Call Success Rate

So you are in the middle of that hot gist or right in the magic moment of that epic negotiation and boom, the line drops! You check your mobile station (also called mobile device or handheld or handset or a mobile phone; Else could be a Personal Digital Assistant–say, a tablet) and your battery is at full bar and your network bars at their prime, smiling right back at your awestruck face. You obviously did not hit the End Call button and your ear did not end the call either, at least you are sure because you have your airpods on. So you call back Emeka and before you ask what happened Emeka goes “Nna na wa o! Na me call you, na you dey cut call, on top my credit!” You are understandably gobsmacked, Emeka does not get the memo and you do not get his drift either. So you both drag on for a little longer and with a pinch of salt settle for blaming it on the network, knowing by now that Emeka’s phone had not tripped off and his network bars are still full, and his earpiece very functional and not touch-sensitive. Hopefully, the dropped call did not ruin the gist or the transaction, so you both pick up from where you dropped off.

Now it doesn’t matter if you both use the same network or not, because what happened is common amongst Mobile Networks Operators (MNOs) and the public is not completely absolved of the blame. Yes, you read right, “The Public!”Established call connections drop for different reasons and can get increasingly frustrating when the rate is high. The most logical term to describe how often calls drop would naturally be something that links rate to calls dropping. So, ladies and gentlemen, I give you the Call Drop Rate (CDR)! 
Now you’re wondering: What has Call Drop Rate got to do with Call Success Rate (CSR)? Is this article not supposed to be about Call Success Rate? Well, thankfully you are wondering and not wandering, and it is completely sane to wonder along that line. In your shoes, I too would do the same, and I too would read on. You would be right to call this edition a very rich burger. Sandwiched between its halves is a promise to be kept from the last edition (those intellectual freebies we agreed to give you in this edition), as well as an introduction of a few new concepts which cannot be separated from the subject of Call Success Rate. Thankfully, the only mathematics you need to wholly appreciate the topic is:

Call Success Rate = Call Setup Success Rate – Call Drop Rate
i.e. CSR = CSSR – CDR

So yeah, you are in luck. You have a fair idea by now of what a dropped call is, and from the previous edition, you already know what Call Setup Success Rate (CSSR) is, so it is safe to warm you into a few more basic things that lead up to a successful call at all before we begin to give reasons why calls drop, as well as justify why it has everything to do with Call Success Rate. 

You pick up your mobile device and you dial a valid mobile phone number, then you hear “kpuun kpuuun” or any variant of it a couple of times, and then Rashidat picks up and says “hello”, then you say “¦\¬°=$#$’&$”*$$%/*” #_”, completely unbothered about what happened between when the call request was sent (by pressing the Send button after typing Rashidat’s mobile phone number) and when you heard the Ring Back Tone (RBT) a.k.a “kpuun kpuuun or any variant of it” (i.e. The tone heard by the caller when the called party is being alerted on an incoming call; also called Caller Ring Back Tone). Why does this concern you?–Because when your call drops inappropriately it concerns your customer satisfaction. You do not want to errantly start blaming Rashidat for being rude and dropping your call once the call connection is successful.

Here’s the catch in the most basic form: When you send a request for a call, a virtual circuit is created (think of it as a private pipe securely linking your handheld with that of the intended recipient of your call, through which you can now verbally exchange all those dirty secrets, business hints, devotionals, raunchy gossips, briefs, vows, pledges, etc. It is virtual because you cannot see this pipe) between the caller (you in this case) and the intended recipient (Rashidat) of the call. You probably are caught up in “how does my mobile phone’s pipe connect to Rashidat’s phone out of nearly 16 billion mobile devices (according to Statista, Sept. 6, 2022) on the planet?”. Well, first of all, only Rashidat has that unique identifier (her mobile phone number). Second of all, Rashidat’s mobile device is not hard to find, wherever in the world it may be hiding, provided it has an active Subscriber Identity Module (SIM) and network service from the SIM’s Mobile Network Operator (MNO) e.g. GLO, Vodafone, MTN, 9Mobile, etc.

Now if you are like me in some way then you are certainly not done with the “how?” —Rashidat is in Maiduguri, I am in far away Ikeja, what sort of sorcery has me speaking with her from a such crazy distance? This is where those tall metallic structures (some of them roof-mounted) that look like isosceles triangles (often painted red and white) come into play, beyond which there are more sophisticated infrastructures at different levels that help to find Rashidat wherever she is–All thanks to Microwave and Fibre Optic technologies.

Basically, these in-between sophisticated infrastructures are the Base Station Controller (BSC) and the Mobile Switching Center (MSC), and together they see to the secure establishment of a call by following a sequence of to and fro electronic requests from your handheld that should normally bore you to bits: Random Access Channel (RACH), Standalone Dedicated Control Channel (SDCCH) and Traffic channel (TCH). A detailed article on how a call is made or received is available upon request if you like to know in finer detail what these jargons mean and what they do. 

