6 ms·

I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about

I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about satellite internet. Lost packets increase latency. And weather conditions cause lost packets.

ffpip 6y ago
> I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about satellite internet. Only on HN
- jjeaff 6y ago
  More like everywhere on the internet. Just the other day, I saw some idiot on facebook try to lecture a board certified pulmonologist at one of the state's largest hospital about how covid is nothing to worry about.
vvanders 6y ago
If you want to get pedantic, the band used will determine what natural phenomenon impacts the received signal. Even in those cases FEC and dynamic modulation will let the signal work(at reduced throughout). That said unless we're talking about lasers air refraction doesn't usually impact RF(there is tropospheric ducting but that's something different).
- walrus01 6y ago
  In an example of a modern highly rain fade resistant ptp microwave system in the 18GHz band, standard fcc part 101 fdd band plan. The radios might be talking to each other in both H and V polarities, 80MHz wide channel in both, at 2048QAM 5/6 during a normal sunny day. In an extreme rain fade event they may go all the way down to QPSK 1/2 and the link's capacity in Mbps could be as poor as 40Mbps (from what is nominally a 900Mbps+ link), but the end to end latency will remain pretty much the same. Latency as experienced by users might be much worse, however, if suddenly 300Mbps of traffic is trying to be shoved through a 40-75Mbps link, for a period of several minutes or more.
ikiris 6y ago
uhhh packet loss doesn't change latency? Its loss, which has its own effects, but jesus dude you're just doubling down on you not knowing what you're talking about.
- walrus01 6y ago
  Packet loss on an oversubscribed tdma, contended, shared access cheap VSAT system is a result of too much traffic and not enough pipe. For an analogy think of a big office sharing a 5Mbps DSL line. A properly implemented dedicated geostationary link doesn't have packet loss except under sun transit events, extreme rain fade (for ku and higher bands), and when too many people try to stuff too much traffic through too narrow of a link without appropriate QoS. From the point of view of an end user on a LAN at a site dependent on two way satellite it may not be possible for them to determine exact why they're seeing packet loss.
- gamblor956 6y ago
  We're taking about two different types of latency. You, and the other people telling me that I'm wrong, are referring to latency at the packet level, and I am referring to latency at the message\data level. https://en.m.wikipedia.org/wiki/Latency_(engineering) https://en.m.wikipedia.org/wiki/Latency_(engineering) Ultimately, the latter is the kind of latency the user cares about.
viraptor 6y ago
Credentials are not that important here. Maybe the random guy also ran satellite internet on a military base, maybe they manufacture the satellite comms gear? The important bit is, are either of those supported by facts and where the technical difference / misunderstanding comes from? (I wouldn't start with "you're wrong" but that's a separate thing) They can both be right as walrus01 seems to talk about latency of a single rtt in isolation, and withinboredom about what does the TCP endpoint effectively see.
- walrus01 6y ago
  What I'm talking about is the nature of a dedicated access (1:1) single carrier per channel geostationary link, via a pair of modems such as comtech cdm760 and appropriately sized rf chains and antennas on both ends. It'll be a rock solid 492ms and the bandwidth (in Mbps) will be proportional to the size of the transponder space leased, and influenced by antenna sizing/gain, overall link budget, tx power on both ends and so forth. Example: at one location, a 3.8 meter ku band dual linear polarity compact cassegrain dish in somalia, a 200W BUC+SSPA, good quality norsat PLL LNB, a cdm760 modem. Ten MHz of transponder space occupied total. Other end, a 5.5m dish with similar gear on it in a teleport in Cyprus. If the person I'm replying to isn't willing or able to clarify whether they were in a contended, or dedicated network, or specify the gear, it's hard to say exactly why they're seeing jitter. But I can quite confidently say that excursions above 495ms are not something seen in a dedicated network. It's how that dedicated capacity can get sliced up and shared that is the most common cause of packet loss, jitter and high latency in geostationary based two way satellite IP links. The most common thing for a cheap VSAT isp to do is to acquire one chunk of Ku transponder capacity (let's say about $8000 a month worth), install something like an idirect hub with line cards in it, and sell access to individual end users in $developingnation at an 8:1 oversubscription ratio or more. Meaning that an end user vsat terminal might see 495ms at a lucky time when its peers in the same network were not also moving traffic, but could also often see latency anywhere from 500 to 850 during busy periods. Now that same 8000 bucks a month of transponder space could equally well be assigned to a single high priority end user with money to pay, in which case they would never see above 495ms. Or it could be oversubscribed to all hell, such as if the ISP wanted to sell $280/month service to a bunch of very cost conscious end users in a developing nation environment who can only afford very cheap VSAT terminal hardware (one 1.2m fiberglass compression molded reflector, a 4W BUC, and an idirect modem) and minimal monthly ongoing payments. In which case each user will be in a 16:1 or worse oversubscribed network. The economics of making a 5500 kilogram $200 million satellite in geostationary orbit pay for itself, before its lifespan is done in 15 years, are not favorable. If you ever want to truly be shocked go price the $ per Mbps per month that results from the 1:1 dedicated setup I described above. On the topic of what the average hn reader considers "satellite internet". Based on consumer experience with the absolute cheapest consumer grade ku and Ka band vsat terminals in the usa, they almost 99% of the time mean Hughesnet or viasat/wildblue. Very few people actually have money or reason to lay their hands on real two way satellite stuff. Generally if you work for a company that needs something like a $3500/month link for a mine in Nunavut you're paying some third party experts to implement it.
walrus01 6y ago
I understand that I am some random guy on the internet, but I've also spent a lot of time in Afghanistan (weird coincidence here, believe me or don't believe me) implementing two way satellite systems, and still work professionally in expensive two way satellite systems. I also happen to be a person who's been doing network engineering for ISPs since 1996-1997 or thereabouts, and currently has business cards that read "Senior Network Engineer" on them. I'm not willing to give up anonymity here, but ask a specific two way satellite technology question and I'll be more than happy to answer. As a note there were lots of people buying and installing cheap COTS 1.2-1.8 meter size ku band vsat terminals at all sorts of military sites in Afghanistan for MWR purposes, it's not rocket science or really hard to do at all. This stuff was, and is, all kept air gapped and separated from anything that is a real DoD or ISAF/RS network. These were networks for peoples' own personal recreational internet and entertainment in their rest time. You absolutely would see weird latency, jitter, packet loss behavior on those.
JimDabell 6y ago
Saying “you’re wrong” is not the same as saying “you don’t know anything about this topic”. Grandparent did the former; you’re accusing them of doing the latter. Everybody can be wrong about something, no matter how smart / credentialed / experienced they are.
robertlagrant 6y ago
> I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about satellite internet. I like that to you only one is a random guy on the internet. And I should know, I'm the president of the World Liking Things club, and you random guy on the internet have no business liking things like I do.

