It's been a few years since I was involved with any of this, but even for higher-bandwidth microwave networks you want to squeeze every last bit out of the protocol.
I'd guess in this instance that they'll skip both the TCP and IP layers completely and essentially be sending minimally encapsulated payloads out almost raw. Minimally encapsulated at this level might actually mean no encapsulation. Maybe some error-detection/CRC type stuff as these links tend to be super lossy.
You probably want to combine in a single raw packet the data, compressed with a prediction codec with the error detection code. Since you also have a lower-latency high-speed link (the transatlantic cable), you can continuously update the probabilistic model used by the compression to squeeze the last bit.
Would you even acknowledge? The data is worthless after one round-trip, so you wouldn't send it twice. The receiver just needs to make sure that they read information correctly and can deal with losses.
Right. A shortwave link would be used in addition to a fiber link, not as a replacement for it. Assuming ACKs aren't latency sensitive, they could flow back over the fiber.
No, your trading engine is on the other end, the link only sends prices. Let's assume you want to trade on a future in Chicago that's based on London prices (e.g. a world wide equity index). You know Chicago prices and NYC prices and what people in Chicago think London prices are. If you then get from London a price indication that this has changed, you can quickly trade against it to make money. The London link never needs to know what happened, they just send prices that could be interesting. All logic sits at the exchange where trades happen since that's dependent on local prices at time of execution.
I haven't worked with microwave feeds, but from the war stories I have heard, not even IP is used but data is sent using whatever low level protocol (Ethernet or something similar) is used by the transport.
In fact the payload might be empty or mostly empty and data can be encoded in protocol fields (for example encoding symbol names in address fields as the link is otherwise point to point).
