Various protocols are mentioned throughout this chapter, as well as in Chapter 16 and Chapter 17. While going into detail about the various protocols is beyond the scope of this book and also not necessary for an understanding of how web services work, some understanding is useful.
A protocol is a set of rules that describe the transmission and receipt of data between two or more computing devices. For example, TCP/IP (Transmission Control Protocol/Internet Protocol) governs the low-level transport of packets of data on the Internet.
Layered on top of TCP/IP is HTTP (the HyperText Transfer Protocol), which is used to enable servers and browsers on the Web to communicate. It is primarily used to establish connections between servers and browsers and to transmit HTML to the client browser.
The client sends an HTTP request to the server, which then processes the request. The server typically returns HTML pages to be rendered by the client browser, although in the case of web services, the server may instead return a SOAP message containing the returned data of the web service method call.
HTTP requests pass name/value pairs from the requesting browser to a server. The request can be either of two types: HTTP-GET, or HTTP-POST.
In GET requests, the name/value pairs are appended directly to the URL. The data is uuencoded (which guarantees that only legal ASCII characters are passed over the wire), then appended to the URL, separated from the URL by ...