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
| Status | Methods |
|---|
| Supported | ACK, BYE, CANCEL, INVITE, OPTIONS, REFER, UPDATE |
| Not supported | INFO, MESSAGE, NOTIFY, PRACK, PUBLISH, REGISTER, SUBSCRIBE |
SIP REFER (Call Transfer)
Plivo supports SIP REFER for call transfers. This enables:
- Blind transfers: Transfer a call to another destination without consultation
- Attended transfers: Consult with the transfer target before completing the transfer
SIP REFER allows your PBX or SIP endpoint to initiate call transfers using standard SIP signaling.
Codecs and Encryption
| Feature | Supported |
|---|
| Codecs | PCMA, PCMU |
| Signaling encryption | TLS |
| Media encryption | SRTP |
| DTMF | RFC-2833 format |
Call recording and T.38 fax are not supported.
Data Center Locations
| Region | Location |
|---|
| North America | North California, Virginia |
| Europe | Frankfurt |
| South America | São Paulo |
| Asia Pacific | Singapore, Sydney, Mumbai |
Calls Per Second (CPS) Limits
| Level | Default | Description |
|---|
| Account-level | 2 CPS | Total calls per second across all trunks |
| Trunk-level | Configurable | Allocated per trunk from account pool |
- Calls exceeding trunk CPS fail immediately
- Calls exceeding account CPS queue for processing
Contact Plivo Sales to increase your CPS allocation.
Resource Limits
| Resource | Limit |
|---|
| Trunks per account | 100 (recommended) |
| IP ACLs per account | Unlimited |
| Concurrent calls | Unlimited (elastic scaling) |
IP Whitelisting Requirements
Whitelist these CIDR blocks for Zentrunk connectivity:
| Region | CIDR Blocks |
|---|
| North California | 13.52.9.0/25, 216.120.187.128/26 |
| Virginia | 18.214.109.128/25, 18.215.142.0/26, 204.89.148.128/26 |
| Frankfurt | 3.120.121.128/26 |
| São Paulo | 18.228.70.64/26 |
| Sydney | 13.238.202.192/26 |
- 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:
- Contact Plivo Support
- Provide use case details
- 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
| Type | Threshold | Surcharge |
|---|
| Abandoned calls (0 seconds) | > 20% monthly | $0.005 per excess call |
| Short calls (≤6 seconds) | > 20% monthly | $0.0025 per excess call |
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
| Type | Examples |
|---|
| IP PBX | FreeSWITCH, Asterisk, FreePBX, 3CX, FusionPBX |
| Session Border Controllers | Various vendors |
| Softphones | Zoiper, X-Lite/Bria |
Softphone Setup
- Create an account in your softphone
- Uncheck “register with domain and receive calls”
- Configure with your Zentrunk SIP URI
Call Detail Records
Access CDRs in the Plivo console:
- Navigate to Zentrunk > Logs
- Filter CDRs as needed
- 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)
