Call Completion Ratio or ASR improvement in C-DOT Exchanges.

Introduction:

In the Multi-operator environment, it becomes very essential that a quality oriented service is to be provided. Then only we can retain our valuable Subscriber in BSNL. When a subscriber originates a call, it should get matured; otherwise the sub is not happy and our revenue is also lost. Let us discuss certain valid points in and around the Switch to improve the Call Completion Ratio and fetch more Revenue.

Terminologies:

1. Originating and Terminating Calls:

Total Local Call Attempts: It indicates the total No. of ORG-TRM calls i.e. intra exchange calls which originated from PSTN subscribers. It includes both successful and unsuccessful calls and is equal to the sum.
Total Success Call Attempts: It indicates total calls which originated from PSTN subscribers, for which information about state of called user was received. The calls which have been processed by our Exchange are put in Successful Attempts.
Total Completed Call Attempts: It indicates total local calls originated from PSTN subscribers and for which an answer signal has been received.

2. Originating and Terminating Calls:

Total Outgoing Call Attempts: It indicates total No. of ORG-OG calls originated from PSTN subscribers. It includes both successful and unsuccessful calls.
Total Successful Outgoing Call Attempts: It indicates total No. of ORG-OG calls which originated from PSTN subscribers, for which information about state of called user was received. Apart from completed calls, they include calls released due to

1. abandoned after dialing complete

2. calls to CP busy subscribers

3. number unobtainable

4. remote congestion

5. any other failure at the succeeding Exchange

Total Completed Calls: It indicates the total No. of ORG-OG calls which originate from the PSTN subscribers and for which an answer signal has been received.

3. Terminating Calls:

· Total Terminating Call Attempts: Total calls terminating on the module, which is the sum of the Total no. of ORG-TRM calls and the total no. of IC-TRM calls.

· Total Completed terminating Calls: Out of the total terminating call attempts, the ones which are answered. i.e. Sum of the total no. of completed ORG-TRM calls and total no. of completed IC-TRM calls.

Call Failure Analysis:

On going through the Traffic Analysis in CDOT Switches, the following reasons are noticed for a call failure. The reasons noted in the Traffic Analysis report are discussed in this paragraph. Then the cause for the failure and remedial action inside the Switch and other external reasons and other environmental changes required would be discussed.

· Abandoned after dialing complete.

· No Answer

· Called subscriber Busy

· Partial Dialing

· No Digits Dialed

Abandoned after dialing complete: Subscriber has completed the dialing, and getting Ring Back Tone. Now the Called party has to answer. Waits for 4 or 5 ring tones and the caller disconnects and the call is accounted in this category. Giving a missed call also comes in this category. Now a days, after the introduction of GSM and CLI to Land Line Phones, it is Quite common that many calls are not answered. More number of nodes in a transient call, with combination of C7 and MOD-R2 signaling also results to this type of failure; Ring will be extended to the caller, but would get disconnected with a time out signal. This could be avoided only by reducing number of nodes in our network. Existing CDOT 256 Exchanges are to be converted as AN-RAX and the SBM Exchanges are to be converted as RSUs.

No Answer: The called subscriber is busy in his/her other works. Attending the phone call is delayed and the ring time out happens and call gets dropped or failed. Actual line fault ‘disconnection in Line’ would also cause this type of failure. A fault in the LCC card or a fault in the SPC card or Faulty Power Supply Card will also cause this No answer failures. Places like Ooty and Yercaud (Hill Stations) where holiday Resorts are available, the telephone is used for only OG purpose that too when the Tourist are staying, No-reply failures are more. In rural areas and in villages, there is nobody to answer the phone call when they in duty at the farms.

Called Party Busy: This is a critical Problem. Actual busy subscribers like heavy callers, Hostel Numbers, College Numbers are causing such failures. A heavy caller who is contributing more than 5000 Units per month, may be provided with a free incoming phone through which his incoming calls will not be missed and it earns a revenue at the originating end in case of BSNL call, and earns IUC charges in case of an inter operator call.

The college Hostels may be provided with free incoming phones and authorities may be requested to provide attendees to attend the call.

