> ## Documentation Index > Fetch the complete documentation index at: https://plivo.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Technical Specifications > SIP methods, codecs, data centers, limits, and networking requirements for Zentrunk > [!NOTE] > > Reference for Plivo Zentrunk SIP trunking specs: supported SIP methods, codecs, data centers, authentication options, and surcharges. Check it when configuring a trunk or diagnosing capacity and compatibility. 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 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](https://plivo.com/docs/sip-trunking/concepts/sip-refer.md) for the full guide, including inbound and outbound transfer flows. *** ## Codecs and Encryption | Feature | Supported | | - | - | | **Codecs** | PCMA, PCMU | | **Signaling encryption** | TLS | | **Media encryption** | SRTP | | **DTMF** | RFC-2833 format | > [!NOTE] > > 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 | *** ## Account, CPS, and Concurrency Limits Account-level CPS, trunk-level CPS, concurrency, and trunk resource limits are documented on [SIP Trunking account limits](https://plivo.com/docs/sip-trunking/concepts/account-limits.md). SIP Trunking rejects calls above any of these limits with hangup cause `5180` (`cps_limit_reached`) or `5190` (`concurrent_call_limit_exceeded`); it does not queue them. *** ## 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` | **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](https://support.plivo.com) 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](https://support.plivo.com) 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](https://www.plivo.com/sip-trunking/pricing/) for current rates. ### Short Duration Call Charges When the percentage of abandoned or short-duration calls exceeds the monthly threshold for that call type, a per-call surcharge applies to the excess calls. | Type | Threshold | Surcharge | | - | - | - | | Abandoned calls (0 seconds) | > 20% monthly | \$0.005 per excess call | | Short calls (≤6 seconds) | > 10% monthly | \$0.015 per excess call | > [!NOTE] > > **Calls to India are excluded** from short-duration surcharges. These thresholds 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 | Type | Examples | | - | - | | **IP PBX** | FreeSWITCH, Asterisk, FreePBX, 3CX, FusionPBX | | **Session Border Controllers** | Various vendors | | **Softphones** | Zoiper, X-Lite/Bria | ### 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) *** ## Related * [Geo Permissions](https://plivo.com/docs/sip-trunking/concepts/geo-permissions.md) * [STIR/SHAKEN](https://plivo.com/docs/sip-trunking/concepts/stir-shaken.md) * [Troubleshooting](https://plivo.com/docs/sip-trunking/troubleshooting/zentrunk-hangup-codes.md)