Setup: FX Providers update their rates

FX Providers send their quotes to their local Nexus Gateway
FX Providers must update Nexus with their current offered exchange rates (1). (The quoting process is described in detail in Providing FX Quotes.)
Quotes can be sent to any Nexus Gateway; it is up to the FX Provider to choose the one most convenient for them. This could be based on jurisdiction, geographical location or any other consideration. The Nexus Gateway will then relay those quotes across the network, ensuring that the quote reaches the Nexus Gateway of the Source Currency.
Quotes can be made public and thus available to any Participating Bank, or made private, in which case the quote is only available to a specific listed subset of banks.
For example, FX Provider A is located in the UK and provides a quote for the SGD-to-INR corridor through their Liquidity Providers. They could send their quote for SGD-to-INR payments to the UK Nexus Gateway. This quote will be relayed to the SG and IN Nexus Gateways (and synchronized across the rest of the network). Now the SG Nexus Gateway can provide quotes to Source Banks in Singapore sending payments to India and the IN-Nexus Gateway can provide quotes to Source Banks in India sending payments to Singapore.
When processing the quote update request, Nexus will validate the request (by checking that the FX Provider is set up to quote for that currency pair and has nominated validated Liquidity Providers in both the Source and Destination Country). It will then save the new quote as current. Nexus will set the old quote to expire five minutes after the new quote is received, to allow any Senders who were shown the old quote time to complete their payment setup.
The Nexus Gateway sends a message to the FX Provider which (a) confirms that their quote has been successfully updated and (b) includes the full list of current quotes from all FX Providers, so that the FX Provider can see how they compare to the market and adjust their rates if they wish to.

Message Flow

Triggered by UpdateQuote API call.
Message flows used when FX Providers update quotes