Connect any carrier, PBX, or contact center to Callers over SIP for inbound and outbound calls: authentication, gateways, headers, and testing.
A SIP connection links Callers to your own telephony: a carrier (Telnyx, Plivo, CommPeak, Twilio Elastic SIP Trunking, and others), a PBX, or a contact-center platform. Your agents then place outbound calls through your trunk and answer calls your carrier routes to Callers, using your numbers and your carrier rates.
Get these details from your carrier or PBX administrator:
Outbound (Callers → carrier): the SIP server address (domain or IP), port, and transport. Also how the carrier authenticates you: username and password (digest), registration, IP allowlisting, or a tech prefix.
Inbound (carrier → Callers): the IP addresses your carrier sends calls from.
Numbers: the phone numbers on the trunk, in E.164 format (for example +12025550123).
Then give your carrier the Callers address to send inbound calls to:
Send inbound calls to:
sip.callers.ai
or IP address 35.245.182.192.This address only receives calls. Outbound calls from Callers come from different addresses. If your carrier authenticates outbound calls by IP, email for the addresses to allowlist.
Go to App Center, find SIP Integration under Telephony & Communication, and click +. The Add SIP window opens.
SIP Integration in the App Center
2
Fill in the general settings
Enter a SIP Name and turn on the options your carrier requires. See General settings.
3
Configure gateways
On the right, set up at least one gateway: an Outgoing gateway to place calls and an Incoming gateway for each IP your carrier sends calls from. See SIP gateways.
Add SIP: general settings and gateways
4
Add phone numbers
Click Next and enter the numbers on the trunk. You can paste several at once. You can also add numbers later from Phone numbers → Add SIP Numbers.
A gateway is a SIP endpoint on your carrier’s side. Add as many as you need with Add Another SIP Gateway.
Setting
Outgoing gateway
Incoming gateway
Gateway Type
Outgoing: Callers sends calls to this address
Incoming: Callers accepts calls from this address
URL / IP
Domain or IPv4 address, for example sip.telnyx.com
IPv4 address only (domains aren’t accepted for incoming)
Port
Default 5060
Default 5060
Netmask
—
Accept a whole range, 1–32. Default 32 (a single IP). For example, 24 accepts x.x.x.0–255.
Protocol
UDP (default), TCP, TLS, or TLS/SRTP
—
Send OPTIONS ping
Sends periodic SIP OPTIONS to keep the gateway’s status and NAT bindings fresh
—
Use sips scheme
Uses sips: URIs. Shown for TLS and TLS/SRTP.
—
Pad crypto
Compatibility option for some SRTP endpoints. Shown for TLS/SRTP.
—
For redundancy, add your carrier’s primary and secondary servers as separate outgoing gateways, and add every signaling IP your carrier uses as an incoming gateway. Calls from IPs that aren’t listed are rejected.
Add each number on the trunk in E.164 format. Callers uses them to:
Route inbound calls: a call to one of these numbers is answered by the incoming agent the number is assigned to.
Set caller ID on outbound calls: agents present the assigned number to the person they call.
To manage numbers later, open the connection and go to the Phone Numbers tab, or use Phone numbers → Add SIP Numbers. You can delete SIP numbers one at a time or in bulk from the Phone numbers page. Numbers in use by an agent are listed with the agents that use them.
Test SIP places a real call through your trunk and reports the SIP response, so you can confirm routing and authentication before you assign numbers to an agent.
1
Open the connection
In the App Center, open your SIP connection. Test SIP is available once the connection is saved, has at least one number, and has no unsaved changes.
2
Choose the numbers
In Call from, pick one of the connection’s numbers. In Call to, enter a phone you can answer.
3
Run the test
Click Test SIP. The result shows the SIP status. Click Try Again to run it again.
Result
Meaning
What to check
200 – SIP connection successful
The carrier accepted the call
Answer the phone to confirm audio in both directions
400 Bad request
The carrier couldn’t parse the request
Number format (E.164 syntax), tech prefix
401 Authentication failed
Credentials were rejected
Auth username and Password, registration settings
403 Authorization failed
The carrier refused the call
IP allowlisting, caller ID authorization (Diversion header), destination permissions
404 Resource not found
The number or route doesn’t exist
Number format, tech prefix, gateway URL
500 Internal server error
The carrier failed
Contact the carrier
503 Service unavailable – Connection refused
The gateway didn’t accept the connection
URL, port, protocol, and firewall
504 Gateway timeout
No response from the gateway
Address and port reachable, correct protocol
Test SIP checks outbound calling. To test inbound, call one of the trunk’s numbers after assigning it to an incoming agent.
Callers can pass contact data to your PBX or contact center as custom SIP headers, so the receiving system can route or screen-pop the call.Outbound calls and transfers. With Send SIP Headers on (agent settings, on by default), each contact variable is added as a custom X- header on the outbound INVITE and on transfers. The contact’s phone number is included as phoneNumber.
