XMPP

What is XMPP?
- XMPP is communication protocol for message-oriented middleware based on XML.
Originally called Jabber, developed for instant messaging, presence info and contact list maintenance.
XMPP specs published in RFC 6120/21/22.

• RFC 6120: XMPP Core
• RFC 6121: XMPP IM
• RFC 6122: XMPP Address Format

Strengths:

• Mature, Open Standards based technology
• Secure (SASL and TLS)
• Extensible – Several extensions exist today (http://xmpp.org/xmpp-protocols/xmpp-extensions/) 

Weaknesses:

• Binary data transfer (e.g. file transfer) is inefficient (as it requires converting to Base64 encoded form).

Core includes:

• XML streaming layer
• Security: SASL and TLS
• Presence: Built-in information about network availability
• Rosters: Presence-enabled contact lists

XMPP defines 2 fundamental terms with respect to messaging:

• Stream – Open XML envelope sent before more XML elements are exchanged between two entities.
• Stanza – XML elements exchanged between 2 entities. 3 types:
• Presence
• Message
• IQ – information or query

Client sends:

xml version="1.0"?>

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

Server acknowledges by sending:

"?>

 <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 ...

Client sends message:

xml:lang="en"> Art thou not Romeo, and a Montague?

Server forwards message to client:

xml:lang="en"> Neither, fair saint, if either thee dislike.

Client closes its stream/session:

</stream:stream>

Server closes its session:

</stream:stream>

Message – to/from = Jabber IDs. 
Wherefore art thou, Romeo?
IQ – Info/Query. 

• Get/Set
• Result
• Error
• Roster - Rosters are stored on the server so that the XMPP client may retrieve the same each time the user logs in. Rosters are a type of IQ Stanza. Example showing IQ message to request for roster.

Presence – the presence info of a user is broadcasted from server to all users in roster list of that user. This works using the PubSub messaging.

Bi-directional streams Over Synchronous HTTP (BOSH)

• It is a long-lived 2 way communication over HTTP.
• Significantly more bandwidth efficient over http (compared to other technologies – such as AJAX)
• Applications requiring both “push” and “pull” communications
• http://xmpp.org/extensions/xep-0124.html
• Avoids http polling for more efficiency and low latency

PubSub

• Each user is assigned a unique Jabber ID. 
• XMPP server manages the messages published to a certain node (topic) and delivers the messages to all subscribers for that node.
• Messages may contain payload.
• Messages may be persistent.

XMPP Libraries for Application Programming

• Smack API – Java API for XMPP clients.
• Can be used to:
• Connect to the XMPP server with user’s JID
• Get the user’s roster from XMPP server
• Sending and receiving different type of Stanzas (IQ, Message and Presence).
• Publish messages to nodes 
• Subscribe to nodes of interest.
• File transfer/Group chat support also available.
• http://www.igniterealtime.org/projects/smack/index.jsp 

Network Management over XMPP

• Arista’s CloudVision framework Multi-Switch CLI extension uses XMPP to provide a shared message bus for managing and configuring switches. This is based on the idea from Internet of Things extension for XMPP (http://xmpp.org/extensions/xep-0324.html). 
• Arista Switches run an XMPP client and respond to CLI commands. 
• User can use any XMPP client (like iChat) on phone or PC to execute CLI on switches.
• A single login to XMPP server gives secure access to all switches.
• Switches can participate in group chats – meaning CLI can be executed on all participating switches in batch.
• A Switch can be in more than one chat room at the same time. Command executed in a given chat room, is executed on all participating switches in that chat room.
• Arista uses ejabberd XMPP server (included with fedora distro).
• Arista uses SleekXMPP client.
• If 2 switches are connected via XMPP, you can run CLI commands on switch A directly from switch B using xmpp send CLI command.

XMPP with Primefaces

• Primefaces uses Atmosphere framework for implementing server push (PrimePush) - http://blog.primefaces.org/?p=2053.
• Atmosphere comes with a plug-in for BOSH/XMPP (https://github.com/Atmosphere/atmosphere/wiki/Atmosphere-PlugIns-and-Extensions#xmpp)

References

• Fun with XMPP and Google Talk - http://www.adarshr.com/papers/xmpp
• Smack API - http://www.igniterealtime.org/projects/smack/index.jsp
• XMPP Technology overview - http://xmpp.org/about-xmpp/technology-overview/
• Arista’s Network Management over XMPP - https://eos.aristanetworks.com/2011/08/management-over-xmpp/