Recommended
Socket 
Python https://docs.python.org/2/howto/sockets.html
Java https://www.geeksforgeeks.org/socket-programming-in-java/
XML https://www.w3schools.com/xml/default.asp
XML-RPC
Java https://www.tutorialspoint.com/xml-rpc/index.htm
Python2 https://docs.python.org/2/library/xmlrpclib.html
Python3 https://docs.python.org/3/library/xmlrpc.client.html
SOAP https://www.w3schools.com/xml/xml_soap.asp
Python library https://python-zeep.readthedocs.io/en/master/

Optional
Cachin book Ch2
Protocol Buffer https://developers.google.com/protocol-buffers/docs/overview
Thrift https://www.scribd.com/presentation/95866167/Thrift-Protobuf