be heavily driven by the waveform and how they do the networking. As complexity increases and they move towards a software defined networking schema, the latency goes up. If they're not using ready-made/proven ASICs, the latency goes up. I don't believe any of this is public from them.
I think so too. In addition, they seem to have regenerative payloads on-board (otherwise I don't get how they get ~20Gbps/sat with a single Ka-band antenna), so they need to do full decoding + encoding on the satellite. Not sure how fast that can be done, but it will add some latency ms probably.
This is the first I've heard someone speculate about that. I didn't think they were doing 20G with a single antenna, but that they were adding all spectrum together that it's capable of processing (even if it doesn't get access to it all). On-board processing would also require a significant amount of power, and it's riskier.
Its an existential threat to some incumbent last mile providers.
I think it's less an existential threat than forcing them into specific geographic areas where they can still compete favorably. I doubt your Starlink speeds will be anything special in a heavily populated area where people are sharing the spectrum, and that heavy population means that fiber is feasible. Fiber means Starlink is competing against Gigabit plus speeds, delivered individually and not shared (to the degree that the ISP provides enough capacity where they aggregate the connections).
Rural areas and coverage across most/all the United States, even in areas where only satellite phones worked previously, are major draws IMO though.
Rural areas and coverage across most/all the United States, even in areas where only satellite phones worked previously, are major draws IMO though.
Agree with this, there’s plenty of areas (Eg non central belt of Scotland from my own experience) outside of cities, where the current provider is the only choice even though the service is slow and unreliable. Starlink could really appeal and gain a solid user base, very quickly.
Starlink is not going to be for end users most likely. The terminal, by all accounts so far, will be far more expensive than a geo terminal due to the motor and the phased array. I guess if you're willing to pay for it, it will certainly solve that problem, but there aren't enough of those customers to be profitable.
There's no need for a motor; that's what the phased array antennas are for.
802.11ac packages already implement MIMO-based beamforming, and I think there are already speciality 802.11ac packages using phased array for backhaul radio links. Phased array beamforming is a matter of size and processing power, but nothing different from cutting edge WiFi and 5G products, and not much different from what's already deployed in many laptops and cellphones. The entire software and hardware stack, including at the consumer level, is already capable of real-time, electronic beamforming. The technology for the Starlink terminals is well established and it could be done cheaply, it's just a matter of whether Starlink has the manufacturing pipeline primed.
Just like with rockets and electric cars, all the pieces exist and are relatively mature. It's just a matter of assembling them cost effectively, and that happens to be Elon Musk's special gift.
802.11ac packages already implement MIMO-based beamforming, and I think there are already speciality 802.11ac packages using phased array for backhaul radio links. Phased array beamforming is a matter of size and processing power, but nothing different from cutting edge WiFi and 5G products, and not much different from what's already deployed in many laptops and cellphones. The entire software and hardware stack, including at the consumer level, is already capable of real-time, electronic beamforming. The technology for the Starlink terminals is well established and it could be done cheaply, it's just a matter of whether Starlink has the manufacturing pipeline primed.
Just like with rockets and electric cars, all the pieces exist and are relatively mature. It's just a matter of assembling them cost effectively, and that happens to be Elon Musk's special gift.
I know that, but there IS a motor. Elon has said this himself. what you are describing is far more expensive than a phased array with the scan needed for no motor. It is not a solved, inexpensive problem. 5G and wifi use significantly lower frequencies, which is much easier and cheaper to implement the phased array. Starlink is Ku and Ka band. There are no examples of a consumer version of these that is cheap enough. The only thing that came close is the oneweb, but that's only Ku, and it only exists in a Wyler tweet.
Satellite will never beat local radio (ex: 5G, WiFi) and local radio will never beat fiber, for physical reasons.
The reason comes from the Shannon theorem: C=B*log2(1+S/N). C is capacity (what we want), B is bandwidth, S/N is the signal/noise ratio.
With modern technologies, we are very close to that limit. Both 5G and satellites are using among the highest radio frequencies the atmosphere can carry, the signal power is limited by electrical power requirements and emission power regulations and there is not much we can do about ambient noise. Fiber uses light which, in theory, can carry many orders of magnitude more information but the problematic is different.
But the thing is that this capacity is per channel, and the narrower the channel, the more we can pack in a given area, and that's where satellites are at a huge disadvantage. Satellites, even Starlink satellites, are really expensive, and they are 100s of km away at best. It means they can only project wide beams, even with they fancy beam forming antennas. Ground based antennas can cover a much smaller area and are much cheaper, as a result they have more channels and therefore more bandwidth. Satellites may prove effective in sparsely populated areas, but not in dense cities.
