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Actually the multicast audio is a pretty good system. There're multiple elevators. Broadcasting makes it simple to sync up the music on them. Using a Wifi sp

by ww520 4y ago

Actually the multicast audio is a pretty good system. There're multiple elevators. Broadcasting makes it simple to sync up the music on them. Using a Wifi speaker has much lower cost than adding a wired speaker to a moving elevator. It’s also simple and low cost to add extra WiFi speakers in other areas of the hotel, creating an ad hoc PA system.

kkielhofner 4y ago
I worked on a WiFi multicast video streaming solution and while it theoretically works as well and is as easy as you describe in practice it can be a complete nightmare. Full disclosure this was a few years ago so things may have improved. I also can’t remember all of the specifics but there was a lot of low-level driver work, firmware tweaks, specific configurations of just about every WiFi param you can think of, etc.
- inferiorhuman 4y ago
  Sonic used to offer mbone connectivity (including BBC channels) back when they were an internet service provider and not a web provider. It was pretty nifty but never very user friendly to set up.
  - op00to 4y ago
    When I worked at a core i2 .edu site, we had all the "hd" mbone tv streams. It was pretty wild considering HD was a "new" thing! Thanks for reminding me of that wonderful time!
    - inferiorhuman 4y ago
      Wikipedia had this quote from Mick Jagger: I wanna say a special welcome to everyone that's, uh, climbed into the Internet tonight and, uh, has got into the M-bone. And I hope it doesn't all collapse. What a time to be alive.
      - hackmiester 4y ago
        Wow... that is certainly a historical artifact.
      - skylanh 4y ago
        BUSINESS TECHNOLOGY; "Peering Out a 'Real Time' Window", By Peter H. Lewis, Feb. 8, 1995 https://www.nytimes.com/1995/02/08/business/business-technology-peering-out-a-real-time-window.html https://www.nytimes.com/1995/02/08/business/business-technol... The article also indicates Internet Multicasting's "Geek of the Week", there's an archive at: https://town.hall.org/radio/Geek/ https://town.hall.org/radio/Geek/ Transcripts available at http://opentranscripts.org/sources/geek-of-the-week/ http://opentranscripts.org/sources/geek-of-the-week/
- thefourthchime 4y ago
  Yeah same. Multicast can work on wired LANs. Any kind of wireless or routing and it breaks pretty quickly. At least a while back. I haven't touched it in years.
  - ta1243 4y ago
    I route multicast across hundreds of routers in dozens of countries over private wires and vpns without problem. Wireless sure, that can be a pain.
mike_d 4y ago
Remember that networks introduce latency. It might be tiny but the human ear can detect speakers being _slightly_ off. For example you wouldn't want a wifi speaker in an elevator using a repeater at the top of the shaft trying to match up to a hardwired speaker in a ground floor vestibule.
- 9dev 4y ago
  Modern wifi speakers can be configured with variable drift for the playback to mitigate this very issue :)
- joshvm 4y ago
  Does network latency dominate over speed of sound? Propagation time is about 3ms / metre in open air.
  - anyfoo 4y ago
    It basically does not matter if you sync your clocks via NTP and play back accordingly.
- anyfoo 4y ago
  You can use NTP to get the devices' clocks synced up to much better than necessary tolerance, and play back accordingly. And then you "just" have the same problems that you have with purely electrically connected, analogue speakers (which are effectively 100% in sync in terms of receiving the signal): Sound is relatively slow, and so the audio from a speaker that is far away will reach you later than the nearby speaker. You can mitigate that by adding a precise delay to the far away speaker... but of course that does not work if you're standing on the other side. Nevertheless, as said, that problem is regardless of whether your speaker is network-connected or not.
  - thfuran 4y ago
    You just need to take a cue from wifi and use beam forming to send separately synced audio to each person.
  - 4y ago
jahewson 4y ago
Surely elevators already come with hardwired speakers?
kccqzy 4y ago
There's nothing in the article that suggests that Wi-Fi is being used on the elevator. In fact I'd say most likely the elevator is using a wired Ethernet connection. It's just that the broadcast domain for the L2 network includes both the wired elevators and guest Wi-Fi.
- anyfoo 4y ago
  Unless I misread, there's nothing that suggests Wi-Fi is involved at all. It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in (making this less of an issue, as some people in this thread thought). But this is not entirely clear to me...
  - Galanwe 4y ago
    > It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in Well it's a bit of a mystery to me as well. The thing is multicast is not anycast, you will not receive multicast traffic unless you specifically ask to join a group. So, he would have to be actually listening somewhere in between the multicast router and the elevator?
    - jhugo 4y ago
      > The thing is multicast is not anycast, you will not receive multicast traffic unless you specifically ask to join a group. Most likely a dumb cheap switch that doesn't snoop on IGMP (or a less dumb switch that wasn't configured to snoop on IGMP) was upstream of both the OP and the device in the elevator. So the frames were being flooded since the switch doesn't know any better, and then normally ignored by OP's network stack since they didn't join that multicast group, until something like tcpdump/wireshark enables promiscuous mode.
  - gkbrk 4y ago
    > there's nothing that suggests Wi-Fi is involved at all. It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in Author here. Everything on the article was received on the guest Wi-Fi network on my laptop without plugging into anything.

