Questions stringlengths 58 216 | Refference Answers stringlengths 132 451 |
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why QoS modification in PDU session fails due to insufficient resources? | Verify available resources in the UPF and gNB. Consider downgrading QoS parameters if maximum resources are reached. Check for congestion in the transport network. Optimize resource allocation policies. Monitor radio resource utilization at serving cells. |
why PDU session modification for handover between access types fails? | Examine N2 interface logs for handover signaling issues. Verify target access network availability and configuration. Check policy rules for access type switching. Ensure UE supports requested access type mobility. Validate session continuity support for the service. |
why GTP-U user plane path failure detected between gNB and UPF? | Verify GTP-U Echo Request/Response configuration. Check physical connectivity and transport network quality. Examine load balancing configuration if multiple paths exist. Verify MTU settings across the path. Implement redundant paths if critical. Ensure ECMP is correctly configured if applicable. |
why UPF receives GTP-U Error Indication from 5G-AN for active PDU session? | Examine Error Indication Report details sent from UPF to SMF. Verify the SMF modifies the PFCP session to buffer downlink packets. Ensure SMF initiates session resource release at the 5G-AN followed by service request procedure to re-establish user plane connection. Check tunnel endpoint identifiers. |
why 5G-AN receives GTP-U Error Indication from UPF for active PDU session? | Verify the 5G-AN initiates PDU Session Resource Notify procedure and releases resources for affected PDU session. Check UE connectivity status to determine if re-establishment is needed. Examine logs for cause of GTP-U context loss at UPF. Validate GTP-U tunnel configuration at both endpoints. |
why PDU session establishment fails due to QoS flow resource allocation failure in RAN? | Check RAN resource utilization and capacity. Verify QoS parameters requested versus available resources. Consider admission control policy adjustments. Examine potential radio interference or coverage issues limiting available resources. Monitor radio resource utilization in affected cells. |
why QoS flow establishment fails during PDU session setup? | Verify QoS parameters against subscription limits. Check RAN capacity to support requested QoS. Examine transport network QoS configuration. Ensure UPF supports the requested QoS enforcement mechanisms. Consider alternative QoS profiles if original cannot be supported. Validate QoS mapping. |
why Guaranteed bit rate (GBR) QoS flow establishment fails? | Verify RAN supports GBR flows and has sufficient resources. Check transport network dimensioning for GBR support. Ensure UPF QoS enforcement capabilities. Validate PCF policy and subscription authorization for GBR services. Monitor current network load affecting GBR resource availability. |
why GTP-U Error Indication received after handover completion? | Verify proper path switch procedure completion. Check target RAN node GTP-U endpoint configuration. Ensure SMF updates UPF with correct RAN GTP-U endpoint after handover. Examine potential race conditions in signaling sequence. Validate tunnel endpoint updates across all nodes. |
why PDU session resource setup fails on target gNB during handover? | Check target gNB resources and capabilities. Verify QoS requirements can be met at target. Ensure proper N2 signaling for PDU session resource setup. Examine logs for specific N2 cause value in setup failure. Validate radio resource availability at target cell. |
why VoLTE call setup delay increasing after UE moves from 5G SA coverage to 4G with IMS registration taking >3 seconds? | Check IMS registration procedure optimization for mobility scenarios. Verify P-CSCF discovery procedure during 4G attachment. Analyze DNS resolution performance for IMS services in 4G. Review Diameter signaling load between MME and HSS. Check for IMS restoration procedures triggering unnecessarily. Optimize SIP compres... |
why Users at cell handover boundaries experiencing 2-3x normal latency in 5G SA deployment? | Optimize handover parameters including A3 offset and time-to-trigger; implement make-before-break handover for critical users; adjust measurement reporting configuration; ensure proper neighbor cell configuration and synchronization |
why UE fails IMS registration with SIP 403 Forbidden response after successful 5G SA registration with error logs showing authentication vector mismatch? | Verify HSS/UDM authentication configuration. Check IMS authentication vectors in UDM. Confirm proper synchronization between UDM and IMS. Inspect UE security capabilities reported in registration request. Verify IMS APN settings in UE. Check encryption algorithm compatibility between UE and network. Examine logs for se... |