Fiber, and even copper wires are the extreme case. The channel is a single wire, you can pack hundreds in a cable you can hold in your hand. Compared to wireless transmission, bandwidth is essentially unlimited.
The reason comes from the Shannon theorem: C=B*log2(1+S/N). C is capacity (what we want), B is bandwidth, S/N is the signal/noise ratio.
With modern technologies, we are very close to that limit. Both 5G and satellites are using among the highest radio frequencies the atmosphere can carry, the signal power is limited by electrical power requirements and emission power regulations and there is not much we can do about ambient noise. Fiber uses light which, in theory, can carry many orders of magnitude more information but the problematic is different.
But the thing is that this capacity is per channel, and the narrower the channel, the more we can pack in a given area, and that's where satellites are at a huge disadvantage. Satellites, even Starlink satellites, are really expensive, and they are 100s of km away at best. It means they can only project wide beams, even with they fancy beam forming antennas. Ground based antennas can cover a much smaller area and are much cheaper, as a result they have more channels and therefore more bandwidth. Satellites may prove effective in sparsely populated areas, but not in dense cities.
Fiber, and even copper wires are the extreme case. The channel is a single wire, you can pack hundreds in a cable you can hold in your hand. Compared to wireless transmission, bandwidth is essentially unlimited.
Radio, whether local or via LEO satellites, absolutely can beat fiber. Routinely. That is much of the value proposition of SpaceX's product.
Microwave links from Chicago to New York claimed hundreds of millions in investment exactly on the prospect of selling reduced transit time at a premium. Similar gains on the New York - London channel, via Starlink, would be much more valuable.
The reason fiber is slow is that the signal does not propagate in a vacuum. It loses 30+% of the speed of signals propagated through air or vacuum.
Where fiber wins is on bulk bandwidth. A radio link has limited capacity, but it can get the first few packets through soonest. Starlink might start out with some pretty draconian tradffic caps.
I have heard of hollow-core fiber, where the beam travels in what amounts to a tube in the middle of the fiber, but I don't know of any deployed.
Microwave links from Chicago to New York claimed hundreds of millions in investment exactly on the prospect of selling reduced transit time at a premium. Similar gains on the New York - London channel, via Starlink, would be much more valuable.
The reason fiber is slow is that the signal does not propagate in a vacuum. It loses 30+% of the speed of signals propagated through air or vacuum.
Where fiber wins is on bulk bandwidth. A radio link has limited capacity, but it can get the first few packets through soonest. Starlink might start out with some pretty draconian tradffic caps.
I have heard of hollow-core fiber, where the beam travels in what amounts to a tube in the middle of the fiber, but I don't know of any deployed.
Fiber actually has limitations based on the length of the cable. Photons that travel perfectly straight arrive faster than photons that enter the cable at a steep angle and bounce off the walls a lot. Because of this, as you increase transmission rate, you start to get interference between signals, and instead of a clear On-Off, you start to get various degrees of brightness until the signal becomes too degraded.
Fixed wireless is that too.
One thing that hasn't been mentioned yet is queuing delay. All networks contain queues to smooth over bursts of packets being sent at once, and the time a packet spends occupying a queue can be significant.
Yes, this is huge, and likely one of the least appreciated aspects. Scheduling and queueing delay (not in the switches and routers) can contribute significantly to that 100ms.
No one forgot about those factors, he was only adding up the numbers to see where the lower physical limit is.
That shouldn't be significant unless:
1. There is a significant serialization/deserialization delay, which I don't think will be the based on my naive understanding of the tech
2. Buffering in time periods even relevant to discussion should really only occur under specific circumstances (like during overutilization)
I don't think that's the round trip time, that's the time it takes to send data over the satellite (ground -> satellite -> ground). A full round trip for data would be two of those since you have to factor in the data being sent back.
No, it's more like 500ms RTT for GEO
If you want a really great visualization and latency estimates for starlink check out the models and videos this guy came up with:
https://www.youtube.com/watch?v=QEIUdMiColU
https://www.youtube.com/watch?v=m05abdGSOxY
The comment from the FCC about it not accounting for "processing [&] routing" is kindof nonsense on its face, those are not novel problems they're already done by ever other router and switch, including several other satellite networks.
https://www.youtube.com/watch?v=QEIUdMiColU
https://www.youtube.com/watch?v=m05abdGSOxY
The comment from the FCC about it not accounting for "processing [&] routing" is kindof nonsense on its face, those are not novel problems they're already done by ever other router and switch, including several other satellite networks.
