Quality of Service (QoS)

The following are the metrics and their definitions for measuring Quality of Service (QoS).

• Call Completion Rate (CCR)
  The ratio of successfully completed calls to the total number of attempted calls (ITU-T E600/2.13). That is, the ratio of the number of completed call attempts to the total number of call attempts, at a given point of a network.

  Note:	This ratio is typically expressed as either a percentage or a decimal fraction. It is the number of calls of specific duration successfully completed; measured per 100 calls.
  Note:	A complete call is a call that is released by normal call clearing (i.e. Released Message "RL_M" and Released Complete Message “RLC_M” has been successfully exchanged in the signaling flow), be it during a ringing phase or conversation phase by either the caller or called party.

• Answer Seizure Ratio (ASR)
  The ratio of the number of successful calls over the total number of outgoing calls from a carrier’s network (i.e. On a route or a Destination Point Code (DPC) basis, and during a specified time interval, the ratio of the number of seizures that result in an answer signal to the total number of seizures: ITU-T E600/2.14).

  Note:	ASR is line seizures that are answered by person or device divided by total number of seizures.
  Note:	Seizure is achieved after a successful “Call setup”. It means seizing a trunk circuit for conversation or other network services. In GSM network, it refers to seizing a Traffic Channel (TCH) after a successful “Call setup”.
  Note:	A successful call is a call that is answered by a called party or machine (e.g., fax machine, answering machine, e.t.c.).

• Call Setup Success Rate (CSSR)
  Number of the unblocked call attempts divided by the total number of call attempts.
  Or (1 - Blocking Probability) x 100%

  Note:

  A call setup is an exchange of signaling information in the call process that leads to Traffic Channel (TCH) seizure.

• Dropped Call Rate (DCR)
  The Dropped Call Rate (sometimes called Call Drop Rate) is the number of dropped calls divided by the total number of call attempts.
  Or (1 - Call Completion Ratio) x 100%

  Note:

  A dropped call is a call that is prematurely terminated before being released normally by either the caller or called party (i.e., the call is dropped before the exchange of Released Message “RL_M” and Released Complete Message “RLC_M” in the signaling flow).

• Post Dialing Delay
  In GSM network, is the average time between pressing send button (after pressing correct digits) and getting a ring back tone. This is also called “Call Setup Time” or time to connect a call. 
• Handover Success Rate (HOSR)
  This is the ratio of the number of successfully completed handovers to the total number of initiated handovers. This ratio can be expressed as a percentage. 
• Bit Error Rate (BER) Per Link
  The link Bit Error Rate (BER) refers to the average bit error rate on the MSC-PSTN link, Inter MSC link, A-Interface and Abis-Inteface. This parameter should not deteriorate above 10^-9. 
• The End-to-End Bit Error Rate
  This refers to the average end-to-end bit error rate. This parameter should not deteriorate above 10^-6. 
• Busy Hour Traffic Channel Congestion (%)
  This is the percentage congestion of the TCH measured at the busy hour and is given by:

  Busy Hour TCH Traffic (Erlang) – Average TCH Traffic (Erlang)	× 100
  Busy Hour TCH Traffic (Erlang)

• % of Failures for Credit Balance Inquiry
  This is the ratio of the number of failures of credit balance inquiry to the total number of credit balance inquiry expressed as a percentage at some instant on the network. This parameter is for a prepaid subscriber.

  Number of failures for credit balance inquiry	× 100
  Total number of credit balance enquiry

• Minimum Data Rate
  This is the minimum TCH encoding rate for data (Half-Rate channel, 4.8kbps: GSM Specification 06.20). 
• Minimum Speech Rate
  This is the minimum TCH encoding rate for speech (Half-Rate channel, 6.5kbps: GSM Specification 06.20). 
• % of SMS-MMS Delivery Failures
  This is the ratio of SMS/MMS to the recipients undelivered to the total number of SMS/MMS received at the Service Center within specified period of 10 days.

  Number of SMS/MMS to recipients undelivered	× 100
  Total Number of SMS/MMS received at Service Center

• % of SMS/MMS Incorrect Feedback
  This is the ratio of the number of SMS/MMS transmitted in which the sender received wrong feedback to the total number of SMS/MMS received at the Service Center at some instant on the network.