Partial dialing: Subscriber starts dialing; in the middle or during the dialing period, he/she forgets some digits of the destination number. He / She abandoned the call and verify the diary or directory and confirm the number and dial the number again. This type of failures can not be eliminated unless the dialing habits are improved by the subscriber.

No Digit Dialed: About 25 % of the attempts are accounted as no digit dialed in every hour, either a busy hour or slack hour. A subscriber lifts the handset and replaces the handset will also be counted as one attempt. Many subscribers are having a habit a flashing the hook switch once or twice and then only starts dialing. This type of failures can not be eliminated.

Factors affecting the ASR / CCR Ratio: The factors affecting the ASR or CCR in our Network are classified in two categories and analyzed. One is the External Reason and the other is Internal Reason.

External Reasons:

Maintenance of external Plant:

1. Cable Network.

2. Maintenance of DP Boxes.

3. Drop wire and Exposure of Joints.

4. Subscriber Instrument. (Faulty instrument and Additional Instruments)

Internal Reasons:

Assuming that the External Plant maintenance is excellent and now it is our duty to improve the ASR / CCR ratio. Let us discuss the areas in which the success rate could be improved.

· Feed the Dial Tone in Time. This only will tell the status of the system to the subscriber.

· Feed proper Announcement in appropriate times.

· Check of call processing.

· Check of Resource allocation.

· Provide adequate trunk Circuits.

· Testing the LCC and TIC / SPC cards.

· Data Check to avoid NO-ANSWER cases.

Solutions to Switch Reasons:

· Dial Tone Delay and No-Dial Tone:

1. In CDOT switches, all subscribers are provided with ‘DTMF’ facility and hence it is emphasized that the subscriber instrument should be modified for ‘Tone working’. Keeping the subs data as ‘dtmf’ and the sub is dialing in decadic method would cause processor over load.

2. Dial Tone is fed by ‘MFC’ cards for a ‘dtmf’ subscriber. In case of MBM Exchange, for given Local BM or Line BM, 4 Number of MFC cards are to be equipped per BM and all the ports are configured as “dtmf” so as to get 4 X 15 = 60 “dtmf” circuits are made available for feeding Dial Tone.

3. In daily Routines, MFC cards are to be tested, using command ‘ tst-srv’ daily. It can be put in Calendar and get it executed. Not only the execution of ‘tst-srv’ card but to go through the log files daily and doing the needful is very important. Yes, one card is found faulty; what to do with this? Normally MFC cards will not become faulty. Put out the card and jack out and jack in the MFC card and bring it to in service. Most of the problems would get solved.

· Feed proper Announcement at appropriate time:

1. Guiding the subscriber properly in case of unforeseen circumstances would result in improved call success ratio. A Subscriber who is in OG-Barring status and dialing a STD call should be fed with “This facility not available in your Telephone”. Otherwise he / she will be continuously attempting the call and exchange is over burdened. What are the situations, in which the Announcement is not proper? One is the “ANNC” card becomes faulty and not taking corrective action immediately and the other is Announcements are not mapped properly. For both the things, take care and do the needful.

2. For a busy call towards a subscriber assigned with “called call waiting”, the caller is fed with an announcement “ Please wait, you are in a Q” in case of “ANNC” card becomes faulty or the ANNC is not mapped properly, then the sub would be wrongly guided and the exchange is again over burdened.

3. “ANNC” card is to be equipped in Trunk BMs also. This will feed the proper announcement for incoming calls from Tax / Other exchanges.

· Check of Call Processing:

The following System Parameters are to be checked for the given values for effective call processing.

1. ROUTING: This is the minimum number of digits that must be received in the exchange whenever some one dials digits corresponding to a route having open numbering scheme. Recommended value for this parameter is ‘6’. Only after the receipt of these digits call will be handled. If IDT occurs before receiving number of digits set in ‘routing’, the subscriber will be fed with a parking tone.

2. MIN-SUBS-DIALS: This parameter indicates the minimum number of digits a subscriber should dial after which the call can be processed in case of local call. The value ‘MIN-SUBS-DIALS’ should always be greater than or equal to number of digits in exchange code but should be less than the number of digits used in the DIRNO in the exchange. For example if the exchange code=248 (3 Digits) and 6 digits numbering scheme is used then MIN-SUBS-DIALS should ‘3’ or ‘4’.