Thanks - those are my videos. If you've got any questions, I'll try and answer them. One key limitation is that they only model the propagation delay, so achieving those latencies also assumes that serialization delays and queuing delays are minimal. Serialization should be pretty negligible, but queuing will greatly depend on the network architecture adopted. There have been a number of ideas developed by the research community over the decades that are hard to apply in the Internet, but which might work well in a private network like Starlink. So I have confidence that it can be done, but I don't know at the moment how SpaceX actually plan to do this part.
no specific questions but thank you for making the videos, they're so much easier to follow than reading an fcc filing (for me at least).
if you setup a patreon, and every time spacex updated a filing you turned around an updated video that week, i'd pitch in. I think you'll find interest in starlink among people with dozens of dollars to spare is pretty high.
if you setup a patreon, and every time spacex updated a filing you turned around an updated video that week, i'd pitch in. I think you'll find interest in starlink among people with dozens of dollars to spare is pretty high.
Generally there are four types of internet delay namely propagation delay, processing delay, queueing delay and transmission delay. For satellite link, regardless of Geo or Leo the propagation delay will be dominating the equations.
I believe Starlink's engineers would have figured all the delay situations to claim less than 100ms latency and hopefully they will publish a credible white paper about it to refute FCC's counter claim.
Elon if you're reading this please send email to my username on Gmail for a third party verification of the latency, and of course with a small amount of fee in USD :-)
I believe Starlink's engineers would have figured all the delay situations to claim less than 100ms latency and hopefully they will publish a credible white paper about it to refute FCC's counter claim.
Elon if you're reading this please send email to my username on Gmail for a third party verification of the latency, and of course with a small amount of fee in USD :-)
I remain sceptical for several reasons:
While these are early alpha at best, so is Starlink atm because it currently lacks the sat to sat laser comms.
[1] https://en.wikipedia.org/wiki/Atmospheric_satellite
Furthermore there are
[2] https://en.wikipedia.org/wiki/ZBLAN and
[3] https://en.wikipedia.org/wiki/Photonic-crystal_fiber
to be taken into account, which all have the potential to change the equations without spamming the skies, or at least less so.
While these are early alpha at best, so is Starlink atm because it currently lacks the sat to sat laser comms.
[1] https://en.wikipedia.org/wiki/Atmospheric_satellite
Furthermore there are
[2] https://en.wikipedia.org/wiki/ZBLAN and
[3] https://en.wikipedia.org/wiki/Photonic-crystal_fiber
to be taken into account, which all have the potential to change the equations without spamming the skies, or at least less so.
The FCC is fairly conservative on what they believe can be delivered and rightly so. However this is the kind of technology that as taxpayers we should be funding. Things that are right at the envelope of possibility. It's not impossible but highly complex and involves a ton of calculations. Sounds exactly the kind of problem that technology is good at solving.
Given the current management, I wouldn’t discount politicking as motivation (to what end I have no clue).
It would be great if LEO could solve the rural broadband access problem, but why should taxpayer dollars be provided to companies that do not have a proven solution? Time after time various businesses such as Frontier have gamed the system without providing any value.
Seems like easy solution is make it a loan. If they make it work, they can keep the money for free, if not, they pay back with interest.
And when they declare bankruptcy because they can't pay back the loan with interest?
Payment upon delivery is how most business-to-business purchases work. You agree a cost, deliver the item, then get paid. Being paid before delivery gives no incentive to deliver what was requested.
Payment upon delivery is how most business-to-business purchases work. You agree a cost, deliver the item, then get paid. Being paid before delivery gives no incentive to deliver what was requested.
payment before delivery is ubiquitous in SaaS
FWIW, SpaceX has proven it can solve problems and make viable, honest business, and Elon's other company, Tesla, is known to repay government loans on time and with interest. So if anyone is to get a taxpayer-funded loan, SpaceX is one of the best bets.
Or we could, you know, take all that money, dig some trenches, and lay a whole lotta fibre.
We can solve rural access. You have a "Rural Fibre Project" like you had the "Rural Electrification Project" and you get on with life.
Ajit Pai and the telecoms simply don't want to because the telecoms would vaporize overnight everywhere that suddenly got fibre.
We can solve rural access. You have a "Rural Fibre Project" like you had the "Rural Electrification Project" and you get on with life.
Ajit Pai and the telecoms simply don't want to because the telecoms would vaporize overnight everywhere that suddenly got fibre.
There are people in rural areas with mile long driveways. Cost-per-mile makes a lot of rural places cost-prohibitive. Not just for fiber; lots of rural areas don’t have sewer or water coverage, either.
