6 ms·

I hate to be negative about progress but I wish companies would stop deploying DOCSIS and other time division multiple access strategies like that. Because DOCS

by edude03 11y ago

I hate to be negative about progress but I wish companies would stop deploying DOCSIS and other time division multiple access strategies like that. Because DOCSIS is TDMA based its always going to have a problem with latency jitter and performance consistency and yet cable companies like to pretend it's the same as active Ethernet. Comparing 1gbit cable to 1gbit Ethernet is like comparing a dslr and a smartphone based on their megapixels.

Dylan16807 11y ago
But how big is the jitter? A bit of searching suggests it's typically under a millisecond, and that's barely anything. Most modems I've seen have a baseline latency of something like 20 milliseconds.
- api 11y ago
  20ms baseline latency is pathetic. Ping from a data center in Los Angeles to one in San Francisco is typically a little over half what it apparently takes your modem to send a packet upstream. 20ms is like half way across the country. Why is latency at the last mile so awful? What is the latency typically like on stuff like Google Fiber?
  - pixl97 11y ago
    The DOCSIS 3.0 modems we use at our local provider have no where near that much latency. 5-8ms is typical.
  - scandinavian 11y ago
    Baseline on my DOCSIS 3.0 modem is as low as 5 ms when I've tested it. That anyone should care about a 5-ish ms overhead is ridiculous imo.
    - edude03 11y ago
      It's great when it's that low, my problem with DOCSIS is that it's not consistent. When there is low utilization in your neighbourhood it's fine but when everyone is home for the holidays for example it becomes unbearable. For example, I usually get about 8ms to a server hosted in the same city as me (10ms to google) but on bad days it gets as high as 60-80ms. I regularly tether my LTE enabled phone where I get around 20ms but it's consistent.
  - xorcist 11y ago
    On my completely regular residental broadband, built with standard ethernet almost fifteen years ago, I have 4 ms to my server in the cloud (same country, different provider). If Google Fiber is built with similar parts it should be comparable.
  - toupeira 11y ago
    Am on gigabit fiber here, next hop is <1ms as it should be.
vardump 11y ago
Switched ethernet is also practically TDMA. You can't send multiple packets in the same time. Although gigabit ethernet is full duplex, so you can receive and send in the same time. Practically DOCSIS adds about 3-5 ms. Which is upper range of how much wifi adds latency. Compare that to usual peripherals. Wireless mouses, about 50-100 ms latency, typical computer displays about 16-50 ms, flat screen TVs 80-200 ms.
- edude03 11y ago
  Practically speaking modern Ethernet switches are non blocking though which allows every port to talk to every other port at full speed. With DOCSIS being TDMA there isn't a way to improve speed to the backbone (other than adding more channels / smaller time slots). Also 3-5ms is probably at the low end since it heavily depends on the usage patterns of those on the same CMTS as you.
mikhailt 11y ago
Progress isn't linear, they're working on all sorts of problems and they're not just deploying DOCSIS for the sake of it. This is the next best solution that Comcast and other ISPs can do with the current infrastructure they have. This is the right way of approaching the problem, deploy DOCSIS 3.1 as the next step and figure out the replacement for DOCSIS in the future. Customers want these bandwidth right now, not later. Also, DOCSIS 3.1 has improvements for bufferbloat issue and it would stabilize the current latency issues. They're not ignoring it completely. If we do what you suggest, we'd be stuck at 10mbps for a long time and instead, we're getting 100mbps bandwidth that does work for your typical usage of netflix, gaming, and so on in a family household. There's a limit we'll reach very soon where no one will care about more bandwidth but they will want rather stability/latency improvements. Data caps is the next biggest issue. A lot of execs from DOCSIS community agrees that 3.1 is the last upgrade to DOCSIS standard and the next replacement would be a Fiber-based one, which will take a few decades to even figure out. I rather have DOCSIS 3.1 now and not in 10 years because you think we should not do this. Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out.
- snorrah 11y ago
  "Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out." Sounds a little similar to what happened in the UK, iirc. British Telecom wanted to do a full fibre deployment but the government upheld complaints of it being anti competitive, and now we have to endure copper *DSL being the default national broadband option and all the pitfalls that entails.
- datashovel 11y ago
  "Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out." I'm not familiar enough with the industry to have an opinion on this, but it sounds very odd that a private corporation is so tied to government that it can't innovate on its own? How does this work? And how did it end up like this? I guess what I'm after is an ELI5 on this last part of your comment :)
cptskippy 11y ago
What do you propose they should do? Is it compatible with their existing infrastructure? Does it play nice with existing consumer devices? What does the roll-out cost and time-frame look like?
gst 11y ago
> Comparing 1gbit cable to 1gbit Ethernet is like comparing a dslr and a smartphone based on their megapixels. In both of those cases the majority of customers doesn't care about the difference.
- pki 11y ago
  People that play games and get 1ms latency vs 20-30ms latency within the same town/city care, and that isn't a very small market..
striking 11y ago
It's not TDMA, it's FDM. (It seems you've severely misunderstood DOCSIS.) And this is the best they can do with the existing network. Feel free to run an Ethernet cable from my house to yours, though.
- edude03 11y ago
  It's both TDMA and FDM. Your modem can bond multiple channels on the same coax but each channel is shared amongst all the subscribes on the CMTS. Each DOCSIS revision ups the spatial efficiency of each channel but also ups the number of channels. On a side note, my ISP incentives users to upgrade their modems by offering more bandwidth for the same money if you buy a modem that can bond more channels. For example I had a 8/3 DOCSIS 3 modem on a 60mb plan, for the same price they gave me 100mbit for upgrading to a modem that could bond 24/8. It allows them to utilize the network more efficiently

by edude03 11y ago

Dylan16807 11y ago

But how big is the jitter? A bit of searching suggests it's typically under a millisecond, and that's barely anything. Most modems I've seen have a baseline latency of something like 20 milliseconds.

