ed port mappers. When an RPC server is started, it tells the port mapper the port number it is listening to and what RPC program numbers it is prepared to serve. When a client wants to make an RPC call to a given pro- gram number, it first checks the port mapper on the server machine to determine the port number where RPC packets should be sent for accessing the specific service. The port mapper program maps RPC program and version numbers to transport-specific port numbers, which enables dynamic binding of remote programs. This mapping is desirable because the range of reserved port numbers is very small and the number of potential remote programs is very large. The port mapper also aids in broadcast RPC. A given RPC program will usually have different port number bindings on different machines, SO there is no way to directly broadcast to all of these programs. To broadcast to a given program, the client actually sends its message to the port mapper that has a fixed port number. The port mapper picks up the broadcast and calls the local service specified by the client. When the port mapper gets the reply from the local service, it sends the reply back to the client. 27.3.6 Broadcasting In broadcast RPC-based protocols, the client sends a broadcast packet to the network and waits for numerous replies. Broadcast RPC uses unreliable, packet- based protocols like UDP as its transport. Servers that support broadcast protocols respond only when the request is successfully processed without any specific point- ers on the errors. Broadcast RPC uses the port mapper to convert RPC program numbers into port numbers. When normal RPC expects one answer, the broadcast RPC expects many answers from each responding machine. A major issue with broadcast RPC is that when there is a version mismatch between the broadcaster and a remote service, the broadcast RPC never detects this error. Also services need to first register with the port mapper to be accessible using the broadcast RPC mechanism. Broadcast requests are limited in s