{"id":1492,"date":"2026-04-28T15:43:47","date_gmt":"2026-04-28T15:43:47","guid":{"rendered":"https:\/\/www.vos3000.com\/blog\/?p=1492"},"modified":"2026-04-28T15:43:56","modified_gmt":"2026-04-28T15:43:56","slug":"vos3000-no-answer-auto-blacklist-proven","status":"publish","type":"post","link":"https:\/\/www.vos3000.com\/blog\/vos3000-no-answer-auto-blacklist-proven\/","title":{"rendered":"VOS3000 No-Answer Auto-Blacklist: Proven SS_BLACK_LIST_NO_ANSWER Configuration"},"content":{"rendered":"\n<h1 class=\"wp-block-heading\" id=\"vos-3000-no-answer-auto-blacklist-proven-ss-black-list-no-answer-configuration\">VOS3000 No-Answer Auto-Blacklist: Proven SS_BLACK_LIST_NO_ANSWER Configuration<\/h1>\n\n\n\n<p>\ud83d\udcde 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 <strong>VOS3000 no-answer auto-blacklist<\/strong> \u2014 controlled by <strong>SS_BLACK_LIST_NO_ANSWER<\/strong> parameters \u2014 automatically identifies and temporarily blocks numbers that repeatedly fail to answer, ensuring your routing engine skips dead endpoints and prioritizes numbers that actually connect. \ud83c\udfaf<\/p>\n\n\n\n<p>\u2699\ufe0f Unlike the malicious caller blacklist which targets the calling party, the <strong>VOS3000 no-answer auto-blacklist<\/strong> targets the <em>callee<\/em> \u2014 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. \ud83d\udd27<\/p>\n\n\n\n<p>\ud83c\udfaf This guide covers all SS_BLACK_LIST_NO_ANSWER parameters from the VOS3000 2.1.9.07 manual \u00a74.3.5.2: 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 <strong>+8801911119966<\/strong> for expert VOS3000 configuration. \ud83d\udcde<\/p>\n\n\n\n<div class=\"wp-block-rank-math-toc-block\" id=\"rank-math-toc\"><h2>Table of Contents<\/h2><nav><ul><li><a href=\"#vos-3000-no-answer-auto-blacklist-proven-ss-black-list-no-answer-configuration\">VOS3000 No-Answer Auto-Blacklist: Proven SS_BLACK_LIST_NO_ANSWER Configuration<\/a><ul><li><a href=\"#\ud83d\udd10-what-is-the-vos-3000-no-answer-auto-blacklist\">\ud83d\udd10 What Is the VOS3000 No-Answer Auto-Blacklist?<\/a><ul><li><a href=\"#\ud83d\udccb-no-answer-vs-other-dynamic-blacklist-types\">\ud83d\udccb No-Answer vs Other Dynamic Blacklist Types<\/a><\/li><\/ul><\/li><li><a href=\"#\u2699\ufe0f-ss-black-list-no-answer-parameters\">\u2699\ufe0f SS_BLACK_LIST_NO_ANSWER Parameters<\/a><ul><li><a href=\"#\ud83d\udccb-parameter-1-expire-duration-ss-black-list-no-answer-expire\">\ud83d\udccb Parameter 1: Expire Duration \u2014 SS_BLACK_LIST_NO_ANSWER_EXPIRE<\/a><\/li><li><a href=\"#\ud83d\udccb-parameter-2-continuous-call-limit-ss-black-list-no-answer-limit\">\ud83d\udccb Parameter 2: Continuous Call Limit \u2014 SS_BLACK_LIST_NO_ANSWER_LIMIT<\/a><\/li><li><a href=\"#\ud83d\udccb-parameter-3-monitor-periods-ss-black-list-no-answer-periods\">\ud83d\udccb Parameter 3: Monitor Periods \u2014 SS_BLACK_LIST_NO_ANSWER_PERIODS<\/a><\/li><\/ul><\/li><li><a href=\"#\ud83d\udda5\ufe0f-how-the-vos-3000-no-answer-auto-blacklist-detection-works\">\ud83d\udda5\ufe0f How the VOS3000 No-Answer Auto-Blacklist Detection Works<\/a><\/li><li><a href=\"#\ud83d\udccb-step-by-step-vos-3000-no-answer-auto-blacklist-configuration\">\ud83d\udccb Step-by-Step VOS3000 No-Answer Auto-Blacklist Configuration<\/a><ul><li><a href=\"#step-1-access-system-parameters-\ud83c\udf10\">Step 1: Access System Parameters \ud83c\udf10<\/a><\/li><li><a href=\"#step-2-set-the-no-answer-limit-threshold-\ud83c\udfaf\">Step 2: Set the No-Answer Limit Threshold \ud83c\udfaf<\/a><\/li><li><a href=\"#step-3-configure-the-monitor-period-\u23f1\ufe0f\">Step 3: Configure the Monitor Period \u23f1\ufe0f<\/a><\/li><li><a href=\"#step-4-set-the-expire-duration-\ud83d\udd50\">Step 4: Set the Expire Duration \ud83d\udd50<\/a><\/li><li><a href=\"#step-5-verify-dynamic-blacklist-entries-\ud83d\udd0d\">Step 5: Verify Dynamic Blacklist Entries \ud83d\udd0d<\/a><\/li><\/ul><\/li><li><a href=\"#\ud83d\udee1\ufe0f-recommended-vos-3000-no-answer-auto-blacklist-settings-by-traffic-type\">\ud83d\udee1\ufe0f