Skip to main content
  • What: Technical specs for Plivo’s Zentrunk SIP trunking: supported SIP methods, codecs (PCMA/PCMU), data centers, authentication, and limits
  • Key limits: Default 2 CPS (account-level), max 100 trunks recommended. Calls exceeding trunk CPS fail immediately; exceeding account CPS are queued
  • Authentication: IP ACLs, username/password, or both. Signaling on ports 5060/5061, media on 10000–30000
  • Cost: Short duration surcharges: USD 0.005 for abandoned calls (0 sec) if >20% monthly; USD 0.0025 for short calls (≤6 sec) if >20% monthly
  • Not supported: Call recording and T.38 fax. Premium number calls blocked by default (requires Support approval, 48+ hours)
This page covers the technical specifications and requirements for Plivo’s Zentrunk SIP trunking service.

​
What is Zentrunk?

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

​
Supported SIP Methods

​
SIP REFER (Call Transfer)

Plivo supports SIP REFER for mid-call transfers on both inbound and outbound SIP trunk calls. Your endpoint sends a REFER request and Plivo handles the new call leg — no re-dial, no dropped caller. See SIP REFER for the full guide, including inbound and outbound transfer flows.

​
Codecs and Encryption

Call recording and T.38 fax are not supported.

​
Data Center Locations

​
Calls Per Second (CPS) Limits

Call queuing behavior:
  • Calls exceeding trunk CPS fail immediately
  • Calls exceeding account CPS queue for processing
Contact Plivo Sales to increase your CPS allocation.

​
Resource Limits

​
IP Whitelisting Requirements

Whitelist these CIDR blocks for Zentrunk connectivity: Required ports:
  • Signaling: 5060 (UDP/TCP), 5061 (TLS)
  • Media: 10000-30000 (UDP/TCP)

​
Authentication Methods

  • IP Access Control Lists
  • Username/password credentials
  • Both combined

​
SIP OPTIONS Pings

  • Send pings to the outbound trunk URI only
  • Maximum frequency: 1 ping per 10-15 seconds
  • Higher frequency may trigger blocking

​
Caller ID Requirements

Plivo numbers are required as caller ID for all outbound calls. Using non-Plivo numbers results in an unknown_caller_id hangup. Options:
  • Rent numbers through the Plivo console
  • Port existing numbers to Plivo
  • Contact Plivo Support for special cases
Countries with guaranteed domestic CLI: US, Canada, UK, Australia, Italy, Peru, and France (beta).

​
Premium Number Restrictions

Zentrunk blocks calls to premium-rate numbers to prevent toll fraud (IRSF - International Revenue Share Fraud). To enable premium number calling:
  1. Contact Plivo Support
  2. Provide use case details
  3. Wait for validation (48+ hours)

​
Pricing

Call rates vary by originating country, not just destination. For example, calls to Germany from Europe cost less than from outside Europe. Check Zentrunk Pricing for current rates.

​
Short Duration Call Charges

When the percentage of abandoned or short-duration calls exceeds 20% of your monthly call volume, a per-call surcharge applies to the excess calls.
Calls to India are excluded from short-duration surcharges. The 20% threshold and surcharges apply only to calls to non-India destinations.

​
Country-Specific Requirements

​
Australia

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

​
China

Prohibited traffic:
  • Gambling, financial services, cryptocurrency
  • Marketing/spam calls
  • Fraudulent calls
  • Politically sensitive content
Outbound requirements:
  • Cannot use Chinese caller IDs
  • Maintain average call duration over 3 minutes
  • Avoid high unanswered rates
  • Don’t use toll-free numbers
Inbound requirements:
  • Chinese numbers can only receive calls from within China

​
Compatible Systems

​
Softphone Setup

  1. Create an account in your softphone
  2. Uncheck “register with domain and receive calls”
  3. Configure with your Zentrunk SIP URI

​
Call Detail Records

Access CDRs in the Plivo console:
  1. Navigate to Zentrunk > Logs
  2. Filter CDRs as needed
  3. Click Export to download
Debug information available (no charge):
  • Call details (basic info)
  • Call stats (origination, termination, trunk info)
  • SIP logs (PCAP, last response, codec)