So why did we go through all these just for Call Success Rate? –It is because if a call is not set up at all we cannot be talking about its success rate. It is more specifically because some of the concepts we have highlighted are determinants of call drops, hence call success rate. Remember: CSR = CSSR – CDRSo what is a dropped call and what causes a call to drop?

A dropped call is a call that abruptly terminates after the call connection has been successfully established. This can happen just before the called party (in this case Rashidat) picks up, or after the called party picks up. Call drops can be caused by a variety of reasons and we would just highlight some of them:

1. SDCCH Congestion: Yes, the BSC does get crammed up sometimes with overwhelming requests or could be slow on many fronts due to constituent hardware faults. Congested SDCCH means that Traffic channel (TCH) assignment becomes a tall task, and this is a crucial Radio Resource (RR) for any call to be set up successfully.

2. Traffic Channel (TCH) Congestion: This can be caused by failing sectors (logical or physical) in the MNO infrastructure side.

3. RACH congestion: This somewhat loosely aligns with SDCCH congestion. The network immediately aborts the RACH request following the unavailability of the SDCCH. 

4. Power Congestion: Yes, telecommunications hardware requires electrical power to run. Sometimes, depending on the installed capacity of network elements, the power available for use becomes very highly contentious and can result in dropped calls. This is common sometimes following some equipment upgrades.

5. Poor signal strength: This can be due to a challenging geographical terrain which dampens reception between your mobile device and the BTS serving it. It could also be due to being in an enclosure with lots of thick barriers, or due to moving away from an area effectively covered by the network. 

5. Hardware fault: This can be from your mobile device (perhaps failing antenna or SIM or some other fault capable of causing poor reception or no reception at all, or from one or more elements from the infrastructure of the Mobile Network Operator. Who would have thought a low battery can sometimes cause an established call to drop? Well, it is the case.

 6. Software Issues: Especially for smartphones, bugs in the software can mess with call connection establishment, call quality, or call sustainability.

7. Poor Handover: Every BTS has a range it covers and as long as the mobile device having the associated network SIM of the MNO is within that range of the BTS, established calls should be seamless. However, although network infrastructure is planned such that moving from one BTS area into another should not lead to any fluctuations in service delivery, sometimes the fluctuation is inevitable due to improper handover perhaps due to inappropriate declaration of neighbour cells (or radio masts if you may), or undershooting range, or overshooting range, or overlap of the sectors (logical divisions or/and physical divisions of the associated sectoral antennas). This can also be due to improper or inefficient configuration of the logical parameters of the BTS.

8. Vandalization: The count keeps going on these days. Telecommunications infrastructures are more commonly vandalized these days and without recourse than ever before. Sadly, asides from the nefarious activities of hoodlums, government-authorized construction activities also have become a menace to network availability. So you see, sometimes when you are on that call and it drops at the juiciest part of the conversation, it just may be that one crazy member of the public has messed with a network infrastructure on which your uninterrupted service depends. Optic fiber cables are the worst hit these days and excavators are not to blame, but the construction team is. Excavators only go where humans send them. At other times, it is the manual labourers who also damage these fiber cables while digging.

9. Depending on your clime, caller ID deactivation and date and time misalignment between your handheld and the local environment can cause your calls to drop.

10. In the case of data calls (Please note That the call establishment procedure is different from that of voice calls covered in this article), the device settings might be responsible for the dropped calls. For instance, attempting a data call in an area with only 3G technology available by your MNO whereas your handheld is set to LTE or ‘2G Only’ can cause your calls to drop. Any inappropriate input in the network settings can also cause your calls to drop. 

There are other causes of Call Drop Rate which are rather more technical. However, it is noteworthy that most of what influence Call Drop Rate also influence Call Setup Success Rate, as well as Call Success Rate.

I am hoping that you have had a worthwhile read so far and would like to ice the cake right away with how the Call Success Rate is defined, and the expectations of the Nigerian Communications Commission (NCC).
A Google search does not return impressive results for the definition of Call Success Rate. However, the following definition agrees absolutely with the formula earlier shared:

Call Success Rate is the rate at which a call is successfully made without abruptly dropping.
By NCC standards, CDR should be at most 1%. When we put this into perspective, considering that the desired value for Call Setup Success Rate (CSSR) is at least 98%, then it makes sense that the NCC recommendation for Call success rate is a value no less than 98%, and this corroborates the above definition for Call Success Rate.

Want to know about data called Key Performance Indicators? You guessed right, I am your plug. See you around.


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