Header names are the fixed prefix X-Voxia- followed by the variable name in lowercase. Characters that aren’t allowed in header names become _. To see the exact names your PBX receives, place a test call and inspect the INVITE.
Each value is limited to 256 bytes, and all variable headers together to about 1 KB. Short values are kept whole. Long values are shortened, and if there are too many variables the longest are dropped. Line breaks in values are replaced with spaces.
Transferred calls also carry X-Parent-Call-Sid with the session ID of the original call (sessionId in the webhook payload).
For a contact with the variables firstName, accountId, and tier, the INVITE your carrier or PBX receives looks like this (headers unrelated to Callers omitted):
Callers sends the names fully lowercased (x-voxia-firstname). SIP header names are case-insensitive, and most PBXs and packet analyzers display them capitalized as above, so match on them case-insensitively. A transfer from that call adds one header:
Use X-Parent-Call-Sid to pull up the AI part of the conversation (transcript, summary) for the person taking the transfer.Turn Send SIP Headers off if your carrier rejects INVITEs with custom headers, or if the variables contain data you don’t want to leave Callers.Inbound calls. Your PBX can set variables for an incoming call by sending an X-Vars header with a JSON object:
The agent can use {{firstName}}, {{accountId}}, and {{tier}} in its script for that call. The contact’s email can also be passed this way for Cal.com bookings.
By default, Callers bridges transferred calls: it stays on the call, can record it, and can play a handoff message for a warm transfer. With SIP REFER, Callers instead asks your carrier to take over the call and hangs up immediately.
With SIP REFER:
The call isn’t recorded after the transfer.
Callers can’t tell whether the transfer was answered.
Warm transfers, handoff messages, and any post-transfer logic don’t run.
SIP REFER is set per SIP connection and applies to every transfer on it. Email to turn it on.
You can create as many SIP connections as you need, for example one per carrier, region, or business unit, or a backup trunk. Each connection has its own settings, gateways, and numbers. Agents use whichever numbers you assign to them.
Your carrier must send calls to sip.callers.ai (or 35.245.182.192).
Add every IP your carrier sends from as an Incoming gateway. Calls from unknown IPs are rejected.
The dialed number must be on the connection in E.164 format and assigned to an incoming agent.
Outbound calls fail with 401 or 407
Turn on Outbound authentication and check the credentials. If your carrier requires registration, turn on Require SIP Register and set SIP Realm.
Outbound calls fail with 403
The carrier refused the call. Common causes: the carrier authenticates by IP (contact support for Callers’ outbound addresses), the caller ID isn’t authorized on the trunk (try SIP Diversion Header), the tech prefix is missing, or the destination country isn’t enabled on your carrier account.
Calls connect but there's no audio, or audio only one way
This is usually a firewall or NAT issue for the media (RTP) stream. Make sure your carrier or PBX allows RTP from Callers, and try Send OPTIONS ping. Download the call’s PCAP from the call view and share it with your carrier or our support team.
Some calls are rejected during busy periods
You may be exceeding your carrier’s calls-per-second limit. Lower Calls Per Second (CPS) Limit to match it.
The carrier rejects calls with large headers
Turn off Send SIP Headers in the agent’s settings, or reduce the number and size of contact variables.
Compare SIP with Twilio and Callers-managed numbers.
Call transfers
Transfer to numbers, SIP URIs, and human operators.
Telnyx
Step-by-step Telnyx trunk setup.
Twilio SIP
Twilio Elastic SIP Trunking and Flex.
Troubleshooting
One-way audio, registration failures, and rejected calls.
Voices and sounds
Background sounds, which play only on SIP calls.