  Number of SMS/MMS in which the senders received wrong feedback	× 100
  Total Number of SMS/MMS received at Service Center

• % of SMS/MMS Multiple Billing
  This is the ratio of the number of SMS/MMS messages in which more than one charges are applied per message to the total number of SMS/MMS received at the Service Center at some instant on the network.

  Number of SMS/MMS in which more than one charges are applied	× 100
  Total Number of SMS/MMS received at Service Center

• Number of Customers Satisfaction Index
  This is the percentage of the number of customers satisfied with the services of an operator in randomly distributed samples of customers. 
• Speed of Problem Resolution
  1. % cleared same day
     This is the percentage of the number of problems resolved on the day they were received.

     Number resolved problems in day one	× 100
     Total number of problems received on that day

  2. % in two days
     This is the percentage of the number of problems resolved within the second day they were received.

     Number resolved problems in day one and two	× 100
     Total number of problems received on day one

  3. % cleared in three days and above
     This is the percentage of the number of problems resolved within three days and above to the day they were received.

     Number resolved problems in day 1, 2, 3 and above	× 100
     Total number of problems received on day one

• Billing Integrity
  1. % of total bills overcharged
     This parameter is the percentage of the number of Post-Paid accounts that are overcharged within a particular month.
  2. % of incorrect credit balance
     This parameter is the percentage of number of Pre-Paid accounts that suffer incorrect credit balance within a particular month.
  3. % of failures for Credit Balance Inquiry
     This is the ratio of the number of failures of credit balance inquiry to the total number of credit balance inquiry expressed as a percentage at some instant on the network. This parameter is for prepaid subscribers.
• Customer Care Accessibility
  1. 100% Call Completion Rate
     This means that all calls to the center must be answered by a customer care personnel or a machine to put a customer on hold for sometime (the line must never be busy at any time). Alternatively, all calls to the center must go through.
  2. Minutes a customer spends on the queue
     This is the average time in minutes a customer is expected to spend on customer care center queue.
• Customer Interface Points
  1. Number of Interface points
     This is an office where a customer can go to lodge complaints. This is in addition to customer care centers.
  2. Minutes a customer spends on the queue
     This is the average time in minutes a customer is expected to spend on customer interface point queue before being attended to by a staff.
• Recharge Cards
  1. % of Recharge Cards Loading Errors
     This is the ratio of the number of times Recharge Card loading failed to the total number of loading attempts at some instant on the network expressed as a percentage.

     Number resolved problems in day one	× 100
     Total number of problems received on that day

  2. % of Recharge Cards loading incorrect feedback
     This is the ratio of the number of times an incorrect feedback is received during Calling Card / voucher loading to the total number of loading attempts expressed as a percentage.

     Number of incorrect feedback received during voucher loading	× 100
     Total Number of loading attempts

Speech quality is a complex psycho-acoustic phenomenon within the process of perception. As such, it is necessarily subjective (i.e., Every person interprets speech quality in a different way).

Nevertheless, if speech quality is to be quantified and measured automatically, the dependence on individual opinion must be eliminated. Therefore speech quality is generally expressed as a Mean Opinion Score (MOS). Speech quality measurements provide a measurement basis in order to specify the requirements that network operators have to fulfill.

Methods for evaluating speech quality are two: Subjective method and Objective. The “Subjective method” makes use of a listener panel to assess speech quality. Speech quality is expressed as MOS, which is average speech quality perceived by the members of the panel.

The “Objective method” however replaced the listener panel by an algorithm to compute MOS value from a speech samples. The Commission expect all Operators to use the “Objective method” (where equipment available) of measurement because it is in good agreement with “exact” speech quality, it is automatic and has easily reproducible result.

The speech quality can be transformed by appropriate statistical methods to a scale as in the table below.

The table below gives the benchmarking for the speech quality adopted by the Commission using the scale in the table above. A Voice Quality Impairment of less than 2%, means that the total number of “Bad Speech” Samples (resulting in only noise) throughout entire conversation must not be up to 2%. This means that the entire conversation must result to predominantly “Excellent and Good” speech Samples.