Step 1: Match each protocol with its architecture.
(A) AMQP (Advanced Message Queuing Protocol): This is a publish-subscribe protocol that uses a central broker to pass messages between publishers and subscribers. The broker acts as a central message (I) Bus.
(B) CoAP (Constrained Application Protocol): This protocol is designed for constrained devices and is modeled on HTTP. It uses a request-response pattern, which is the hallmark of a (II) Client-server architecture.
(C) DDS (Data Distribution Service): This is a data-centric middleware standard for real-time systems. It operates without a central broker, allowing nodes to communicate directly. This is a (III) P2P (Peer-to-Peer) or publish-subscribe architecture.
(D) XMPP (Extensible Messaging and Presence Protocol): This is a protocol for instant messaging and presence. While it is client-server, its federated nature, where servers communicate with other servers, can be represented as a hierarchical or (IV) Tree structure.
Step 2: Combine the matches.
The correct matching is A-I, B-II, C-III, D-IV.