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Also how the carrier authenticates you: username and password (digest), registration, IP allowlisting, or a tech prefix.`]}),`\n`,_jsxs(_components.li,{children:[_jsx(_components.strong,{children:`Inbound (carrier → Callers)`}),`: the IP addresses your carrier sends calls from.`]}),`\n`,_jsxs(_components.li,{children:[_jsx(_components.strong,{children:`Numbers`}),`: the phone numbers on the trunk, in E.164 format (for example `,_jsx(_components.code,{children:`+12025550123`}),`).`]}),`\n`]}),`\n`,_jsx(_components.p,{children:`Then give your carrier the Callers address to send inbound calls to:`}),`\n`,_jsxs(Note,{children:[_jsx(_components.p,{children:`Send inbound calls to:`}),_jsx(CodeBlock,{filename:``,numberOfLines:`2`,language:`text`,children:_jsx(_components.pre,{className:`shiki shiki-themes dark-plus dark-plus`,style:{backgroundColor:`#0B0C0E`,\"--shiki-dark-bg\":`#0B0C0E`,color:`#D4D4D4`,\"--shiki-dark\":`#D4D4D4`},language:`text`,children:_jsxs(_components.code,{language:`text`,numberOfLines:`2`,children:[_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`sip.callers.ai`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{})})]})})}),_jsxs(_components.p,{children:[`or IP address `,_jsx(_components.code,{children:`35.245.182.192`}),`.`]}),_jsxs(_components.p,{children:[`This address only `,_jsx(_components.strong,{children:`receives`}),` calls. 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The `,_jsx(_components.strong,{children:`Add SIP`}),` window opens.`]}),_jsx(Frame,{caption:`SIP Integration in the App Center`,children:_jsx(OptimizedImage,{src:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=1dd17e17a3e5fe9172c5c3210adecf2c`,alt:`App Center search for SIP showing the SIP Integration card under Telephony \u0026 Communication with a plus button`,\"data-og-width\":`1986`,width:`1986`,\"data-og-height\":`377`,height:`377`,\"data-path\":`images/documentation/integrations/connect-sip-button.png`,\"data-optimize\":`true`,\"data-opv\":`3`,srcset:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=280\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=2c190b99ef519c4c69d19f3766c9b191 280w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=560\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=071528aa2555081aa02b1be9e18e6cfd 560w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=840\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=a99899ad722ae4766f61c169bbc95281 840w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=1100\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=827f0c8d98f147d11eaa93fd5ad717e1 1100w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=1650\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=5c00b22baf825e711cc5f20025853eda 1650w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/connect-sip-button.png?w=2500\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=d7dcb5079de770bd161457a491d70696 2500w`})})]}),_jsx(Step,{title:`Fill in the general settings`,children:_jsxs(_components.p,{children:[`Enter a `,_jsx(_components.strong,{children:`SIP Name`}),` and turn on the options your carrier requires. See `,_jsx(_components.a,{href:`#general-settings`,children:`General settings`}),`.`]})}),_jsxs(Step,{title:`Configure gateways`,children:[_jsxs(_components.p,{children:[`On the right, set up at least one gateway: an `,_jsx(_components.strong,{children:`Outgoing`}),` gateway to place calls and an `,_jsx(_components.strong,{children:`Incoming`}),` gateway for each IP your carrier sends calls from. See `,_jsx(_components.a,{href:`#sip-gateways`,children:`SIP gateways`}),`.`]}),_jsx(Frame,{caption:`Add SIP: general settings and gateways`,children:_jsx(OptimizedImage,{src:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=91a1a27765fb584666e0e15e500f5c04`,alt:`Add SIP window with general settings and gateways`,\"data-og-width\":`2438`,width:`2438`,\"data-og-height\":`1375`,height:`1375`,\"data-path\":`images/documentation/integrations/configure-sip.png`,\"data-optimize\":`true`,\"data-opv\":`3`,srcset:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=280\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=161aa2ae4ff8e7b70570951b78b79a75 280w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=560\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=499232456857c4685c3a7ef38af68a6b 560w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=840\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=655b3beaf8424c96f30460458d692682 840w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=1100\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=0628059a965a52724d29ec5b809d8123 1100w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=1650\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=4c95de1f2cb03be077218ff53719f134 1650w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/configure-sip.png?w=2500\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=9ccf60be853de2d32e638c73c5122d61 2500w`})})]}),_jsx(Step,{title:`Add phone numbers`,children:_jsxs(_components.p,{children:[`Click `,_jsx(_components.strong,{children:`Next`}),` and enter the numbers on the trunk. You can paste several at once. You can also add numbers later from `,_jsx(_components.strong,{children:`Phone numbers → Add SIP Numbers`}),`.