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Presence: SIMPLE versus XMPP

SIMPLE and XMPP are the two main presence-associated standards. Learn about these standards and how to leverage them to your advantage.

Two main camps have evolved around presence standards. On one hand, the wildly popular free social chat applications from companies like Jabber and Google have been driving the use of XMPP (Extensible Messaging and Presence Protocol). On the other, the major VoIP solution providers have been focusing on SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions). The mobile operators also appear to be moving toward IMPS (Instant Messaging and Presence Service).

The major office productivity providers have thus far been focusing on their own particular flavors, and while they are not necessarily standards compliant, they are likely to play a significant role in future interoperability efforts. Microsoft has incorporated a SIMPLE-like protocol in Office Communication Server (OCS), while IBM has developed its own version of presence that is built into IBM Lotus Sametime.

"The beauty about standards is that there are so many to choose from," said Brent Kelly, senior analyst and partner at Wainhouse Research. "A number of vendors and open source groups are building gateways to allow federation. IBM has built one gateway, and Microsoft another, but neither one talks to [the] other directly."

For example, there is a Sametime gateway that allows you to share presence and IM with Yahoo, AOL, Google and XMPP, but it cannot share it with Microsoft users. Microsoft has federation capability with MSN, AOL and Yahoo, but not with Google. To help companies integrate presence into other areas, Microsoft also has the Open Interoperability Program to provide support for PBX manufacturers and gateways to link seamlessly with OCS.

The SIMPLE working group was formed by the IETF in 2001 to develop a suite of standards for presence and IM using SIP. A number of rich presence extensions to SIMPLE are being developed for privacy control, past and future presence, and watcher information. The protocol has been adopted by some of the largest IP PBX manufacturers, including Avaya, Nortel, Siemens and Cisco.

Some industry participants believe, however, that the protocol has significant challenges associated with scaling and complexity, stemming from the way it was developed. Jason Fischl, CTO of Counterpath, explained: "The IETF did not do a great job on the definition of SIMPLE. The issue was how they separated the provision of presence authorization versus provisioning the IM connection. The IM is done through SIP, and the authentication is done through Xcap. The problem was that lots of vendors have been confused about how to implement SIMPLE. This allowed XMPP to have a bit of an advantage."

The XML-based XMPP is widely used in the IM community and is part of Jabber, an open source and commercial client, as well as Google Talk. XMPP supporters argue that its roots in XML make it easier to write extensions for activities like remote client control and integration with location services.

Will Sheward, VP of marketing at Isode, said there are three factors in XMPP's favor:

  • It scales better.
  • Its XML base makes it easier to integrate into a wide range of applications.
  • All messages in XMPP pass via a server, whereas SIMPLE is peer-to-peer, so anyone worried about compliance issues who needs a permanent record of conversations is going to feel much more comfortable with an XMPP solution.

Little standards work has been done to extend XMPP into the voice arena, however. There is one XMPP extension, Jingle, for doing phone calls, but the only real deployment is with Google Talk, and the standards are still being worked out. In the meantime, XMPP users have to rely on gateways to interoperate with VoIP equipment.

Presence mobility (IMPS)
The mobile phone vendors Nokia, Motorola and Ericsson have developed their own flavor of presence called mobile Instant Messaging and Presence Services (IMPS). This group formed the Open Mobile Alliance, which later released an XML version of this protocol.

Bridging SIMPLE and XMPP 
"This standards war stuff is overrated," said Peter Saint-Andre, executive director of the XMPP Standards Foundation. "There is presence information that comes from different sources, and intelligent presence engines will track all of it. Typically, if you have a smart presence engine, whether it comes from Avaya or someone else, it will accept whatever format comes in. The standards holy war is a thing of the past. Line-of-business people simply choose whatever product suits their organization."

Companies like Counterpath are focusing on finding the best way of bridging the worlds. "We recommend doing your calls using SIP and IM and presence using XMPP," Fischl explained. "Then the trick becomes: How do you correlate the two together? If I am in an IM conversation and I want to upgrade the connection to audio or video, there are no standards-based protocol mechanisms for associating those together."

In practice, companies like Counterpath are finding non-standard ways to combine them. "We have tactical solutions to that problem, but it needs to get solved at a standards level," Fischl said. "It can work between our clients, but if we want it to work with other clients, we have to do more kludging."

There are substantial advantages to having VoIP and IP presence protocols working together. For example, Counterpath has been using an internal VoIP client for about three years with SIMPLE and recently moved to an all-XMPP implementation.

"One of the nice things we got when we moved was that we could prepopulate the buddy list with the corporate directory," Fischl said. "I don't have to add everyone on my team manually, as I have them by default." It is also helpful that when calls are placed over Bria, the company's internal VoIP client, presence information is available across the company. "I don't have to manually change the status from available to busy," he said, "and when I hang up, it will automatically revert my presence status to available."

For more information: View this article on standardizing on unified communications standards.

About the author: George Lawton is a journalist based near San Francisco, California. Over the last fifteen years he has written over two thousand stories for publications about computers, communications, knowledge management, business, health, and other areas which interest him.

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