Recommended VOS3000 No-Answer Auto-Blacklist Settings by Traffic Type<\/a><\/li><li><a href=\"#\ud83d\udee1\ufe0f-common-vos-3000-no-answer-auto-blacklist-problems-and-solutions\">\ud83d\udee1\ufe0f Common VOS3000 No-Answer Auto-Blacklist Problems and Solutions<\/a><ul><li><a href=\"#\u274c-problem-1-no-answer-blacklist-not-working-no-entries-appear\">\u274c Problem 1: No-Answer Blacklist Not Working \u2014 No Entries Appear<\/a><\/li><li><a href=\"#\u274c-problem-2-legitimate-numbers-getting-blacklisted-after-temporary-outage\">\u274c Problem 2: Legitimate Numbers Getting Blacklisted After Temporary Outage<\/a><\/li><li><a href=\"#\u274c-problem-3-blacklist-entries-not-expiring-numbers-stay-blocked-forever\">\u274c Problem 3: Blacklist Entries Not Expiring \u2014 Numbers Stay Blocked Forever<\/a><\/li><\/ul><\/li><li><a href=\"#\ud83d\udca1-vos-3000-no-answer-auto-blacklist-best-practices\">\ud83d\udca1 VOS3000 No-Answer Auto-Blacklist Best Practices<\/a><\/li><li><a href=\"#\ud83d\udcca-complete-vos-3000-no-answer-auto-blacklist-parameter-reference\">\ud83d\udcca Complete VOS3000 No-Answer Auto-Blacklist Parameter Reference<\/a><\/li><li><a href=\"#\u2753-frequently-asked-questions\">\u2753 Frequently Asked Questions<\/a><ul><li><a href=\"#\u2753-what-is-the-vos-3000-no-answer-auto-blacklist\">\u2753 What is the VOS3000 no-answer auto-blacklist?<\/a><\/li><li><a href=\"#\u2753-why-is-the-no-answer-auto-blacklist-disabled-by-default\">\u2753 Why is the no-answer auto-blacklist disabled by default?<\/a><\/li><li><a href=\"#\u2753-what-is-the-difference-between-no-answer-blacklist-and-malicious-caller-blacklist\">\u2753 What is the difference between no-answer blacklist and malicious caller blacklist?<\/a><\/li><li><a href=\"#\u2753-how-long-should-i-set-the-no-answer-blacklist-expire-duration\">\u2753 How long should I set the no-answer blacklist expire duration?<\/a><\/li><li><a href=\"#\u2753-can-i-manually-remove-numbers-from-the-no-answer-dynamic-blacklist\">\u2753 Can I manually remove numbers from the no-answer dynamic blacklist?<\/a><\/li><li><a href=\"#\u2753-does-the-no-answer-auto-blacklist-work-with-all-sip-response-codes\">\u2753 Does the no-answer auto-blacklist work with all SIP response codes?<\/a><\/li><\/ul><\/li><li><a href=\"#\ud83d\udcde-need-expert-help-with-vos-3000-no-answer-auto-blacklist\">\ud83d\udcde Need Expert Help with VOS3000 No-Answer Auto-Blacklist?<\/a><\/li><li><a href=\"#\ud83d\udcde-need-call-center-setup-support\">\ud83d\udcde Need Professional VOS3000 Setup Support?<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udd10-what-is-the-vos-3000-no-answer-auto-blacklist\">\ud83d\udd10 What Is the VOS3000 No-Answer Auto-Blacklist?<\/h2>\n\n\n\n<p>\u23f1\ufe0f The <strong>VOS3000 no-answer auto-blacklist<\/strong> 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 \u00a74.3.5.2 and \u00a72.13.6, the no-answer blacklist is one of three dynamic blacklist types \u2014 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. \ud83d\udcde<\/p>\n\n\n\n<p>\ud83d\udca1 <strong>Why a no-answer blacklist matters:<\/strong> 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.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udce1 Detects callee numbers with repeated no-answer results<\/li>\n\n\n\n<li>\ud83d\udd04 Temporarily removes dead numbers from the routing pool<\/li>\n\n\n\n<li>\ud83d\udcca Improves ASR by skipping known non-answering destinations<\/li>\n\n\n\n<li>\ud83d\udee1\ufe0f Frees gateway port capacity for calls that can connect<\/li>\n\n\n\n<li>\ud83c\udfaf Reduces PDD by eliminating unnecessary timeout waits<\/li>\n<\/ul>\n\n\n\n<p>\ud83d\udccd <strong>Location in VOS3000 Client:<\/strong> View entries at Navigation \u2192 Number management \u2192 Dynamic black list; Configure at Navigation \u2192 Operation management \u2192 Softswitch management \u2192 Additional settings \u2192 System parameter<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\ud83d\udccb-no-answer-vs-other-dynamic-blacklist-types\">\ud83d\udccb