Comment by Karrot_Kream
21 hours ago
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.
Circuit switching is not harder to do, it's simply less efficient. In the PSTN and ISDN world, circuits consumed bandwidth regardless of whether it was actively in use or not. There was no statistical multiplexing as a result.
Circuit switching packets means carrying metadata about the circuit rather than simply using the destination MAC or IP address to figure out routing along the way. ATM took this to an extreme with nearly 10% protocol overhead (48 bytes of payload in a 53 byte cell) and 22 bytes of wasted space in the last ATM cell for a 1500 byte ethernet packet. That inefficiency is what really hurt. Sadly the ATM legacy lives on in GPON and XGSPON -- EPON / 10GEPON are far better protocols. As a result, GPON and XGSPON require gobs of memory per port for frame reassembly (128 ONUs x 8 priorities x 9KB for jumbo frames = 9MB per port worst case), whereas EPON / 10GEPON do not.
MPLS also has certain issues that are solved by using the IPv6 next header feature which avoids having to push / pop headers (modifying the size of the packet which has implications for buffering and the associated QoS issues making the hardware more complex) in the transport network. MPLS labels made sense at the time of introduction in the early 2000s when transport network hardware was able to utilize a small table to look up the next hop of a frame instead of doing a full route lookup. The hardware constraints of those early days requiring small SRAMs have effectively gone away since modern ASICs have billions of transistors which make on chip route tables sufficient for many use-cases.
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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.