3 ms·

> the cables themselves are different per protocol I feel this is a transient rather than inherent problem of running different stacks over the same physical

> the cables themselves are different per protocol I feel this is a transient rather than inherent problem of running different stacks over the same physical layer. If the physical layer can "miss pairs" then I agree we lose the whole point. One way is to have some sort of official certificate system enforced by USB.org and adopted by major manufacturers. Basically "guaranteed to support a few pre-defined subsets of protocols".

weinzierl 10y ago
> If the physical layer can "miss pairs" then I agree we lose the whole point. It's not about missing pairs, Thunderbolt 3 cables are active in the sense that they contain electronics. That's why a Thunderbolt USB-C cable has much larger plugs than a regular USB-C cable.
- smilekzs 10y ago
  Having never used Thunderbolt myself, I feel this "cable chip" is an intentionally retarded design that violates the end-to-end principle. Is there anything technical that prevents it from being absorbed into interface controller chips inside devices?
  - tmzt 10y ago
    It might be providing timing information for the SERDES based on the length of the cord. Edit: it looks like it might be that and/or an active PHY similar to 10Gbps Ethernet.
  - weinzierl 10y ago
    I'm not a Thunderbolt expert, but I think the reason is twofold. Thunderbolt was originally designed as an optical link and optical connectors are highly problematic. Misalign the fiber just a tiny bit and you have considerable losses. So they went with a hybrid design where the converter is in the plugs and the connector is electrical. Later it was changed to all electrical but the design where the connection between the two plugs and the plugs and the devices are two separate things was retained. The second reason is that this design still makes sense. With traditional designs the driver in the end device is always a compromise. For example the Ethernet driver has to be able to drive lines up to 100m long, but how many Ethernet lines are really that long? For Thunderbolt they dis-coupled the physical characteristics of the line driver from the driver in the end device. They basically move all the problems of the physical connection (line length, EMV and so on) form the end device to the cable.

weinzierl 10y ago

> If the physical layer can "miss pairs" then I agree we lose the whole point. It's not about missing pairs, Thunderbolt 3 cables are active in the sense that they contain electronics. That's why a Thunderbolt USB-C cable has much larger plugs than a regular USB-C cable.

smilekzs 10y ago
Having never used Thunderbolt myself, I feel this "cable chip" is an intentionally retarded design that violates the end-to-end principle. Is there anything technical that prevents it from being absorbed into interface controller chips inside devices?
- tmzt 10y ago
  It might be providing timing information for the SERDES based on the length of the cord. Edit: it looks like it might be that and/or an active PHY similar to 10Gbps Ethernet.
- weinzierl 10y ago
  I'm not a Thunderbolt expert, but I think the reason is twofold. Thunderbolt was originally designed as an optical link and optical connectors are highly problematic. Misalign the fiber just a tiny bit and you have considerable losses. So they went with a hybrid design where the converter is in the plugs and the connector is electrical. Later it was changed to all electrical but the design where the connection between the two plugs and the plugs and the devices are two separate things was retained. The second reason is that this design still makes sense. With traditional designs the driver in the end device is always a compromise. For example the Ethernet driver has to be able to drive lines up to 100m long, but how many Ethernet lines are really that long? For Thunderbolt they dis-coupled the physical characteristics of the line driver from the driver in the end device. They basically move all the problems of the physical connection (line length, EMV and so on) form the end device to the cable.