Zones, Zones, Everywhere a Zone

There are many zones in Cisco TelePresence products; so many, in fact, that there is a lot of confusion about the different zones and their uses. This post should help clarify the many zones and their uses within Cisco TelePresence products.

The Concept of Zones

The concept of zones came from the well-established protocol, H.323 RAS, which stands for Registration Admission and Status (RAS) and is used with H.323 Gatekeepers. Gatekeepers are used in Voice over IP (VoIP) networks to resolve phone number (E.164) to IP address. This phone number to IP address mapping is one of the required roles of a Gatekeeper. Another required role of the Gatekeeper is Call Admission Control (CAC). CAC monitors the number of active calls for all devices in a local zone and when the configured bandwidth is maxed, the CAC will deny all additional call requests until enough active calls drop off, and there is sufficient bandwidth available for another call.

H.323 Gatekeepers only have two zones, “local” zones and “remote” zones. Local zones are used by Gatekeepers to indicate the Call Admission Control (CAC) and phone number (E.164) resolution processing would be done by itself, the “local” gatekeeper. Remote zones indicate the CAC and E164 resolution processing for a particular call would be done by a “remote” device, and we would need to ask the remote device for the CAC and E.164 processing results, before we could route the call.

Cisco’s TelePresence Video Communication Server (VCS) uses the same H.323 RAS zones concept and adds additional capabilities to better suit the user’s needs.

Cisco TelePresence VCS

The VCS supports H.323 and all its features (local and remote zones) and adds some additional features called Subzones. These subzones perform the same functions as H.323 “local” zones but allow us to have several “local” zones (now called subzones) that still fall under the control of the original “local” zone. By adding subzones, we have a more granular CAC and phone number resolution in the local zone. This is a new feature in H.323. Let’s look at the two basic functions of these subzones: phone number (E.164) resolution and CAC.

Phone Number Resolution

Phone number (E.164) resolution is handled by registrations. By allowing a device to register to a gatekeeper, the gatekeeper is then aware of the device’s phone number and its IP address, the two things required to perform the phone number resolution. Thus, I can call a phone number or an IP address, and the VCS can resolve into the IP address.

Call Admission Control (CAC)

CAC is done by three parameters defined within each subzone. They are called Within, In&Out, and Total. All three of these parameters have maximum limits of bandwidth allowed relative to its particular subzone.

Within: Defines the maximum allowed bandwidth of all calls that stay contained within the subzone. If there are two devices registered to the same subzone, a call between those same two devices would be classified as within.
In&Out: Defines the maximum allowed bandwidth of all calls that have an endpoint in this subzone and another party that resides in different zone or subzone.
Total: Defines the maximum allowed bandwidth of all calls both within and in&out.

Zones in Action

Now let’s put this all together to see how it works. Let’s say we have a company, and the corporate office is in San Jose CA, with a branch office in Portland OR and another in Houston, TX.

IP Addressing

A feature of subzones is the ability to control what endpoints are registered to what subzones using rules. For example, let’s use an IP address to dictate where a device registers. This use of IP addresses is straight forward enough, but you could also use domain names if you prefer. You can also create filters that identify what is allowed or what is denied. You have the flexibility to choose whatever works best for your situation.

CAC Capabilities

Next we will want to consider the CAC capabilities of the subzones. There are three parameters to work with: Within, In&Out, and Total.

Within Parameter

The Within parameter defines the maximum bandwidth of all calls originating and terminating “within” this subzone. For example; Endpoint 1 can call Endpoint 2 as long as the bandwidth stays below 3Mb/sec. Endpoint 3 can also join in the same call with Endpoint 1 and Endpoint 2 as long as all the aggregate bandwidth of all three endpoints does not exceed 3Mb/sec.

In&Out Parameter

The In&Out parameter defines the maximum amount of bandwidth that originates inside a particular subzone and terminates in a different zone or subzone. For this particular call, the VCS system verifies that this call does not exceed the In&Out limit set in the originating Portland Subzone, and then it would also verify that this call would not exceed the In&Out bandwidth limit of the terminating San Jose subzone as well. If this call does not exceed either subzone In&Out bandwidth limit, then the call is allowed.

Total Parameter

The Total parameter looks at the big picture of a subzone; the total bandwidth is a maximum amount allowed of both Within and In&Out parameters combined. These parameters are the three CAC mechanisms used to limit the maximum amount of bandwidth of subzones and can be very useful to prevent oversubscribing on the LANs and WANs in our corporate networks.

Reproduces from Global Knowledge White Paper: Cisco Telepresence Zones

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