VOS3000 No-Answer Auto-Blacklist: Proven SS_BLACK_LIST_NO_ANSWER Configuration
Every time your softswitch routes a call to a number that never answers, you waste port capacity, increase Post Dial Delay (PDD), and depress your Answer Seizure Ratio (ASR). The VOS3000 no-answer auto-blacklist — controlled by SS_BLACK_LIST_NO_ANSWER parameters — automatically identifies and temporarily blocks numbers that repeatedly fail to answer, ensuring your routing engine skips dead endpoints and prioritizes numbers that actually connect.
Unlike the malicious caller blacklist which targets the calling party, the VOS3000 no-answer auto-blacklist targets the callee — the destination number that consistently fails to answer. This is a critical distinction: the callee blacklist prevents your softswitch from repeatedly routing calls to numbers that are offline, unreachable, or configured to reject calls silently. By automatically detecting and blocking these dead endpoints, you free gateway capacity for calls that have a genuine chance of connecting.
This guide covers all SS_BLACK_LIST_NO_ANSWER parameters from the VOS3000 2.1.9.07 manual §4.3.5.2: the expire duration (how long the block lasts), the limit threshold (how many no-answer events trigger blacklisting), and the monitor periods (the time window for counting). We will walk through configuration examples for different traffic profiles and show how this feature works alongside other VOS3000 security mechanisms. Need help? WhatsApp us at +8801911119966 for expert VOS3000 configuration.
Table of ContentsVOS3000 No-Answer Auto-Blacklist: Proven SS_BLACK_LIST_NO_ANSWER Configuration What Is the VOS3000 No-Answer Auto-Blacklist? No-Answer vs Other Dynamic Blacklist Types SS_BLACK_LIST_NO_ANSWER Parameters Parameter 1: Expire Duration — SS_BLACK_LIST_NO_ANSWER_EXPIRE Parameter 2: Continuous Call Limit — SS_BLACK_LIST_NO_ANSWER_LIMIT Parameter 3: Monitor Periods — SS_BLACK_LIST_NO_ANSWER_PERIODS How the VOS3000 No-Answer Auto-Blacklist Detection Works Step-by-Step VOS3000 No-Answer Auto-Blacklist ConfigurationStep 1: Access System Parameters Step 2: Set the No-Answer Limit Threshold Step 3: Configure the Monitor Period Step 4: Set the Expire Duration Step 5: Verify Dynamic Blacklist Entries Recommended VOS3000 No-Answer Auto-Blacklist Settings by Traffic Type Common VOS3000 No-Answer Auto-Blacklist Problems and Solutions Problem 1: No-Answer Blacklist Not Working — No Entries Appear Problem 2: Legitimate Numbers Getting Blacklisted After Temporary Outage Problem 3: Blacklist Entries Not Expiring — Numbers Stay Blocked Forever VOS3000 No-Answer Auto-Blacklist Best Practices Complete VOS3000 No-Answer Auto-Blacklist Parameter Reference Frequently Asked Questions What is the VOS3000 no-answer auto-blacklist? Why is the no-answer auto-blacklist disabled by default? What is the difference between no-answer blacklist and malicious caller blacklist? How long should I set the no-answer blacklist expire duration? Can I manually remove numbers from the no-answer dynamic blacklist? Does the no-answer auto-blacklist work with all SIP response codes? Need Expert Help with VOS3000 No-Answer Auto-Blacklist? Need Professional VOS3000 Setup Support?
What Is the VOS3000 No-Answer Auto-Blacklist?
The VOS3000 no-answer auto-blacklist is a dynamic blacklist mechanism that automatically adds callee numbers to a temporary block list when they fail to answer a configurable number of consecutive calls within a monitoring period. According to the official VOS3000 2.1.9.07 manual §4.3.5.2 and §2.13.6, the no-answer blacklist is one of three dynamic blacklist types — the others being malicious caller and concurrent call abuse. The no-answer type specifically monitors destination numbers and blocks those that consistently generate no-answer results.
Why a no-answer blacklist matters: Dead endpoints silently erode your call completion metrics. Every call attempt to a number that never answers consumes INVITE timeout duration, gateway port capacity, and billing system resources. In high-volume wholesale operations, routing to dead numbers can depress ASR by 5-15%, directly impacting your revenue and carrier reputation. The VOS3000 no-answer auto-blacklist solves this by removing dead numbers from your active routing pool automatically.