why UE shows 5G SA connectivity but fails to establish VoNR with SIP 404 Not Found error during IMS registration. Device logs show IMS APN resolution failure? | Check DNS server configuration for IMS APN. Verify DNN/APN configuration in SMF. Examine PDU session parameters for IMS traffic. Verify IMS service status in UDM subscription data. Check UE IMS configuration parameters. Validate SMF session policy for IMS traffic. Verify FQDN resolution path through core network. Inspe... |
why VoNR to VoLTE fallback fails during UE mobility from 5G to 4G coverage area. Call drops instead of continuing as VoLTE. UE supports both VoNR and VoLTE? | Check SRVCC configuration in MME and AMF. Verify inter RAT handover policies. Examine E UTRAN target cell preparation messages. Check IMS continuity support status. Validate UE SRVCC capability. Examine SMF to PGW C signaling during handover. Check for session continuity support in HSS. Review core network timers for h... |
why VoNR emergency calls fail to establish with SIP 503 Service Unavailable. Regular VoNR calls work fine. UE location information is properly included in SIP headers? | Verify emergency call routing configuration in IMS. Check PSAP connectivity status. Examine emergency bearer QoS policy configuration. Verify emergency call prioritization in RAN. Check for capacity issues in emergency call servers. Validate location service functionality. Review emergency APN configuration. Check emer... |
why VoNR calls drop during handover between gNBs with SIP BYE message containing reason header RTP Timeout. Radio measurements show good coverage from both cells? | Check X2/Xn interface configuration between gNBs. Verify QoS flow handover procedures. Examine data forwarding setup during handover. Check handover command timing and execution. Verify UPF path switch timing. Examine handover interruption time measurements. Check gNB release coordination. Verify RTP timeout timer sett... |
why UE fails VoNR but succeeds with VoLTE despite good 5G coverage. UE capability shows support for both services. IMS registration fails only in 5G mode? | Check UE voice domain preference settings. Verify UE radio capability for VoNR. Examine IMS configuration specific to 5G. Check UE firmware/software version compatibility. Verify UE voice client implementation for 5G SA. Examine PDU session parameters for IMS in 5G. Check for mismatches in security algorithms between 4... |
why Unnecessary RRC state transitions between RRC_CONNECTED and RRC_INACTIVE increasing latency for bursty traffic? | Optimize inactivityTimer in RRC; implement RRC state prediction based on traffic patterns; consider keeping critical devices in RRC_CONNECTED state; adjust CDRX instead of state transitions for power saving |
why Many UEs report synchronization failures (time/freq sync loss);Timing synchronization issue (GPS or network time sync lost) impacting multiple UEs? | Check synchronization source (GPS/PTP) for the cell site; look for sync failure alarms; restore sync via backup if primary is down; monitor that cells regain and maintain sync (important for TDD networks to avoid desense) |
why Connected UEs but no user data passing;User-plane issue such as missing bearer setup or GTP-U tunnel failure; despite RRC connected? | Verify that PDU sessions are established for the UEs (check SMF/UPF for tunnels); ensure gNodeB has the user-plane configured (DRB active); if control-plane is fine; troubleshoot user-plane path (firewall; routing) that might block user data |
why Downlink throughput fine; uplink nearly zero;Uplink path issue (interference or hardware fault) while downlink remains good? | Investigate uplink interference or noise floor in the cell; check UE power headroom reports to see if UEs are power-limited; verify uplink hardware (connectors; TMA) at site; possibly a faulty uplink chain if downlink is unaffected |
why Poor SINR in otherwise strong signal area;Significant interference or noise is present even though RSRP is high? | Locate potential interference sources (could be external like repeaters or internal PIM issues); perform spectrum analysis on the frequency band; adjust antenna orientation or apply filtering to improve SINR; ensure no overlapping cells with same PCI causing confusion |
why Sudden increase in scheduling request failures;Uplink scheduling requests from UEs not being granted; possibly due to scheduler overload or PUCCH issues? | Check if too many UEs are contending for uplink at once; verify PUCCH configuration and resources for scheduling requests; ensure scheduler is not starved (consider enabling additional uplink symbols if TDD); address any identified contention or configuration problem |
