Telephone Naming Concepts

Before we get started with configuring Asterisk for our telephones, we are going to recommend some best practices regarding telephone naming, abstracting the concepts of users, extension numbers, and telephones from each other.

In Asterisk, all the system cares about is the channel name. There is really no concept of a user at all,[43] and extensions are simply ways of directing call flow through the system. For example, your dialplan might inform Asterisk that when extension number 100 is requested it should call the phone on my desk, but extension 100 could just as easily call a company voicemail box, play back a prompt, or join a conference room. We can even specify that extension 100 should ring the device on my desk from Monday to Friday between 9 A.M. and 5 P.M., but ring a device on someone else’s desk the rest of the time. Inversely, when a call is made from a device during business hours, the callerID could show a daytime number, and the rest of the time could show an after-hours number (many reception desks become security desks at night).

The abstraction between the name of an extension and what that extension does is a powerful concept in Asterisk, as extension 100 could do a number of things depending on any number of variables that are programmed into the system. This is especially relevant in the context of features such as hot-desking.

Hot-desking is a feature that allows someone to log into a device and receive his calls at that device. Let’s say we have three sales agents who typically work outside of the office, but spend a couple of days each month in the office to do paperwork. Since they are unlikely to be on-site at the same time, instead of having a separate telephone for each of those three sales agents, they could share a single office phone (or on a larger scale, a dozen folks could share a pool of, say, three phones). This scenario illustrates the convenience (and necessity) of allowing the system to separate the concept of a user and extension from the physical phone.

So what are some examples of bad names for telephone devices? Something like a person’s name, such as [SimonLeBon], would be a poor name for a telephone as the phone may also be used by Joan Jett and Rick Astley. The same reasoning can be applied to why you would not want to name a phone based on an extension number: a phone name of [100] would be a poor choice since you might want to reprovision the device for extension 160 in the future, or it might be used by several people with different extensions in a hot-desking solution. Using numeric account names is also very bad from a security perspective and is discussed in more detail in Chapter 26, Security.

A popular way to name a phone is using the MAC address of the device. This is a unique identifier specific to the phone that follows it where it goes and doesn’t directly relate to the user operating the phone or the extension number currently associated with it. Some corporations have stickers they place on their equipment with a bar code and other information that allows them to keep stock of provisioned equipment; these unique codes would also be an acceptable choice to use for phone names as they don’t provide any logical relation to a particular person, but do provide specific information about the devices themselves.

The choice is yours as to how you want to name your phones, but we primarily want to abstract any concept of the telephone being owned by a person, or even its location in the network, since these concepts are outside the realm of Asterisk and can change at any time.

Throughout this book, you’ll see us using phone names that look like MAC addresses (such as 0000FFFF0001 and 0000FFFF0002) to differentiate between devices. You will want to use phone names that match the hardware you are using (or some other string that is unique to the device you are registering).

As a final consideration, we should make it clear that what we are suggesting regarding device names is not a technical requirement. You are free to name your devices anything you want, as long as they meet the requirements of Asterisk’s naming conventions for devices (stay with alphanumeric characters with no spaces and you’ll be fine).

[43] Actually, Asterisk does try to implement and abstract the concepts of users and devices internally by using the users.conf file; however, it is typically only used by the Asterisk GUI. Abstracting the concepts logically using the dialplan is easier to understand and far more flexible.