`]})}),_jsx(Step,{title:`Test the connection`,children:_jsxs(_components.p,{children:[`Open the connection again and click `,_jsx(_components.strong,{children:`Test SIP`}),`. See `,_jsx(_components.a,{href:`#test-your-connection`,children:`Test your connection`}),`.`]})})]}),`\n`,_jsxs(_components.p,{children:[`Once saved, the numbers appear on the `,_jsx(_components.strong,{children:`Phone numbers`}),` page under `,_jsx(_components.strong,{children:`SIP - \u003cSIP Name>`}),`. You can assign them to any voice agent.`]}),`\n`,_jsx(Heading,{level:`2`,id:`general-settings`,children:`General settings`}),`\n`,_jsxs(Table,{children:[_jsx(_components.thead,{children:_jsxs(_components.tr,{children:[_jsx(_components.th,{children:`Setting`}),_jsx(_components.th,{children:`What it does`}),_jsx(_components.th,{children:`When to use it`})]})}),_jsxs(_components.tbody,{children:[_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`SIP Name`})}),_jsx(_components.td,{children:`Name for the connection. It can’t be changed after creation.`}),_jsx(_components.td,{children:`Always. Use something descriptive, such as “Telnyx US”.`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`E.164 syntax`})}),_jsxs(_components.td,{children:[`Adds a leading `,_jsx(_components.code,{children:`+`}),` to numbers on outbound calls`]}),_jsxs(_components.td,{children:[`Your carrier expects `,_jsx(_components.code,{children:`+14155552671`}),` rather than `,_jsx(_components.code,{children:`14155552671`})]})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Outbound authentication`})}),_jsxs(_components.td,{children:[`Sends `,_jsx(_components.strong,{children:`Auth username`}),` and `,_jsx(_components.strong,{children:`Password`}),` when the carrier challenges an outbound call (SIP digest authentication)`]}),_jsx(_components.td,{children:`Your carrier gave you SIP credentials`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Require SIP Register`})}),_jsx(_components.td,{children:`Registers with the carrier before sending outbound calls. Shown when outbound authentication is on.`}),_jsx(_components.td,{children:`Your carrier requires registration (common with credential-based trunks)`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`SIP Realm`})}),_jsx(_components.td,{children:`Realm (domain) to register with`}),_jsx(_components.td,{children:`Your carrier specifies a realm that differs from the gateway address`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Specify user part of SIP From header`})}),_jsxs(_components.td,{children:[`Overrides the user part of the `,_jsx(_components.code,{children:`From`}),` header on registration`]}),_jsx(_components.td,{children:`Your carrier requires a specific user, often the auth username`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Specify host part of SIP From header`})}),_jsxs(_components.td,{children:[`Overrides the host part of the `,_jsx(_components.code,{children:`From`}),` header on registration`]}),_jsx(_components.td,{children:`Your carrier requires a specific domain`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Use public IP in contact`})}),_jsxs(_components.td,{children:[`Uses the public IP in the `,_jsx(_components.code,{children:`Contact`}),` header on registration`]}),_jsx(_components.td,{children:`Your carrier rejects registrations with a private contact address`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Tech prefix`})}),_jsx(_components.td,{children:`Adds a prefix before the dialed number on outbound calls`}),_jsx(_components.td,{children:`Your carrier routes or authenticates by prefix (for example Squaretalk, CommPeak)`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`SIP Diversion Header`})}),_jsxs(_components.td,{children:[`Adds a `,_jsx(_components.code,{children:`Diversion`}),` header with the `,_jsx(_components.strong,{children:`Phone number or SIP URI`}),` you enter`]}),_jsx(_components.td,{children:`Your carrier authorizes the caller ID by the Diversion header`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Outbound SIP Proxy`})}),_jsxs(_components.td,{children:[`Sends all outbound SIP traffic through a proxy at the `,_jsx(_components.strong,{children:`Proxy IP`}),` you enter`]}),_jsx(_components.td,{children:`Your network or carrier requires a specific proxy or SBC`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Calls Per Second (CPS) Limit`})}),_jsx(_components.td,{children:`Caps how many new calls per second Callers sends over this trunk. Range 0.5–1000.`}),_jsx(_components.td,{children:`Set it to your carrier’s CPS limit to avoid rejected calls. Default 10.`})]})]})]}),`\n`,_jsx(Heading,{level:`2`,id:`sip-gateways`,children:`SIP gateways`}),`\n`,_jsxs(_components.p,{children:[`A gateway is a SIP endpoint on your carrier’s side. Add as many as you need with `,_jsx(_components.strong,{children:`Add Another SIP Gateway`}),`.