After declaring its variables, call_server() first makes a connection with the server:
if ((s = connect_to_server(host, port)) < 0) return -1;
where s is a file descriptor (an int, initially returned by a call to socket()).
connect_to_server() is a simple function that uses sockets to create a connection. Because it doesn't use the GSS-API, it's skipped here. You can see it at connect_to_server().