After reading through the 2019 FMS whitepaper, I was left wondering why FIRST created such a small bandwidth limit for teams. I understand that they do not want to tax the robot networks and cause the driverstation to excessively drop packets. From what I’ve read though, even while multiplexed, the 4Mbps limit is not even getting near the point of causing issues. Am I missing something?
There definitely are issues even with that limited amount of bandwidth. I refer you to this dumpster fire of a thread: Stop it! You're not fooling anyone
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This was discussed earlier this season, but I can’t find the thread. If someone could post it that would be great.
I’m not too sure about the technical details, but interference means that it’s hard to consistently maintain a high bandwidth connection fairly all teams, meaning the effective limit is much lower than the theoretical limit.
Network issues can and do cause issues at events.
I believe you’re looking for this:
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Something else to consider, you need to look at the worst expected case and design for that.
For FIRST, this tends to happen at the larger events. With multiple simultaneous fields running, they start to interfere with each other. That really leaves two options: set a “safe” limit for that situation and have it be the limit for all events… set different limits at different events.
I think it’d be far more frustrating to have 12Mbps all season and then drop to 4Mbps for the most important event of the year. Instead, learning to work with that constraint and tweak behavior/design with that all season puts teams in a better place to be prepared at the year end events.
I’ve CSAd multiple champs. At each one, there’s at least a few times FTAs have asked for help with getting teams to reduce their BW after their field was struggling. It appears the maximum rate was implemented to help with those types of issues. It was always a frustrating experience to talk to a team and say “hey, I know you’re at 6.7 and the maximum allowed is 7. Your field’s FTA is hoping we can find a way to reduce that because it’s hurting the field’s overall network”
See my post here (and actually the entire thread…): Is there any reason to not allow anything above 4 mbps? - #6 by Peter_Johnson
My understanding is that when multiplexed over multiple antennas with separate channels then the bandwidth does not get divided. So as long as you are getting ~1Gbps to the field AP then it will split 72Mbps to each robot minus interference and other suboptimal conditions.
Last year I worked with several teams that were ‘maximizing the bandwidth’ at 7mb. The FTA would show me the team b/w while on the field. I think things ran ok with one team did this, but if two or more teams with the same usage were on at once, network traffic started to lag.
We were attempting to run two cameras at 480p both streaming at the same time and had many issues with cameras being slow not because our usage was above 7mbps, but because the field couldn’t actually supply the 7mbps. We eventually dropped them both down to 240p and even that sometimes had issues (this year we are down to one stream @ 240p, with buttons to switch them).
It is somewhat sad that we can not solve this, but I see no easy solution.
No. The typical setup is one 20MHz channel in the 5GHz band for all of the robots.
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No (also). Radio send their signal in all directions, so all APs are going to get hit with their signal. An AP needs to look at the ID in order to know whether to handle it or not, so even if it is going to drop the packets (since another antenna will handle it), it still takes up a bandwidth/time slice. Until all APs and client radio use high-tech beam forming to talk to each other in a narrow beam, more radios means less bandwidth.
It’s a common misunderstanding that each team gets a separate WiFi channel. All six teams are multiplexed over one WiFi channel in the 5 GHz band. I guess the confusion comes when WiFi channels are confused with SSIDs. Each team gets their own (hidden) SSID and their own IP subnet but all robot traffic is crammed into one WiFi channel.
The practical maximum for all six robots is around 24-27 Mbs. Therefore it was acceptable in past years when one or two teams wanted to use 7 of that.
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Thanks for clarifying. The white paper seemed vague in regards to that part of the config.
As long as it is permissible by FIRST and the FTA at Hudson Valley Regional, I borrowed one of those expensive spectrum analyzers from work and am hoping to run and put together some data figures for interference among other things. I’ll keep you guys posted on CD.
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