why Massive MIMO beams not switching properly causing coverage holes;Massive MIMO beamforming malfunction or calibration issue affecting signal directionality? | Run antenna calibration procedures; verify beamforming algorithm performance via test UEs; update beam management software if needed |
why UE randomly switches to 4G despite strong 5G coverage;Inter-RAT reselection threshold misconfigured or UE preference causing unnecessary fallback? | Check idle mode reselection priorities and thresholds (ensure 5G has higher priority when coverage is sufficient); confirm no coverage gaps or periodic 5G outages triggering fallback; update UE configuration if its preferring LTE (e.g.; ensure SA mode is prioritized) |
why Sector shows abnormally low user count (underutilized due to issues);Sector-specific fault (perhaps a configuration error or broadcast issue) deterring UEs from camping? | Verify that the cell is properly advertising itself (correct PLMN; TAC; cell ID); ensure no inadvertent barring or low priority set; check coverage and interference for that sector; once corrected; monitor UE count normalization |
why Network reports excessive HO oscillations between two cells;Coverage overlap or hysteresis misconfiguration leading to ping-pong handovers? | Adjust handover hysteresis and time-to-trigger values to add stability; possibly shrink overlap by tuning antenna tilt/power if cells overlap too much; use mobility optimization features (like conditional handover) if available to reduce oscillations |
why All UEs in cell dropping to idle at same time sporadically;Potential cell outage or eNodeB/gNodeB software crash causing mass disconnects? | Check if there are any cell reset or outage alarms corresponding to those times; analyze core logs to see if gNodeB sent failure indications; if software crash; upgrade to latest firmware; ensure power and transport to site are stable (no periodic power losses) |
why UEs get high ping times when on 5G (radio side);Possibly scheduling or TDD configuration causing increased latency? | Inspect frame configuration for TDD (if applicable) to ensure enough UL/DL switching to handle ping; check if scheduler is deprioritizing ping (ICMP) over other traffic; measure RLC and PDCP latency; if needed; adjust scheduling to reduce RTT for small packets |
why Frequent MAC layer resets in logs;Underlying MAC/RLC issues possibly due to buffer overflow or protocol error requiring reset? | Analyze eNodeB/gNodeB logs around reset events to determine trigger (e.g.; a particular UE or traffic type); update node software if it's a known bug; ensure configuration (like RLC AM window size) is compatible with UEs; if a specific UE triggers it; test that device for compliance |
why TDD synchronization issues causing slot alignment errors;Timing synchronization loss (GPS/PTP failure) leading to out-of-sync operation? | Check synchronization source status (GPS clock or PTP link); restore sync service; ensure backup sync available to prevent recurrence |
why RAN slicing quality degraded for a specific slice (users complaining);Resource partition misconfiguration for that network slice or scheduler issue in RAN? | Review RAN slice (Network Slice Subnet) resource allocation (PRBs; QoS) for the affected slice; ensure slice has adequate configured resources and priority; adjust scheduling weights or algorithms if one slice starves another; verify improvements by measuring slice-specific KPIs |
why Beamforming not effective (users not benefiting from beams);Beam management algorithm not optimally assigning beams or line-of-sight issues limiting beam gain? | Review drive test data to see if beamforming is improving signal as expected; calibrate the beamforming weights if needed; ensure line-of-sight to users or use beam refinement for non-LOS; update beam selection algorithm to respond faster to UE movement or orientation |
why Coverage hole in area that previously had coverage;New obstruction (building or terrain change) or antenna issue causing a coverage gap? | Conduct a new site survey to identify changes (construction; foliage growth); if obstruction; consider adding a small cell or repeater to cover the hole; check antenna and feeder for damage that might reduce coverage; adjust antenna pattern if possible to cover the gap |
why Abnormal uplink noise floor elevation;External uplink interference or hardware fault (e.g.; PIM) raising the noise floor? | Use spectrum analyzer to scan the uplink band for interfering signals; inspect antenna system for PIM (loose connectors; corrosion); implement filtering or replace faulty components; coordinate with regulatory body if an external interferer (like illegal repeater) is found |