No-Answer vs Other Dynamic Blacklist Types<\/h3>\n\n\n\n<p>\ud83c\udf10 Understanding how the no-answer type differs from other dynamic blacklists helps you configure each appropriately:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Blacklist Type<\/th><th class=\"has-text-align-left\" data-align=\"left\">Target<\/th><th class=\"has-text-align-left\" data-align=\"left\">Trigger<\/th><th class=\"has-text-align-left\" data-align=\"left\">Default Expire<\/th><\/tr><tr><td>\ud83d\udd34 Malicious Caller<\/td><td>Caller (originating)<\/td><td>Excessive call attempts<\/td><td>3600 seconds<\/td><\/tr><tr><td>\ud83d\udfe1 No Answer<\/td><td>Callee (destination)<\/td><td>Repeated no-answer events<\/td><td>2 days<\/td><\/tr><tr><td>\ud83d\udfe0 Concurrent Abuse<\/td><td>Caller (originating)<\/td><td>Exceeds concurrent call limit<\/td><td>86400 seconds<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\ud83d\udd11 <strong>Key distinction:<\/strong> The no-answer blacklist uniquely targets the <em>callee<\/em> 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 <a href=\"https:\/\/multahost.com\/blog\/vos3000-dynamic-blacklist-anti-fraud\/\" target=\"_blank\" rel=\"noopener\">dynamic blacklist anti-fraud guide<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u2699\ufe0f-ss-black-list-no-answer-parameters\">\u2699\ufe0f SS_BLACK_LIST_NO_ANSWER Parameters<\/h2>\n\n\n\n<p>\ud83d\udd27 The VOS3000 no-answer auto-blacklist is controlled by three parameters from the official manual \u00a74.3.5.2:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\ud83d\udccb-parameter-1-expire-duration-ss-black-list-no-answer-expire\">\ud83d\udccb Parameter 1: Expire Duration \u2014 SS_BLACK_LIST_NO_ANSWER_EXPIRE<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Attribute<\/th><th class=\"has-text-align-left\" data-align=\"left\">Value<\/th><\/tr><tr><td>\ud83d\udccc Parameter Name<\/td><td>SS_BLACK_LIST_NO_ANSWER_EXPIRE<\/td><\/tr><tr><td>\ud83d\udd22 Default Value<\/td><td>2<\/td><\/tr><tr><td>\ud83d\udcd0 Unit<\/td><td>Days<\/td><\/tr><tr><td>\ud83d\udcdd Description<\/td><td>No answer call dynamic black list expired duration<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\ud83d\udca1 <strong>How the expire duration works:<\/strong> Unlike the malicious caller blacklist which uses seconds, the no-answer blacklist expire duration is measured in <strong>days<\/strong>. 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 \u2014 a disconnected phone, an unregistered SIP device, or a misconfigured route \u2014 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.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\ud83d\udccb-parameter-2-continuous-call-limit-ss-black-list-no-answer-limit\">\ud83d\udccb Parameter 2: Continuous Call Limit \u2014 SS_BLACK_LIST_NO_ANSWER_LIMIT<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Attribute<\/th><th class=\"has-text-align-left\" data-align=\"left\">Value<\/th><\/tr><tr><td>\ud83d\udccc Parameter Name<\/td><td>SS_BLACK_LIST_NO_ANSWER_LIMIT<\/td><\/tr><tr><td>\ud83d\udd22 Default Value<\/td><td>None<\/td><\/tr><tr><td>\ud83d\udcdd Description<\/td><td>No answer call dynamic black list continuous call times<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u26a0\ufe0f <strong>Critical note:<\/strong> Just like the malicious caller limit, the <strong>VOS3000 no-answer auto-blacklist<\/strong> 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.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\ud83d\udccb-parameter-3-monitor-periods-ss-black-list-no-answer-periods\">\ud83d\udccb Parameter 3: Monitor Periods \u2014 SS_BLACK_LIST_NO_ANSWER_PERIODS<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Attribute<\/th><th class=\"has-text-align-left\" data-align=\"left\">Value<\/th><\/tr><tr><td>\ud83d\udccc Parameter Name<\/td><td>SS_BLACK_LIST_NO_ANSWER_PERIODS<\/td><\/tr><tr><td>\ud83d\udd22 Default Value<\/td><td>(Empty\/None)<\/td><\/tr><tr><td>\ud83d\udcdd Description<\/td><td>No answer call dynamic black list monitor period<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\ud83d\udca1 <strong>How the monitor period works:<\/strong> 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 \u2014 only persistent non-answer behavior qualifies.