Internet SIP Trunk licenses, HA topologies, call transfer, and technical limits

Reference guide for Internet SIP Trunk licenses, 2T/4T High Availability topologies, Blind and Attended call transfer, Caller ID display headers, and technical limits.

Written by B3Networks Academy

Updated at November 12th, 2026

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This page provides the authoritative reference for Internet SIP Trunk licenses, High Availability topologies, call transfer methods, and signaling limits.

Licenses and HA entitlement matrix

Active add-on licenses must be assigned to the specific trunk you are configuring:

License Name	What it enables
SIP Trunk (Base)	Base trunk subscription and portal access.
Concurrent Call (Add-on)	Shared simultaneous call pool across all accounts, regions, and zones on the trunk (up to 300 on Standard SIP Trunk).
Number (Add-on)	Assigns PSTN / mobile numbers to the trunk.
IP Authentication Mode (Add-on)	Unlocks the IP Peer authentication tab and CPE IP configuration (max 1 per SIP trunk).
High Availability (Add-on)	Primary/secondary SIP account failover (`Only primary`, `Load Balancing`, `Auto Fail-over`).
High Availability Plus (Add-on)	Enables 2 zones per region (`2T` topology, or `2T + 4T` when combined with Geo-Redundancy).
Geo-Redundancy (Add-on)	Enables Primary and Secondary regions (`4T` topology: 2 regions with 1 zone each, or 2 zones each when combined with High Availability Plus).

Advanced HA region / zone topology summary

Active Advanced HA Add-ons	Topology Label	Region & Zone Layout
Neither	Standard	1 region, 1 zone (or Primary/Secondary account if `High Availability` add-on is active).
High Availability Plus only	`2T`	1 region, 2 zones (round-robin routing between zones; 2.5s failover).
Geo-Redundancy only	`4T`	2 regions, 1 zone each (Primary region fails over to Secondary region).
High Availability Plus + Geo-Redundancy	`2T + 4T`	2 regions, 2 zones each (4 CPE peer groups; fails over across zones inside Primary region first, then to Secondary region).

Supported SIP domains and call transfer methods

Regional SIP Domains

Singapore: sipsg02.b3networks.com
Indonesia: sipid01.b3networks.com
Thailand: sipth01.b3networks.com

Call Transfer Methods

Blind Transfer (SIP REFER): Client B sends REFER to the SIP cluster and hangs up; the SIP cluster dials Callee C via a standard SIP INVITE.
Attended Transfer (DTMF ##2): Client B sends DTMF ##2 to the SIP cluster; the cluster dials Callee C; once C answers and B hangs up, Caller A is bridged to Callee C.

Inbound Caller Name & Number Display Priority

Caller Name: Extracted from the Display Name part of the From header.
Caller Number: Extracted from the From Display Name (if numeric); otherwise From User Part; then P-Asserted-Identity (PAI) header.
Called Number Delivery (SIP INVITE): Newly provisioned trunks deliver the incoming DID in the Request-URI by default.

Setting / Policy	Limit / Rule
IP Allowlist limit	Maximum 2 single public IPv4 addresses (`/32`). CIDR subnets, IPv6, hostnames, and malformed addresses are rejected.
Same-IP conflict prevention	The platform blocks reusing the same IP Peer address across multiple active SIP accounts on the same domain.
Wholesale Token Number Sharing (`Access Token`)	• Resale depth capped at 1 tier: Root Telco A → Reseller Telco B (redeemed in Telco Hub / Number Management) is permitted; Telco B → Telco C sub-resale is blocked. • 30-day recovery window: When a shared number link is released or expires, numbers remain locked to the tenant domain for a 30-day recovery SLA before returning to the general pool.
Auto Fail-over speed	2.5 seconds (triggered by `401`/`407` auth failure, `FAREND_CONNECTION_ERROR`, or `USER_NOT_REGISTERED`).

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