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Dynamic SIP Trunking

Connect your SIP system to Exotel's PSTN infrastructure via REST API. Create trunks, whitelist IPs, map phone numbers, and configure routing — all programmatically.

How it works​

Outbound:  Your SIP system → Exotel SIP trunk → PSTN
Inbound:   PSTN → Exotel → Flow (Connect applet) → SIP trunk → Your SIP system

Call directions​

DirectionPathRequires
Outbound (SIP → PSTN)Your SIP → Exotel → PSTNWhitelisted IP (ACL) + phone number mapped to trunk
Inbound (PSTN → SIP)PSTN → Exotel Flow → SIP trunk → Your systemDestination URI + Flow with Connect applet using sip:<trunk_sid>
BidirectionalBoth aboveBoth above

Routing modes​

ModeUse when
pstnStandard PSTN inbound/outbound (default)
flowRoute calls through a Voice AI / StreamKit flow

Quick setup​

1. Create trunk           →  get trunk_sid
2. Map phone number       →  get phone_number_id
3. Whitelist your IP      →  enables outbound
4. Set destination URI    →  enables inbound

API reference​

Base URLs

RegionURL
Mumbaihttps://api.in.exotel.com
Singaporehttps://api.exotel.com

Auth: HTTP Basic — API key as username, API token as password.

Rate limit: 200 requests/minute.

All endpoints are prefixed with /v2/accounts/{account_sid}.

Create trunk​

POST /v2/accounts/{account_sid}/trunks
ParameterRequiredDescription
trunk_nameYesAlphanumeric + underscores, max 16 chars
nso_codeYesUse "any any"
domain_nameYes{account_sid}.pstn.exotel.com
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks' \
  -H 'Content-Type: application/json' \
  -d '{
    "trunk_name": "outbound_trunk",
    "nso_code": "any any",
    "domain_name": "<account_sid>.pstn.exotel.com"
  }'
{
  "trunk_sid": "TKxxxxxxxxxxxxxxxx",
  "trunk_name": "outbound_trunk",
  "status": "active",
  "auth_type": "ip whitelist",
  "domain_name": "<account_sid>.pstn.exotel.com",
  "date_created": "2026-05-14T10:00:00Z"
}
note

Save trunk_sid — required for all subsequent API calls.

Map phone number​

POST /v2/accounts/{account_sid}/trunks/{trunk_sid}/phone_numbers
ParameterRequiredDescription
phone_numberYesE.164 format (+919876543210)
modeNopstn (default) or flow (Voice AI)
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/phone_numbers' \
  -H 'Content-Type: application/json' \
  -d '{
    "phone_number": "+919876543210",
    "mode": "pstn"
  }'
{
  "id": 41523,
  "phone_number": "+919876543210",
  "trunk_sid": "TKxxxxxxxxxxxxxxxx",
  "mode": "pstn"
}
note

Save the numeric id — needed for mode updates.

Whitelist IP (outbound)​

Registers your server's IP for outbound call authentication.

POST /v2/accounts/{account_sid}/trunks/{trunk_sid}/whitelisted_ips
ParameterRequiredDescription
ipYesYour server's public IPv4 address
maskNoCIDR subnet mask (default: 32)
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/whitelisted_ips' \
  -H 'Content-Type: application/json' \
  -d '{
    "ip": "44.248.146.11",
    "mask": 32
  }'
{
  "id": 123,
  "ip": "44.248.146.11",
  "mask": 32,
  "trunk_sid": "TKxxxxxxxxxxxxxxxx"
}

Set destination URI (inbound)​

Configures where Exotel routes incoming calls.

POST /v2/accounts/{account_sid}/trunks/{trunk_sid}/destination_uris
ParameterRequiredDescription
destinations[].destinationYesSIP URI: <ip_or_fqdn>:<port>;transport=<tls|tcp>

Supported transports: tls (port 5061, recommended) · tcp (port 5060)

# IP-based
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/destination_uris' \
  -H 'Content-Type: application/json' \
  -d '{
    "destinations": [
      { "destination": "44.248.146.11:5061;transport=tls" }
    ]
  }'
# FQDN-based
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/destination_uris' \
  -H 'Content-Type: application/json' \
  -d '{
    "destinations": [
      { "destination": "sip.yourcompany.com:5061;transport=tls" }
    ]
  }'
{
  "id": 456,
  "destination": "sip:44.248.146.11:5061;transport=tls",
  "type": "public",
  "priority": 0,
  "weight": 1,
  "trunk_sid": "TKxxxxxxxxxxxxxxxx"
}

SIP digest credentials​

Use instead of (or alongside) IP whitelisting for cloud platforms with dynamic IPs (e.g. ElevenLabs, LiveKit).

