[PPT] - Corso di Applicazioni Telematiche A.A. 2009-10 Prof. Simon Pietro PowerPoint Presentation

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XMPP Extensible Messaging and Presence Protocol

Corso di Applicazioni Telematiche

A.A. 2009-10

Prof. Simon Pietro Romano

Università degli Studi di Napoli Federico II Facoltà di Ingegneria

SLIDE 2

XMPP: eXtensible Messaging and Presence Protocol

Formerly known as Jabber
Jeremie Miller began the project in 1998
first release in May 2000
The project's main product was jabberd
XML-based
Extensible to other features
Open
open standard
open source implementations
open system

SLIDE 3

XMPP: eXtensible Messaging and Presence Protocol

Standardization
IETF XMPP Working Group (2002)
RFC 3920: Core features
RFC 3921: Instant Messaging and Presence

SLIDE 4

RFC 3920: Overview and Architecture

… is a protocol for streaming Extensible Markup

Language (XML) elements in order to exchange structured information in close to real time between any two network endpoints…

Architecture
XMPP servers
XMPP servers
Manage TCP connections
route messages
server-to-server (5269)
XMPP clients
connect to server (5222)
multiple resources simultaneously
Gateway
translates XMPP into the protocol used by a foreign (non-XMPP)

messaging system

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RFC 3920: Addressing Scheme

All XMPP entities are uniquely addressable
JID (Jabber Identifier)

[ node "@" ] domain [ "/" resource ]

domain identifier: FQDN / address-literal
FQDN (Fully Qualified Domain Name ): (sub-domain_1)".“(sub-

domain) domain)

address-literal: IPv4address / IPv6address
usually represents servers or gateways (REQUIRED)
node identifier
a simple string
usually represents a client (OPTIONAL)
resource identifier
usually represents a specific session, connection or object

belonging to the entity associated with a node identifier (OPTIONAL).

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JID: examples

domain

meetecho.com

node@domain

tcastaldi@meetecho.com

node@domain/resource

tcastaldi@meetecho.com/Spark tcastaldi@meetecho.com/iMeetecho

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SLIDE 7

XML example

SLIDE 8

RFC 3920: XML Stream

XML Stream
container for the exchange of XML Stanzas between

any two entities over a network

start
<stream> tag with appropriate attributes

and namespace

end
</stream> tag
end
</stream> tag
the stream enables unidirectional communication
qualified by the default namespace for the stream
jabber:client (client and server )
jabber:server (server-to-server)

SLIDE 9

Stream example

1. Client initiates stream to server

<?xml version='1.0'?> <stream:stream to='example.com' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>

2. Server responds by sending a stream tag to
2. Server responds by sending a stream tag to

client

<?xml version='1.0'?> <stream:stream from='example.com' id='someid' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>

…encryption, authentication, and resource binding…

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SLIDE 10

Encryption: use of TLS

Method for securing the stream
Transport Layer Security (TLS) protocol
"STARTTLS" extension
namespace name

– 'urn:ietf:params:xml:ns:xmpp-tls‘

3. Server sends the STARTTLS extension to client
3. Server sends the STARTTLS extension to client

<stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'> <required/> </starttls> <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'> <mechanism>DIGEST-MD5</mechanism> <mechanism>PLAIN</mechanism> </mechanisms> </stream:features>

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Use of TLS (2)

4. Client sends the STARTTLS command to server

<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>

5. Server informs client that it is allowed to proceed

<proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>

6. Client and server attempt to complete TLS

negotiation over the existing TCP connection negotiation over the existing TCP connection

7. If TLS negotiation is successful, client initiates a new

stream to server

8. Server responds by sending a stream header to client

along with any available stream features

9. Client continues with SASL negotiation

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SLIDE 12

RFC 3920: XML Stanza

XML Stanza
discrete semantic unit of structured information

that is sent over an XML stream

exists at the direct child level of the root
exists at the direct child level of the root

