Connecting a PBX or SBC to Twilio with BYOC trunks and SIP Domains

See also

Sources

1. 1
   Twilio's April 2020 BYOC launch post stated that the Twilio Super Network is used by default as a failover if all targets in the BYOC trunk's origination connection policy fail to route the call.

   Announcing Twilio's Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Announcement post, outbound/origination paragraph · Checked 2026-10-14
2. 2
   Twilio's BYOC guide says IP Access Control List entries can be IP addresses or ranges in CIDR notation, and they should be the outbound SIP source addresses of the customer's border elements.

   Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · IP Access Control Lists - Settings · Checked 2026-10-14
3. 3
   The Twilio Calls API accepts a Byoc parameter carrying the SID (BY prefix, 34 characters) of the BYOC trunk to route the call with.

   Call resource · Create a Call resource > Request body parameters > Byoc · Checked 2026-10-14
4. 4
   The Byoc parameter on the Twilio Create a Call API is marked Beta in the API reference.

   Call resource · Create a Call resource > Request body parameters > Byoc (Beta label) · Checked 2026-10-14
5. 5
   The Byoc parameter on a Twilio Calls API request only takes effect when To is a phone number and is otherwise ignored.

   Call resource · Create a Call resource > Request body parameters > Byoc · Checked 2026-10-14
6. 6
   A Twilio Conference Participant can be dialled out through a BYOC trunk by supplying the Byoc parameter on the Participant resource.

   Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Making Outbound Calls to your PSTN Carrier (Origination) > Conference · Checked 2026-10-14
7. 7
   A carrier connects to a Twilio BYOC trunk either over the public internet to a Twilio-provided FQDN or over a Private Connection to a single static IP address, and the private option requires Twilio Interconnect.

   Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Requirements; Termination SIP Domains - Settings (Static IP Address warning) · Checked 2026-10-14
8. 8
   According to the Twilio ByocTrunk API reference, if from_domain_sid is not configured, the From domain on originating calls defaults to sip.twilio.com.disputed

   ByocTrunk Resource · Properties > from_domain_sid; Create parameters > FromDomainSid · Checked 2026-10-14
9. 9
   According to the Twilio BYOC setup guide, if a BYOC trunk's From Domain is left unset, Twilio uses the first Termination SIP Domain on the trunk as the From-URI domain for outbound calls.disputed

   Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · BYOC Trunks - Overview > Trunks, From Domain · Checked 2026-10-14
10. 10
    Twilio announced general availability of BYOC Trunking for Programmable Voice on 2020-04-30, with static IP termination offered under Limited Availability.

    Announcing Twilio's Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Announcement post, opening and connectivity paragraphs · Checked 2026-10-14
11. 11
    Custom SIP headers included in INVITEs that arrive from a BYOC trunk are discarded and are not passed to the customer's webhook.

    Inbound - Sending SIP to Twilio · Advanced Features > SIP Custom Headers · Checked 2026-10-14
12. 12
    Twilio recommends that carrier equipment sending to a BYOC termination domain use all of Twilio's IP addresses, move to the next IP after 4 seconds without a response to an INVITE, and fail over to another region if needed.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings, failover guidance · Checked 2026-10-14
13. 13
    Twilio's BYOC guide warns that IP ACLs alone do not protect against certain types of attacks and strongly recommends adding credentials, in which case inbound INVITEs are challenged with a 407.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings, Authentication note; Credential Lists - Settings · Checked 2026-10-14
14. 14
    Twilio publishes localized BYOC termination SIP URIs per region, including us1, us2, ie1, de1, sg1, jp1, br1 and au1, in the form name.sip.region.twilio.com.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings, localized Termination SIP URIs list · Checked 2026-10-14
15. 15
    Twilio does not support credential (digest) authentication toward the carrier on BYOC origination calls, so the carrier must trust Twilio's regional signaling IP addresses.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Origination Connection Policy - Settings · Checked 2026-10-14
16. 16
    Twilio BYOC Trunking connects a customer's existing PSTN carrier to Twilio Programmable Voice over a SIP trunk, so calls can use numbers the customer already holds with other carriers.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Bring Your Own Carrier (BYOC) Trunking for Programmable Voice (intro); Trunks · Checked 2026-10-14
17. 17
    On a BYOC Termination SIP Domain, the Secure Media (TLS/SRTP) switch only affects termination (inbound) traffic, not origination.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings, Secure Media · Checked 2026-10-14
18. 18
    The BYOC static IP termination option is not available when using the Twilio Regions Ireland (IE1) or Australia (AU1).

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings, Static IP Address warning · Checked 2026-10-14
19. 19
    A Twilio BYOC Termination SIP Domain must have a domain URI and at least one authentication scheme (an IP Access Control List or a Credential List), and if both are configured both are enforced.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Termination SIP Domains - Settings · Checked 2026-10-14
20. 20
    A Twilio BYOC trunk has two directions: termination is carrier-to-Twilio (inbound) traffic and origination is Twilio-to-carrier (outbound) traffic.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · Getting Started: Configure your BYOC Trunk · Checked 2026-10-14
21. 21
    A Twilio BYOC trunk's settings comprise a friendly name, one or more Termination SIP Domains, an Origination Connection Policy, an application configuration for incoming calls (with optional primary-handler-fails and call-status-changes handlers), and a From Domain.