why RACH (Random Access) failures observed;Random access failures likely due to PRACH configuration errors or contention overload? | Verify PRACH parameters (preambles; power levels) in gNodeB config; ensure no excessive collisions by adjusting backoff; monitor RA success rate after changes |
why One cell not accepting any new connections (access failures);Cell is barred or in an abnormal state preventing new UEs from connecting? | Check cell status in OAM; verify that cell barring settings are correct; if cell is faulty; reset the cell or resolve alarms; then re-allow access |
why Cell's power output suddenly reduced (coverage shrank);Radio power output reduced due to hardware failure (power amplifier) or misconfiguration? | Examine base station TX power settings and alarms; replace or repair faulty power amplifier; recalibrate output power to restore coverage |
why One sector experiencing much lower throughput than others on same site;Sector-specific issue (potential hardware degradation or interference localized to that sector)? | Compare performance counters across sectors; inspect that sectors radio unit and feed lines for faults; resolve any interference affecting only that sector |
why Persistent high TA (timing advance) values even for close UEs;Timing misalignment causing UEs to use excess timing advance (possible sync issue or configuration error)? | Verify cell radius and timing advance configuration; ensure synchronization is correct; recalibrate or restart timing modules to correct TA calculations |
why UEs not receiving paging in this cell (missed pages);Paging issue in the cell; possibly due to paging channel overload or configuration error? | Monitor paging success rate; ensure paging capacity (paging occasions) is sufficient; check core network paging distribution to this cell and adjust tracking area if needed |
why Reduced cell capacity after software upgrade;Software upgrade introduced a bug or changed configuration; affecting cell capacity or performance? | Review release notes for known issues; engage vendor support if bug; if necessary; roll back to previous software or apply patches; fine-tune new parameters introduced in upgrade |
why UEs experiencing jittery voice in VoNR calls;Quality of Service (QoS) issue for voice (VoNR) likely due to scheduling or packet loss on the radio link? | Ensure voice bearers have high priority QoS (5QI=1) configured; check for any packet loss on the radio and fix underlying issues; adjust scheduler to reduce latency for voice |
why Frequent radio link recovery events logged;Temporary radio link degradations triggering RRC recovery; likely due to intermittent interference or fading? | Identify patterns in recovery events timing; correlate with external factors (e.g.; heavy machinery; weather); mitigate by adjusting link failure detection thresholds or addressing interference sources |
why Intra-frequency interference detected by spectrum analysis;Co-channel interference from nearby cells on same frequency or external emitters? | Audit frequency planning to avoid same-frequency neighbors; if external; coordinate spectrum usage or apply interference cancellation techniques; possibly retune or reassign frequencies |
why Massive MIMO calibration errors affecting performance;Antenna array calibration issue impacting beamforming and MIMO performance? | Perform a calibration routine for the massive MIMO antennas; ensure calibration data is updated after any hardware change; schedule periodic auto-calibration to maintain performance |
why UE attach delayed at the RAN stage (long initial RRC setup);Delay in RAN initial access; possibly due to overloaded random access or slow processing at gNB? | Examine random access channel load; ensure enough RA preambles and appropriate backoff; check gNB CPU usage and optimize processing or upgrade hardware if needed |
why Phantom cell (ghost PCI) observed causing confusion in scanning;Conflicting PCI or an unintended test cell broadcast causing confusion in UE cell selection? | Verify PCI planning to ensure unique identifiers; scan area for unknown cell broadcasts; eliminate rogue cell transmissions or reconfigure conflicting PCI to resolve confusion |
why Multiple UEs simultaneously experience data stall;gNodeB scheduling or buffer issue causing data stall for multiple UEs? | Check gNodeB for any resource buffer overflow or scheduler halt conditions; capture trace to see if data packets are queued but not sent; consider rebooting or upgrading gNodeB if a known issue |
why Cell selection issues: UE prefers far cell over closer one;Neighboring cell reselection priorities misconfigured; causing UE to prefer a distant cell? | Review cell reselection parameters (priority; thresholds) broadcasted; adjust so that the closer cell has higher priority; update neighbor lists if any entry missing |
