HTTP is the Internet protocol specifically designed for use with the World Wide Web, and thus will be the most common scheme you are likely to use. Its syntax is:
http://<host>:<port>/<path>?<searchpart>
FTP is a well-used means for transmitting files over the Internet. While there are many advantages to using HTTP instead, many systems don't offer full support of HTTP and clients are not as well developed as they are for FTP. Thus, many times files are distributed via FTP. Its syntax is:
ftp://<user>:<password>@<host>:<port>/<cwd1>/<cwd2>/.../<cwdN>/<name>;type=<typecode>
The Gopher protocol syntax is very similar to FTP and HTTP:
gopher://<host>:<port>/<gopher-path>
The Mailto URL scheme is different from the previous three schemes, and it does not identify a file available over the Internet, but rather the email address of someone that can be reached via the Internet. The syntax is:
mailto:<account@site>
The News URL scheme allows for the referencing of Usenet newsgroups or specific articles. The syntax is either of the following:
news:<newsgroup-name>
news:<message-id>
The Telnet URL designates an interactive session to a remote host on the Internet via the Telnet protocol. Its syntax is:
telnet://<user>:<password>@<host>:<port>/
The WAIS URL refers to WAIS databases, searches, or documents on a WAIS database. The WAIS URL scheme has one of the three following forms:
wais://<host>:>port>/<database>
wais://<host>:<port>/<database>?<search>
wais://<host>:<port>/<database>/<wtype>/<wpath>
The File URL scheme indicates a file which can be obtained by the client machine. In many sources, this scheme is confused with the FTP scheme. FTP refers to a specific protocol for file transmission, and while the File URL leaves the retrieval method up to the client, which in some circumstances, might be via the FTP protocol. When the file is intended to be obtained via FTP, I recommend designating that URL scheme. The syntax for the File scheme is:
file://<host>/<path>
The NNTP URL scheme is an alternative method to the News scheme for referencing Usenet articles and newsgroups. It has the syntax of:
nntp://<host>:<port>/<newsgroup-name>/<article-number>