POST /v2/accounts/{account_sid}/trunks/{trunk_sid}/credentials
ParameterRequiredDescription
user_nameYesSIP digest username
passwordYesStrong password
friendly_nameNoLabel, max 32 chars
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/credentials' \
  -H 'Content-Type: application/json' \
  -d '{
    "user_name": "voice_ai_user",
    "password": "strong_password_here",
    "friendly_name": "elevenlabs_prod"
  }'

List credentials

curl -u '<api_key>:<api_token>' 'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/credentials'

Delete credentials

curl -u '<api_key>:<api_token>' -X DELETE \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/credentials?id=<credential_id>'

Update phone number mode​

Switch a mapped number between PSTN and Flow (Voice AI) routing.

PUT /v2/accounts/{account_sid}/trunks/{trunk_sid}/phone_numbers/{phone_number_id}
curl -u '<api_key>:<api_token>' -X PUT \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/phone_numbers/41523' \
  -H 'Content-Type: application/json' \
  -d '{
    "phone_number": "+919876543210",
    "mode": "flow"
  }'
note

Use the numeric id from the Map Phone Number response, not the phone number itself.

Set caller ID (trunk alias)​

Sets the number displayed to called parties on outbound calls.

POST /v2/accounts/{account_sid}/trunks/{trunk_sid}/settings
curl -u '<api_key>:<api_token>' -X POST \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks/<trunk_sid>/settings' \
  -H 'Content-Type: application/json' \
  -d '{
    "settings": [
      { "name": "trunk_external_alias", "value": "+919876543210" }
    ]
  }'

Delete trunk​

DELETE /v2/accounts/{account_sid}/trunks?trunk_sid={trunk_sid}
curl -u '<api_key>:<api_token>' -X DELETE \
  'https://api.in.exotel.com/v2/accounts/<account_sid>/trunks?trunk_sid=<trunk_sid>'
warning

Permanently deletes the trunk and all associated phone numbers, ACLs, and destination URIs.

IP whitelist vs credentials​

ScenarioMethod
On-premises PBX / SBC with fixed IPIP whitelist only
Cloud AI platforms (ElevenLabs, LiveKit)Credentials only
High-security productionBoth

Network & firewall​

For the full list of SIP signaling endpoints, inbound source IPs, media IP ranges, and firewall rules, refer to the official source of truth:

Network & Firewall Configuration →

No audio?

If calls connect but have no audio or one-way audio — UDP 10 000–40 000 is likely blocked on your firewall.

SIP error codes​

4xx — Client errors​

CodeMeaningFix
400Bad requestReview SIP headers / SDP
401UnauthorizedCheck digest credentials
403ForbiddenIP not whitelisted — check ACL
404Not foundVerify phone number mapping
408Request timeoutCheck firewall / reachability
415Unsupported mediaEnable G.711 A-Law; disable other codecs
480Temporarily unavailableCheck PBX/SBC availability
484Address incompleteUse E.164 format for numbers
486BusyDestination busy — normal
488Not acceptableSDP/codec mismatch — enable G.711 A-Law only

5xx — Server errors​

CodeMeaningFix
500Server errorRetry
502Bad gatewayUpstream routing issue — retry
503Service unavailableCheck network / routing
504Gateway timeoutCheck firewall latency

Audio issues (no SIP error)​

SymptomCauseFix
No audio both waysRTP blockedOpen UDP 10 000–40 000
One-way audioNAT / firewallCheck public IP in SDP
Audio drops mid-callRTP idle timeoutAdjust firewall timeout

API error codes​

CodeHTTPMeaningFix
1000404Resource not foundVerify trunk SID / phone number ID
1001400Mandatory parameter missingCheck all required fields
1002400Invalid parameterValidate formats (E.164, IP, etc.)
1007400Malformed JSONFix JSON syntax
1008409Duplicate resourceAlready configured — safe to ignore
1011415Wrong content typeAdd Content-Type: application/json