<stream> element

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XMPP stanzas

defined stanzas are:
<message> entity pushes information to another entity
<presence> availaibility information
<iq>

info/query request-response mechanism

qualified by the default namespace for the stream
qualified by the default namespace for the stream
Common Attributes
to, from, type, id, xml:lang

<message type='chat' from='juliet@exmpl.com' to='romeo@exmpl.net'> <body>Art thou not Romeo, and a Montague?</body> </message>

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RFC 3921: Instant Messaging and Presence

Describes extensions to and applications of the

core features XMPP that provide the basic instant messaging (IM) and presence functionality

Requirements
Requirements
Exchange messages with other users
Exchange presence information with other users
Manage subscriptions to and from other users
Manage items in a contact list (in XMPP this is

called a "roster")

Block communications to or from specific other

users

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RFC 3921: Message Syntax

Possible values of types for Message packets
chat: sent in the context of a one-to-one chat
groupchat: sent in the context of a multi-user chat
Child Elements
<subject/> contains the topic of the message
<body/> the textual content of the message
<body/> the textual content of the message
<thread/> identifier that is used for tracking a

conversation thread

<message to='romeo@ex.net' from='juliet@exm.com/balcony' type='chat' xml:lang='en'> <subject>The balcony scene!</subject> <subject xml:lang=‘it'>La scena del balcone!</subject> <body>Wherefore art thou, Romeo?</body> <body xml:lang=‘it'>Perché sei tu, Romeo?</body> </message>

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RFC 3921: Presence Syntax

Possible values of types for Presence packets
subscribe: the sender wishes to subscribe to the recipient's

presence

unavailable: signals that the entity is no longer available
probe: request for an entity's current presence
Child Elements
<show/> specifies the particular availability status
<show/> specifies the particular availability status
away, chat, dnd = "Do Not Disturb“ and xa = "eXtended Away"
<status/> a description of availability status
<priority/> the priority level of the resource [-128, +127]

<presence xml:lang='en'> <show>dnd</show> <status>Wooing Rupert</status> <priority>1</priority> </presence>

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RFC 3921: IQ Syntax

Extended namespace
defines all data contained within the child element
Possible values of types for IQ packets
get
set
result
Use case: retrieving One's Roster on Login
'jabber:iq:roster' namespace
'jabber:iq:roster' namespace

<iq from='juliet@example.com/balcony' type='get' id='roster_1'> <query xmlns='jabber:iq:roster'/> </iq> <iq to='juliet@example.com/balcony' type='result' id='roster_1'> <query xmlns='jabber:iq:roster'> <item jid='romeo@example.net' name='Romeo‘ subscription='both'> <group>Friends</group> </item> </query> </iq>

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XEP: XMPP Extension Protocol

Is a pure XMPP signalling protocol
Designed to interwork with SIP
Initiating and managing media sessions between two XMPP

entities

negotiation occurs over the XMPP "channel"
media is exchanged outside the XMPP using RTP, UDP….
How it works: File transfer

!""#$%

How it works: File transfer

% &

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XEP: XMPP Extension Protocol

Is a pure XMPP signalling protocol
Designed to interwork with SIP
Initiating and managing media sessions between two XMPP

entities

negotiation occurs over the XMPP "channel"
media is exchanged outside the XMPP using RTP, UDP….
How it works: File transfer

!""#$%

<iq from=‘romeo@shakespeare.lit/castle' id='jingle1' to=‘juliet@shakespeare.lit/castle' type='set'> <jingle xmlns='urn:xmpp:tmp:jingle' action='session-initiate' initiator=‘romeo@shakespeare.lit/castle' sid='851ba2'> <content creator='initiator' name='a-file-offer'> <description xmlns='urn:xmpp:tmp:jingle:apps:file-transfer'> <offer> <file xmlns='http://jabber.org/protocol/si/profile/file-

How it works: File transfer

% &

<offer>

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XEP: XMPP Extension Protocol

Is a pure XMPP signalling protocol
Designed to interwork with SIP
Initiating and managing media sessions between two XMPP

entities

negotiation occurs over the XMPP "channel"
media is exchanged outside the XMPP using RTP, UDP….
How it works: File transfer