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udda5\ufe0f-how-the-vos-3000-no-answer-auto-blacklist-detection-works\">\ud83d\udda5\ufe0f How the VOS3000 No-Answer Auto-Blacklist Detection Works<\/h2>\n\n\n\n<p>\ud83d\udd04 The detection mechanism evaluates callee behavior over time to identify consistently non-answering numbers:<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">\ud83d\udcde VOS3000 No-Answer Auto-Blacklist Detection Flow:\n\nCall arrives \u2192 VOS3000 routes to Callee Number X\n    \u2502\n    \u251c\u2500\u2500 Callee X does NOT answer (no-answer result)\n    \u2502   \u2502\n    \u2502   \u251c\u2500\u2500 Increment no-answer counter for Callee X\n    \u2502   \u2502\n    \u2502   \u251c\u2500\u2500 Within MONITOR_PERIODS window:\n    \u2502   \u2502   \u2502\n    \u2502   \u2502   \u251c\u2500\u2500 Count &lt; LIMIT  \u2192  \u2705 Not yet flagged\n    \u2502   \u2502   \u2502   Continue routing to Callee X\n    \u2502   \u2502   \u2502\n    \u2502   \u2502   \u2514\u2500\u2500 Count &gt;= LIMIT  \u2192  \ud83d\udfe1 FLAGGED!\n    \u2502   \u2502       \u2502\n    \u2502   \u2502       \u251c\u2500\u2500 Add Callee X to Dynamic Blacklist\n    \u2502   \u2502       \u2502   Type: No Answer\n    \u2502   \u2502       \u2502\n    \u2502   \u2502       \u251c\u2500\u2500 Block duration = NO_ANSWER_EXPIRE\n    \u2502   \u2502       \u2502   (2 days default)\n    \u2502   \u2502       \u2502\n    \u2502   \u2502       \u2514\u2500\u2500 Future calls to Callee X are\n    \u2502   \u2502           rejected\/skipped during block\n    \u2502   \u2502\n    \u2502   \u2514\u2500\u2500 After EXPIRE duration passes:\n    \u2502       \u2514\u2500\u2500 Remove Callee X from Dynamic Blacklist\n    \u2502           Number can receive calls again\n    \u2502\n    \u2514\u2500\u2500 \ud83d\udcca Entry visible in: Navigation &gt; Number management\n        &gt; Dynamic black list\n<\/pre>\n\n\n\n<p>\ud83d\udca1 <strong>Practical example:<\/strong> 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 <a href=\"https:\/\/multahost.com\/blog\/vos3000-call-routing\/\" target=\"_blank\" rel=\"noopener\">call routing<\/a> efficiency.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udccb-step-by-step-vos-3000-no-answer-auto-blacklist-configuration\">\ud83d\udccb Step-by-Step VOS3000 No-Answer Auto-Blacklist Configuration<\/h2>\n\n\n\n<p>\ud83d\udda5\ufe0f Follow these steps based on the VOS3000 2.1.9.07 manual \u00a74.3.5.2:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-1-access-system-parameters-\ud83c\udf10\">Step 1: Access System Parameters \ud83c\udf10<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\ud83d\udd10 Log in to VOS3000 Client<\/li>\n\n\n\n<li>\ud83d\udccc Navigate: <strong>Operation management \u2192 Softswitch management \u2192 Additional settings \u2192 System parameter<\/strong><\/li>\n\n\n\n<li>\ud83d\udd0d Locate the SS_BLACK_LIST_NO_ANSWER group in the parameter list<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-2-set-the-no-answer-limit-threshold-\ud83c\udfaf\">Step 2: Set the No-Answer Limit Threshold \ud83c\udfaf<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\ud83d\udcdd Find <strong>SS_BLACK_LIST_NO_ANSWER_LIMIT<\/strong><\/li>\n\n\n\n<li>\u270f\ufe0f Set the number of consecutive no-answer events that triggers blacklisting (e.g., 5)<\/li>\n\n\n\n<li>\u26a0\ufe0f <strong>Important:<\/strong> Default is None (disabled). You MUST set a value to activate<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-3-configure-the-monitor-period-\u23f1\ufe0f\">Step 3: Configure the Monitor Period \u23f1\ufe0f<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\ud83d\udcdd