`]}),`\n`,_jsxs(Table,{children:[_jsx(_components.thead,{children:_jsxs(_components.tr,{children:[_jsx(_components.th,{children:`Setting`}),_jsx(_components.th,{children:`Outgoing gateway`}),_jsx(_components.th,{children:`Incoming gateway`})]})}),_jsxs(_components.tbody,{children:[_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Gateway Type`})}),_jsxs(_components.td,{children:[_jsx(_components.strong,{children:`Outgoing`}),`: Callers sends calls to this address`]}),_jsxs(_components.td,{children:[_jsx(_components.strong,{children:`Incoming`}),`: Callers accepts calls from this address`]})]}),_jsxs(_components.tr,{children:[_jsxs(_components.td,{children:[_jsx(_components.strong,{children:`URL`}),` / `,_jsx(_components.strong,{children:`IP`})]}),_jsxs(_components.td,{children:[`Domain or IPv4 address, for example `,_jsx(_components.code,{children:`sip.telnyx.com`})]}),_jsx(_components.td,{children:`IPv4 address only (domains aren’t accepted for incoming)`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Port`})}),_jsx(_components.td,{children:`Default 5060`}),_jsx(_components.td,{children:`Default 5060`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Netmask`})}),_jsx(_components.td,{children:`—`}),_jsxs(_components.td,{children:[`Accept a whole range, 1–32. Default 32 (a single IP). For example, `,_jsx(_components.code,{children:`24`}),` accepts `,_jsx(_components.code,{children:`x.x.x.0–255`}),`.`]})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Protocol`})}),_jsxs(_components.td,{children:[_jsx(_components.strong,{children:`UDP`}),` (default), `,_jsx(_components.strong,{children:`TCP`}),`, `,_jsx(_components.strong,{children:`TLS`}),`, or `,_jsx(_components.strong,{children:`TLS/SRTP`})]}),_jsx(_components.td,{children:`—`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Send OPTIONS ping`})}),_jsx(_components.td,{children:`Sends periodic SIP OPTIONS to keep the gateway’s status and NAT bindings fresh`}),_jsx(_components.td,{children:`—`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Use sips scheme`})}),_jsxs(_components.td,{children:[`Uses `,_jsx(_components.code,{children:`sips:`}),` URIs. Shown for TLS and TLS/SRTP.`]}),_jsx(_components.td,{children:`—`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`Pad crypto`})}),_jsx(_components.td,{children:`Compatibility option for some SRTP endpoints. Shown for TLS/SRTP.`}),_jsx(_components.td,{children:`—`})]})]})]}),`\n`,_jsx(Tip,{children:_jsx(_components.p,{children:`For redundancy, add your carrier’s primary and secondary servers as separate outgoing gateways, and add every signaling IP your carrier uses as an incoming gateway. Calls from IPs that aren’t listed are rejected.`})}),`\n`,_jsx(Heading,{level:`2`,id:`phone-numbers`,children:`Phone numbers`}),`\n`,_jsx(_components.p,{children:`Add each number on the trunk in E.164 format. Callers uses them to:`}),`\n`,_jsxs(_components.ul,{children:[`\n`,_jsxs(_components.li,{children:[_jsx(_components.strong,{children:`Route inbound calls`}),`: a call to one of these numbers is answered by the incoming agent the number is assigned to.`]}),`\n`,_jsxs(_components.li,{children:[_jsx(_components.strong,{children:`Set caller ID on outbound calls`}),`: agents present the assigned number to the person they call.`]}),`\n`]}),`\n`,_jsxs(_components.p,{children:[`To manage numbers later, open the connection and go to the `,_jsx(_components.strong,{children:`Phone Numbers`}),` tab, or use `,_jsx(_components.strong,{children:`Phone numbers → Add SIP Numbers`}),`. You can delete SIP numbers one at a time or in bulk from the `,_jsx(_components.strong,{children:`Phone numbers`}),` page. Numbers in use by an agent are listed with the agents that use them.`]}),`\n`,_jsx(Heading,{level:`2`,id:`test-your-connection`,children:`Test your connection`}),`\n`,_jsxs(_components.p,{children:[_jsx(_components.strong,{children:`Test SIP`}),` places a real call through your trunk and reports the SIP response, so you can confirm routing and authentication before you assign numbers to an agent.`]}),`\n`,_jsxs(Steps,{children:[_jsx(Step,{title:`Open the connection`,children:_jsxs(_components.p,{children:[`In the App Center, open your SIP connection. `,_jsx(_components.strong,{children:`Test SIP`}),` is available once the connection is saved, has at least one number, and has no unsaved changes.`]})}),_jsx(Step,{title:`Choose the numbers`,children:_jsxs(_components.p,{children:[`In `,_jsx(_components.strong,{children:`Call from`}),`, pick one of the connection’s numbers. In `,_jsx(_components.strong,{children:`Call to`}),`, enter a phone you can answer.`]})}),_jsx(Step,{title:`Run the test`,children:_jsxs(_components.p,{children:[`Click `,_jsx(_components.strong,{children:`Test SIP`}),`. The result shows the SIP status. Click `,_jsx(_components.strong,{children:`Try Again`}),` to run it again.