Calling Search Spaces and Partitions

Since I started this blog today I might as well get to work at publishing something relevant to the blog.  Just last week I was showing a technical architect / Pre-sales guy in our company a demo lab we had designed for an upcoming event this week in Austin, TX.  I was basically giving him the low down on all the features we installed and have functional such as:

1. Basic VoIP calling
2. Hold/resume, transfers
3. Video calls
4. Jabber IM and Presence with both standard dialing and SIP URI dialing 
5. Unity Connection
6. Cisco Prime Collaboration Provisioning
7. Cisco Prime Collaboration Assurance

The list just goes on from there so you can get an idea of what we were setting up.  His role in the company isn't system engineering but knowing some of that information can go a long way in getting a customer through the door.  The more you know up front, the more warm and fuzzies the customer will get.

I was going through showing him how to setup a Jabber device for Android on CUCM 10.5.  While I was going through the initial Cisco Jabber for Android Dual mode setting with him, I started rambling off into line settings and everything else.  Why would he want to know any of this?  Well, from my perspective, if you know the inner workings well enough, you can better sell a product.  I had started on Calling Search Spaces and Partitions and was going to breeze past it but decided to get a little in depth on him.

From my perspective, learning CSS's (Calling Search Spaces) and partitions was at first such a ridiculously hard concept that I had nearly given up on voice.  After all, CSS's are a huge design portion of your UC environment.  I would almost say, this is where you start since you need to know what the customers dialing needs are.  I told him some people read a book and learn about CSS's and others watch videos but they all share one thing on common, they talk about CSS's as a lock and key system, which to me, can be confusing.  I broke it down in a better manner, at least I thought so.

I began to tell him think of partitions as labels or names.  That is all they are, labels or names.  The do nothing other than slap something on a device, line, pattern, etc.  Below is an image of a line with a partition and CSS.  I hope it's big enough, if it isn't I'll attempt to resize it better.

Anyways, if partitions are simply labels what do CSS's do?  Well, I told him think of this as a sort of musical chairs only your name gets called out and if you aren't on the list you are hosed when the music stops.  Think of these calling search spaces as boxes with those labels or names in them (remember the technical term is partition!).  So if these boxes / calling search spaces contain those names/labels aka Partitions what does that mean?  Basically, if I call your name and your name is in the box then I can talk to you and you can keep dancing around the musical circle of chairs.  If your name isn't in that box or CSS, you are out of the game I can't talk to you, just go home son.

If that analogy was to nerdy, childish, or easy then let me explain it another way.  If your line is assigned a partition, it gets a name.  If your buddies line gets assigned a partition he gets a name too.  So lets just say this:

Your Line - Johnny Boy
You Buddies Line - Rick James

So at this point your buddies line and your line have names, lets assign them a calling search space, or box.  Keep in mind that this box/CSS contains the partitions or "names/labels" Johnny Boy and Rick James.  These were assigned to the respective lines above.

Your Line CSS - "Johnny and Rick"
Your Buddies Line CSS - "Johnny and Rick"

Since both you and your buddy have the same box this makes life a bit easier.  He calls you and the phone rings, you pick up and he says "I'm RICK JAMES!!!!"  Why did this happen?  Well inside his box he had two names/partitions:

1. Johnny Boy
2. Rick James

Since your line was assigned a name or label or partition (whatever you want to call it!) and was in that box / calling search space his line was given, he could call you and continue to dance around the chairs.  Now lets flip the scenario.

Your Line: Johnny Boy

Your Buddies Line: Rick James

Your Line CSS: "Johnny and Rick"

Your Buddies Line CSS: "Joe Dirt and Elvis"

In this scenario, you keep the same names / partitions so nothing from that perspective changes.  The CSS's however have changed.  You have a CSS / box with "Johnny and Rick" that contain the names/partitions of Johnny Boy and Rick Games.  If you place a call to Rick James, your call will proceed because you have Rick James inside your CSS / box.  

Let's look at Rick's side of things.  He has a CSS / box that contains the partitions / names Joe Dirt and Elvis.  Rick James tries to call you but gets a re-order tone.  WHAT HAPPENED!!!!  Well, Rick had a box with two partitions / names that didn't include your's (Johnny Boy).  Since he didn't have your name in that CSS you had to go home and couldn't continue to play musical chairs.

I hope this has brought a bit of a light to this topic.  Basically, the CSS is what defines who you can call since it has a ordered list of partitions from top to bottom.  If your CSS does not contain the called numbers partition/name then you will not be able to complete the call.  The only exception not this rule is if the called party does not have a partition assigned at all but that is another discussion for another day!  There is much more to CSS's and partitions that I can cover in another blog.  I just wanted to get this portion out which I consider the very basics.  I hope this helped and please leave comments.