Detects callee numbers with repeated no-answer results
Temporarily removes dead numbers from the routing pool
Improves ASR by skipping known non-answering destinations
Frees gateway port capacity for calls that can connect
Reduces PDD by eliminating unnecessary timeout waits
Location in VOS3000 Client: View entries at Navigation → Number management → Dynamic black list; Configure at Navigation → Operation management → Softswitch management → Additional settings → System parameter
No-Answer vs Other Dynamic Blacklist Types
Understanding how the no-answer type differs from other dynamic blacklists helps you configure each appropriately:
Blacklist TypeTargetTriggerDefault Expire Malicious CallerCaller (originating)Excessive call attempts3600 seconds No AnswerCallee (destination)Repeated no-answer events2 days Concurrent AbuseCaller (originating)Exceeds concurrent call limit86400 seconds
Key distinction: The no-answer blacklist uniquely targets the callee side. This means it protects your outbound routing from dead destinations, while the malicious caller and concurrent abuse blacklists protect your inbound side from abusive originating numbers. Together they form a comprehensive defense. For the full picture, see our dynamic blacklist anti-fraud guide.
SS_BLACK_LIST_NO_ANSWER Parameters
The VOS3000 no-answer auto-blacklist is controlled by three parameters from the official manual §4.3.5.2:
Parameter 1: Expire Duration — SS_BLACK_LIST_NO_ANSWER_EXPIRE
AttributeValue Parameter NameSS_BLACK_LIST_NO_ANSWER_EXPIRE Default Value2 UnitDays DescriptionNo answer call dynamic black list expired duration
How the expire duration works: Unlike the malicious caller blacklist which uses seconds, the no-answer blacklist expire duration is measured in days. The default of 2 days means a dead-end number will remain blocked for 48 hours before being automatically removed. This longer duration makes sense because a number that never answers is likely a permanent dead endpoint — a disconnected phone, an unregistered SIP device, or a misconfigured route — and such numbers typically do not recover within minutes. The day-based unit allows you to set blocks lasting from 1 to 30 days depending on the nature of your dead endpoints.
Parameter 2: Continuous Call Limit — SS_BLACK_LIST_NO_ANSWER_LIMIT
AttributeValue Parameter NameSS_BLACK_LIST_NO_ANSWER_LIMIT Default ValueNone DescriptionNo answer call dynamic black list continuous call times
Critical note: Just like the malicious caller limit, the VOS3000 no-answer auto-blacklist is disabled by default because SS_BLACK_LIST_NO_ANSWER_LIMIT is set to None. You must configure a numeric threshold to activate the feature. This limit represents the number of consecutive no-answer events for a callee number within the monitoring period that triggers blacklisting.
Parameter 3: Monitor Periods — SS_BLACK_LIST_NO_ANSWER_PERIODS
AttributeValue Parameter NameSS_BLACK_LIST_NO_ANSWER_PERIODS Default Value(Empty/None) DescriptionNo answer call dynamic black list monitor period
How the monitor period works: The monitor period defines the time window during which the no-answer events are counted. Together with the limit parameter, it creates the detection rule: if a callee number fails to answer at least N times within the monitor period, it is added to the dynamic blacklist. This prevents single no-answer events from triggering a block — only persistent non-answer behavior qualifies.
How the VOS3000 No-Answer Auto-Blacklist Detection Works
The detection mechanism evaluates callee behavior over time to identify consistently non-answering numbers:
VOS3000 No-Answer Auto-Blacklist Detection Flow:
Call arrives → VOS3000 routes to Callee Number X
│
├── Callee X does NOT answer (no-answer result)
│ │
│ ├── Increment no-answer counter for Callee X
│ │
│ ├── Within MONITOR_PERIODS window:
│ │ │
│ │ ├── Count < LIMIT → Not yet flagged
│ │ │ Continue routing to Callee X
│ │ │
│ │ └── Count >= LIMIT → FLAGGED!
