Suggestions to improve ASR & CCR - Part 1
By A.K.Kalaiarasu,
DE, RMC, Chennai
Introduction
With active monitoring by authorities at different level, it has been now possible to achieve improved ‘Call Completion Ratio’ and ‘Answer to Seizure Ratio’ in the local network as well as in Tandem / TAX. Applying usual methods of reducing faults in telephone line, avoiding congestion by strengthening circuit group, increasing digit seize forward, etc, are not probably yielding any result in further improving CCR to achieve the target of 55 to 65% fixed by TRAI.
The major factors which are pulling down the ASR/CCR are now identified as the WLL-F/ Mobile / Cell phone connections whose total capacity has increased enormously in the past 2 years. Also, software upgradation of CDOT exchanges, commissioning of new AXE TAXs, etc, have resulted in increased call attempts due to failure of certain types of calls.
It has been found that unless and until new methods, even non-conventional sometimes, are adopted in switches like CDOT / OCB / EWSD / AXE, it is not possible to improve ASR/CCR.
2.0Reasons for low ASR / CCR
Reasons for low ASR/CCR and infructuous call attempts can be broadly classified as
i)due to subscriber behavior
ii)due to overloading of exchange equipments
iii)due to technical problems in different switches.
3.0Subscriber behavior
Some of the reasons for repeat call attempts by subscribers are explained below:
i)Feeding of misleading tones or announcements from exchange e.g.:
- In some exchanges busy tone is fed for calls to faulty (PG) & disconnected (DNP) numbers. Busy tone creates the impression that subscriber is really busy.
- Feeding Busy tone or Ring-back tone, for calls to WLL numbers which are ‘switched off’ or ‘out of coverage area’.
ii)In OCB, there is no routing tone for outgoing calls involving CCS#7 circuits. Hence, there is long silence period before getting ring-back for some calls like ISD calls, calls involving more R2 links, satellite link, etc. Since subscribers are allergic to no-tone condition due to fear of such calls may be metered (if any C7 PCM is in local loop), premature disconnection and redialing are more.
iii)In OCB, routing (pip-pip) tone is connected for long duration (in some cases upto 30 seconds) before starting of any announcement. This arrangement is adopted in ‘broadcast mode’ to commence announcements from the beginning. When the pip-pip is for long duration, subscribers do not have the patience and disconnect the call and redial.
iv)In most of the switches, ring-back tone is fed for the second call when ‘call waiting’ facility is activated. If the call is not answered within few seconds, call is abandoned assuming there is no reply.
3.1Suggestions to reduce repeat calls
To reduce repeat call attempts explained above, following suggestions can be implemented:
3.1.1 Announcements
In OCB, announcements can be fed directly without pip-pip by changing CL as 2 in XATR FIDIF file records, to work in ‘non-synchronous’ mode. Starting the announcement in the middle may not have any adverse effect since announcements are bilingual and repeated continuously.
3.1.2Call-waiting
For ‘call waiting’ and ‘not answering’ conditions, announcements can be fed in all systems wherever possible. In OCB, it can be done by a simple file modification. By feeding ‘please hold; subscriber is in conversation with another number’, instead of ring-back tone, subscribers are informed of ‘call waiting’ condition. Also, by feeding ‘subscriber is not answering; please try after sometime’ announcement for ‘not-answering condition’, subscriber gets an idea not to redial immediately.
3.1.3Partial dialing
‘Please check the number you have dialed’ announcement can be fed, instead of busy tone, for calls with incomplete digits. Incomplete digits calls may be due to change of number length, inadvertent dialing, etc.
3.1.4Faulty / Disconnected number
Correct announcements are to be fed for calls to PG (line fault) & non-payment disconnected (DNP) numbers, instead of busy tone.
3.1.5‘Number changed’ announcement
‘Number changed’ announcements both for individual numbers as well as for level/code change shall be kept for maximum possible period. This helps in feeding exact information to subscribers, instead of feeding ‘this number does not exist’ announcement. By this arrangement, such calls are treated as effective calls in OCB.