api 11y ago
20ms baseline latency is pathetic. Ping from a data center in Los Angeles to one in San Francisco is typically a little over half what it apparently takes your modem to send a packet upstream. 20ms is like half way across the country. Why is latency at the last mile so awful? What is the latency typically like on stuff like Google Fiber?
- pixl97 11y ago
  The DOCSIS 3.0 modems we use at our local provider have no where near that much latency. 5-8ms is typical.
- scandinavian 11y ago
  Baseline on my DOCSIS 3.0 modem is as low as 5 ms when I've tested it. That anyone should care about a 5-ish ms overhead is ridiculous imo.
  - edude03 11y ago
    It's great when it's that low, my problem with DOCSIS is that it's not consistent. When there is low utilization in your neighbourhood it's fine but when everyone is home for the holidays for example it becomes unbearable. For example, I usually get about 8ms to a server hosted in the same city as me (10ms to google) but on bad days it gets as high as 60-80ms. I regularly tether my LTE enabled phone where I get around 20ms but it's consistent.
- xorcist 11y ago
  On my completely regular residental broadband, built with standard ethernet almost fifteen years ago, I have 4 ms to my server in the cloud (same country, different provider). If Google Fiber is built with similar parts it should be comparable.
- toupeira 11y ago
  Am on gigabit fiber here, next hop is <1ms as it should be.

vardump 11y ago

Switched ethernet is also practically TDMA. You can't send multiple packets in the same time. Although gigabit ethernet is full duplex, so you can receive and send in the same time. Practically DOCSIS adds about 3-5 ms. Which is upper range of how much wifi adds latency. Compare that to usual peripherals. Wireless mouses, about 50-100 ms latency, typical computer displays about 16-50 ms, flat screen TVs 80-200 ms.

edude03 11y ago
Practically speaking modern Ethernet switches are non blocking though which allows every port to talk to every other port at full speed. With DOCSIS being TDMA there isn't a way to improve speed to the backbone (other than adding more channels / smaller time slots). Also 3-5ms is probably at the low end since it heavily depends on the usage patterns of those on the same CMTS as you.

mikhailt 11y ago

Progress isn't linear, they're working on all sorts of problems and they're not just deploying DOCSIS for the sake of it. This is the next best solution that Comcast and other ISPs can do with the current infrastructure they have. This is the right way of approaching the problem, deploy DOCSIS 3.1 as the next step and figure out the replacement for DOCSIS in the future. Customers want these bandwidth right now, not later. Also, DOCSIS 3.1 has improvements for bufferbloat issue and it would stabilize the current latency issues. They're not ignoring it completely. If we do what you suggest, we'd be stuck at 10mbps for a long time and instead, we're getting 100mbps bandwidth that does work for your typical usage of netflix, gaming, and so on in a family household. There's a limit we'll reach very soon where no one will care about more bandwidth but they will want rather stability/latency improvements. Data caps is the next biggest issue. A lot of execs from DOCSIS community agrees that 3.1 is the last upgrade to DOCSIS standard and the next replacement would be a Fiber-based one, which will take a few decades to even figure out. I rather have DOCSIS 3.1 now and not in 10 years because you think we should not do this. Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out.

snorrah 11y ago
"Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out." Sounds a little similar to what happened in the UK, iirc. British Telecom wanted to do a full fibre deployment but the government upheld complaints of it being anti competitive, and now we have to endure copper *DSL being the default national broadband option and all the pitfalls that entails.
datashovel 11y ago
"Our US congress had the chance to fix this back in 1990s and they screwed up with enforcing it properly. We could've had a better pure fiber-based national build out but it didn't work out." I'm not familiar enough with the industry to have an opinion on this, but it sounds very odd that a private corporation is so tied to government that it can't innovate on its own? How does this work? And how did it end up like this? I guess what I'm after is an ELI5 on this last part of your comment :)

cptskippy 11y ago

What do you propose they should do? Is it compatible with their existing infrastructure? Does it play nice with existing consumer devices? What does the roll-out cost and time-frame look like?

gst 11y ago

> Comparing 1gbit cable to 1gbit Ethernet is like comparing a dslr and a smartphone based on their megapixels. In both of those cases the majority of customers doesn't care about the difference.

pki 11y ago
People that play games and get 1ms latency vs 20-30ms latency within the same town/city care, and that isn't a very small market..

striking 11y ago

It's not TDMA, it's FDM. (It seems you've severely misunderstood DOCSIS.) And this is the best they can do with the existing network. Feel free to run an Ethernet cable from my house to yours, though.

edude03 11y ago
It's both TDMA and FDM. Your modem can bond multiple channels on the same coax but each channel is shared amongst all the subscribes on the CMTS. Each DOCSIS revision ups the spatial efficiency of each channel but also ups the number of channels. On a side note, my ISP incentives users to upgrade their modems by offering more bandwidth for the same money if you buy a modem that can bond more channels. For example I had a 8/3 DOCSIS 3 modem on a 60mb plan, for the same price they gave me 100mbit for upgrading to a modem that could bond 24/8. It allows them to utilize the network more efficiently