> but FireWire was actually meant to replace SCSI. SCSI and FireWire are peer-to-peer: any device on the bus can talk to any other device, unlike USB where each bus has at most one host and the host does all the initiation of data transfer. (USB On-The-Go still has one host and one host only; it just allows certain devices like your mobile phone to swing both ways.) The point-to-point capabilities of USB 3 notwithstanding, a USB hub has one upstream port for the host and multiple downstream ports for the devices. A FireWire hub, however, is like getting a longer internal SCSI cable; more devices simply exist on the same bus. Connecting multiple FireWire hubs just makes a bigger bus because all the ports are the same.
I'd love a comprehensive review of how host-to-host networking works under USB4, for comparison. USB4 is the first significant overhaul of USB, a move from switched links to a packet switching system, where-by various protocols such as USB3, PCIe, DisplayPort are multiplexed over the USB4 links & across 40Gbps packet-switching hub chips.
There still seems to be a fairly top-down tree architecture to USB4[1], but there is also mandatory host-to-host networking support: one of the most exciting things about the new Intel laptop offerings, to me, is that they almost all offer 40Gbps host-to-host communication over a good variety of plain-old usb-c cables (20Gbps for less speedy cables). It's an interesting capability, but how technically the packet-switching system works to implement this is very interesting to me, something I'm not clear on, especially as compared to FireWire.
I'd also love to know whether this host-to-host networking functions (& how) if there are routers/"hubs" between the different hosts (the linked [1] implies it ought work). This could all behave like USB-OTG, where one computer starts looking like a device, but I'm not sure if it's that fixed a system: does USB4 begins to permit slightly more bus-like non-top-down behaviors. Does a usb hub/router have to be entirely top-down in USB4, or can it negotiate different hosts access to different devices?
Still missing is DMA (short of USB4 PCIe transport, which again raises the host versus device question in my mind! Is there NTB support on PCIe over USB4 anywhere? That would be kicking rad) which FireWire obviously has had in it's wheelhouse for a long long time now.
Thunderbolt is really poorly documented in general and the only documentation for Thunderbolt networking and the underlying XDomain stuff appears to the Linux patches: https://lwn.net/Articles/734019/ USB4 appears to have only minor changes compared to Thunderbolt.
I'd love a comprehensive review of how host-to-host networking works under USB4, for comparison. USB4 is the first significant overhaul of USB, a move from switched links to a packet switching system, where-by various protocols such as USB3, PCIe, DisplayPort are multiplexed over the USB4 links & across 40Gbps packet-switching hub chips.
There still seems to be a fairly top-down tree architecture to USB4[1], but there is also mandatory host-to-host networking support: one of the most exciting things about the new Intel laptop offerings, to me, is that they almost all offer 40Gbps host-to-host communication over a good variety of plain-old usb-c cables (20Gbps for less speedy cables). It's an interesting capability, but how technically the packet-switching system works to implement this is very interesting to me, something I'm not clear on, especially as compared to FireWire.
I'd also love to know whether this host-to-host networking functions (& how) if there are routers/"hubs" between the different hosts (the linked [1] implies it ought work). This could all behave like USB-OTG, where one computer starts looking like a device, but I'm not sure if it's that fixed a system: does USB4 begins to permit slightly more bus-like non-top-down behaviors. Does a usb hub/router have to be entirely top-down in USB4, or can it negotiate different hosts access to different devices?
Still missing is DMA (short of USB4 PCIe transport, which again raises the host versus device question in my mind! Is there NTB support on PCIe over USB4 anywhere? That would be kicking rad) which FireWire obviously has had in it's wheelhouse for a long long time now.
[1] https://www.usb.org/sites/default/files/D1T1-3%20-%20USB4%20...