Find <strong>SS_BLACK_LIST_NO_ANSWER_PERIODS<\/strong><\/li>\n\n\n\n<li>\u270f\ufe0f Set the time window for counting no-answer events<\/li>\n\n\n\n<li>\ud83d\udca1 A longer period means more tolerance before flagging<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-4-set-the-expire-duration-\ud83d\udd50\">Step 4: Set the Expire Duration \ud83d\udd50<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\ud83d\udcdd Find <strong>SS_BLACK_LIST_NO_ANSWER_EXPIRE<\/strong><\/li>\n\n\n\n<li>\u270f\ufe0f Set the blacklist duration in days (default: 2)<\/li>\n\n\n\n<li>\ud83d\udcbe Save and apply the configuration<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-5-verify-dynamic-blacklist-entries-\ud83d\udd0d\">Step 5: Verify Dynamic Blacklist Entries \ud83d\udd0d<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\ud83d\udccb Navigate: <strong>Number management \u2192 Dynamic black list<\/strong><\/li>\n\n\n\n<li>\ud83d\udd0d Check that flagged numbers appear with Type = &#8220;No answer&#8221;<\/li>\n\n\n\n<li>\ud83d\udcca Verify Effective date and Expiration time are correct<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udee1\ufe0f-recommended-vos-3000-no-answer-auto-blacklist-settings-by-traffic-type\">\ud83d\udee1\ufe0f Recommended VOS3000 No-Answer Auto-Blacklist Settings by Traffic Type<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Traffic Type<\/th><th class=\"has-text-align-left\" data-align=\"left\">No-Answer Limit<\/th><th class=\"has-text-align-left\" data-align=\"left\">Expire Duration<\/th><th class=\"has-text-align-left\" data-align=\"left\">Rationale<\/th><\/tr><tr><td>\ud83c\udfe2 Retail<\/td><td>3-5<\/td><td>1-2 days<\/td><td>\u2705 Dead retail numbers stay dead; quick block saves resources<\/td><\/tr><tr><td>\ud83c\udf10 Wholesale<\/td><td>5-10<\/td><td>2-3 days<\/td><td>\ud83d\udd27 Higher tolerance for temporary network issues<\/td><\/tr><tr><td>\ud83d\udce1 High-Volume Carrier<\/td><td>10-15<\/td><td>1-2 days<\/td><td>\ud83d\udce1 Allow for peak-hour congestion before flagging<\/td><\/tr><tr><td>\u26a0\ufe0f Premium Routes<\/td><td>3<\/td><td>7 days<\/td><td>\ud83d\udee1\ufe0f Aggressive blocking; dead premium routes waste margin<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\ud83d\udca1 <strong>Pro tip:<\/strong> The <strong>VOS3000 no-answer auto-blacklist<\/strong> works best when combined with ASR-based <a href=\"https:\/\/multahost.com\/blog\/vos3000-gateway-configuration-routing-mapping\/\" target=\"_blank\" rel=\"noopener\">gateway analysis<\/a>. 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 <strong>+8801911119966<\/strong> for guidance on optimizing your routing configuration. \ud83d\udd27<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udee1\ufe0f-common-vos-3000-no-answer-auto-blacklist-problems-and-solutions\">\ud83d\udee1\ufe0f Common VOS3000 No-Answer Auto-Blacklist Problems and Solutions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u274c-problem-1-no-answer-blacklist-not-working-no-entries-appear\">\u274c Problem 1: No-Answer Blacklist Not Working \u2014 No Entries Appear<\/h3>\n\n\n\n<p>\ud83d\udd0d <strong>Symptom:<\/strong> Known dead-end numbers continue receiving calls, but the dynamic blacklist shows no no-answer entries.<\/p>\n\n\n\n<p>\ud83d\udca1 <strong>Cause:<\/strong> SS_BLACK_LIST_NO_ANSWER_LIMIT is set to None (default), disabling the feature entirely.<\/p>\n\n\n\n<p>\u2705 <strong>Solutions:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udd27 Set SS_BLACK_LIST_NO_ANSWER_LIMIT to a numeric value (e.g., 5)<\/li>\n\n\n\n<li>\ud83d\udcca Configure the monitor period to define the evaluation window<\/li>\n\n\n\n<li>\ud83d\udcde Verify the expire duration is set to a reasonable number of days<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u274c-problem-2-legitimate-numbers-getting-blacklisted-after-temporary-outage\">\u274c Problem 2: Legitimate Numbers Getting Blacklisted After Temporary Outage<\/h3>\n\n\n\n<p>\ud83d\udd0d <strong>Symptom:<\/strong> Destination numbers that are normally reachable get blacklisted after a temporary network outage or maintenance window.