why High number of BBU processing errors in counters;Baseband processing errors indicate possible firmware issues or overload conditions in the BBU? | Analyze error logs from the baseband unit; ensure no memory or CPU overload; update BBU firmware if available; if hardware issue; consider replacement |
why RF module overheat alarm correlates with degraded service;Radio unit overheating leading to throttling or shutdown and degraded service? | Check site cooling and ventilation; clean filters or improve air conditioning; if persistent; replace or repair overheated module; possibly reduce transmit power temporarily to reduce heat |
why Users report service loss when entering a certain building (5G indoor issue);Indoor coverage gap or signal attenuation by building materials causing service loss inside? | Conduct in-building coverage survey; deploy indoor 5G small cells or DAS to improve indoor signal; leverage lower frequency band (if available) for better penetration |
why Sector swap issues causing neighbor mismatch;Configuration mix-up (sector swap) where sector mapping is incorrect leading to neighbor mismatches? | Audit the physical-to-logical sector mapping for the site; correct any swapped feeder connections in configuration; verify by testing handovers and ensuring coverage matches the intended sectors |
why UE uplink power maxed out but throughput low;UE at cell edge or heavy uplink interference causing UE to transmit at max power with limited throughput? | Improve uplink coverage with better cell placement or tilt adjustments; reduce uplink interference by identifying noise sources; consider adding an uplink repeater or a closer cell site |
why One carrier (NR band) having issues while others are fine;Single carrier frequency or band experiencing a fault (hardware or config) while others operate normally? | Compare configuration across carriers; test hardware (radio unit; filter) for the problematic band; recalibrate or swap hardware for that carrier; if config error (like wrong frequency or PA bias); correct it |
why Frequent SRS (Sounding Reference Signal) failures logged;Sounding Reference Signal (SRS) misconfiguration or interference causing uplink sounding issues? | Verify that SRS settings (periodicity; power) align with UE capabilities; check if any interfering uplink signals coincide with SRS; adjust SRS configuration or scheduling to avoid conflicts |
why Sudden cell reset/restart events observed in logs;Base station is restarting unexpectedly due to a fault or watchdog timeout? | Examine core dumps or logs around reset time; identify if a specific trigger (load; message) causes reset; apply vendor patch or replace unit if hardware fault; monitor after fix |
why Packet duplication feature malfunctioning (causing overhead);Misconfiguration in dual connectivity or duplication causing extra overhead and confusion? | Review dual connectivity settings and ensure duplication is only enabled where needed; correct any mismatched parameters between Master and Secondary nodes; test that duplication stops for normal flows |
why UE failing to camp on 5G after leaving 4G (redirection failure);5G cell reselection issue; possibly due to missing broadcast info or priority for 5G after LTE? | Check that 5G cell is broadcasting proper SIB for reselection; ensure 5G has higher priority when available; adjust idle mode parameters so UE returns to 5G when back in coverage |
why Abnormal handover preparation failures in core logs (from this cell);Core network or signaling issue (NGAP/N2) during handover preparation from this cell? | Inspect AMF and gNB logs for handover preparation errors (e.g.; N2 message failures); ensure target cell is reachable via core and authorized; address any security or context issues causing preparation to fail |
why User equipment see high RLF when moving at high speed (mobility failure);Mobility parameters not optimized for high-speed scenario; causing late handovers or no handovers? | Activate high-speed (UE speed category) mobility settings on the network; increase measurement frequency for fast-moving UEs; possibly add more sites or adjust antenna patterns along highways |
why Multiple UEs stuck in RRC Inactive; not resuming properly;UE context in RRC Inactive not being resumed properly due to a signaling or core issue? | Verify that paging for inactive UEs is functioning; ensure the AMF is triggering resume for inactive UEs; check if any known issue with inactive state; and consider adjusting timers or disabling the feature if problematic |