!""#$%

How it works: File transfer

% &

<iq from=‘juliet@shakespeare.lit/castle'

id='jingle1' to=‘romeo@shakespeare.lit/castle' type='result'/>

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XEP-0167: Jingle Audio via RTP

This document specifies an application format for

negotiating Jingle audio sessions, where the media is exchanged over the Realtime Transport Protocol

Mapping to Session Description Protocol
m=<media> <port> <transport> <fmt list>
In the context of Jingle audio sessions
<media> = audio

<port> is the preferred port

<port> is the preferred port
<transport> is whatever profile is negotiated
<fmt list> is the payload-type ID
static payload-type:
dynamic payload-type

m=audio 9999 RTP/AVP 96 a=rtpmap:96 speex/16000 <payload-type id='96' name='speex' clockrate='16000' ptime='40'> <parameter name='vbr' value='on'/> <parameter name='cng' value='on'/> </payload-type> <payload-type id="13" name="CN"/> m=audio 9999 RTP/AVP 13

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Strengths

Decentralization
anyone can run his own XMPP server
there is no central master server
Open standards
No royalties are required to implement support of these

specifications

History
History
Multiple implementations of the XMPP standards exist for

clients, servers, components, and code libraries

Security
XMPP servers may be isolated from the public Jabber

network (e.g., on a company intranet)

Flexibility
Custom functionality can be built on top of XMPP

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Weaknesses

Presence data overhead
With typically over 70% of XMPP inter-server traffic

being presence data, and close to 60% of it being redundantly transmitted

No binary data
The way XMPP is encoded as a single long XML
The way XMPP is encoded as a single long XML

document makes it impossible to deliver unmodified binary data

File transfers are therefore arranged to happen using

external protocols like HTTP

If unavoidable, XMPP also provides in-band file

transfers by encoding all data using base64

Other binary data like encrypted conversations or

graphic icons are embedded using the same method.

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Demo scenario

XMPP Client

XMPP

Client

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XMPP Server

XMPP

Server

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Open source XMPP servers…

chime (Java) http://www.codecobra.com/chime/
DJabberd (Perl) http://danga.com/djabberd/
ejabberd (Erlang) Home page and Community Site
jabberd14 (C) http://jabberd.org/
jabberd2 (C) http://jabberd2.xiaoka.com/
Openfire (Wildfire) (Java)

http://www.igniterealtime.org/projects/openfire/ http://www.igniterealtime.org/projects/openfire/

OpenIM (Java) http://www.open-im.net/
Pretzel (Python) http://code.google.com/p/pretzel/
psyced (LPC) http://www.psyced.org/
Tigase (Java) http://www.tigase.org/
WPJabber (C) http://spik.wp.pl/jabber.html
xmppd.py (Python) http://xmpppy.sourceforge.net/

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… and free clients

Bombus J2ME (MIDP2.0)/WinCE
Bombusmod J2ME (MIDP2.0)
Coccinella Cross-platform Tcl/Tk
Exodus Windows
Gabber Linux/Unix GTK+
Gajim Cross-platform GTK+
GOIM Cross-platform Eclipse Rich Client Platform
Spark Cross-platform Java
Spark Cross-platform Java
Gossip Linux/Unix GTK+
Jabbim Cross-platform PyQt
Jabbin Cross-platform Qt
MCabber Cross-platform (ncurses)
Mobber J2ME (MIDP1.0)
MOO-XMPP MOO
Psi Cross-platform Qt
Tapioca
Tkabber Cross-platform Tcl/Tk
Wija Java

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References

XMPP Working Group
Charter
http://www.ietf.org/html.charters/OLD/xmpp-charter.html
RFC 3920 XMPP: Core
http://www.ietf.org/rfc/rfc3920.txt
RFC 3921 XMPP: Instant Messaging and Presence
RFC 3921 XMPP: Instant Messaging and Presence
http://www.ietf.org/rfc/rfc3921.txt
XEP-0166: Jingle
http://www.xmpp.org/extensions/xep-0166.html

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Domande?

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