<\/p>\n\n\n\n<p>\ud83d\udca1 <strong>Cause:<\/strong> The no-answer limit is set too low, and a brief outage caused enough consecutive no-answer events to trigger blacklisting.<\/p>\n\n\n\n<p>\u2705 <strong>Solutions:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udd27 Increase the no-answer limit to tolerate temporary outages (e.g., 10 instead of 3)<\/li>\n\n\n\n<li>\ud83d\udcca Extend the monitor period to avoid flagging numbers during short outages<\/li>\n\n\n\n<li>\ud83d\udcde Manually remove entries from the dynamic blacklist after outage recovery<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u274c-problem-3-blacklist-entries-not-expiring-numbers-stay-blocked-forever\">\u274c Problem 3: Blacklist Entries Not Expiring \u2014 Numbers Stay Blocked Forever<\/h3>\n\n\n\n<p>\ud83d\udd0d <strong>Symptom:<\/strong> Numbers added to the no-answer blacklist remain blocked indefinitely and never get removed.<\/p>\n\n\n\n<p>\ud83d\udca1 <strong>Cause:<\/strong> The expire duration may be set to an extremely high value, or there may be a system time synchronization issue affecting the expiration check.<\/p>\n\n\n\n<p>\u2705 <strong>Solutions:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udd27 Verify SS_BLACK_LIST_NO_ANSWER_EXPIRE is set to a reasonable value (e.g., 2 days)<\/li>\n\n\n\n<li>\ud83d\udcca Check system NTP synchronization with <a href=\"https:\/\/multahost.com\/blog\/vos3000-call-termination-reasons\/\" target=\"_blank\" rel=\"noopener\">call termination monitoring<\/a><\/li>\n\n\n\n<li>\ud83d\udcde Manually remove stale entries from the Dynamic black list table<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udca1-vos-3000-no-answer-auto-blacklist-best-practices\">\ud83d\udca1 VOS3000 No-Answer Auto-Blacklist Best Practices<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Best Practice<\/th><th class=\"has-text-align-left\" data-align=\"left\">Recommendation<\/th><th class=\"has-text-align-left\" data-align=\"left\">Reason<\/th><\/tr><tr><td>\ud83d\udcca Set limit before enabling<\/td><td>Always configure LIMIT before relying on the feature<\/td><td>\u2705 Feature is disabled by default (None)<\/td><\/tr><tr><td>\ud83d\udd27 Match limit to traffic type<\/td><td>Higher limits for wholesale, lower for retail<\/td><td>\ud83c\udfaf Prevents false positives on high-volume routes<\/td><\/tr><tr><td>\ud83d\udccb Monitor the blacklist table<\/td><td>Check Dynamic black list daily for no-answer entries<\/td><td>\ud83d\udcde Identifies vendor quality issues early<\/td><\/tr><tr><td>\ud83d\udd04 Coordinate with vendor management<\/td><td>Report dead destinations to upstream vendors<\/td><td>\ud83d\udee1\ufe0f Addresses root cause, not just symptom<\/td><\/tr><tr><td>\u23f1\ufe0f Use day-based expire<\/td><td>Set expire in days, not seconds, for dead endpoints<\/td><td>\ud83d\udd27 Dead numbers rarely recover quickly<\/td><\/tr><tr><td>\ud83d\udcc8 Combine with ASR monitoring<\/td><td>Use gateway ASR data alongside no-answer blacklist<\/td><td>\ud83d\udd0d Comprehensive routing quality view<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udcca-complete-vos-3000-no-answer-auto-blacklist-parameter-reference\">\ud83d\udcca Complete VOS3000 No-Answer Auto-Blacklist Parameter Reference<\/h2>\n\n\n\n<p>\ud83d\udccb Complete reference from the official VOS3000 2.1.9.07 manual \u00a74.3.5.2:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th class=\"has-text-align-left\" data-align=\"left\">Parameter<\/th><th class=\"has-text-align-left\" data-align=\"left\">Default<\/th><th class=\"has-text-align-left\" data-align=\"left\">Unit<\/th><th class=\"has-text-align-left\" data-align=\"left\">Purpose<\/th><\/tr><tr><td>SS_BLACK_LIST_NO_ANSWER_EXPIRE<\/td><td>2<\/td><td>Days<\/td><td>Duration to keep callee in dynamic blacklist<\/td><\/tr><tr><td>SS_BLACK_LIST_NO_ANSWER_LIMIT<\/td><td>None<\/td><td>Count<\/td><td>Consecutive no-answer events before blacklisting<\/td><\/tr><tr><td>SS_BLACK_LIST_NO_ANSWER_PERIODS<\/td><td>None<\/td><td>Time window<\/td><td>Monitoring period for counting no-answer events<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u2753-frequently-asked-questions\">\u2753 Frequently Asked Questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-what-is-the-vos-3000-no-answer-auto-blacklist\">\u2753 What is the VOS3000 no-answer auto-blacklist?