XMPP

1
XMPP

• Extensible Messaging and Presence Protocol

2
Chat

• In the beginning there was instant messaging and
  chat.
• Lots of binary standards
• Unix talk, IRC, AOL Instant Messaging (AIM)
  Yahoo, MS, etc.
• The commercial implementations quickly tried to
  achieve user lock-in via proprietary protocols.
  (Aside you make money in the computer industry
  by owning standards, such as the Windows API. If
  you own the standard you can lock other
  implementors out.)

3
Better Way

• Why not do something open standards that any one
  can implement.
• Which is what XMPP is--open standard, published
  by the IETF, that uses XML to exchange
  information.
• XML allows user-readability the classic benefits
  of XML

4
Whats Handled?

• Presence who is online right now? Are they
  willing to talk?
• Instant Messaging real-time communications
  between two or more users
• real time roughly means that you see the
  text each time the user hits return
• Some show each character as it is typed
• Chat groups of people exchanging information in
  a chat room
• Information exchange Since XMPP uses XML, we can
  exchange information that can be expressed in XML

5
Presence Buddy List
My status--available for IMs
Buddies
Off Line buddies
6
How Does XMPP Work?
ltmessage to'romeo_at_example.net'
from'juliet_at_example.com/balcony'
type'chat'
xmllang'en'gt ltbodygtWherefore art
thou, Romeo?lt/bodygt lt/messagegt
7
XMPP Stanzas

• There are three basic stanzas or elements in
  XMPP
• message
• presence here I am. Tell all my subscribers
  about my status
• iq info/query, request/response
• In addition these elements all have five common
  attributes defined
• to JID of recipient
• from JID of sender
• id can be a unique ID assigned to each stanza
• type varies by stanza
• xmllang used to specify human language

8
XMPP
Server
Client
TCP connection between client and server.
Typically this is negotiated over SSL or TLS (a
follow-on version of SSL) so that the traffic is
encrypted and secure. XML stanzas are exchanged
across this channel
9
XMPP

• The XML is sent as an open-ended stream. A stream
  starts with ltstreamgt, then an open-ended series
  of ltpresencegt, ltmessagegt, and ltiqgt tags are sent.
• When the closing lt/streamgt tag is sent, the
  underlying TCP connection is torn down

10
XML Communications Backplane

• We can also add new XML to the existing standard
  to get new capabilities
• You should think of XMPP not as strictly chat,
  but as an XML-enabled communications backplane
• Anyone can subscribe to a server and receive XML
  messages from other users. We can use this as a
  way to do lots of things besides chat.

11
XMPP
Device
User
XMPP Communications
Device
User
12
Communications

• You can place programs or devices that listen on
  an XMPP chat room or that exchange information
  directly.
• Now there are devices or programs listening
  rather than humans
• Can use XML to exchange data objects
• You can also tie in XMPP with multimedia,
  including voice
• The jingle API (included w/ smack) allows voice

13
XMPP Basics

• You have a client that connects to and
  authenticates to a server.
• Users are uniquely identified by their JID, in
  the form username_at_fqhn.com, eg jamesbond_at_mi6.gov.u
  k

14
Multi User Chat (MUC)

• Multiuser chat is an add-on to the XMPP
  specification. It allows several users to be in a
  chat room.
• The convention is for a chat server to have the
  DNS name conference.machine.name, eg
  conference.savage.nps.edu
• The muc is identified by the jid
  roomname_at_conference.machine.name, eg
• Moves_at_conference.savage.nps.edu

15
Server-to-Server

• Notice that a client connects to a local server,
  but the JID for a chat or muc may be on another
  machine
• Example you log onto savage.nps.edu, and you
  specify that you want to chat with someone at
  smith_at_googletalk.com
• (For firewall reasons this wont work right now.)
• To do this, the server you have logged onto
  establishes a server-to-server connection to the
  machine specified in the JID

16
Server-to-Server
remote.com
Local.com
Local Chat Server
Remote Chat Server
Client Foo_at_local.com
Client Bar_at_remote.com
17
Server-to-Server

• If the user isnt on the same box that you logged
  onto, the server will contact the server the user
  is logged onto and pass the message to that
  server
• The users do not need to be logged onto the same
  machine to chat with each other

18
APIs

• What does it take to write an XMPP participant?
  It turns out, not very much.
• The Smack API from Ignite Realtime lets you get
  up and running fairly quickly.
• The examples Ill show use the Smack 3.0 API
  available at http//www.igniterealtime.org/downloa
  ds/index.jsp

19
Smack API
// Creates a new connection, using TLS if
possible. XMPPConnection connection
new XMPPConnection("savage.nps.edu") connection.c
onnect() // Login connection.login("testuser",
"foobar")
20
Smack API
MultiUserChat muc new MultiUserChat(connectio
n,
"moves_at_conference.savage.nps.edu"
) muc.join("studmuffin") for(int
idx 0 idx lt 10 idx)
muc.sendMessage("Hello world")
Thread.sleep(1000)