`]})})]}),`\n`,_jsxs(Table,{children:[_jsx(_components.thead,{children:_jsxs(_components.tr,{children:[_jsx(_components.th,{children:`Result`}),_jsx(_components.th,{children:`Meaning`}),_jsx(_components.th,{children:`What to check`})]})}),_jsxs(_components.tbody,{children:[_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`200 – SIP connection successful`})}),_jsx(_components.td,{children:`The carrier accepted the call`}),_jsx(_components.td,{children:`Answer the phone to confirm audio in both directions`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`400 Bad request`})}),_jsx(_components.td,{children:`The carrier couldn’t parse the request`}),_jsxs(_components.td,{children:[`Number format (`,_jsx(_components.strong,{children:`E.164 syntax`}),`), tech prefix`]})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`401 Authentication failed`})}),_jsx(_components.td,{children:`Credentials were rejected`}),_jsxs(_components.td,{children:[_jsx(_components.strong,{children:`Auth username`}),` and `,_jsx(_components.strong,{children:`Password`}),`, registration settings`]})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`403 Authorization failed`})}),_jsx(_components.td,{children:`The carrier refused the call`}),_jsx(_components.td,{children:`IP allowlisting, caller ID authorization (Diversion header), destination permissions`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`404 Resource not found`})}),_jsx(_components.td,{children:`The number or route doesn’t exist`}),_jsx(_components.td,{children:`Number format, tech prefix, gateway URL`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`500 Internal server error`})}),_jsx(_components.td,{children:`The carrier failed`}),_jsx(_components.td,{children:`Contact the carrier`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`503 Service unavailable – Connection refused`})}),_jsx(_components.td,{children:`The gateway didn’t accept the connection`}),_jsx(_components.td,{children:`URL, port, protocol, and firewall`})]}),_jsxs(_components.tr,{children:[_jsx(_components.td,{children:_jsx(_components.strong,{children:`504 Gateway timeout`})}),_jsx(_components.td,{children:`No response from the gateway`}),_jsx(_components.td,{children:`Address and port reachable, correct protocol`})]})]})]}),`\n`,_jsx(_components.p,{children:`Test SIP checks outbound calling. To test inbound, call one of the trunk’s numbers after assigning it to an incoming agent.`}),`\n`,_jsx(Heading,{level:`2`,id:`sip-headers`,children:`SIP headers`}),`\n`,_jsx(_components.p,{children:`Callers can pass contact data to your PBX or contact center as custom SIP headers, so the receiving system can route or screen-pop the call.`}),`\n`,_jsxs(_components.p,{children:[_jsx(_components.strong,{children:`Outbound calls and transfers.`}),` With `,_jsx(_components.strong,{children:`Send SIP Headers`}),` on (agent settings, on by default), each contact variable is added as a custom `,_jsx(_components.code,{children:`X-`}),` header on the outbound INVITE and on transfers. The contact’s phone number is included as `,_jsx(_components.code,{children:`phoneNumber`}),`.`]}),`\n`,_jsxs(_components.ul,{children:[`\n`,_jsxs(_components.li,{children:[`Header names are the fixed prefix `,_jsx(_components.code,{children:`X-Voxia-`}),` followed by the variable name in lowercase. Characters that aren’t allowed in header names become `,_jsx(_components.code,{children:`_`}),`. To see the exact names your PBX receives, place a test call and inspect the INVITE.`]}),`\n`,_jsx(_components.li,{children:`Each value is limited to 256 bytes, and all variable headers together to about 1 KB. Short values are kept whole. Long values are shortened, and if there are too many variables the longest are dropped. Line breaks in values are replaced with spaces.`}),`\n`,_jsxs(_components.li,{children:[`Transferred calls also carry `,_jsx(_components.code,{children:`X-Parent-Call-Sid`}),` with the session ID of the original call (`,_jsx(_components.code,{children:`sessionId`}),` in the `,_jsx(_components.a,{href:`/documentation/webhook/webhook-payload`,children:`webhook payload`}),`).`]}),`\n`]}),`\n`,_jsxs(_components.p,{children:[`For a contact with the variables `,_jsx(_components.code,{children:`firstName`}),`, `,_jsx(_components.code,{children:`accountId`}),`, and `,_jsx(_components.code,{children:`tier`}),`, the INVITE your carrier or PBX receives looks like this (headers unrelated to Callers omitted):`]}),`\n`,_jsx(CodeBlock,{filename:``,numberOfLines:`9`,language:`text`,children:_jsx(_components.pre,{className:`shiki shiki-themes dark-plus dark-plus`,style:{backgroundColor:`#0B0C0E`,\"--shiki-dark-bg\":`#0B0C0E`,color:`#D4D4D4`,\"--shiki-dark\":`#D4D4D4`},language:`text`,children:_jsxs(_components.code,{language:`text`,numberOfLines:`9`,children:[_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`INVITE sip:+14155552671@sip.carrier.example SIP/2.0`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`From: \u003csip:+15555551234@…>;tag=…`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`To: \u003csip:+14155552671@sip.carrier.example>`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Voxia-Name: Dana Levi`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Voxia-Phonenumber: 14155552671`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Voxia-Firstname: Dana`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Voxia-Accountid: A-1029`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Voxia-Tier: