What is an ideal CST of VoLTE call?

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Hi Experts.

What is an ideal CST of VoLTE call?

Admin note: this post was updated with image below.
What is an ideal CST of VoLTE call

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2-3 seconds.

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Thanks @RFSpecialist for getting back.
And it will be form UL INVITE till DL 180 Ringing ?

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Invite to 180 ringing difference sometime high value observed due to various SIP reason.

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Yes, but alerting phase is 180 ringing?
What SIP to follow then?

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Without Prack and Update procedures possible cst ~1sec

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CST is Time between the start of the call and the moment the phone of the called party starts ringing.

CST Healthy range is <2.5s

Formulae ( Sec )

: Avg of (Time(180 Ringing) - Time( SIP INVITE Request ) )

Impact: High CST will lead to delays & Silence period before Ring; High CST will obviously will deteriorate user experience.

What is an ideal CST of VoLTE call

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1 Like
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2.1 Seconds for VoLTE-VoLTE calls
this can be achieved by:

  1. Preconditions removal (Update message to be removed).
  2. RX Settings to be final (Activate dedicated bearer at the INVITE message)
  3. Disable DRX at call setup .
  4. VoLTE specific inactivity timer at the Call end (to avoid RRC connection setup in the following Call)
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Which vendor(s) allow to configure these 4 settings?

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If volte specific inactive timer & normal inactive timer are different, after Volte calls end when ue rrc is released?

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Volte inactivity timer starts at end of volte call and normal timer starts when data buffer becomes empty. Ue is released when both timers expire

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normal inactive timer is usually set as 10s.
How about default value of volte inactive timer?
During Volte calls in progress, UE are in still in RRC-connected mode, after Volte calls end, for example:

  1. normal inactive timer = 10s, volte inactive timer = 5s. What is going to happen after 5s, after 10s volte calls end?
  2. normal inactive timer = 10s, volte inactive timer = 20s. What is going to happen after 10s, after 20s volte calls end?
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Assume data session ends 2 secs after volte call ends
Case 1- ue is released 12 secs after end of volte call
Case 2- ue is released 20 seconds after end of volte call

Assume data session ends 7 secs before volte call ends
Case 1- ue is released 5 secs after end of volte call
Case 2- ue is released 20 seconds after end of volte call

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Hi Expert,
i have trouble that CST volte high, i found in flow that occur some RTP Message after SIP 183 and before SIP PRACK Request at MT UE, after SIP PRACK Request and before SIP 200 OK at MO UE,
Please tell me the reason this happen
thanks,

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Around < 2 Second…and the formula to calculate CST in volte

Volte CST time = Time (180 Ringing)- Time (SIP Invite)