Haven't we already paid for the rural broadband access project a bunch of times, both at a state and local level?
If starlink does what it's supposed to, it should provide a pretty good experience that works best in rural areas precisely because of the sparseness of users that makes wiring each home expensive.
Certainly, giving the money and hoping it works as advertised isn't a good idea --- for all providers. For nationwide providers, these should be allocated whatever way, then the provider should post a bond and get their money and the grant money upon completion. If they don't complete it on time, the grant money and the bond roll down to the projects that were approved but didn't get funded because of the spending cap. Posting a bond for a hyper local provider might be problematic, but hyper local providers probably have a better track record of delivery, so they could have more generous pay as you go grant terms.
If starlink does what it's supposed to, it should provide a pretty good experience that works best in rural areas precisely because of the sparseness of users that makes wiring each home expensive.
Certainly, giving the money and hoping it works as advertised isn't a good idea --- for all providers. For nationwide providers, these should be allocated whatever way, then the provider should post a bond and get their money and the grant money upon completion. If they don't complete it on time, the grant money and the bond roll down to the projects that were approved but didn't get funded because of the spending cap. Posting a bond for a hyper local provider might be problematic, but hyper local providers probably have a better track record of delivery, so they could have more generous pay as you go grant terms.
YES. ATT collected a half-trillion dollars in authorized overcharges to existing landlines, on the promise to build out rural fiber. They did do some build-out. (One such fiber bundle terminates a few yards from my house.) ATT did not promise to light it up, and haven't, in ten years. But they pocketed the money.
How about money back if they don't deliver? Even better would be bounty after delivering the service, but I do see how it's hard to combine that with the (reverse) auction mechanism.
It would be nice if we could get back the hundreds of billions given to telecoms in the 90s so that they could wire the whole US instead
Indeed!
I'm going to miss looking at the stars and not seeing satellites.
I suspect a large portion of this latency will arise from the use of error correcting codes, time division multiplexing, and utilization tricks (i.e. compression) employed on the RF uplink and downlink.
And that’s ignoring the queuing delay that anyone who is within three hours/150 miles of a major city will experience. Users from the cities will choke the satellites.
And that’s ignoring the queuing delay that anyone who is within three hours/150 miles of a major city will experience. Users from the cities will choke the satellites.
This feels like FCC just making noise to prove that they won't just grant it to SpaceX because they're hot right now
Why the snarkiness from the FCC? They could have just said, "you can have the funding if you can show low latency, please prove it to us" -- end of story. It sort of reveals that they are already siding with / super-chummy with / in the pocket of the terrestrial ISPs, no?
Of course it does. How many billions have the terrestrial ISPs lobbied over the years. They expect results for all that money and they want competitors to be severely discouraged or downright banned.
It could be that the FCC has seen a lot of presentations on the difficulties in assuring low latency and how it has been tackled.
Or the technical people in the FCC understand the technical difficulties and can't let any player make claims without ensuring they back it up.
(Or the FCC has a strong well funded relationship with incumbent telecommunications carriers)
Or the technical people in the FCC understand the technical difficulties and can't let any player make claims without ensuring they back it up.
(Or the FCC has a strong well funded relationship with incumbent telecommunications carriers)
[deleted]
It’s amazing to me that we allow a regulatory body the power to decide, before a system is even built, whether it qualifies as a “such-and-such performance” system. Why not just wait and see before potentially excluding LEO providers from certain spectrum auctions? Why? Hmmm... the idea of regulatory capture by incumbents provides one potential answer.
Then again what’s the risk? If the new folks meet the bar, you can always change the rules.
Then again what’s the risk? If the new folks meet the bar, you can always change the rules.
They are rejecting them from the low-latency category, which includes most of the funds, until LEO providers prove they are in fact low latency. If they manage to prove their network's merits then they will be eligible for future auctions. Seems fair to me.
> If SpaceX and similar companies are rejected from the low-latency category, they will be at a disadvantage in a reverse auction that will distribute $16 billion—$1.6 billion yearly, over ten years—from the Rural Digital Opportunity Fund (RDOF). The auction, scheduled to begin on October 29, will give ISPs funding to deploy broadband in census blocks where no provider offers home-Internet speeds of at least 25Mbps downstream and 3Mbps upstream.
>The FCC will prioritize low-latency networks when awarding funding, so SpaceX and other LEO providers could come up short against terrestrial networks. Even DSL providers would have an advantage over LEO networks in funding battles if the satellite companies are placed in the FCC's high-latency category.