    Bring Your Own Carrier (BYOC) Trunking for Programmable Voice · BYOC Trunks - Overview > Trunks · Checked 2026-10-14
22. 22
    In TwiML, an outbound call is sent through a BYOC trunk by setting the byoc attribute of <Number> inside <Dial> to the BYOC Trunk SID.

    TwiML Voice: <Number> · Attributes > byoc · Checked 2026-10-14
23. 23
    BYOC trunks are managed through the Twilio Voice v1 API at https://voice.twilio.com/v1/ByocTrunks, and their SIDs start with BY.

    ByocTrunk Resource · Create a ByocTrunk resource (endpoint); Properties > sid · Checked 2026-10-14
24. 24
    When cnam_lookup_enabled is true on a Twilio BYOC trunk, inbound calls from the United States and Canada automatically get a CNAM (caller ID name) lookup.

    ByocTrunk Resource · Properties > cnam_lookup_enabled · Checked 2026-10-14
25. 25
    The Twilio Calls API reference states that a phone-number From must be a Twilio number or a verified outgoing caller ID for the account, and it documents no BYOC-specific exception.

    Call resource · Create a Call resource > Request body parameters > From · Checked 2026-10-14
26. 26
    A Twilio Connection Policy (SID prefix NY, API base https://voice.twilio.com/v1/ConnectionPolicies) is a list of URI entries used to route origination traffic to the PSTN carrier over a BYOC trunk.

    ConnectionPolicy Resource · ConnectionPolicy resource description; Properties > sid · Checked 2026-10-14
27. 27
    TwiML <Sip> accepts a region URI parameter (us1, us2, ie1, de1, sg1, jp1, br1, au1) that selects where SIP-out traffic leaves Twilio; without it, traffic is sent from North America Virginia.

    TwiML Voice: <Sip> · Region · Checked 2026-10-14
28. 28
    TwiML <Sip> accepts a transport URI parameter of UDP, TCP or TLS; UDP is the default, and TLS defaults to port 5061.

    TwiML Voice: <Sip> · Transport · Checked 2026-10-14
29. 29
    Twilio announced on 2026-07-02 that SIP signaling IPs for Programmable Voice SIP and Elastic SIP Trunking over Interconnect will move to 159.26.160.0/20 in the second half of 2027.

    Interconnect SIP Signaling IP Addresses · Changelog entry body · Checked 2026-10-14
30. 30
    Twilio's 2027 Interconnect signaling IP migration does not affect SIP FQDNs, TLS certificates, public-internet SIP signaling IPs or media IP ranges.

    Interconnect SIP Signaling IP Addresses · Changelog entry, not-affected list · Checked 2026-10-14
31. 31
    Twilio's SIP IP address page lists the media destination range as 168.86.128.0/18 on UDP ports 10000 to 60000.

    Elastic SIP Trunking IP addresses · Media IP addresses section · Checked 2026-10-14
32. 32
    Twilio advises against sending SIP traffic directly to its listed IP addresses and recommends using the configured FQDN instead.

    Elastic SIP Trunking IP addresses · Signaling gateways introduction · Checked 2026-10-14
33. 33
    Twilio's SIP IP address page lists signaling ports 5060 for UDP/TCP and 5061 for TLS on every regional gateway.

    Elastic SIP Trunking IP addresses · Signaling gateways table, Ports column · Checked 2026-10-14
34. 34
    If the byoc attribute of TwiML <Number> is not set, the call is routed via the Twilio Super Network.

    TwiML Voice: <Number> · Attributes > byoc (default) · Checked 2026-10-14
35. 35
    Twilio's US pay-as-you-go list price for BYOC trunking was $0.0040 per minute for making calls and $0.0040 per minute for receiving calls, with secure media included, as of August 2026.

    Programmable Voice pricing - United States · BYOC trunking pricing table · Checked 2026-10-14
36. 36
    Twilio's US pay-as-you-go list price for the SIP interface was $0.0040 per minute to make or receive calls, $0.10 per SIP REFER from Twilio, and secure media included, as of August 2026.

    Programmable Voice pricing - United States · Voice pricing table, SIP interface row · Checked 2026-10-14
37. 37
    A Twilio SIP Domain allows at most 10 active endpoint registrations per address-of-record; the 11th is rejected.

    SIP registration · Limits · Checked 2026-10-14
38. 38
    For outbound SIP from Twilio, Secure Media is requested by adding secure=true to the SIP URI, which also uses TLS on port 5061 by default.

    Secure Media · How it works / outbound · Checked 2026-10-14
39. 39
    Twilio Secure Media accepts AES_CM_128_HMAC_SHA1_80 and AES_CM_128_HMAC_SHA1_32 inbound, offers only AES_CM_128_HMAC_SHA1_80 outbound, and does not support the MKI parameter.

