Which protocol is used by a client system to request a service from a server?

Which protocol is used by a client system to request a service from a server?

• A. RPC
• B. HTTP
• C. DNS
• D. SMTP

Answer: (A)

The main idea is how a client asks a server to perform a function or service across a network. Remote Procedure Call (RPC) is built for this purpose: the client invokes a procedure on the server as if it were a local function, sending the needed parameters and receiving the result. The RPC framework handles the details of marshaling arguments, sending them over the network, and returning the outcome, making the interaction feel like a simple local call. This fits the question because it highlights requesting a service through a remote invocation rather than just fetching a resource. HTTP, while also used for client–server interactions, is primarily about requesting and transferring web resources (pages, data, APIs) rather than presenting a generalized remote service-call mechanism. DNS is about translating human-friendly names to IP addresses, not invoking services on a server. SMTP is designed for delivering email between servers, not for requesting arbitrary services on a server.

The main idea is how a client asks a server to perform a function or service across a network. Remote Procedure Call (RPC) is built for this purpose: the client invokes a procedure on the server as if it were a local function, sending the needed parameters and receiving the result. The RPC framework handles the details of marshaling arguments, sending them over the network, and returning the outcome, making the interaction feel like a simple local call.

This fits the question because it highlights requesting a service through a remote invocation rather than just fetching a resource. HTTP, while also used for client–server interactions, is primarily about requesting and transferring web resources (pages, data, APIs) rather than presenting a generalized remote service-call mechanism. DNS is about translating human-friendly names to IP addresses, not invoking services on a server. SMTP is designed for delivering email between servers, not for requesting arbitrary services on a server.