Comment by lxgr
19 hours ago
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.
19 hours ago
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.
> Circuit switching is not harder to do, it's simply less efficient
I did specify more expensive. Even with ASICs it’s more expensive to scale up.
> 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.
ATM was a technology designed and pushed by the traditional voice telecoms long before everything converged on IP. The smaller byte sizes were designed to have less jitter/latency for voice, QoS (also to prioritize voice), and more fine-grained multiplexing for voice traffic, where other data was secondary. ATM was originally designed in the late 1980s before Ethernet won out and bulk data transfer was a novelty; the traditional telecoms wanted something that mapped into their current circuits.
ATM’s overhead for IP was arguably too much, but it wasn’t what killed ATM. It was the fact that speeding the sending of such small packets up to and past gigabit speeds was too expensive, which was made worse by the fact that Ethernet became a commodity due to scale.
> 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.
This isn’t quite the same argument. I agree that 10GEPON is “better” and I wish it was THE standard (especially for pure ISPs), but it ignores that most ISPs using XGSPON are multiplexing voip, TV, emergency, and other traditional networks. If anything, it’s what ATM should have been, where they could have had a different priority for small celled VOIP and larger packets for other services. I say this as a person who thinks all this is dumb and consumers should just be given an internet connection at this point - I hope 10GEPON wins out in the end - it is certainly already cheaper. I much more hate the fact that I have to use PPPoE than some memory overhead for the ports reassembling GEM packets, though.
As for MPLS, well yeah it was certainly faster than IP lookups, but the circuits also often result in sub-optimal routing as the MPLS “tunnels” don’t always reflect otherwise ideal physical paths. IIRC, about half of the IPv6 internet’s core is actually routed over MPLS tunnels and it can be a large reason IPv6 routing can often have higher TTLs than IPv4 (because the paths often aren’t as efficient). That being said, we’ll have to see if segment routing takes off, and what approaches stick.