When a station user goes off-hook, Communication Manager assigns an available time slot and a touch tone receiver (TTR) that listens to that time slot. The TTR collects the digits, formats a message, and sends the message uplink to the Communication Manager server. Communication Manager sends a downlink message to disconnect the TTR after all the digits have been collected.
For all intercom and auto route selection (ARS) trunk calls, the port on the Tone Detector circuit pack is released immediately when the last digit is dialed. In the case of non-ARS calls (operator-assisted calls, international calls, credit card calls) where the number of digits in a call may be unknown, there is a 10-s time-out period after each digit. If no new digit is generated during this time-out period, the port on the Tone Detector circuit pack is disconnected from the calling station.
If all TTRs in the system are busy, the request is put in a queue. The event of a full queue is treated as an error and results in intercept treatment; that is, a reorder tone is returned to the caller.
TTRs are used to collect digits from the following originating endpoints:
analog sets
DCP sets
DS1 OPS (line-side T1)
DS1 OPS (line-side E1)
BRI sets
analog trunks
RBS digital trunks (T1)
CAS digital trunks (E1)
TTRs are not used to collect digits from the following originating endpoints:
TTR resources are determined by the originating station or trunk. For an outbound PSTN call, its TTR resource must reside in the same port network or branch gateway as the originating station, which is not necessarily the same port network or branch gateway as the trunk. IP or SIP endpoints do not need the use of a TTR. Incoming DID calls that do not use touch-tone dialing do not require TTRs. Incoming PRI calls that use authorization codes do require TTRs.
TTRs are engineered to 0.001 blocking using the blocked calls cleared model. This is conservative in that there is a small (4 entries) buffer for calls who find all TTRs busy.
Default holding time values for the different calls can be obtained by multiplying the number of digits in the call by 0.65 s and adding 3 s, which represents the period from off-hook to the first digit. The TTR usage, expressed in Erlangs, is calculated by multiplying the TTR holding time by the calls per hour, then dividing by 3600. The Erlang B formula with a P001 grade of service is then used to determine the required number of TTR resources. Each G430 branch gateway supports 32 TTR resources, and each G450 branch gateway supports 64 TTR resources. The TTR resources on a port network are scalable through the use of various circuit packs supporting TTR.