<\/h3>\n\n\n\n<p>\u23f1\ufe0f The <strong>VOS3000 no-answer auto-blacklist<\/strong> 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 \u00a74.3.5.2.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-why-is-the-no-answer-auto-blacklist-disabled-by-default\">\u2753 Why is the no-answer auto-blacklist disabled by default?<\/h3>\n\n\n\n<p>\ud83d\udd27 The <strong>VOS3000 no-answer auto-blacklist<\/strong> is disabled by default because SS_BLACK_LIST_NO_ANSWER_LIMIT has a default value of <strong>None<\/strong>. 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 \u2014 for example, 5 consecutive no-answer events.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-what-is-the-difference-between-no-answer-blacklist-and-malicious-caller-blacklist\">\u2753 What is the difference between no-answer blacklist and malicious caller blacklist?<\/h3>\n\n\n\n<p>\ud83d\udccb The <strong>VOS3000 no-answer auto-blacklist<\/strong> targets the <em>callee<\/em> (destination) side \u2014 it blocks numbers that fail to answer. The malicious caller blacklist targets the <em>caller<\/em> (originating) side \u2014 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.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-how-long-should-i-set-the-no-answer-blacklist-expire-duration\">\u2753 How long should I set the no-answer blacklist expire duration?<\/h3>\n\n\n\n<p>\u23f1\ufe0f 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 \u2014 this reflects the fact that dead destination numbers typically do not recover quickly. Refer to <a href=\"https:\/\/www.rfc-editor.org\/rfc\/rfc3261\" target=\"_blank\" rel=\"noopener\">RFC 3261<\/a> for SIP call flow standards.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-can-i-manually-remove-numbers-from-the-no-answer-dynamic-blacklist\">\u2753 Can I manually remove numbers from the no-answer dynamic blacklist?<\/h3>\n\n\n\n<p>\ud83d\udcca Yes, you can manually remove entries from the dynamic blacklist. Navigate to <strong>Number management \u2192 Dynamic black list<\/strong>, 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 <a href=\"https:\/\/multahost.com\/blog\/vos3000-number-management\/\" target=\"_blank\" rel=\"noopener\">number management<\/a> tools.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u2753-does-the-no-answer-auto-blacklist-work-with-all-sip-response-codes\">\u2753 Does the no-answer auto-blacklist work with all SIP response codes?<\/h3>\n\n\n\n<p>\ud83d\udcde The <strong>VOS3000 no-answer auto-blacklist<\/strong> specifically targets scenarios where the callee fails to answer \u2014 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 &#8220;no-answer&#8221; conditions \u2014 they are explicit call rejections. For related <a href=\"https:\/\/multahost.com\/blog\/vos3000-call-end-reasons\/\" target=\"_blank\" rel=\"noopener\">call end reasons<\/a>, check our detailed reference guide. WhatsApp us at <strong>+8801911119966<\/strong> for more information. \ud83d\udcde<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udcde-need-expert-help-with-vos-3000-no-answer-auto-blacklist\">\ud83d\udcde Need Expert Help with VOS3000 No-Answer Auto-Blacklist?<\/h2>\n\n\n\n<p>\ud83d\udd27 Proper <strong>VOS3000 no-answer auto-blacklist<\/strong> 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 <strong>+8801911119966<\/strong> for professional VOS3000 configuration services. \ud83d\udcde<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\ud83d\udcde-need-call-center-setup-support\">\ud83d\udcde Need Professional VOS3000 Setup Support?