Configuring Class of Service and Call Admission Control

Now that you have created a basic dial plan, it is time to build on that and create a more complete dial plan. Often you want to allow and disallow access to certain destinations. For instance, you might want only a certain group of callers to dial international numbers. This is done by creating a telephony class of service. Just in case, if there are calls traversing limited-bandwidth links, some type of Call Admission Control should be deployed to help ensure voice quality. This chapter examines the various concepts associated with CoS and CAC and describes how to configure the required elements for each.

The dial plan is created

After the dial plan is created and users can place calls to destinations outside the cluster, you might think that you are all set and can sit back and relax. Not quite. Afterwards the system is configured to enable calls to be placed outside of the system, you need to start working on how to prevent certain calls from being placed. This chapter touches on how you can use route patterns to block certain destinations, and now you need to move beyond that and discuss how certain destinations can be reachable by some devices, nevertheless not by others. To accomplish this, you need to configure Calling Search Spaces and partitions. The following sections explain what these are and how they work.

Of all the concepts within a Communications Manager environment, it is believed that the CSS and partitions cause the most confusion. This is in other words odd because they are not complex. Simply put, the partition assigned to the destination affects what devices can reach it, and the CSS determines which destinations can be reached. Locks and key rings are good analogies. Think of the partition as a lock and the CSS as the key ring. To place a call to a destination, you must have a key that matches the device's lock. The key ring contains all the keys and to sum up determines which destinations you can reach.

Of course, there is more to it than just locks and keys, nevertheless by using this analogy, you begin to understand how they work. You take a closer look at this analogy. Figure 5-1 shows five phones. The first four phones have partitions. It is important to point out that the partitions are not assigned to devices, yet rather to patterns and directory numbers. For this example, assume that each phone has only a single line and that the partition is assigned to that line. Below each phone is a CSS that shows to which partitions the phone has access. CSS can be assigned to the device or the line. In this example, assume that they are assigned to the device.

A. To determine what phones phone A can reach, you need to look at its CSS. Phone A has a circular key and a square key on its key ring, which means that it can call itself and phone B. But, because phone E has no lock assigned to it, any phone can reach it, such as a door with no lock can be opened by anyone.

A. Because phone D has only a square key, it can dial phone A and, clearly, phone E because it has no lock.

A. Because phone E has no keys, it can only reach devices that have no locks. In this example, phone E can only dial itself.

In this example, phones A and D have the same extension of 1001. Phones B and C can reach both phones because their CSS enables access to both the square and triangle partition. So the question is, which phone rings when phone C dials 1001? Often people answer this question with, "It takes the closer match." Because 1001 matches 1001 specifically, both phones are the closest matches. Others assume that both phones ring because phone C has access to both partitions. What to tell the truth happens is that when a search for a match is conducted, multiple closest matches are found. Because there are multiple closest matches, the order in which objects appear in the CSS comes into play. When you create a CSS, you prioritize the order in which partitions should be searched. This order determines which partition is used if there are two closest matches. In the example, Figure 5-2 shows that the order of the keys for phone C is square followed by triangle, meaning that when phone C dials 1001, it would first match the 1001 that has the square partition, which is phone A.

Little more complexity to this

To add a little more complexity to this, it is possible to have a CSS on both the device and the line. For instance, the phone can have a CSS that grants access to the square partition, and a line on the phone can have a CSS that grants access to the triangle partition. In this case, the line CSS takes priority. Figure 5-3 shows an example of this. This example moves away from the locks and keys analogy to focus more on the actual terms.

In Figure 5-3, phone A has two lines, 1001 and 1010. 1001 has no CSS, and line 1010 has a CSS that grants access to devices in the executive partition. Phone A as well has a CSS at the device level, which enables access to devices in the lobby and employee partitions. Because the 1001 line does not have a CSS of its own, it has access only to devices that can be reached using the device's CSS. Because line 1010 has a CSS of its own, it has access to devices that can be reached using its CSS and the device's CSS. This means that when dialing from line 1001, only devices in the lobby and employee partitions are accessible; nevertheless when dialing from line 1010, devices in the lobby, employee, and exec partitions are accessible.

Now, take a look at the other three phones. Phone B has the extension of 1004, and that line is in the employee partition. Phone C has the extension of 1003, and that line is in the lobby partition. Phone D has the extension of 1004, and that line is in the exec partition.

A. Because line 1001 has no CSS of its own, it relies solely on the device's CSS. The device's CSS has access to the employee and lobby partitions, so line 1001 can reach only the 1004 on phone B because it is in the employee partition.

A. Because line 1010 has a CSS, it has access to all devices to which the line and device's CSS grants access. Because it can reach phones B and D and both of them match 1004, the line's CSS takes priority and phone D rings.