3. DNA-TMR: This parameter is effective for the feature ‘Diversion on NO Reply’. The value against this specify that after how much time the call is to be diverted to the predetermined number if no answer is received. Recommended value is 280.

· Resource Allocation:

1. For a LINE BM in a MBM Exchange, all the 4 MFC cards should be created as “dtmf” ports.

2. In case of RBM also, all the 4 MFC cards are to be equipped as “dtmf” ports only.

3. For a VU BM, connect only the DTKs working for AN-RAX or V 5.2 Interface. Equip the MFC cards as “dtmf” ports only, because this only will feed the dial tone for a AN-SUB who is provided with ‘dtmf’ facility.

4. For a Trunk BM, where there is no subscriber, equip all the MFC cards as MF-SNDR / MF-RCVR so that they will be responsible to handle the MOD-R2 calls.

5. In case of SBM Exchanges, 30 ‘DTMF’ circuits and 15 ‘MF-SNDR’ and 15 ‘MF-RCVR’ are sufficient for handling 1400 subs with ‘dtmf’ facility and 4 DTK traffic.

· Providing Required Trunk Circuits:

1. Sufficient junctions are to be provided towards the parent exchange / TAX exchange. Traffic report on TGP’s should be analyzed for call failure due to non-availability of trunks.

2. In present days the usage of “EMF” and “TWT” circuits are not in use and only DTKs are in use. Daily take test over the DTS and DTK cards using the command “tst-trml-card” put in calendar file. This will improve the originating-outgoing traffic efficiency.

3. In a Trunk BM, 21^st slot in the 4^th TU equipped as DTK was giving some call failures; In the new software 2_2_1_6 (7.7) patch release this has been sorted out and 21^st slot in the 4^th TU is working fine. In other versions avoid equipping this slot.

4. “TUC” cards used in the DTU frame are to be tested once in a week and active standby cards are to be interchanged.

· Check of LCC and TIC / SPC cards:

To eliminate the call failure due to NO-ASWER, the failure due to SUB reason, ie the sub is not available and the other is ‘ringing not extended properly’ are to be taken care. Following preventive maintenance would help improve the case of NO-ANSWER cases.

1. The LCC / CCM cards are to be tested properly in a periodic manner. Keep the TTC card in good condition. Using the command ‘tst-trm’ for test set 103, testing of line ports should be put in calendar for testing the LCC / CCM cards, so that in a month’s time all the subs ports are covered at least once.

2. The testing of TIC / SPC cards to be done periodically depends on the local conditions. Since these are responsible for extending the Ringing Current to the called subscriber.

· Data check for avoiding NO-ANSWER cases:

For an incoming TAX call and OG TAX call, disconnection in case of no answer condition is to be taken care. Keep the ringing duration for 60 sec. thus call failure due to no-answer is reduced to some extent.

1. RING-TAX-TM-OUT ….. This system parameter is effective for the calls for which the exchange is working as TAX. This parameter decides the duration of the ring to be fed to the called party. This value is recommended as 600.

2. CSH-TAX-TM-OUT…… This parameter is effective for the calls for which the exchange is working as leading TAX. This parameter governs the CSH timeout for the OG calls. Recommended value for this parameter is 600.

In both case the ring face timing is set as 60 sec and the ringing is extended upto 60 sec.

Conclusion:

Reduction of number of nodes in the Network would solve the CLI problem and transit functions and improves the call success ratio.
Provision of “Call Waiting Facility” to all the subscribers and wide publicity to be done for using the feature.
Provision of ‘DTMF’ facility to all the Subscribers in the CDOT Switches including AN-RAX sub and converting the Telephone Instrument for ‘TONE’ Dialing.
Providing free incoming Phones to College Hostel Numbers and other Heavy callers and Public Institutions would solve the “called subscriber busy” problem and in turn fetches revenue in other areas of our network.
Daily inter action with your Exchange as discussed above would definitely improve the call completion ratio.

Prepared by: M.Pandian, Divisional Engineer, CDOT Installation, Salem.

E-Mail: [email protected]

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