4.0Suggestions to reduce equipment load & infructuous calls
In OCB exchanges, due to overloading of equipments like C7 Protocol Controller (PC) , Protocol Handler (PUPE), Rings, Buffers, etc, some calls are dropped during processing stage itself. By adopting methods explained below (wherever possible), equipment ‘Load modifications’ can be avoided by reducing number of internal messages between different units in the switch and by reducing number of infructuous calls.
a)Selection of free circuit: Large size Bothway Trunk Groups can be split into two or more small TGPs (say 600 CICs maximum) and routing can be separate for O/G & I/C. If more than one TGP is justified for O/G itself, some levels are to be routed to TGP1 and other levels to TGP2, so that trunk selection is limited to a small group.
b)Deeper analysis at TAXs upto the working levels of all intra-circle STD codes may reduce the overall call processing efficiency. But ASR in different routes will increase. Deeper analysis can be done in local exchanges for 92, 93, 94, 95, 98, etc, so that only working codes are routed to TAX and offered calls are reduced at TAX.
c)Minimum number length (RCMI in OCB) shall not be kept uniformly 6 for NSD & ISD codes. Minimum number length shall be defined as 6 to 8 (i.e. 0/95+STD code+ 3) only where 131, 141, 195, etc are allowed on STD. For other levels 2/3/5 on STD, minimum number length shall be 11/12 for 0/95 codes. For Cell codes RCMI shall be 10/11 on level 9/0. For ISD codes, minimum digit shall be kept as 6 only for 000 codes. For other 00 codes it shall be as per VSNL guidelines e.g. 13 for 001.
d)To reduce processed/offered calls: In OCB, partial dialing calls can be avoided from counted as processed calls by defining ‘number of digits required for analysis (RCA in preanalysis)’ as 6/7/10 for levels 0/95/94,98, etc. By this arrangement, any 94/98 level call (with complete C7 signaling) disconnected before 10 digits will not be counted as processed/offered call in the entire chain.
e)Digit Seize Forward (RCR in OCB) is kept normally maximum possible. But, for calls to codes involving satellite links, more R2MF links, etc, Digit Seize Forward (DSF) shall be reduced in the entire chain upto the terminating TAX/GDC, to avoid timing problem. Most advantageous DSF is to be decided by trial and error method which gives maximum ASR without any subscriber complaint.
f)Busy calls to Hostel numbers: In many educational institutions and hostels only one or two single lines are available for incoming calls for hundreds of students. Due to limited period of service, lot of busy calls to such numbers are generated in the network, pulling down the ASR/CCR and result in infructuous load on equipments. To reduce busy calls to such numbers, additional numbers can be given (even free of charge) with incoming facility alone and all the available numbers can be given PBX hunting. Incoming calls fetch very good revenue since Interconnect Usage Charge for terminating call is minimum Rs 0.30 per minute.
g)Mass calling numbers: Sudden announcement of dial-in programme (mass calling) by TV/ Radio channels result in huge call attempts and poor ASR/CCR. Since 1707 codes are not accessible from most of non-BSNL networks (and also permanent call filtering is enabled in BSNL for 1707 codes), some programmers use direct telephone/cell number of other operators so that subscribers of all networks can get access. This problem of network congestion due to mass calling can be discussed with other operators so that common mass calling codes only are used for such programmes and the codes shall be accessible from all networks with compulsory call-filtering. Direct numbers shall not be allowed for such programmes.
h)Timing for ‘Open number working’ can be reduced to 3 seconds instead of standard 5 seconds. In the present scenario of all the telephone instruments are of push button type and majority lines with tone dialing facility, reducing the open number timing to 3 seconds may not have adverse effect. Since this arrangement reduces call setup time by 2 seconds in some cases, this may reduce the possibility of call failure due to timing problem in CDOT, AXE, etc.
4.1Overloading of Lowest Number Trunk BM in CDOT
In CDOT, to search for a free trunk, always thelowest number BM is selected first. If there is no free trunk in that BM in the required TGP, searching takes place in other BMs in the ascending order of BM number (i.e. there is no random selection of BM). This results in overloading of lowest number BM. Overloading of any one BM affects C7 working in entire exchange and ASR/CCR falls.
Suggestion: Instead of having a TGP with trunks distributed in different BMs, different TGPs can be created with trunks in one BM only. Different route codes are to be assigned priorities to different TGPs with cyclic overflow such that all TGPs handle maximum calls as first choice.
To be continued in Part-2
Suggestions and queries are most welcome.
A.K.Kalaiarasu,
DE, RMC, Chennai.
Ph: 044- 25368595 (O), 26542500 (R)
Fax: 044 – 25368820
e-mail: ,
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