│ │ │
│ │ ├── Add Callee X to Dynamic Blacklist
│ │ │ Type: No Answer
│ │ │
│ │ ├── Block duration = NO_ANSWER_EXPIRE
│ │ │ (2 days default)
│ │ │
│ │ └── Future calls to Callee X are
│ │ rejected/skipped during block
│ │
│ └── After EXPIRE duration passes:
│ └── Remove Callee X from Dynamic Blacklist
│ Number can receive calls again
│
└── Entry visible in: Navigation > Number management
> Dynamic black list
Practical example: If you set SS_BLACK_LIST_NO_ANSWER_LIMIT to 5 and the monitor period to 1 hour, then any callee number that fails to answer 5 consecutive calls within an hour will be automatically blacklisted for 2 days. During those 2 days, VOS3000 will skip routing calls to that number, saving port capacity and improving overall call routing efficiency.
Step-by-Step VOS3000 No-Answer Auto-Blacklist Configuration
Follow these steps based on the VOS3000 2.1.9.07 manual §4.3.5.2:
Step 1: Access System Parameters
Log in to VOS3000 Client
Navigate: Operation management → Softswitch management → Additional settings → System parameter
Locate the SS_BLACK_LIST_NO_ANSWER group in the parameter list
Step 2: Set the No-Answer Limit Threshold
Find SS_BLACK_LIST_NO_ANSWER_LIMIT
Set the number of consecutive no-answer events that triggers blacklisting (e.g., 5)
Important: Default is None (disabled). You MUST set a value to activate
Step 3: Configure the Monitor Period
Find SS_BLACK_LIST_NO_ANSWER_PERIODS
Set the time window for counting no-answer events
A longer period means more tolerance before flagging
Step 4: Set the Expire Duration
Find SS_BLACK_LIST_NO_ANSWER_EXPIRE
Set the blacklist duration in days (default: 2)
Save and apply the configuration
Step 5: Verify Dynamic Blacklist Entries
Navigate: Number management → Dynamic black list
Check that flagged numbers appear with Type = “No answer”
Verify Effective date and Expiration time are correct
Recommended VOS3000 No-Answer Auto-Blacklist Settings by Traffic Type
Traffic TypeNo-Answer LimitExpire DurationRationale Retail3-51-2 days Dead retail numbers stay dead; quick block saves resources Wholesale5-102-3 days Higher tolerance for temporary network issues High-Volume Carrier10-151-2 days Allow for peak-hour congestion before flagging Premium Routes37 days Aggressive blocking; dead premium routes waste margin
Pro tip: The VOS3000 no-answer auto-blacklist works best when combined with ASR-based gateway analysis. If a particular vendor gateway consistently routes to dead numbers, the no-answer blacklist will catch individual dead destinations, but you should also evaluate the overall gateway ASR performance. WhatsApp us at +8801911119966 for guidance on optimizing your routing configuration.
Common VOS3000 No-Answer Auto-Blacklist Problems and Solutions
Problem 1: No-Answer Blacklist Not Working — No Entries Appear
Symptom: Known dead-end numbers continue receiving calls, but the dynamic blacklist shows no no-answer entries.
Cause: SS_BLACK_LIST_NO_ANSWER_LIMIT is set to None (default), disabling the feature entirely.
Solutions:
Set SS_BLACK_LIST_NO_ANSWER_LIMIT to a numeric value (e.g., 5)
Configure the monitor period to define the evaluation window
Verify the expire duration is set to a reasonable number of days
Problem 2: Legitimate Numbers Getting Blacklisted After Temporary Outage
Symptom: Destination numbers that are normally reachable get blacklisted after a temporary network outage or maintenance window.
Cause: The no-answer limit is set too low, and a brief outage caused enough consecutive no-answer events to trigger blacklisting.
Solutions:
Increase the no-answer limit to tolerate temporary outages (e.g., 10 instead of 3)
Extend the monitor period to avoid flagging numbers during short outages
Manually remove entries from the dynamic blacklist after outage recovery
Problem 3: Blacklist Entries Not Expiring — Numbers Stay Blocked Forever
Symptom: Numbers added to the no-answer blacklist remain blocked indefinitely and never get removed.
Cause: The expire duration may be set to an extremely high value, or there may be a system time synchronization issue affecting the expiration check.
