network protocols handbook.pdf

320Protocols GuideOther ProtocolsProtocol NameMicrosoft SOAP: Simple ObjectAccess ProtocolProtocol DescriptionThe Simple Object Access Protocol (SOAP) is a lightweight andsimple XML-based protocol that is designed to exchange structuredand typed information on the Web. SOAP can be used incombination with a variety of existing Internet protocols and formatsincluding Hypertext Transfer Protocol (HTTP), Simple MailTransfer Protocol (SMTP), and Multipurpose Internet Mail Extensions(MIME), and can support a wide range of applicationsfrom messaging systems to remote procedure calls (RPCs).SOAP consists of three parts:• The SOAP envelope construct defines an overall frameworkfor expressing what is in a message; who shoulddeal with it and whether it is optional or mandatory.• The SOAP encoding rules define a serialization mechanismthat can be used to exchange instances of application-defineddata types.• The SOAP RPC representation defines a conventionthat can be used to represent remote procedure callsand responses.SOAP messages are basically one-way transmissions from asender to a receiver, but SOAP messages are often combinedto implement patterns such as request/response. All SOAPmessages are encoded using XML. A SOAP message is anXML document that consists of a mandatory SOAP envelope,an optional SOAP header and a mandatory SOAP body.Binding SOAP to HTTP provides the advantage of being ableto use the formalism and decentralized flexibility of SOAP withthe rich feature set of HTTP. Carrying SOAP in HTTP does notmean that SOAP overrides existing semantics of HTTP butrather that the semantics of SOAP over HTTP map naturallyto HTTP semantics. In the case of using HTTP as the protocolbinding, an RPC call maps naturally to an HTTP request andan RPC response maps to an HTTP response. However, usingSOAP for RPC is not limited to the HTTP protocol binding.Protocol StructureSOAP message format:SOAP header