    Secure Media · Requirements / crypto suites · Checked 2026-10-14
40. 40
    Because Twilio's guide and API reference give different defaults for a BYOC trunk's From domain, a deployment whose carrier validates the From host should set the From Domain explicitly rather than rely on either default.inferred

    ByocTrunk Resource · Properties > from_domain_sid (read together with the BYOC guide, Trunks > From Domain) · Checked 2026-10-14
41. 41
    Twilio's Sending SIP guide says SIP Domain IP ACL entries must be full IP addresses and that no IP wildcarding is supported.

    Inbound - Sending SIP to Twilio · IP Access Control Lists (ACL) · Checked 2026-10-14
42. 42
    Twilio Programmable Voice SIP supports the G.711 mu-law (PCMU) and A-law (PCMA) codecs for media.

    Use SIP with Twilio Voice · Features > Media codec · Checked 2026-10-14
43. 43
    On Programmable Voice SIP Domain calls, only custom headers beginning with X- (plus User-to-User) are passed to the webhook, as parameters prefixed SipHeader_.

    Inbound - Sending SIP to Twilio · Advanced Features > SIP Custom Headers; UUI (User-to-User Information) Header · Checked 2026-10-14
44. 44
    For its complete IP list, Twilio's Programmable Voice SIP page links to the same IP address page that is titled for Elastic SIP Trunking, which suggests the two products share signaling and media ranges.inferred

    Use SIP with Twilio Voice · IP addresses · Checked 2026-10-14
45. 45
    Twilio Programmable Voice does not support the sips URI scheme; encrypted signaling uses a sip URI with transport=tls.

    Use SIP with Twilio Voice · Features > Securing SIP Traffic using TLS · Checked 2026-10-14
46. 46
    TLS for Twilio Programmable Voice SIP uses port 5061, is available without extra setup, and supports only TLSv1.2 (not TLSv1.0 or 1.1).

    Use SIP with Twilio Voice · Features > Securing SIP Traffic using TLS > TLS Specifications · Checked 2026-10-14
47. 47
    Sending TLS SIP traffic to a Twilio IP address instead of the SIP domain name is a common misconfiguration that causes a 403 error not visible in the Twilio account.

    Use SIP with Twilio Voice · Features > Securing SIP Traffic using TLS · Checked 2026-10-14
48. 48
    A Twilio SIP Domain with no mapped authentication method (IP ACL or credential list) blocks requests sent to it.

    SIP Domain Resource · SIP Domain resource overview (authentication mapping note) · Checked 2026-10-14
49. 49
    A Twilio SIP Domain is associated with a BYOC trunk through its byoc_trunk_sid property (a BY SID).

    SIP Domain Resource · Properties > byoc_trunk_sid · Checked 2026-10-14
50. 50
    The emergency_caller_sid property of a Twilio SIP Domain names a phone number (PN SID) that is used as the callback number for emergency calls.

    SIP Domain Resource · Properties > emergency_caller_sid · Checked 2026-10-14
51. 51
    The emergency_calling_enabled property on a Twilio SIP Domain allows emergency calls on the domain from phone numbers with validated addresses.

    SIP Domain Resource · Properties > emergency_calling_enabled · Checked 2026-10-14
52. 52
    Twilio allows at most 100 SIP Domains per account or subaccount.

    Use SIP with Twilio Voice · What is SIP? > Limits · Checked 2026-10-14
53. 53
    A Twilio SIP Domain name may contain letters, digits and hyphens and must end with sip.twilio.com.

    SIP Domain Resource · Properties > domain_name · Checked 2026-10-14
54. 54
    When the secure property of a Twilio SIP Domain is true, TLS is enforced on incoming calls and SRTP is negotiated for media.

    SIP Domain Resource · Properties > secure · Checked 2026-10-14
55. 55
    All users of one Twilio SIP Domain webhook to the same application URL; per-user routing has to be done inside that application.

    Inbound - Sending SIP to Twilio · Call Control Configuration · Checked 2026-10-14
56. 56
    The Twilio SourceIpMapping resource, which describes static IPs used to receive traffic from a BYOC carrier, requires the account to have a Twilio Interconnect connection configured.

    SourceIpMapping Resource · SourceIpMapping resource description (requirement notice) · Checked 2026-10-14
57. 57
    Twilio Connection Policy targets take a priority from 0 to 65535, where the lowest number is tried first, and a weight from 1 to 65535 that shares load among targets of equal priority.

    ConnectionPolicyTarget Resource · Properties > priority; Properties > weight · Checked 2026-10-14
58. 58
    A Twilio Connection Policy target URI must use the sip: scheme; sips: is not supported.

    ConnectionPolicyTarget Resource · Properties > target · Checked 2026-10-14

Documents

Cite this page

WarmTransfer. (2026, October 14). Connecting a PBX or SBC to Twilio with BYOC trunks and SIP Domains. WarmTransfer. https://warmtransfer.net/knowledge/twilio-byoc-sip-domains

@misc{warmtransfer-twilio-byoc-sip-domains,
  title  = {Connecting a PBX or SBC to Twilio with BYOC trunks and SIP Domains},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/twilio-byoc-sip-domains},
  note   = {Verified 2026-10-14}
}