by ww520 4y ago

kkielhofner 4y ago

I worked on a WiFi multicast video streaming solution and while it theoretically works as well and is as easy as you describe in practice it can be a complete nightmare. Full disclosure this was a few years ago so things may have improved. I also can’t remember all of the specifics but there was a lot of low-level driver work, firmware tweaks, specific configurations of just about every WiFi param you can think of, etc.

inferiorhuman 4y ago
Sonic used to offer mbone connectivity (including BBC channels) back when they were an internet service provider and not a web provider. It was pretty nifty but never very user friendly to set up.
- op00to 4y ago
  When I worked at a core i2 .edu site, we had all the "hd" mbone tv streams. It was pretty wild considering HD was a "new" thing! Thanks for reminding me of that wonderful time!
  - inferiorhuman 4y ago
    Wikipedia had this quote from Mick Jagger: I wanna say a special welcome to everyone that's, uh, climbed into the Internet tonight and, uh, has got into the M-bone. And I hope it doesn't all collapse. What a time to be alive.
    - hackmiester 4y ago
      Wow... that is certainly a historical artifact.
    - skylanh 4y ago
      BUSINESS TECHNOLOGY; "Peering Out a 'Real Time' Window", By Peter H. Lewis, Feb. 8, 1995 https://www.nytimes.com/1995/02/08/business/business-technology-peering-out-a-real-time-window.html https://www.nytimes.com/1995/02/08/business/business-technol... The article also indicates Internet Multicasting's "Geek of the Week", there's an archive at: https://town.hall.org/radio/Geek/ https://town.hall.org/radio/Geek/ Transcripts available at http://opentranscripts.org/sources/geek-of-the-week/ http://opentranscripts.org/sources/geek-of-the-week/
thefourthchime 4y ago
Yeah same. Multicast can work on wired LANs. Any kind of wireless or routing and it breaks pretty quickly. At least a while back. I haven't touched it in years.
- ta1243 4y ago
  I route multicast across hundreds of routers in dozens of countries over private wires and vpns without problem. Wireless sure, that can be a pain.

mike_d 4y ago

Remember that networks introduce latency. It might be tiny but the human ear can detect speakers being _slightly_ off. For example you wouldn't want a wifi speaker in an elevator using a repeater at the top of the shaft trying to match up to a hardwired speaker in a ground floor vestibule.

9dev 4y ago
Modern wifi speakers can be configured with variable drift for the playback to mitigate this very issue :)
joshvm 4y ago
Does network latency dominate over speed of sound? Propagation time is about 3ms / metre in open air.
- anyfoo 4y ago
  It basically does not matter if you sync your clocks via NTP and play back accordingly.
anyfoo 4y ago
You can use NTP to get the devices' clocks synced up to much better than necessary tolerance, and play back accordingly. And then you "just" have the same problems that you have with purely electrically connected, analogue speakers (which are effectively 100% in sync in terms of receiving the signal): Sound is relatively slow, and so the audio from a speaker that is far away will reach you later than the nearby speaker. You can mitigate that by adding a precise delay to the far away speaker... but of course that does not work if you're standing on the other side. Nevertheless, as said, that problem is regardless of whether your speaker is network-connected or not.
- thfuran 4y ago
  You just need to take a cue from wifi and use beam forming to send separately synced audio to each person.
- 4y ago

jahewson 4y ago

Surely elevators already come with hardwired speakers?

kccqzy 4y ago

There's nothing in the article that suggests that Wi-Fi is being used on the elevator. In fact I'd say most likely the elevator is using a wired Ethernet connection. It's just that the broadcast domain for the L2 network includes both the wired elevators and guest Wi-Fi.

anyfoo 4y ago
Unless I misread, there's nothing that suggests Wi-Fi is involved at all. It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in (making this less of an issue, as some people in this thread thought). But this is not entirely clear to me...
- Galanwe 4y ago
  > It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in Well it's a bit of a mystery to me as well. The thing is multicast is not anycast, you will not receive multicast traffic unless you specifically ask to join a group. So, he would have to be actually listening somewhere in between the multicast router and the elevator?
  - jhugo 4y ago
    > The thing is multicast is not anycast, you will not receive multicast traffic unless you specifically ask to join a group. Most likely a dumb cheap switch that doesn't snoop on IGMP (or a less dumb switch that wasn't configured to snoop on IGMP) was upstream of both the OP and the device in the elevator. So the frames were being flooded since the switch doesn't know any better, and then normally ignored by OP's network stack since they didn't join that multicast group, until something like tcpdump/wireshark enables promiscuous mode.
- gkbrk 4y ago
  > there's nothing that suggests Wi-Fi is involved at all. It rather sounds to me like the author was listening at the Ethernet port that the TV was plugged in Author here. Everything on the article was received on the guest Wi-Fi network on my laptop without plugging into anything.