Case Study on Using the α-Command Analysis Support Tool for Handling Problems Occurring during Use of Business Phone Systems

2.1 What is an α-command?

As control commands for business phone systems, α-commands are exchanged between the α-Series main unit and telephone terminals. α-commands control operations such as operating a telephone, displaying information, and switching display lights on and off. However, operations of this kind are not recorded in the system log, so it is impossible to confirm the status of telephone operation when a problem occurs. To address this issue, TASC developed the α-command analysis support tool that can visualize α-commands from packet data and use that information to resolve problems caused by unintended operations due to incorrect telephone operation or equipment-specification constraints.

2.2 Methods for obtaining the data required for analysis

To analyze α-commands with this tool, it is necessary to acquire packet data during communication using α-commands; however, the acquisition method used depends on the main-unit type. The α Series of business phone systems (called SmartNetcommunity αZX) are available in four types (H, S, M, and L), which are chosen according to communication capacity.

The differences in places that α-commands are acquired are listed in Table 1. Regarding telephones with local area network (LAN) wiring, α-commands are acquired by capturing packets in the LAN segment connecting telephones and the main unit. Regarding telephones with star wiring, Type L enables α-commands to be acquired by capturing packets in the LAN segment connecting the central control unit (CCU) and time-division multiplexing CCU (TCCU). Regarding Types H, S, and M, the segment connecting the telephones and main unit do not have a LAN segment, so data are acquired using the “α-command acquisition device for star wiring” developed by TASC [1].

Table 1. Methods for obtaining α-commands when using the α-command analysis support tool.

2.3 Examples of α-commands

Examples of α-commands visualized using the α-command analysis support tool are listed in Table 2. This table shows the operations when an internal call is made between two key telephones—“TEN (terminal equipment number) 101/Extension number 101” and “TEN 102/Extension number 102”—connected to an αZX Type S main unit. The specific operation flow follows five steps: (1) TEN 101 goes off-hook; (2) the number of TEN 102 (the destination) is pressed; (3) TEN 102 goes off-hook and the call is established; (4) TEN 102 goes on-hook and the call ends; and (5) TEN 101 also goes on-hook. By using the α-command analysis support tool, it is thus possible to understand the specific operations carried out by customers on their telephones when a problem occurs.

Table 2. Examples of α-commands exchanged during internal telephone calls.

3.1 Case 1: Analysis of a problem caused by incorrect operation

After upgrading from another company’s business phone system to the SmartNetcommunity αZX Type L, the customer encountered the same problem several times a month: the line key (LK) assigned to the analog line lights up in red and the line becomes unusable. The configuration of the customer’s equipment is shown in Fig. 1.

Fig. 1. Configuration of customer equipment in Case 1.

To identify the cause of this problem, we verified telephone operations through packet capture and α-command analysis and confirmed the usage status and analog sequence by measuring the voltage on the analog line using a MEMORY HiCORDER. The results visualized with the α-command analysis support tool are listed in Table 3.

Table 3. α-commands during problem occurrence in Case 1.

When the main unit accepted the operation of pressing the LK5 button on digital cordless telephone personal station (DCL-PS) TEN 53, the status of the analog line was changed to “in use” (green light) by TEN 53 [(1) in Table 3], and the ZXL main unit sent an instruction to other telephones, such as star-wired standard telephone (STEL) TEN 10, to change the status to “unable to connect” (red light), which caused the LK5 button of all other telephones to light up in red at the same time [(2) in Table 3].

When we checked the analog sequence before the problem occurred, we found that the “off-hook” state had continued immediately after the LK button on TEN 53 (DCL-PS) was pressed. These results confirmed that pressing the LK button on TEN 53 (DCL-PS) caused the LK buttons on other telephones to light up in red during normal operation.

Analysis of the α-commands clarified on which telephone the LK button was pressed, so when the user of the telephone in question was interviewed, it was found that the telephone is usually carried in a pocket. We thus surmised that it is highly likely that the LK button on the telephone was pressed unintentionally while the telephone was being carried. In this case, the α-command analysis revealed that the problem was caused by a customer operating the telephone incorrectly. The problem was resolved by reviewing the telephone-operation method and changing the LK settings according to the intended use.

3.2 Case 2: Analysis of a problem caused by a specification constraint

The problem that occurred in this case was an external call being disconnected mid-call on a DCL-PS connected to a SmartNetcommunity αZX Type L main unit. The configuration of the customer’s equipment is shown in Fig. 2.

Fig. 2. Configuration of customer equipment in Case 2.

To confirm the entire call process (from receiving an INVITE message and the telephone ringing to disconnect the call), we used the α-command analysis support tool and captured packets between the optical network unit (ONU) and main unit. The communication content at the time the problem occurred is shown sequentially in Fig. 3.

Fig. 3. Hikari Denwa sequence and α-commands at the time the problem occurred in Case 2.

The analysis results confirmed the following sequence:

This sequence of operations revealed that the problem was caused by the call being disconnected during the handover process. When we checked the customer’s settings while referencing the installation and maintenance manual, we discovered that the “automatic call recording” function was enabled. Since (according to the specifications) the handover function and automatic-call-recording function cannot be used simultaneously, we concluded that the presence of both functions was the cause of the problem.

This case involved α-command analysis and visualization of the Hikari Denwa sequence, which revealed that the problem was due to a specification constraint. The problem was solved by reviewing the telephone settings and adjusting them to better suit the customer’s operational environment.