VoNR Call Setup Time – 5G Performance Analysis

5G Call Flow


5G Stand Alone (SA) data services are rolling out throughout the world, it is very much essential for MNOs to provide services such as Voice/Video calls. To achieve this, 3GPP standards have defined that the 5G network must provide the Voice services using 5G RAN, 5GC and IMS. 5G radio technology is known as New Radio (NR), and the Voice services using 5G RAN, 5G Core and IMS is referred to as Voice over New Radio-VoNR .

As these networks are getting matured, Service providers starting measuring the KPI to meet the enhance the Customer user experience. The one of the most commonly used KPI for VoNR is Call setup time discussed in the this post.


Key Pointers

  • Call setup time is a standard term for Voice user experience and independent to technology
  • Call setup time definition remains same for VoIP, VoLTE and VoNR
  • It is the time calculated from User#1 dialing  to User #2 receives the alter tone
  • Considering SIP messaging the call setup time is calculated from SIP invite to SIP-180-Ringing
  • Call setup time is less when UEs are in RRC-Connected mode and higher when UEs are in RRC-Idle
  • Average VoNR call setup time measured in RRC-Connected mode can be in range of 2 sec-3 sec
  • Average call setup time measured in RRC-Idle mode can be in range of 3 sec-3.5 sec
  • A healthy operator network should have Call Setup Time is Less than 2.5 sec
  • Each technology have its own techniques to optimize the call setup time

VoNR Call Setup Time

VoNR Call setup time a critical KPI for network operator. In layman terms, it is the time different when User#1 dials User#2 number and the User#2 receives the ring. Here User#1 is considered as the Mobile Originating (MO) end and User#2 is considered as Mobile Terminating (MT) end.

When the call is setup (VoNR Call flow is available here), there are multiple procedure happens which includes, IMS registration, establishing IMS PDU with signaling bearer, paging the other end if it is in RRC idle, establishing the dedicated bearer for Voice Traffic.

For IMS signaling messages point of view, the MO call setup time can be calculated from SIP-Invite to SIP-180-Ringing SIP messages. The Call setup time is consist of two components i.e. Call Access Delay and Call Processing Delay.

  • VoNR Call Setup Time = Call Access Delay + Call Processing Delay

Call Access Delay

In VoNR , call access delay can be defined as processing delay between MO and MT device while MT device being paged and setting up IMS dedicated bearer. In IMS signaling point of view, it can be measured from SIP-Invite to SIP-183-Session-Progress.

Call Processing Delay

Call processing delay can be defined as the radio delays where in this period, NR in VoNR air interface messages flow between MO UE and gNB in addition to 5GC core network delays for MO side Dedicated Bearer Setup till the final step of establishing the call between MO and MT in the ringing stage. For signaling point of it can be measured from SIP-183-Session-Progress till SIP-180-Ringing.

Calculating the Call Setup Time from UE Logs

We have following sample logs for a VoNR Call. It shows only filtered IMS SIP Message only. Please do not consider these logs for any pass/fail decision, many message information are altered, it just for study and reference purpose.


  • Note the time stamp when UE sending the SIP Invite as per about logs that is (t1) 06:30:29:864
  • Note the time stamp when UE got the 180-Ringing, as per about logs that is (t2) 06:30:31:774
  • Call Setup Time = t2 – t1= 06:30:31:774 – 06:30:29:864 = 1:910 sec

Test Scenarios while capturing Call setup time 

When a engineer is capturing data and establishing the KPI report for Call setup time, he should consider following test scenarios.

  • Measure VoNR call setup time When UE#1 and UE#2 both are in RRC-Idle state
  • Measure VoNR call setup time when MO user is RRC-Connected and MT user is RRC-Idle
  • Measure VoNR call setup time, when MO user is in RRC-Idle and MT user is RRC-Connected
  • Measure VoNR call setup time when MO and MT users are from different chipset vendor
  • Measure the VoNR call setup time when 5GC has requested the Identity request for MO or MT user
  • Measure the VoNR call setup time when establishing a 3-way conference call
  • Measure the VoNR call setup time when MT user is from different Operator

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