> If SpaceX and similar companies are rejected from the low-latency category, they will be at a disadvantage in a reverse auction that will distribute $16 billion—$1.6 billion yearly, over ten years—from the Rural Digital Opportunity Fund (RDOF). The auction, scheduled to begin on October 29, will give ISPs funding to deploy broadband in census blocks where no provider offers home-Internet speeds of at least 25Mbps downstream and 3Mbps upstream.
>The FCC will prioritize low-latency networks when awarding funding, so SpaceX and other LEO providers could come up short against terrestrial networks. Even DSL providers would have an advantage over LEO networks in funding battles if the satellite companies are placed in the FCC's high-latency category.
There is a subtext here that is not about the facts. Speculating, people influencing the FCC might be trying to reduce the availability of investment capital to SpaceX, and increase it to incumbents.
If I were an incumbent, I would be very worried indeed. If I supplied capital to incumbents, I would be demanding a greater risk premium, about now.
If I were an incumbent, I would be very worried indeed. If I supplied capital to incumbents, I would be demanding a greater risk premium, about now.
Why give money to unproven technology when we know ground networks work and can be low latency?
Surely there is a market for Starlink even without government funding. Then after they prove it is reliably low latency they can apply again. This isn't DARPA it's the FCC.
Surely there is a market for Starlink even without government funding. Then after they prove it is reliably low latency they can apply again. This isn't DARPA it's the FCC.
Because in the US broadband ISPs wont wire up rural areas. My local school district has 40% of homes that cable will not wire. 13% of them can not get cell service at home. They have taken so many millions of dollars in state and federal money to provide service, but utterly fail to do so. We had a real good opportunity to build a public ISP to service our school district. A local Indian reservation had built up the expertise as they had accomplished it on their lands and was offering it to us. We partnered with a quasi-public development authority to handle purchasing and installation of equipment. Site surveys. State/Federal licencing. Starting an ISP is hard. The week before we were to start installing equipment on end users homes the cable company, who previously said they no objection to this, dropped a lawsuit. This was after thousands of hours of work and many thousands of dollars spent. We knew we didn't have the money to fight it in courts so we folded. If they had said they would have objected from the start we would not have gone done the path we did.
This venture was to provide students internet access for a tiny rural school district. They have YET to increase their footprint in this rural area.
So I hope starlink takes every fucking customer they have.
This venture was to provide students internet access for a tiny rural school district. They have YET to increase their footprint in this rural area.
So I hope starlink takes every fucking customer they have.
Given the cost of a Starlink ground terminal, I suspect many won’t be able to afford the service.
That's the whole point of the subsidy program SpaceX is applying for.
> If SpaceX and similar companies are rejected from the low-latency category, they will be at a disadvantage in a reverse auction that will distribute $16 billion—$1.6 billion yearly, over ten years—from the Rural Digital Opportunity Fund (RDOF). The auction, scheduled to begin on October 29, will give ISPs funding to deploy broadband in census blocks where no provider offers home-Internet speeds of at least 25Mbps downstream and 3Mbps upstream.
> If SpaceX and similar companies are rejected from the low-latency category, they will be at a disadvantage in a reverse auction that will distribute $16 billion—$1.6 billion yearly, over ten years—from the Rural Digital Opportunity Fund (RDOF). The auction, scheduled to begin on October 29, will give ISPs funding to deploy broadband in census blocks where no provider offers home-Internet speeds of at least 25Mbps downstream and 3Mbps upstream.
We've looked at getting the cable provider to run cable to area of the district. I could be as high as 10k per house to get them to do the work. How much are downlinks. You may not understand what a school district will go to to make sure its students are served.
Ground networks work… where someone bothers to deploy one.
The problem in rural areas is that no one does.
The problem in rural areas is that no one does.
And places with no competition. Some times there is a ground network, or at most two (in the US, this tends to be Comcast and AT&T).
And most of the undeveloped world.
https://www.youtube.com/watch?v=QEIUdMiColU
And here without ISLs:
https://www.youtube.com/watch?v=m05abdGSOxY
Now, these videos assume no queuing delay. It's really hard to guarantee low queuing delay in a traditional IP network, but there's been a lot of research over the years, and we have a range of ideas that can be used to deliver minimal queuing with reasonable utilization. In fact doing this for Starlink is something I'm actively researching at the moment. I'm convinced it can be done, but it won't look like a conventional IP network internally. I don't know what SpaceX will actually do, so if the FCC has doubts, this is perhaps where they are concerned. Other delays might be in the ground segment, but that's more or less the same for SpaceX's terestrial competitors, and the FCC seems to think they can do it.