<\/h2>\n\n\n\n<p>For professional VOS3000 installations and deployment, VOS3000 Server Rental Solution:<\/p>\n\n\n\n<p>\ud83d\udcf1 <strong>WhatsApp:<\/strong> <a href=\"https:\/\/wa.me\/8801911119966\" target=\"_blank\" rel=\"noopener\">+8801911119966<\/a><br>\ud83c\udf10 <strong>Website:<\/strong> <a href=\"https:\/\/www.vos3000.com\">www.vos3000.com<\/a><br>\ud83c\udf10 <strong>Blog:<\/strong> <a href=\"https:\/\/multahost.com\/blog\" target=\"_blank\" rel=\"noopener\">multahost.com\/blog<\/a><br>\ud83d\udce5 <strong>Downloads:<\/strong> <a href=\"https:\/\/www.vos3000.com\/downloads.php\">VOS3000 Downloads<\/a><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><img decoding=\"async\" src=\"https:\/\/www.vos3000.com\/blog\/wp-content\/uploads\/2026\/04\/VOS3000-RTP-Lock-In-VOS3000-Aggressive-Gateway-Failover-768x1024.png\" alt=\"VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Period Capacity Configuration, VOS3000 Period Dial Plan, VOS3000 RTP Interrupt Detection, VOS3000 Lowest Profit Rate Limit, VOS3000 Max Minute Rate Cap, VOS3000 Sort Lowest Rate Per Second, VOS3000 Check Rate Before Routing, VOS3000 Sort by Lowest Rate, VOS3000 Bilateral Reconciliation, VOS3000 SIP OPTIONS Online Check, VOS3000 T38 Fax Over IP, VOS3000 G729 Annex B Silence, VOS3000 Gateway Group Reserved Lines, VOS3000 Auxiliary Ring Tone, VOS3000 Black White List Groups, VOS3000 System White List, VOS3000 Callee Balance Verification, VOS3000 Dial Plan Wildcards, VOS3000 Number Length Matching, VOS3000 Random Routing Patterns, VOS3000 Position Keeper Dollar, VOS3000 LRN Number Portability, VOS3000 LRN Numbers\"><\/td><td><img decoding=\"async\" src=\"https:\/\/www.vos3000.com\/blog\/wp-content\/uploads\/2026\/04\/VOS3000-RTP-Lock-In-VOS3000-Aggressive-Gateway-Failover-768x1024.png\" alt=\"VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Period Capacity Configuration, VOS3000 Period Dial Plan, VOS3000 RTP Interrupt Detection, VOS3000 Lowest Profit Rate Limit, VOS3000 Max Minute Rate Cap, VOS3000 Sort Lowest Rate Per Second, VOS3000 Check Rate Before Routing, VOS3000 Sort by Lowest Rate, VOS3000 Bilateral Reconciliation, VOS3000 SIP OPTIONS Online Check, VOS3000 T38 Fax Over IP, VOS3000 G729 Annex B Silence, VOS3000 Gateway Group Reserved Lines, VOS3000 Auxiliary Ring Tone, VOS3000 Black White List Groups, VOS3000 System White List, VOS3000 Callee Balance Verification, VOS3000 Dial Plan Wildcards, VOS3000 Number Length Matching, VOS3000 Random Routing Patterns, VOS3000 Position Keeper Dollar, VOS3000 LRN Number Portability, VOS3000 LRN Numbers\"><\/td><td><img decoding=\"async\" src=\"https:\/\/www.vos3000.com\/blog\/wp-content\/uploads\/2026\/04\/VOS3000-RTP-Lock-In-VOS3000-Aggressive-Gateway-Failover-768x1024.png\" alt=\"VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Gateway Switch Limit, VOS3000 RTP Lock-In, VOS3000 Aggressive Gateway Failover, VOS3000 Busy Stop Switch, VOS3000 real-time gateway ASR, VOS3000 ASR Cost Routing, VOS3000 Prefix Mode Extension, VOS3000 Period Capacity Configuration, VOS3000 Period Dial Plan, VOS3000 RTP Interrupt Detection, VOS3000 Lowest Profit Rate Limit, VOS3000 Max Minute Rate Cap, VOS3000 Sort Lowest Rate Per Second, VOS3000 Check Rate Before Routing, VOS3000 Sort by Lowest Rate, VOS3000 Bilateral Reconciliation, VOS3000 SIP OPTIONS Online Check, VOS3000 T38 Fax Over IP, VOS3000 G729 Annex B Silence, VOS3000 Gateway Group Reserved Lines, VOS3000 Auxiliary Ring Tone, VOS3000 Black White List Groups, VOS3000 System White List, VOS3000 Callee Balance Verification, VOS3000 Dial Plan Wildcards, VOS3000 Number Length Matching, VOS3000 Random Routing Patterns, VOS3000 Position Keeper Dollar, VOS3000 LRN Number Portability, VOS3000 LRN Numbers\"><\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Configure VOS3000 no-answer auto-blacklist with SS_BLACK_LIST_NO_ANSWER. 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