gold`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{})})]})})}),`\n`,_jsxs(_components.p,{children:[`Callers sends the names fully lowercased (`,_jsx(_components.code,{children:`x-voxia-firstname`}),`). SIP header names are case-insensitive, and most PBXs and packet analyzers display them capitalized as above, so match on them case-insensitively. A transfer from that call adds one header:`]}),`\n`,_jsx(CodeBlock,{filename:``,numberOfLines:`2`,language:`text`,children:_jsx(_components.pre,{className:`shiki shiki-themes dark-plus dark-plus`,style:{backgroundColor:`#0B0C0E`,\"--shiki-dark-bg\":`#0B0C0E`,color:`#D4D4D4`,\"--shiki-dark\":`#D4D4D4`},language:`text`,children:_jsxs(_components.code,{language:`text`,numberOfLines:`2`,children:[_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Parent-Call-Sid: c2f1e0b4-7a51-4d0e-9a8f-2b6f1d3e4a5c`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{})})]})})}),`\n`,_jsxs(_components.p,{children:[`Use `,_jsx(_components.code,{children:`X-Parent-Call-Sid`}),` to pull up the AI part of the conversation (transcript, summary) for the person taking the transfer.`]}),`\n`,_jsxs(_components.p,{children:[`Turn `,_jsx(_components.strong,{children:`Send SIP Headers`}),` off if your carrier rejects INVITEs with custom headers, or if the variables contain data you don’t want to leave Callers.`]}),`\n`,_jsxs(_components.p,{children:[_jsx(_components.strong,{children:`Inbound calls.`}),` Your PBX can set `,_jsx(_components.a,{href:`/documentation/build-your-agent/agent-variables`,children:`variables`}),` for an incoming call by sending an `,_jsx(_components.code,{children:`X-Vars`}),` header with a JSON object:`]}),`\n`,_jsx(CodeBlock,{filename:``,numberOfLines:`2`,language:`text`,children:_jsx(_components.pre,{className:`shiki shiki-themes dark-plus dark-plus`,style:{backgroundColor:`#0B0C0E`,\"--shiki-dark-bg\":`#0B0C0E`,color:`#D4D4D4`,\"--shiki-dark\":`#D4D4D4`},language:`text`,children:_jsxs(_components.code,{language:`text`,numberOfLines:`2`,children:[_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{children:`X-Vars: {\"firstName\":\"Dana\",\"accountId\":\"A-1029\",\"tier\":\"gold\"}`})}),`\n`,_jsx(_components.span,{className:`line`,children:_jsx(_components.span,{})})]})})}),`\n`,_jsxs(_components.p,{children:[`The agent can use `,_jsx(_components.code,{children:`{{firstName}}`}),`, `,_jsx(_components.code,{children:`{{accountId}}`}),`, and `,_jsx(_components.code,{children:`{{tier}}`}),` in its script for that call. The contact’s email can also be passed this way for `,_jsx(_components.a,{href:`/documentation/integrations/cal-com`,children:`Cal.com`}),` bookings.`]}),`\n`,_jsx(Heading,{level:`2`,id:`transfers-over-sip`,children:`Transfers over SIP`}),`\n`,_jsxs(_components.p,{children:[`Agents on SIP calls can transfer to a phone number or directly to a SIP URI on your PBX (for example `,_jsx(_components.code,{children:`sip:queue@pbx.example.com`}),`). See `,_jsx(_components.a,{href:`/documentation/voice/call-transfers`,children:`Call transfers`}),`.`]}),`\n`,_jsx(Heading,{level:`3`,id:`sip-refer`,children:`SIP REFER`}),`\n`,_jsxs(_components.p,{children:[`By default, Callers bridges transferred calls: it stays on the call, can record it, and can play a handoff message for a warm transfer. With `,_jsx(_components.strong,{children:`SIP REFER`}),`, Callers instead asks your carrier to take over the call and hangs up immediately.`]}),`\n`,_jsxs(Warning,{children:[_jsx(_components.p,{children:`With SIP REFER:`}),_jsxs(_components.ul,{children:[`\n`,_jsx(_components.li,{children:`The call isn’t recorded after the transfer.`}),`\n`,_jsx(_components.li,{children:`Callers can’t tell whether the transfer was answered.`}),`\n`,_jsx(_components.li,{children:`Warm transfers, handoff messages, and any post-transfer logic don’t run.`}),`\n`]})]}),`\n`,_jsxs(_components.p,{children:[`SIP REFER is set per SIP connection and applies to every transfer on it. Email `,_jsx(_MdxComponentBoundary,{name:`ContactEmail`,children:_jsx(ContactEmail,{})}),` to turn it on.`]}),`\n`,_jsx(Heading,{level:`2`,id:`multiple-sip-connections`,children:`Multiple SIP connections`}),`\n`,_jsx(_components.p,{children:`You can create as many SIP connections as you need, for example one per carrier, region, or business unit, or a backup trunk. Each connection has its own settings, gateways, and numbers. Agents use whichever numbers you assign to them.