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Zentrunk is Plivo’s cloud-based SIP trunking service that connects IP PBX systems to PSTN and mobile networks.

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Overview

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Supported Features

FeatureSupport
SIP MethodsACK, BYE, CANCEL, INVITE, OPTIONS, UPDATE
AuthenticationIP ACL, Username/Password, or both
CodecsPCMA, PCMU
DTMFRFC-2833
EncryptionTLS (signaling), SRTP (media)
E.164 FormatRequired for all calls
Call RecordingNot supported
T.38 FaxNot supported

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Not Supported

  • INFO, MESSAGE, NOTIFY, PRACK, PUBLISH, REFER, REGISTER, SUBSCRIBE SIP methods
  • Call recording
  • T.38 fax

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Points of Presence (PoPs)

Zentrunk routes calls through the nearest PoP for optimal latency.
RegionLocation
North AmericaNorth California, Virginia
EuropeFrankfurt
South AmericaSão Paulo
Asia PacificSingapore, Sydney, Mumbai

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Calls Per Second (CPS)

CPS limits control outbound call initiation rate.
LevelDefaultDescription
Account-level2 CPSTotal calls per second across all trunks
Trunk-levelConfigurableAllocated per trunk from account pool
Example allocations:
  • 3 trunks with 25 account CPS: 10 + 10 + 5 CPS
  • 10 trunks with 10 account CPS: Each trunk gets 10 CPS (first-come allocation)
Notes:
  • No limit on concurrent calls
  • Calls exceeding trunk CPS fail; calls exceeding account CPS queue
  • Contact Plivo Sales to increase CPS

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Configuration

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IP Addresses to Whitelist

RegionIP AddressesSignaling PortsMedia Ports
North California13.52.9.0/25, 216.120.187.128/265060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
Virginia18.214.109.128/25, 18.215.142.0/26, 204.89.148.128/265060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
Frankfurt3.120.121.128/265060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
São Paulo18.228.70.64/265060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
Sydney13.238.202.192/265060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
SingaporeCheck Zentrunk documentation5060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)
MumbaiCheck Zentrunk documentation5060 (UDP/TCP), 5061 (TLS)10000-30000 (UDP/TCP)

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Authentication Methods

  1. IP Access Control List: Whitelist your PBX IP addresses
  2. Credentials: Username and password authentication
  3. Both: IP ACL combined with credentials

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Limits

ResourceLimit
Trunks per account100 (recommended)
IP ACLs per accountUnlimited
Concurrent callsUnlimited (elastic scaling)

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SIP OPTIONS Pings

Zentrunk supports OPTIONS pings for health checks. Requirements:
  • Send to outbound trunk URI only (not trunk IP addresses)
  • Maximum frequency: 1 ping per 10-15 seconds
  • Higher frequency may result in blocking

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Caller ID Requirements

Plivo numbers are required as caller ID for all outbound calls. Using a non-Plivo number results in unknown_caller_id hangup cause. Options:
  1. Rent numbers from Plivo
  2. Port existing numbers to Plivo
For use cases requiring non-Plivo caller IDs, contact Plivo Support with your requirements.

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Domestic Caller ID Support

Plivo guarantees domestic CLI presentation in:
  • United States
  • Canada
  • United Kingdom
  • Australia
  • Italy
  • Peru
  • France (beta)

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Premium and High-Risk Numbers

By default, Zentrunk blocks calls to premium-rate numbers to prevent toll fraud (IRSF - International Revenue Share Fraud).

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What are Premium Numbers?

Numbers that charge higher rates for special services (e.g., adult content, contest lines, directory services).

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Request Access

If your use case requires calling premium numbers:
  1. Contact Plivo Support
  2. Provide your use case details
  3. Wait for validation (48+ hours)
If a number is incorrectly classified as high-risk, contact support for review.

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Pricing

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Origin-Based Pricing

Call rates vary by originating country, not just destination. Example: Calls to Germany from within Europe may cost less than calls from outside Europe. Check Zentrunk Pricing for current rates.

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Abandoned and Short Duration Call Charges

MetricThresholdSurcharge
Abandoned calls> 20% of monthly calls$0.005 per excess call
Short duration calls> 20% of monthly calls$0.0025 per excess call
Definitions:
  • Abandoned call: Zero-second duration (unanswered, rejected, missed)
  • Short duration call: ≤ 6 seconds (excluding abandoned)

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Troubleshooting

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Access Call Detail Records (CDRs)

  1. Navigate to Zentrunk > Logs in the console
  2. Filter CDRs as needed
  3. Click Export to download

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Debug Logs

Available information:
  • Call details (basic info)
  • Call stats (origination, termination, trunk info)
  • SIP logs (PCAP download, last SIP response, codec)
Notes:
  • No charge for debug logs
  • Audio quality parameters not available in debug logs
  • Download SIP PCAPs from the call detail record

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Common Hangup Causes

Hangup CauseDescriptionSolution
unknown_caller_idNon-Plivo number used as caller IDUse Plivo number or port your number
dno_caller_idNumber on US “Do Not Originate” listUse a different caller ID
destination_country_barredGeo permissions not enabledEnable country in console
See Zentrunk Hangup Codes for the complete list.

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Country-Specific Restrictions

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Australia

Per ACMA regulations, calls with these CLI prefixes are blocked:
  • +6113
  • +611300
  • +611800
  • +611900

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China

Prohibited traffic:
  • Gambling, betting
  • Financial services, cryptocurrency
  • Marketing/spam calls
  • Fraudulent calls (“fake police,” etc.)
  • Politically sensitive topics
Outbound requirements:
  • Cannot use Chinese numbers as caller ID
  • Maintain average call duration > 3 minutes
  • Avoid high unanswered call rates
  • Don’t use toll-free numbers
Inbound requirements:
  • Chinese numbers can only receive calls from within China
Contact Plivo Support to enable China calling with your use case.

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Compatible Equipment

Zentrunk works with:
  • IP PBX systems (FreeSWITCH, Asterisk, FreePBX, 3CX, FusionPBX)
  • Session Border Controllers (SBC)
  • Softphone clients (Zoiper, X-Lite/Bria)

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Softphone Setup

  1. Create an account in your softphone
  2. Uncheck “register with domain and receive calls”
  3. Configure with your Zentrunk SIP URI
See PBX Integration Guides for detailed setup instructions.

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API Integration

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Map Numbers to Inbound Trunks

Use the Account Phone Number API with inbound trunk_id parameter.