why Differing speeds when connected to NSA vs SA mode in same cell;Architectural difference or configuration causing SA mode to deliver lower throughput than NSA? | Examine SA user-plane path for extra bottlenecks (UPF placement; slice limits); ensure SA bearers use all available spectrum; update core or gNB software if SA performance bug; optimize accordingly |
why Cell throughput drops drastically in rainy weather;Rain-induced attenuation (rain fade) especially on high-frequency (mmWave) links causing throughput drop? | Implement adaptive modulation or fallback to lower band during heavy rain; ensure backhaul links have weather mitigation (like higher fade margin); optimize link budget for rain conditions in planning |
why Frequent PDCCH decoding errors leading to retransmissions;Downlink control channel interference or overload leading to decoding failures? | Increase PDCCH power or adjust CORESET configuration to improve decoding; reduce interference on control channel (e.g.; reassign resources or coordinate with neighbors); ensure UEs have latest firmware for better decoding algorithms |
why Spurious emissions cause interference in adjacent channels;Equipment malfunction or external device causing out-of-band emissions interfering with 5G channel? | Conduct spectrum analysis to identify spurious emission frequencies; isolate and repair or replace faulty transmitter; if external; coordinate with spectrum authorities to remove or mitigate the interference source |
why Sector experiencing strong uplink interference intermittently;Intermittent uplink interference from external sources (e.g.; jammer or malfunctioning device) raising the noise floor? | Use direction finding during interference events to locate source; apply uplink filters or change frequency if possible; engage with source owner or authorities to eliminate the interference |
why UE signaling loops (repeated RRC messages) observed;Signaling procedure fault (RRC/NAS bug or misconfig) causing abnormal repeated messaging? | Trace RRC/NAS messages to pinpoint the looping message sequence; check for misconfigured timers or incompatibilities; apply vendor patch if it's a known bug; reset the affected UE contexts to clear the loop |
why Cell not releasing connections (UE stays connected long after use);Stuck session due to signaling message failure or bug? | Check for known release bugs in gNB/AMF; ensure RRC release and NAS deregistration timers are appropriately set (UE and network side); implement periodic context release cleanup in core if needed; update software to fix any identified bugs causing this |
why High downlink modulation fallback (256QAM rarely used);Poor radio conditions not meeting high modulation requirements (falling back to lower QAM)? | Improve signal quality (reduce interference; better coverage) so that higher SINR can be achieved; ensure 256QAM is enabled in cell configuration and UEs support it; if many UEs are at cell edge; consider cell splitting or adding mid-band coverage to allow higher modulations |
why Downlink control channel congestion (PDCCH capacity reached);Too many users or high control overhead usage causing PDCCH to reach its limit? | Optimize control channel usage (adjust PDCCH aggregation or enable additional control channel elements if available); reduce unnecessary control signaling (e.g.; disable verbose SI messages if not needed frequently); consider spreading users across more cells or carriers |
why UEs report network rejection in this cell (attach reject at RAN);Cell-specific access issue; such as forbidden PLMN or cell barred status being incorrectly set? | Review cell access configuration (allowed PLMN list; access class barring); adjust settings to allow intended users; if core instructed reject due to overload; coordinate with core to remove per-cell restrictions once load is managed |
why UE unable to register with 5G network (attach failure);Core network registration issue (e.g.; subscription data missing or authentication problem)? | Validate UE subscription on UDM (proper provisioning); check authentication logs in AUSF; ensure the UE's credentials and network security settings match |
why Frequent authentication failures for new UEs;Authentication procedure is failing; likely due to incorrect keys or mismatch between SIM and network? | Examine authentication vectors (AVs) for the UE; verify that the SIM (USIM) keys are in sync with the network (AUSF/ARPF); if multiple failures; check if a known algorithm incompatibility exists and update configuration |
why Massive attach attempts failing simultaneously (signaling storm);Signaling overload (potential DDoS or mass simultaneous attach) overwhelming the control plane? | Enable overload controls on AMF (throttle or reject excess requests); identify source of storm (misbehaving devices or attack) and mitigate (block or stagger requests); scale out control-plane nodes if necessary to handle load spikes |
