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Voice Feature Guide 01

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Ringing and CLIP Services for IP Z Interface Extension Feature

Ringing and CLIP Services for IP Z Interface Extension Feature

When a PSTN network is restructured into an IP network, the ringing and calling line identification presentation (CLIP) services for IP Z interface extension users need some implementation changes accordingly. This topic describes the context and implementation changes for the FXO port to support the ringing and CLIP services for IP Z interface extension users serving as the called parties.

Context

  • Figure 1-127 illustrates the intervals of the ringing and CLIP signals in the on-hook process specified in ETSI EN 300 659-1.

    Figure 1-127 Intervals of the ringing and CLIP signals in the on-hook process (ETSI EN 300 659-1)

    According to the preceding figure, the interval between the first ring pattern signal and the FSK modulation transmission signal (CLIP signal) is T5 (500 ms ≤ T5 ≤ 2000 ms); the interval between the FSK modulation transmission signal and the second ring pattern signal is T6.

    The First Ring parameter in the protocol is the Initial Ring parameter of the MSAN, and the Second Ring parameter in the protocol is the Cadence Ring parameter of the MSAN.

  • Compared with a PSTN network, an IP network needs more time (delay T) to send ringing signals of a Z interface extension call from the PBX to the telephone, because the ringing signals require processing by the MSAN on an IP network, as shown in Figure 1-128.

    However, both PSTN and IP networks transparently transmit FSK modulation transmission signals from the PBX to the telephone and thereby spend the same time. As a result, an IP network has a shorter T5 (interval between the first ring pattern signal and the FSK modulation transmission signal) than a PSTN network does.

    Figure 1-128 T5 difference between a PSTN network and an IP network

    Theoretically, when a call to an IP Z interface extension user is ended before it is answered, the PBX hook on then stop sending a ringing message to the MSAN_1 and then the MSAN_1 detect ringing missing message to send a ringing stop message to the MSAN_2. However, the ringing stop message is also delayed due to MSAN processing.

    If the delay is not properly handled, the CLIP service may be affected, and the telephone may still ring after a call is ended.

Implementation Changes

  • According to the preceding analysis, delay T must be shorter than T5 to ensure that the CLIP service is normal.

    Delay T = Ringing signal detection time of the FXO board + Time used by Z interface extension (about 150 ms, including codec, jitter buffer, and other message processing time)

    The ringing signal detection time of the FXO board can be configured using the min-ontime parameter of the fxoport attribute set command.

    The value of the min-ontime parameter must meet the following requirement: min-ontime < T5-150 ms.

    NOTE:
    For the value of T5, see ETSI EN 300 659-1.
  • The FXO board must spend as little time as possible in detecting ringing missing message to avoid the undesired telephone ringing after a call is ended.

    The ringing missing signal detection time of the FXO board can be configured using the max-offtime parameter of the fxoport attribute set command.

    NOTE:
    When you configure the max-offtime parameter, take the ringing break-make ratio into consideration. If the max-offtime parameter is set to a time shorter than the ringing break, ringing signals cannot be detected.
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Updated: 2019-02-22

Document ID: EDOC1100067358

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