Remote Procedure Calls (RPC) are an essential technology in modern distributed computing. They allow for software applications running on different machines or networks to communicate with each other effectively. Suppose a scenario where one machine needs to access a resource or a service that is running on another machine. In that case, RPC is used to initiate communication and request the resource or service.

However, to enable communication between systems, there needs to be a common protocol, agreed upon by all parties. This protocol describes the communication between the caller and the callee, and it's where rpcbind comes in.

Rpcbind is a crucial part of the RPC architecture, acting as a mediator between the client and the server processes in a system. It is the component responsible for mapping the relevant ports on the server and client systems so that communication can occur.

According to the man page, rpcbind is an RPC service that converts RPC program numbers into DARPA assigned protocol port numbers. It is also responsible for providing the dynamic port mapping mechanism that is widely used in RPC communication.

As part of its process, rpcbind listens on a well-known port known as port 111. This port acts as the default port for all RPC requests that get sent to the host machine. When a request reaches the host, rpcbind receives the request and maps it to the relevant port that corresponds to the requested service.

However, it is important to note that rpcbind doesn't handle the actual communication between the client and server processes. Instead, it is a mediator between these processes that happens in the background.

To illustrate how rpcbind works, imagine two systems A and B that need to communicate. System A sends an RPC request to system B, which includes the RPC program number and version number of the service being requested. Rpcbind on system B then looks up the program number in its bindery and returns the TCP or UDP port number registered for that service.

After this, the source program on system A initiates a connection to system B's port number returned by rpcbind, which is already registered to the corresponding service. It's at this point that the actual service request is passed to the server on system B.

Without rpcbind, understanding the structure of the software architecture and how systems communicate with one another becomes much more complicated. As an example, consider Sun RPC, which was one of the earliest RPC mechanisms. In this model, clients had to hard code the port number of the server they wanted to communicate with.

If the port number changed, the client needed to be re-compiled and re-installed. This was a time-consuming and inefficient process that often led to software bugs and errors.

Rpcbind solves this issue by providing a mapping between the RPC program number and the service port number dynamically. This way, clients can easily connect with the server without the need to know the specific port number explicitly.

In summary, rpcbind is a critical component of the RPC architecture that enables secure and efficient communication between systems in a distributed environment. Without it, the complexities of the software structure become impossible to handle, leading to a less efficient, more error-prone system. As such, rpcbind is an integral part of any distributed application stack, and its importance to the world of distributed computing cannot be overstated.