The signals over cat5 are transmitted using the TCP protocol
They don’t have to be! There is another Internet Protocol called User Datagram Protocol (UDP) which like TCP runs on Internet Protocol (IP). UDP is often used for streaming where it is more important to keep something flowing than to ensure accuracy. Note that TCP cannot guarantee how long it will take to get a correct packet to its destination. Think about that!
So TCP/IP is perfect for file transfers, and is the reason that software transmitted over the internet retains the exactly the same number of bugs at each end, provided you are prepared to wait!
Moving down the chain, Ethernet is a low-level protocol that by itself guarantees neither delivery nor timing, which is unsurprising because it does not guarantee delivery of any data packet at all. In effect it just throws packets into the air and hopes that the right receiver catches them.
Ethernet is a development of the Aloha radio network built for data communication between the Hawiian islands before the advent of satellites and undersea cables. It is an example of Carrier-sense multiple access with collision detection (CSMA/CD). Multiple Access means there is no central controller, any device can blast the airwaves with data packets. To avoid two devices obliterating each other’s packet, each device must make sure the airwaves are clear before transmitting (Carrier-sense).
But this alone is not enough. Two devices on distant islands can each sense that the airwaves are free, and transmit simultaneously with the result that the signal is scrambled in between. Two conditions must be satisfied to correct for this.
Firstly, after transmitting, each device must also listen to ensure the airwaves are still clear. If not, there has definitely been a collision (collision detection) and the device must wait a randomised time before trying again. This randomised time is initially 0 or 1 periods, but if another collision is detected, the number of possible wait periods is doubled and so on in exponential progression.
The second condition is that every message must be long enough to ensure collisions are detected even by the most separated, furthest flung islands.
There is no way of knowing if the intended receiver is even on-air unless a higher-level protocol like TCP/IP is used on top of Ethernet.
So do audio protocols always use TCP/IP? A big no.
I2S for example was designed in 1957 to allow two chips on a board to pass 2-channel 16-bit PCM data. It has no, that is zilch, error detection let alone error correction.
How about USB then? While USB can carry TCP/IP it has a special mode for streaming. Remember, streaming requires a near constant stream of packets. So in streaming mode, USB does not implement re-transmission of faulty packets.
Unlike Ethernet, USB does have a central controller, which polls every connected device to see if it wants to transmit. As I understand it, there can only be one root USB controller per box which polls every device.
Qobuz claims to use TCP/IP but to do this with streaming content, the Qobuz app(lication) must itself implement the computer code for acknowledging packet receipt, waiting doe missing packets and assembling the received packets back into the correct order. Qobuz must therefore have an app installed on the last digital device in your chain to ensure accuracy. Even then, it cannot guarantee timing across the mess of the Internet in order to avoid dropouts.
There is a properly engineered networking stack called the Open Systems Interconnect (OSI) which defines seven protocol layers. The Internet on the other hand has grown like topsy and only has four layers. Most of its ’standards’ are just Requests for Comment (RFC).
Silver disks and HDMI for me!