otal number of outside lines. If you have ten outside lines and receive four telephone calls at the same time as six people are placing outgoing calls, the next caller to your tele- phone number will hear a busy signal. Outside lines are also called telephone numbers, dial tone lines, trunks and POTS lines (plain old telephone service). What we have described above, with all calls coming into a switchboard operator, is a traditional telephone system design (Figure 2.3). With the increasing use of Voice Mail and Auto- mated Attendant, many systems are being set up differently. For example, a type of outside line called a Direct Inward Dial trunk may be used. This allows each person using the system to have a separate telephone number to give to callers SO that their specific extension may be called directly without the intervention of the switchboard operator. If the directly-dialed extension is not an- swered or is busy, the call may then go to the switchboard operator or it may be answered by Voice Mail. The caller hears the voice of the person called. "This is Christine Kern. I'm not at my desk right now, but please leave a message and I will return your call, or dial 0 for immediate assistance." The caller may then leave a message that will, in turn, activate a message waiting indicator on the telephone of the person called (Figure 2.4). An Automated Attendant can take the place of the switch- board operator answering the main telephone number with an announcement such as the following: "Thank you for calling CMP Books. If you know the extension of the person you are calling, The Telecom Handbook * 37 Figure 2.3 Traditional Telephone System Combination Trunks For Incoming And Outgoing Calls Switchboard Attendant Console Local Telephone Co. Central Office Telephone Extensions Incoming Call - A call comes in on a combination trunk and is answered by the switchboard attendant. Caller is then sent to the correct extension. Outgoing Call - Extensions dial 9 to get dial tone from the combination trunk for placing an