In the previous post, I used the term presence, and while I'm sure most readers are familiar with the word, and possibly the application in a Unified Communications environment, I wanted to explore the term here in more depth. The concept of presence is generally simple, with the basis being the ability to see a person's or resource's status and availability at any time.
The benefit is being able to use that information to make a decision. A simple example would be if I wanted to call a colleague named Jim. With presence, I could look at my IP phone or messaging client on my computer depending on the setup and technology used and see if Jim is available before even dialing a number. This way, I know if I should call now, or wait until he is available later.
With the first iterations of presence, the concept was limited to simply checking if a user’s line was busy and displaying the status with a LED indicator on a shared or "watcher" line on your phone. This is still commonly used, now with text and images on some phones, in addition to more advanced features such as integration with a messaging client on your computer or smartphone and email program. As the features have become more advanced, so have the benefits. I can now see on a presence client that Jim is in a meeting, then check his availability, and find out that he will be free in 30 minutes. While waiting, I can send an instant message to his computer letting him know what I will call, tell him why, about and if I wanted to, could send a meeting invite.
For anyone using a computer and an instant messaging client, the concepts have been around for awhile. Being able to see if someone is logged in on your buddy list, and then seeing updated status symbols such as busy or typing are also examples of presence. While progress has been made with what information we can see, it's still a simple, but very useful concept. In the IP Voice and Video world, it has quickly caught on and every major vendor, including Cisco, Tandberg, Microsoft, Polycom, Avaya, Shoretel, Skype, etc have implementations for presence capabilities and many even interface with each other.
The only piece of the picture that can be complicated is the terminology. The breakdown of the common terms is below, and should help when you're trying to setup a presence configuration (which we will cover in a upcoming post with a Cisco CUCM and CUPS integration walkthrough).
Watcher: The person or device that is watching or monitoring the remote person/device. (In the example above, I was the watcher, monitoring Jim's status).
Presentity: A person/device that is being monitored or watched. (In this example, Jim).
Subscribe: A watcher can subscribe/be a subscriber of a presentity to monitor them. (I was subscribed to Jim's status)
Publish: A presentity can publish or push their information to a presence server. (Jim's status was published, or pushed to a presence server).
State: The status of a presentity (Available, Away, Busy, etc) (Often referred to as status).
URI: Uniform Resource Identifier - Most presence systems use SIP (Session Initiation Protocol) for the basis of their communication. SIP URIs are an address and are used across many platforms including web addressing, and they identify the various endpoints. An example of an URI - email@example.com:5060
Now that you've seen some of the terms and understand the concept, you can see that it really is a basic idea, but one that has a lot of purpose.
Josh Finke, CCIE No. 25707, is the Engineering and Services Manager for Iron Bow Technologies, a Cisco Gold and Master Unified Communications Partner. Josh was previously a lead instructor and Director Of Operations for Internetwork Expert, a leading CCIE training company.
Josh has multiple certifications, including the Cisco Voice CCIE, CCNP, CCDP, CCNA, CCDA, and Cisco Meeting Place Specialist. Josh specializes in Cisco UC, routing & switching, and network design. Josh started working with Cisco networking technologies in 2000, and later became one of the youngest Voice CCIE's in the world. He lives with his wife in Seattle, Washington.