ffpip 6y ago

> I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about satellite internet. Only on HN

jjeaff 6y ago
More like everywhere on the internet. Just the other day, I saw some idiot on facebook try to lecture a board certified pulmonologist at one of the state's largest hospital about how covid is nothing to worry about.

vvanders 6y ago

If you want to get pedantic, the band used will determine what natural phenomenon impacts the received signal. Even in those cases FEC and dynamic modulation will let the signal work(at reduced throughout). That said unless we're talking about lasers air refraction doesn't usually impact RF(there is tropospheric ducting but that's something different).

walrus01 6y ago
In an example of a modern highly rain fade resistant ptp microwave system in the 18GHz band, standard fcc part 101 fdd band plan. The radios might be talking to each other in both H and V polarities, 80MHz wide channel in both, at 2048QAM 5/6 during a normal sunny day. In an extreme rain fade event they may go all the way down to QPSK 1/2 and the link's capacity in Mbps could be as poor as 40Mbps (from what is nominally a 900Mbps+ link), but the end to end latency will remain pretty much the same. Latency as experienced by users might be much worse, however, if suddenly 300Mbps of traffic is trying to be shoved through a 40-75Mbps link, for a period of several minutes or more.

ikiris 6y ago

uhhh packet loss doesn't change latency? Its loss, which has its own effects, but jesus dude you're just doubling down on you not knowing what you're talking about.

walrus01 6y ago
Packet loss on an oversubscribed tdma, contended, shared access cheap VSAT system is a result of too much traffic and not enough pipe. For an analogy think of a big office sharing a 5Mbps DSL line. A properly implemented dedicated geostationary link doesn't have packet loss except under sun transit events, extreme rain fade (for ku and higher bands), and when too many people try to stuff too much traffic through too narrow of a link without appropriate QoS. From the point of view of an end user on a LAN at a site dependent on two way satellite it may not be possible for them to determine exact why they're seeing packet loss.
gamblor956 6y ago
We're taking about two different types of latency. You, and the other people telling me that I'm wrong, are referring to latency at the packet level, and I am referring to latency at the message\data level. https://en.m.wikipedia.org/wiki/Latency_(engineering) https://en.m.wikipedia.org/wiki/Latency_(engineering) Ultimately, the latter is the kind of latency the user cares about.

