"srbMaster" is the frontend server.
The srbMaster listens on the port defined in srb.h or specified in srbPort environment variable (often set in the runsrb script). By default, srb.h has DefaultPort "5544" but this can be changed via the configure --enable-srbport=value option. Regardless of the DefaultPort value, the srbMaster will listen on the port specified in the srbPort environment variable value if it is defined. You can edit the runsrb script to change this.
The srbMaster will then spawn srbServers or each client connection.