`}),`\n`,_jsx(Frame,{caption:`Add another SIP connection with the plus button`,children:_jsx(OptimizedImage,{src:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=610d3dca4cdf2db1e773bfe35d8ecd68`,alt:`App Center with an existing SIP connection named SIP1 under Connected and an arrow pointing to the plus button on the SIP Integration card`,\"data-og-width\":`2208`,width:`2208`,\"data-og-height\":`727`,height:`727`,\"data-path\":`images/documentation/integrations/multiple-sip.png`,\"data-optimize\":`true`,\"data-opv\":`3`,srcset:`https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=280\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=095eb929ac7618d34d56d74457d72ebf 280w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=560\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=a7260909001b1d9371766737dd21b2d6 560w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=840\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=eba92a591834319e4545743da990a2c7 840w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=1100\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=d3737329e3f25096901c68dc4a1e8d38 1100w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=1650\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=4fd33bda843aa10493eea74be0c2a109 1650w, https://mintcdn.com/voxiaai/UGuY0UNIphM-6pUX/images/documentation/integrations/multiple-sip.png?w=2500\u0026fit=max\u0026auto=format\u0026n=UGuY0UNIphM-6pUX\u0026q=85\u0026s=d95ab89ce29eed4ebeecf1536cd8d99a 2500w`})}),`\n`,_jsx(Heading,{level:`2`,id:`troubleshooting`,children:`Troubleshooting`}),`\n`,_jsxs(AccordionGroup,{children:[_jsx(Accordion,{title:`Inbound calls don't reach the agent`,id:`inbound-calls-dont-reach-the-agent`,children:_jsxs(_components.ul,{children:[`\n`,_jsxs(_components.li,{children:[`Your carrier must send calls to `,_jsx(_components.code,{children:`sip.callers.ai`}),` (or `,_jsx(_components.code,{children:`35.245.182.192`}),`).`]}),`\n`,_jsxs(_components.li,{children:[`Add every IP your carrier sends from as an `,_jsx(_components.strong,{children:`Incoming`}),` gateway. Calls from unknown IPs are rejected.`]}),`\n`,_jsx(_components.li,{children:`The dialed number must be on the connection in E.164 format and assigned to an incoming agent.`}),`\n`]})}),_jsx(Accordion,{title:`Outbound calls fail with 401 or 407`,id:`outbound-calls-fail-with-401-or-407`,children:_jsxs(_components.p,{children:[`Turn on `,_jsx(_components.strong,{children:`Outbound authentication`}),` and check the credentials. If your carrier requires registration, turn on `,_jsx(_components.strong,{children:`Require SIP Register`}),` and set `,_jsx(_components.strong,{children:`SIP Realm`}),`.`]})}),_jsx(Accordion,{title:`Outbound calls fail with 403`,id:`outbound-calls-fail-with-403`,children:_jsxs(_components.p,{children:[`The carrier refused the call. Common causes: the carrier authenticates by IP (contact support for Callers’ outbound addresses), the caller ID isn’t authorized on the trunk (try `,_jsx(_components.strong,{children:`SIP Diversion Header`}),`), the tech prefix is missing, or the destination country isn’t enabled on your carrier account.`]})}),_jsx(Accordion,{title:`Calls connect but there's no audio, or audio only one way`,id:`calls-connect-but-theres-no-audio-or-audio-only-one-way`,children:_jsxs(_components.p,{children:[`This is usually a firewall or NAT issue for the media (RTP) stream. Make sure your carrier or PBX allows RTP from Callers, and try `,_jsx(_components.strong,{children:`Send OPTIONS ping`}),`. Download the call’s PCAP from the call view and share it with your carrier or our support team.`]})}),_jsx(Accordion,{title:`Some calls are rejected during busy periods`,id:`some-calls-are-rejected-during-busy-periods`,children:_jsxs(_components.p,{children:[`You may be exceeding your carrier’s calls-per-second limit. 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operators.`})}),_jsx(Card,{title:`Telnyx`,icon:`tower-broadcast`,href:`/documentation/integrations/telnyx-integration`,children:_jsx(_components.p,{children:`Step-by-step Telnyx trunk setup.`})}),_jsx(Card,{title:`Twilio SIP`,icon:`phone`,href:`/documentation/integrations/twilio-sip`,children:_jsx(_components.p,{children:`Twilio Elastic SIP Trunking and Flex.`})}),_jsx(Card,{title:`Troubleshooting`,icon:`screwdriver-wrench`,href:`/documentation/resources/troubleshooting#sip-and-telephony`,children:_jsx(_components.p,{children:`One-way audio, registration failures, and rejected calls.`})}),_jsx(Card,{title:`Voices and sounds`,icon:`waveform-lines`,href:`/documentation/voice/voices-and-sounds`,children:_jsx(_components.p,{children:`Background sounds, which play only on SIP calls.`})})]})]})}function MDXContent(props={}){const{wrapper:MDXLayout}={..._provideComponents(),...props.components};return MDXLayout?_jsx(MDXLayout,{...props,children:_jsx(_createMdxContent,{...props})}):_createMdxContent(props)}return{__snippet_CONTACT_EMAIL_12i9flv,ContactEmail,Flow,default:MDXContent};function _missingMdxReference(id,component){throw new Error(`Expected `+(component?`component`:`object`)+\" `\"+id+\"` to be defined: you likely forgot to import, pass, or provide it.\")}","frontmatter":{},"scope":{"codeStyling":"dark","config":{},"pageMetadata":{"title":"SIP Trunk Setup","sidebarTitle":"SIP trunk","description":"Connect any carrier, PBX, or contact center to Callers over SIP for inbound and outbound calls: authentication, gateways, headers, and testing.","icon":"network-wired","href":"/documentation/integrations/sip"}}},"mdxSourceWithNoJs":null,"noJsSplices":[[166,1688,"undefined;const ContactEmail=()=>null;const Flow=()=>null;fu"]]},"mdxExtracts":{"tableOfContents":[{"title":"Before you start","slug":"before-you-start","depth":2,"children":[]},{"title":"Create a SIP 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