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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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XMPP server<br />

An XMPP server acts as an intelligent abstraction layer for XMPP<br />

communications. Its primary responsibilities are:<br />

► To manage connections from or sessions for other entities, in the form of XML<br />

streams to <strong>and</strong> from authorized clients, servers, <strong>and</strong> other entities<br />

► To route appropriately-addressed XML stanzas among such entities over<br />

XML streams<br />

An XML stream is a container for the exchange of XML elements between any<br />

two entities over a network <strong>and</strong> an XML stanza is a discrete semantic unit of<br />

structured information that is sent from one entity to another over an XML<br />

stream.<br />

Most XMPP-compliant servers also assume responsibility for the storage of data<br />

that is used by clients (for example, contact lists for users of XMPP-based instant<br />

messaging <strong>and</strong> presence applications). In this case, the XML data is processed<br />

directly by the server itself on behalf of the client <strong>and</strong> is not routed to another<br />

entity.<br />

XMPP client<br />

Most clients connect directly to a server over a <strong>TCP</strong> connection <strong>and</strong> use XMPP<br />

to take full advantage of the functionality provided by a server <strong>and</strong> any<br />

associated services. Multiple resources (for example, devices or locations) can<br />

connect simultaneously to a server on behalf of each authorized client, with each<br />

resource differentiated by the resource of an XMPP address (for example,<br />

versus ) as defined under<br />

addressing scheme. The recommended port for connections between a client<br />

<strong>and</strong> a server is 5222, as registered with the IANA.<br />

Non-XMPP client<br />

This client does not use XMPP <strong>and</strong> uses a different protocol.<br />

Gateway<br />

The gateway is a special-purpose, server-side service whose primary function is<br />

to translate XMPP into the protocol used by a foreign (non-XMPP) system, as<br />

well as to translate the return data back into XMPP. Examples are gateways to<br />

e-mail (refer to 15.1, “Simple Mail Transfer Protocol” on page 556), Internet Relay<br />

Chat (IRC), Short Message Service (SMS), <strong>and</strong> enterprise instant messaging<br />

services such as AIM, ICQ, MSN® Messenger, <strong>and</strong> Yahoo! Instant Messenger.<br />

Network<br />

Because each server is identified by a network address <strong>and</strong> because<br />

server-to-server communications are a straightforward extension of the<br />

Chapter 19. Presence over <strong>IP</strong> 717

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