The most popular underlying protocol for supporting Web Service communication is HTTP. Please note we are not speaking of HTML.
HTTP is a stateless (each transaction stands on its own) protocol for managing the transfer of data. Typically the protocol that underlies HTTP is TCP. TCP handles the reliability and user identification aspects of Internet transmission. And HTTP handles the transactions, by setting standards for controlling things like message length, buffer and cache management, and security considerations. TCP thinks one block at a time. HTTP thinks one transaction at a time. A transaction consists of an inquiry
and, optionally, a response
Web Services can use HTTP for managing it's transactions, which unlike HTML, do not imply the involvement of a human being. Web Services can handle machine to machine communication. There are several protocols that perform various functions for Web Services. However Simple Open Access Protocol (SOAP) is the most significant data formatting protocol in that environment. A description of SOAP can be found here:https://www.w3.org/TR/2000/NOTE-SOAP-20000508/#_Toc478383490
As technology moves toward support for the Internet of Things (IOT) I can envision the day when a generic Home Controller will communicate with plug and play devices such as lamps or garage door openers using SOAP and the other Web Service protocols.
The BR Web Server supports the most recent HTTP protocol which is level 1.1. This includes a concept called chunking which breaks longer messages into chunks for applications such as large web pages, query responses, or file transfer. It also supports data encryption using SLL with certificates. Actually the SSL (secure) form of HTTP (called HHTPS) is mandatory with the BR Web Server. It is optional as to whether or not an application needs to support user login sessions. But HTTPS is a BR Web Server requirement with or without login support.
The IOT industry is in its infancy right now and it remains to be seen whether JSON will replace XML as the protocol underlying SOAP. I suspect it will one day because JSON is about as efficient and flexible as any text formatting protocol can get. Note that both JSON and XML are limited to text and are not useful for formatting lots of binary data values. Binary values can be converted to text using character sets such as UTF-8 but that is an inefficient way to manage the transfer of binary data.
Right now SOAP uses XML and HTML mainly uses JSON. Both use HTTP and HTTP uses TCP.
The BR Web Server supports all of this focusing mainly on the HTTP protocol. It also provides a convenient way to parse and compose JSON.