eNB inactivity timer reset

[mutley2202]

Hi All,
I am trying to see if I have come across a common problem which other LTE engineers have come across. On testing we appear to of had a couple of different expierences relating to either duplicate or Missing/delayed sms.

The testing was sending several sms's while registered on LTE, I have seen duplicate or missing/delayed sms alot. The traces show that at the start of the MO SMS RRC is established along with S1, sms's are sent in the uplink direction as expected however after 10 seconds from the start of RRC establishment the eNB tears down S1 and RRC due to user inactivity. We also see the same expierenced in the downlink direction ovbiously depending on if the sms delivery hits the eNB at a certain time.

As sms's are sent across the SRB the E******* inactivity timer appears to only be reset if traffic passes the DRB meaing SRB traffic will not reset the inactivity counter.

Has anyone else seen this in E******* or any other vendor eNB's ? I have also tested Huawei and dont appear to have the same issue. I am currently finding out from Huawei R&D if the include all SRB and DRB traffic to trigger inactivity timer reset.

Huawei's description of the timer states the below however doesnt confirm if SRB will reset.

Indicates the length of the UE inactivity timer. The eNodeB monitors whether UEs are receiving or sending data. When a UE has neither received nor sent data for a duration exceeding this period of time, the eNodeB releases the radio resources for the UE. If this parameter is set to 0, the UE inactivity timer is not used.

Yes there is the ability to up the inactivity timer however due to other reasons it has to be set to 10.

Any info would be much appreaited.

[Nyquist]

Hi.
Just a curiosity. Do you have VoLTE for CS services? SMS is sent over CS and in case of not implementing VoLTE, CSFB is the solution. If CSFB is implemented, SMS is sent over a overlapped 3G/2G network.
Regards

[mutley2202]

Hi Nyquist I have only just seen this post as I havent been on for a while, No we don't have VOLTE and yes we use CSFB for voice services. Your statement regarding sms delivered over CS while registered on LTE isn't correct. SMS is delivered over LTE and doesnt require CSFB. This is achieved by using SMS via Sgs which enables the ability for a LTE registered subscriber to have sms delivered via the LTE RAN. The traces capture also show this.

Hi.
Just a curiosity. Do you have VoLTE for CS services? SMS is sent over CS and in case of not implementing VoLTE, CSFB is the solution. If CSFB is implemented, SMS is sent over a overlapped 3G/2G network.
Regards

[mutley2202]

We got to the bottom of this in the end, E******* have a hidden tunable parameter in L13a CP2 which is a NAS inactivity timer. The standard operator changeable inactivity parameter is for DRB traffic only, as SMS is sent via the eNB as SRB traffic the inactivity timer doesnt get reset causing it to be dropped after no DRB traffic has passed for however many seconds you have configured. CP2 actually has the Nas timer on by default and set to 4 seconds. This is not a value that can be seen by any operator(unless the vendor has given the access you shouldnt have). In the times of multiple messages being sent having the SRB traffic included the RRC connection never gets release until SRB and DRB traffic are inactive for the configured period of time.