The BGD Company has deployed a Communications Manager solution and has configured the route patterns that are shown in Table 5-1. As you can see, the route patterns enable callers to reach anywhere they need to dial with the exception of 1-900 numbers, which are blocked. The problem is that these patterns as well enable some callers to make unauthorized calls that the company disapproves of. For instance, if a person's job does not require the placement of international calls, the dial plan should not enable the employee's phone to place them.

In this example, BGD has decided that it to tell the truth has four classes of users. The first class, the executives, can make any calls they want, other than 1-900 calls. The second class, the administrative assistants, are not allowed to make 1-900 calls or international calls. The third class, standard users, can only reach internal extensions, local numbers, and emergency services. The fourth class, lobby phones, for instance, can only make calls internally and to emergency services. To accomplish this, partitions and CSS must be configured and assigned to patterns and devices.

In this example, five types of calls are allowed: internal, local, long-distance, international, and emergency. The following is the list of partitions that are needed, and to which patterns they are assigned:

Now that partitions and CSS are defined, take a look at what each is assigned to. First, examine the partitions. You need to understand that partitions are assigned to patterns of DNs, not devices. This means that if you want to prevent a device from making long-distance calls, you assign a partition to the patterns that match long-distance numbers, and make sure that the device's CSS does not have access to the partition. Table 5-3 shows the five partitions that have been created and the patterns to which each is assigned.

You might notice that the 9.1900[2-9]XXXXXX pattern has not been assigned to a partition nevertheless will nevertheless work. Remember, if a pattern does not have a partition explicitly assigned, it falls into the null partition, and all devices have access to the null partition. Because the 9.1900[2-9]XXXXXX pattern is set up so that it blocks all calls that match it, you want all devices to have access to it so that no one can place these types of calls. For all that, it is suggested to apply partitions to all patterns to ensure that no calls can be placed by phones that do not have the proper CSS. With this is mind, the Internal_PT partition can be applied to the 9.1900[2-9]XXXXXX pattern because all devices can reach that partition.

Now that you understand which CSS and partitions are needed for BGD, and where each is applied, take a look at the big picture. Table 5-5 shows which CSS is assigned to each of the four different classes of phones. In accordance with the CSS heading is a list of the partitions that can be accessed. Pursuant to this agreement the partitions is a list of patterns. Using this table, it is easy to see what destinations various phones can reach.

Up to this point, only the assigning of CSS to phones and lines has been discussed. CSS are assigned to devices, which include gateways. A CSS is assigned to a gateway so that inbound calls can reach internal destinations. In the example of BGD, all the internal phones are placed in the Internal_PT partition. If the gateways do not have access to this partition, no incoming calls are allowed. So you can see that not only must phones have CSS, however gateways require them as so then. In the case of BGD, the Internal_CSS can be assigned to the gateways, which would grant outside calls access to all internal phones.

The BGD example

In the BGD example, all internal phones were in the Internal_PT partition, meaning that because all devices had a CSS that granted access to the Internal_PT partition, all phones could be reached. In part, this is undesirable. At times there are certain numbers that should be reached only by certain devices. An example often used is that of an executive's phone. Often it is desired that only the executive's assistant be able to reach the executive. To accomplish this, the executive's phone is placed in a separate partition, to which only the assistant's phone has access.

Often people want their assistants to answer their lines for them. To do this, you must put the directory number on the assistant's phone. The CSS assigned to the line stays with the line, no matter which phone the line is on. This means that if the boss's line has the rights to call international numbers, the assistant can do so as so then, if the boss's line is on the assistant's phone. To deal with this, it is suggested that the more generous CSS be applied to the device, not the line.

Change to the directory number configuration

When you make a change to the directory number configuration and click Update, the line will be reset on all the phones that appear on this line. If a caller is currently on a call, the line resets afterwards the call is ended.

When configuring CSS for Session Initiation Protocol trunks, additional CSSs are configured. In the Inbound Call section, select the desired AAR CSS from the AAR Calling Search Space drop-down list. In accordance with the Outbound Calls section, select the desired CSS from the Called Party Transformation CSS and Calling Party Transformation CSS drop-down lists. Pursuant to this agreement the SIP Information section, there are additional CSSs that should be configured. These included the Rerouting Calling Search Space, Out-Of-Dialog Refer Calling Search Space, and SUBSCRIBE Calling Search Space.

Two alert windows can appear. If you have not assigned authorization codes to this pattern, an alert will inform you of this. You can click OK. The other alert informs you that any update to a route pattern automatically resets the route list or gateway; click OK.

The partitions are applied

After the partitions are applied, you can begin testing the system to ensure that allowed calls can be placed, and those that are not allowed cannot be placed.