Overview of services

An overview of common Internet protocols and services

It is a pre-requisite for this course that you have some experience with using Internet services as an ordinary user. The course is not on how to use the services, it is about the protocols used to provide them.

Last revision: 10 August, 2002 by Jacob Palme.

Protocol name Main usage Clients Servers

DNS

Translating domain names to numerical host addresses.

Finding the e-mail server handling mail to e-mail addresses with certain domain names.

All kinds of clients and name servers. (DNS) name servers.

HTTP (and HTML, GIF, JPEG as formats) Downloading web pages in the WWW. Can also be used to send in filled in forms and to send in files. Also used for many specialized protocols based on HTTP. Web browsers. HTTP servers.

SMTP (and RFC822 and MIME as formats) Sending and forwarding of e-mail to and between MTAs (Message Transfer Agents). Mail clients and SMTP servers. SMTP servers.

(SMIME and PGP) Adding security features to e-mail. Mail clients. SMTP servers, certificate servers.

POP and IMAP Downloading of incoming e-mail to the mail clients for their recipients. Mail clients. POP or IMAP servers.

NNTP Submission, downloading and forwarding of Usenet News articles. News clients and news servers. News servers.

FTP Anonymous downloading of files, non-anonymous transfer of files between directories protected by log in. FTP clients, Web browsers. FTP servers.

Gopher An old, nowadays not much used protocols, which can be seen as a limited subset of HTTP. Web browsers, Gopher clients. Gopher servers.

PICS Protection of children from material on the net regarded as unsuitable for them, and other kinds of controlled censorship. All kinds of clients. PICS servers, PICS labels on, for example, HTML pages.

LDAP Searching in directories. LDAP clients, often built into e-mail clients. LDAP servers.

WebDav Uploading and downloading of web pages edited by a group of people. WebDav clients. WebDav-compliant HTTP servers.

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Protocol name	Main usage	Clients	Servers
DNS	Translating domain names to numerical host addresses. Finding the e-mail server handling mail to e-mail addresses with certain domain names.	All kinds of clients and name servers.	(DNS) name servers.
HTTP (and HTML, GIF, JPEG as formats)	Downloading web pages in the WWW. Can also be used to send in filled in forms and to send in files. Also used for many specialized protocols based on HTTP.	Web browsers.	HTTP servers.
SMTP (and RFC822 and MIME as formats)	Sending and forwarding of e-mail to and between MTAs (Message Transfer Agents).	Mail clients and SMTP servers.	SMTP servers.
(SMIME and PGP)	Adding security features to e-mail.	Mail clients.	SMTP servers, certificate servers.
POP and IMAP	Downloading of incoming e-mail to the mail clients for their recipients.	Mail clients.	POP or IMAP servers.
NNTP	Submission, downloading and forwarding of Usenet News articles.	News clients and news servers.	News servers.
FTP	Anonymous downloading of files, non-anonymous transfer of files between directories protected by log in.	FTP clients, Web browsers.	FTP servers.
Gopher	An old, nowadays not much used protocols, which can be seen as a limited subset of HTTP.	Web browsers, Gopher clients.	Gopher servers.
PICS	Protection of children from material on the net regarded as unsuitable for them, and other kinds of controlled censorship.	All kinds of clients.	PICS servers, PICS labels on, for example, HTML pages.
LDAP	Searching in directories.	LDAP clients, often built into e-mail clients.	LDAP servers.
WebDav	Uploading and downloading of web pages edited by a group of people.	WebDav clients.	WebDav-compliant HTTP servers.