5 ms·

And that's why we invented multiplexing and even better: store and forward packets.

dredmorbius 1y ago
More specifically, packet-based rather than switched telecoms. Using a switch, each connection is a literal physical circuit. Multiplexing allows multiple circuits per phone line (through frequency separation at the carrier-frequency level), and much early telephony research involved increasing the multiplexing capacity and consequent issues. With packet-switched networks, the only circuits are the interconnects between routers, and each individual data packet can take a different route. Subject to quality of service / service level agreements (QoS / SLA), it's possible to support far more distinct individual connections over packet-switched networks, though there still remains a maximum total bandwidth. For time-sensitive modalities (e.g., realtime voice or video), excess traffic leads to congestion and buffering, distortion, or interference, so limits remain. But they're far more generous than with circuit-based networks. Put another way, packets give a greater assurance of establishing a link between any two nodes, whilst circuits give a greater assurance of a minimum bandwidth floor between those nodes. If you can get a connection, circuit-based line quality is often (though not always) superior, in terms of consistency, clarity, and low latency.
- ssl-3 1y ago
  That doesn't necessarily line up with my understanding of reality. In the US, a PRI can handle up to exactly 23 concurrent, native g.711u phone calls. That's it's capacity: No more, and no less. It's always 23, with each concurrent call using exactly 64kbps of symmetric bandwidth....just because that's the number of B channels provided. But if we take that same PRI and make it do IP packets instead using MLPPP, then our capacity is actually reduced. By adding the magic of packet switching, we also add overhead. And with that added overhead, we can only get only get ~19 g.711u calls through that same circuit. (Now, sure: In a bigger picture, that PRI may be better utilized as an IP pipeline than as a dedicated telephony circuit. It's certainly more flexible that way. But packetization is not something that automatically improves capacity. It often does the opposite.)
  - dredmorbius 1y ago
    This is well outside my area of expertise, assess accordingly. From some quick DDGing, PRI (primary rate interface) is one of several possible options for a packet-switched telephony system, and is specifically contrasted with SIP VOIP connections in this article: <https://enterprise.spectrum.com/support/faq/voice-and-collaboration/what-is-a-pri-phone-system.html https://enterprise.spectrum.com/support/faq/voice-and-collab...> NB, "always 23" ... unless you're in Europe, in which case 23 === 30. More on PRI vs. SIP: <https://enterprise.spectrum.com/support/faq/voice-and-collaboration/what-is-the-difference-between-pri-and-sip-trunk.html https://enterprise.spectrum.com/support/faq/voice-and-collab...>. (Other than being able to spell PRI and the above articles, I've no knowledge on the topic.)
    - ssl-3 1y ago
      PRI is TDM. It isn't packet-switched; there are no packets on the voice-carrying B channels. It uses timeslots, instead. > NB, "always 23" ... unless you're in Europe, in which case 23 === 30. I believe I was very specific about the locality I was referring to, but I am appreciative of the seemingly-disingenuous pedantry that is apparently unfettered by such arcane concepts as "context".
      - dredmorbius 1y ago
        Where TDM == "time-division multiplexing". Expanding acronyms, particularly those from less-mainstream concepts and fields, is appreciated. It wasn't clear from your comment (or the source I'd read) that PRI is circuit based. The fact that circuits can be multiplexed (whether through frequency-separation, timeslicing, or other mechanisms, see <https://en.wikipedia.org/wiki/Multiplexing https://en.wikipedia.org/wiki/Multiplexing> for general MUXology) is irrelevant. They are still circuits. And there are limits to how many circuits can be maintained at a single time, regardless of the apparent endpoint combinatorial possibilities. Packet-based switching has far greater capacity and flexibility, as I, my sources, and several other comments to this thread, have noted. Pedantry aside, you seem to be confirming my initial point.

More specifically, packet-based rather than switched telecoms. Using a switch, each connection is a literal physical circuit. Multiplexing allows multiple circuits per phone line (through frequency separation at the carrier-frequency level), and much early telephony research involved increasing the multiplexing capacity and consequent issues. With packet-switched networks, the only circuits are the interconnects between routers, and each individual data packet can take a different route. Subject to quality of service / service level agreements (QoS / SLA), it's possible to support far more distinct individual connections over packet-switched networks, though there still remains a maximum total bandwidth. For time-sensitive modalities (e.g., realtime voice or video), excess traffic leads to congestion and buffering, distortion, or interference, so limits remain. But they're far more generous than with circuit-based networks. Put another way, packets give a greater assurance of establishing a link between any two nodes, whilst circuits give a greater assurance of a minimum bandwidth floor between those nodes. If you can get a connection, circuit-based line quality is often (though not always) superior, in terms of consistency, clarity, and low latency.

ssl-3 1y ago
That doesn't necessarily line up with my understanding of reality. In the US, a PRI can handle up to exactly 23 concurrent, native g.711u phone calls. That's it's capacity: No more, and no less. It's always 23, with each concurrent call using exactly 64kbps of symmetric bandwidth....just because that's the number of B channels provided. But if we take that same PRI and make it do IP packets instead using MLPPP, then our capacity is actually reduced. By adding the magic of packet switching, we also add overhead. And with that added overhead, we can only get only get ~19 g.711u calls through that same circuit. (Now, sure: In a bigger picture, that PRI may be better utilized as an IP pipeline than as a dedicated telephony circuit. It's certainly more flexible that way. But packetization is not something that automatically improves capacity. It often does the opposite.)
- dredmorbius 1y ago
  This is well outside my area of expertise, assess accordingly. From some quick DDGing, PRI (primary rate interface) is one of several possible options for a packet-switched telephony system, and is specifically contrasted with SIP VOIP connections in this article: <https://enterprise.spectrum.com/support/faq/voice-and-collaboration/what-is-a-pri-phone-system.html https://enterprise.spectrum.com/support/faq/voice-and-collab...> NB, "always 23" ... unless you're in Europe, in which case 23 === 30. More on PRI vs. SIP: <https://enterprise.spectrum.com/support/faq/voice-and-collaboration/what-is-the-difference-between-pri-and-sip-trunk.html https://enterprise.spectrum.com/support/faq/voice-and-collab...>. (Other than being able to spell PRI and the above articles, I've no knowledge on the topic.)
  - ssl-3 1y ago
    PRI is TDM. It isn't packet-switched; there are no packets on the voice-carrying B channels. It uses timeslots, instead. > NB, "always 23" ... unless you're in Europe, in which case 23 === 30. I believe I was very specific about the locality I was referring to, but I am appreciative of the seemingly-disingenuous pedantry that is apparently unfettered by such arcane concepts as "context".
    - dredmorbius 1y ago
      Where TDM == "time-division multiplexing". Expanding acronyms, particularly those from less-mainstream concepts and fields, is appreciated. It wasn't clear from your comment (or the source I'd read) that PRI is circuit based. The fact that circuits can be multiplexed (whether through frequency-separation, timeslicing, or other mechanisms, see <https://en.wikipedia.org/wiki/Multiplexing https://en.wikipedia.org/wiki/Multiplexing> for general MUXology) is irrelevant. They are still circuits. And there are limits to how many circuits can be maintained at a single time, regardless of the apparent endpoint combinatorial possibilities. Packet-based switching has far greater capacity and flexibility, as I, my sources, and several other comments to this thread, have noted. Pedantry aside, you seem to be confirming my initial point.