Comment by bobmcnamara
1 day ago
> If you start with the problem of how to create a reliable stream of data on top of an unreliable datagram layer, then the solution that comes out will look virtually identical to TCP.
I'll add that at the time of TCP's writing, the telephone people far outnumbered everyone else in the packet switching vs circuit switching debate. TCP gives you a virtual circuit over a packet switched network as a pair of reliable-enough independent byte streams over IP. This idea, that the endpoints could implement reliability through retransmission came from an earlier French network, Cylades, and ends up being a core principle of IP networks.
We're still "suffering" from the latency and jitter effects of the packet switching victory. (The debate happened before my time and I don't know if I would have really agreed with circuit switching.) Latency and jitter on the modern Internet are very best effort emphasis on "effort".
True, but with circuit switching, we'd probably still be paying by the minute, so most of these jittery/bufferbloated connections would not exist in the first place.
Also, circuit switching is harder (well, more expensive) to do at scale, especially with different providers (probably a reason the traditional telecoms pushed it so hard - to protect their traditional positions). Even modern circuit technologies like MPLS are mostly contained to within a network (though there can be and is cross-networking peering) and aren't as connection oriented as previous circuits like ATM or Frame Relay.
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As someone who at one point was working with people that were trying to keep an ATM network reliable there is a reason packet switching won.
L4S should improve latency and jitter.
The telephone people were basically right with their criticisms of TCP/IP such as:
What about QoS? Jitter, bandwidth, latency, fairness guarantees? What about queuing delay? What about multiplexing and tunneling? Traffic shaping and engineering? What about long-haul performance? Easy integration with optical circuit networks? etc. ATM addressed these issues, but TCP/IP did not.
All of these things showed up again once you tried to do VOIP and video conferencing, and in core ISPs as well as access networks, and they weren't (and in many cases still aren't) easy to solve.
How could a circuit switched network look like at today’s scale?
The optical layer is still circuit-switched.
Also MPLS is basically a virtual circuit network.
If that is true, then why did the telcos rapidly move the entire backbone of the telephone network to IP in the 1990s?
And why are they trying to persuade regulators to let them get rid of the remaining (peripheral) part of the old circuit-switched network, i.e., to phase out old-school telephone hardware, requiring all customers to have IP phone hardware?
They moved to IP because it was improving faster in speed and commoditization vs. ATM. But in order to make it work, they had to figure out how to make QoS work on IP networks, which wasn't easy. It still isn't easy (see: crappy zoom calls.)
Modern circuit switched networks use optics rather than the legacy copper circuits which date back to telegraphy.
Packet switching is cheaper; even though it can't make any guarantees about latency and bandwidth the way circuit switching could, it uses scarce long-haul bandwidth more efficiently. I regularly see people falling off video calls, like, multiple times a week. So, in some ways, it's a worse product, but costs much less.
You can criticize something and still select it as the best option. I do this daily with Apple. If you can’t find a flaw in a technical solution you probably aren’t looking close enough.