why Intermittent NAS signaling timeouts during registration;Network latency or missing response from core NFs causing NAS message timeouts? | Trace NAS message flow (e.g.; using a protocol analyzer) to find where delay occurs; ensure AMF and gNB connectivity is stable; adjust NAS timers to tolerate slightly longer latency if needed while underlying issue is resolved (e.g.; by fixing network lag or server performance) |
why Multiple UEs stuck in authentication stage;UE remains in authentication because of an unresolved challenge (perhaps AUSF or UDM not responding correctly)? | Check communication between AMF and AUSF/UDM for this UE; verify that the authentication server is reachable and functioning; possibly reset the subscriber's profile and have UE retry |
why High paging failure rate in core metrics;High paging failure may result from tracking area misconfiguration or overloaded paging channels? | Verify that UEs are registered in correct Tracking Area Lists; ensure paging messages are sent to all cells where UE might be; check if gNBs are receiving and handling paging (no congestion on PCCH); adjust paging strategy or add more paging capacity if needed |
why UE gets deregistered unexpectedly after some time;The core network is deregistering UEs due to an error or policy (could be a software crash or implicit deregistration on failure)? | Inspect AMF logs for deregistration cause (e.g.; implicit dereg due to internal error); monitor stability of AMF instance (no crashes or restarts); if a software bug is identified; apply fix or workaround; otherwise adjust timers/policies that might prematurely drop connections |
why Periodic loss of connectivity for all UEs (core resets);Core network node (AMF/SMF) is restarting or failing periodically; causing session drops for all UEs? | Identify which core component is resetting (check heartbeats and service restarts); investigate root cause (resource exhaustion; software bug); failover to standby nodes if available during fix; apply vendor patches to stabilize the network |
why Session setup fails for certain data slices;Network slicing issue; where the requested slice isn't properly configured or available? | Ensure S-NSSAI for that slice is configured in NSSF and supported by all components (AMF; SMF; RAN); update slice configurations in core and gNB; if slice is at capacity or down; allocate more resources or bring it online |
why Inability to handover from 4G to 5G (core NWDAF issues possibly);Inter-RAT handover failure due to missing interworking configuration (N26 interface issues or subscription not allowing handover)? | Check 4G-5G interworking setup (N26 between AMF and MME); confirm that the UE's subscription permits 5G access; ensure the 5G core has the context from 4G (via N26 or via a new registration if fallback); test the handover procedure in a controlled environment |
why SMF not allocating IP addresses (PDU session fails);IP address allocation issue in SMF (possibly no available addresses in pool or DHCP failure)? | Verify the data network (DN) configuration and IP pools in SMF; ensure the DHCP server (if used) is reachable and has free IPs; expand IP pool or fix DHCP configuration; monitor PDU Session Establishment logs for IP assignment messages |
why Frequent PDU Session Establishment Rejects;Session establishment being rejected; possibly due to unsupported DNN/slice or resource limitation? | Check reject cause codes from SMF logs; if DNN not allowed; correct the subscription or network config; if resource unavailable (e.g.; no available user plane); verify UPF availability and capacity; ensure the UE's requested PDU session type is supported |
why UE sees 'service not available' error in 5G SA;UE is in a Tracking Area or slice with no service (perhaps not configured or restricted) leading to service unavailability? | Ensure the UEs tracking area is served by the 5G core (TAI list includes that area); confirm that the requested slice/service is active and not barred; update broadcast PLMN/service information if needed to reflect available services |
why Abnormal increase in core CPU usage causing signaling delay;Core network function is overloaded (high CPU or process delay); causing slow response? | Profile the performance of core components during high load; scale out or add CPU resources to the VNFs; optimize configurations (e.g.; disable verbose logging); consider deploying additional instances for load sharing |
why Core network function instance failures (like AMF crash) affecting service;Core network function (e.g.; AMF or SMF) crashed or became unresponsive due to a software bug or exception? | Collect crash logs for the network function; restart the service and shift load to redundant instances; apply any available software update or patch; implement monitoring to automatically recover or alert on future crashes |