Solutions:
Verify SS_BLACK_LIST_NO_ANSWER_EXPIRE is set to a reasonable value (e.g., 2 days)
Check system NTP synchronization with call termination monitoring
Manually remove stale entries from the Dynamic black list table
VOS3000 No-Answer Auto-Blacklist Best Practices
Best PracticeRecommendationReason Set limit before enablingAlways configure LIMIT before relying on the feature Feature is disabled by default (None) Match limit to traffic typeHigher limits for wholesale, lower for retail Prevents false positives on high-volume routes Monitor the blacklist tableCheck Dynamic black list daily for no-answer entries Identifies vendor quality issues early Coordinate with vendor managementReport dead destinations to upstream vendors Addresses root cause, not just symptom Use day-based expireSet expire in days, not seconds, for dead endpoints Dead numbers rarely recover quickly Combine with ASR monitoringUse gateway ASR data alongside no-answer blacklist Comprehensive routing quality view
Complete VOS3000 No-Answer Auto-Blacklist Parameter Reference
Complete reference from the official VOS3000 2.1.9.07 manual §4.3.5.2:
Frequently Asked Questions
What is the VOS3000 no-answer auto-blacklist?
The VOS3000 no-answer auto-blacklist is a dynamic blacklist feature that automatically blocks callee (destination) numbers that repeatedly fail to answer calls within a configurable monitoring period. When a destination number generates a specified number of consecutive no-answer results, VOS3000 adds it to the dynamic blacklist for a configurable duration (default: 2 days). During the block period, the softswitch skips routing calls to that number, saving gateway capacity and improving overall ASR. This feature is documented in the VOS3000 2.1.9.07 manual §4.3.5.2.
Why is the no-answer auto-blacklist disabled by default?
The VOS3000 no-answer auto-blacklist is disabled by default because SS_BLACK_LIST_NO_ANSWER_LIMIT has a default value of None. Without a numeric limit, the system never flags any callee number regardless of how many times it fails to answer. This conservative default prevents accidental blocking of destination numbers in environments where the feature has not been explicitly configured. To activate the feature, you must set a numeric value for the limit parameter — for example, 5 consecutive no-answer events.
What is the difference between no-answer blacklist and malicious caller blacklist?
The VOS3000 no-answer auto-blacklist targets the callee (destination) side — it blocks numbers that fail to answer. The malicious caller blacklist targets the caller (originating) side — it blocks numbers that make excessive calls. The no-answer blacklist expire is measured in days (default: 2 days), while the malicious caller expire is measured in seconds (default: 3600 seconds). Both are part of the dynamic blacklist system but serve different purposes: no-answer protects routing efficiency, while malicious caller protects against fraud and abuse.
How long should I set the no-answer blacklist expire duration?
The optimal expire duration depends on your traffic type. For retail operations, 1-2 days is usually sufficient since dead retail numbers rarely recover. For wholesale, 2-3 days provides tolerance while still removing dead endpoints. For premium routes where margin matters, 7 days ensures dead numbers stay blocked longer. The default of 2 days works well for most deployments. Remember that the expire is measured in days, not seconds — this reflects the fact that dead destination numbers typically do not recover quickly. Refer to RFC 3261 for SIP call flow standards.
Can I manually remove numbers from the no-answer dynamic blacklist?
Yes, you can manually remove entries from the dynamic blacklist. Navigate to Number management → Dynamic black list, select the entry you want to remove, and delete it. This is useful when a previously dead destination number has been restored and you want to resume routing calls to it immediately, without waiting for the expire duration to pass. However, if the number is genuinely dead, it will be re-added to the blacklist after the next monitoring cycle. For persistent management, use the number management tools.
Does the no-answer auto-blacklist work with all SIP response codes?
The VOS3000 no-answer auto-blacklist specifically targets scenarios where the callee fails to answer — meaning the call was delivered to the far end but no 200 OK (answer) response was received within the configured timeout. This includes scenarios where the far end returns 180 Ringing without ever answering, or where the call times out after ringing. It does not typically apply to immediate rejection responses like 486 Busy or 404 Not Found, as these are not “no-answer” conditions — they are explicit call rejections. For related call end reasons, check our detailed reference guide. WhatsApp us at +8801911119966 for more information.
Need Expert Help with VOS3000 No-Answer Auto-Blacklist?
Proper VOS3000 no-answer auto-blacklist configuration is essential for maximizing call completion rates, eliminating dead-end routing, and preserving gateway port capacity for calls that can actually connect. Whether you need help setting thresholds, tuning expire durations, or integrating the no-answer blacklist with your overall routing optimization strategy, our team is ready to assist. Reach us on WhatsApp at +8801911119966 for professional VOS3000 configuration services.
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