viraptor 6y ago

Credentials are not that important here. Maybe the random guy also ran satellite internet on a military base, maybe they manufacture the satellite comms gear? The important bit is, are either of those supported by facts and where the technical difference / misunderstanding comes from? (I wouldn't start with "you're wrong" but that's a separate thing) They can both be right as walrus01 seems to talk about latency of a single rtt in isolation, and withinboredom about what does the TCP endpoint effectively see.

walrus01 6y ago
What I'm talking about is the nature of a dedicated access (1:1) single carrier per channel geostationary link, via a pair of modems such as comtech cdm760 and appropriately sized rf chains and antennas on both ends. It'll be a rock solid 492ms and the bandwidth (in Mbps) will be proportional to the size of the transponder space leased, and influenced by antenna sizing/gain, overall link budget, tx power on both ends and so forth. Example: at one location, a 3.8 meter ku band dual linear polarity compact cassegrain dish in somalia, a 200W BUC+SSPA, good quality norsat PLL LNB, a cdm760 modem. Ten MHz of transponder space occupied total. Other end, a 5.5m dish with similar gear on it in a teleport in Cyprus. If the person I'm replying to isn't willing or able to clarify whether they were in a contended, or dedicated network, or specify the gear, it's hard to say exactly why they're seeing jitter. But I can quite confidently say that excursions above 495ms are not something seen in a dedicated network. It's how that dedicated capacity can get sliced up and shared that is the most common cause of packet loss, jitter and high latency in geostationary based two way satellite IP links. The most common thing for a cheap VSAT isp to do is to acquire one chunk of Ku transponder capacity (let's say about $8000 a month worth), install something like an idirect hub with line cards in it, and sell access to individual end users in $developingnation at an 8:1 oversubscription ratio or more. Meaning that an end user vsat terminal might see 495ms at a lucky time when its peers in the same network were not also moving traffic, but could also often see latency anywhere from 500 to 850 during busy periods. Now that same 8000 bucks a month of transponder space could equally well be assigned to a single high priority end user with money to pay, in which case they would never see above 495ms. Or it could be oversubscribed to all hell, such as if the ISP wanted to sell $280/month service to a bunch of very cost conscious end users in a developing nation environment who can only afford very cheap VSAT terminal hardware (one 1.2m fiberglass compression molded reflector, a 4W BUC, and an idirect modem) and minimal monthly ongoing payments. In which case each user will be in a 16:1 or worse oversubscribed network. The economics of making a 5500 kilogram $200 million satellite in geostationary orbit pay for itself, before its lifespan is done in 15 years, are not favorable. If you ever want to truly be shocked go price the $ per Mbps per month that results from the 1:1 dedicated setup I described above. On the topic of what the average hn reader considers "satellite internet". Based on consumer experience with the absolute cheapest consumer grade ku and Ka band vsat terminals in the usa, they almost 99% of the time mean Hughesnet or viasat/wildblue. Very few people actually have money or reason to lay their hands on real two way satellite stuff. Generally if you work for a company that needs something like a $3500/month link for a mine in Nunavut you're paying some third party experts to implement it.

walrus01 6y ago

I understand that I am some random guy on the internet, but I've also spent a lot of time in Afghanistan (weird coincidence here, believe me or don't believe me) implementing two way satellite systems, and still work professionally in expensive two way satellite systems. I also happen to be a person who's been doing network engineering for ISPs since 1996-1997 or thereabouts, and currently has business cards that read "Senior Network Engineer" on them. I'm not willing to give up anonymity here, but ask a specific two way satellite technology question and I'll be more than happy to answer. As a note there were lots of people buying and installing cheap COTS 1.2-1.8 meter size ku band vsat terminals at all sorts of military sites in Afghanistan for MWR purposes, it's not rocket science or really hard to do at all. This stuff was, and is, all kept air gapped and separated from anything that is a real DoD or ISAF/RS network. These were networks for peoples' own personal recreational internet and entertainment in their rest time. You absolutely would see weird latency, jitter, packet loss behavior on those.

JimDabell 6y ago

Saying “you’re wrong” is not the same as saying “you don’t know anything about this topic”. Grandparent did the former; you’re accusing them of doing the latter. Everybody can be wrong about something, no matter how smart / credentialed / experienced they are.

robertlagrant 6y ago

> I like that some random guy on the internet is telling a guy who was in charge of the satellite internet on a military base that he doesn't know anything about satellite internet. I like that to you only one is a random guy on the internet. And I should know, I'm the president of the World Liking Things club, and you random guy on the internet have no business liking things like I do.