why Non-standalone mode: 5G bearer not added (user stuck on LTE data);EN-DC issue where the 5G leg (secondary node) is not established; possibly due to X2 interface or config problem? | Check the X2 connection between LTE eNB and 5G gNB; verify that the Master eNB has the correct configuration to add the secondary node; ensure UE and network support the same NSA options; troubleshoot any X2 Setup failures |
why UE fails to get a user plane established (no data bearer);PDU session not successfully established despite registration (control plane okay; data plane setup failing)? | Examine SMF and UPF logs for session establishment; ensure that the UPF has an active GTP-U tunnel to the gNB; verify that the selected DNN is reachable; correct any PFCP errors or data path issues |
why Network slicing selection fails (UE cannot use specific slice);Requested network slice not found or not permitted; leading to fallback or failure? | Validate slice availability: confirm that AMF can query NSSF and find a matching slice for the S-NSSAI; if slice isn't deployed; either deploy it or configure AMF/NSSF to redirect to a default slice; update UE subscription if it requests an unauthorized slice |
why Unexpected network function relocation triggers (like AMF change often);Frequent mobility management relocation (e.g.; AMF change) possibly due to load balancing thresholds being too sensitive? | Review AMF load balancing and relocation settings; if relocation is triggered by load changes; increase thresholds or hysteresis; ensure stable connections by keeping UEs on the same AMF unless necessary; coordinate among AMFs to reduce churn |
why 5G to 5G handover fails (core Xn or N2 issues);Handover signaling failure at core level (possibly NG-RAN to NG-RAN via AMF) or direct Xn failure? | Check that both source and target gNBs are configured with Xn connectivity or via core N2 handover; ensure security contexts are forwarded correctly; analyze NGAP messages in AMF for errors; rectify any mismatched configs like PLMN or slice differences preventing handover |
why UE keep receiving registration reject cause 'PLMN not allowed';UE's home PLMN is not allowed on this network or SIM is attempting to register to a forbidden network? | Verify that the PLMN ID the UE is trying to attach to is listed as allowed in the core and gNB; check if the SIM has roaming restrictions; instruct UE to select the correct PLMN if it's on the wrong one; update core configuration to allow the PLMN if it should be allowed |
why Intermittent service due to core network software bug;Intermittent service issues caused by software defects in core network software? | Correlate outages with core network logs to identify potential bug triggers; consult vendor documentation for similar reported issues; apply recommended patches or temporary workarounds; consider rolling back recent updates if the problem started after an upgrade |
why AMF rejects connection due to overloaded state;AMF is in an overload state and actively rejecting new connections to protect itself? | Examine AMF load (CPU; memory; signaling rate); implement overload control mechanisms to gracefully shed load (e.g.; redirect requests to other AMFs or send back-off indications); if capacity consistently insufficient; deploy additional AMF instances or optimize signaling |
why NSSF returns no suitable network slice for UE;Network slice selection issue where no matching slice is found; possibly due to misconfiguration? | Verify that the UE's subscription S-NSSAI matches an existing slice in NSSF configuration; ensure slice is deployed and NFs (AMF/SMF) are mapped to that slice; update NSSF or subscription data so that a valid slice can be selected |
why UPF not reachable by control plane (PFCP association fail);SMF is unable to establish PFCP (control) connection with UPF; suggesting UPF is down or network issue? | Check UPF status (is it running and registered to NRF?); ensure IP reachability between SMF and UPF (no firewall blocking PFCP port); if UPF crashed; restart it and investigate cause; confirm UPF is configured with correct SMF address and is discoverable via NRF |
why Abnormal NF deregistrations in NRF logs;Network Functions are deregistering from NRF unexpectedly; possibly due to connectivity or keep-alive failures? | Check network connectivity and latency between NFs and NRF; ensure NF instances have stable IP and are not restarting; adjust NRF heartbeat timers if needed for reliability; look into NF logs for reasons of deregistration and address underlying issues |
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