SIP signalling and telephony edge
The SIP edge that carriers connect to, the methods, transports, timers and responses it supports, how it hands calls to the voice service and how SIP traffic is captured for diagnosis. Browse the feature map or configuration finder.
Availability: Next. Entries that depend on an optional feature, a role or a deployment choice name it in their own Availability line.
Features in this family
- SIP edge proxy
- SIP transports and ports
- Supported SIP methods
- Responses generated by the edge
- OPTIONS keepalive
- Reliable provisional responses (100rel and PRACK)
- SIP transaction and dialog timers
- SDP, codecs and number format at the edge
- Public and private edge addresses (NAT)
- SIP termination headers
- Voice host selection by the edge
- Voice service control interface (ARI and AMI)
- Handoff of an inbound call to the voice runtime
- Rejected and unknown SIP traffic
- SIP edge health
SIP edge proxy
A SIP proxy at the platform boundary receives every carrier call, identifies the trunk, applies edge policy and forwards the call to a voice host.
For: Integrators, Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelPro environment(DOMAIN_TELPRO, SIP_DOMAIN, KAMAILIO_INSTANCE_ID, KAMAILIO_LOG_LEVEL) | TelPro variables |
Read more:
- How it works: Edge components
- Reference: Configuration sources
- Set it up: Restart order
- Troubleshoot: Common failures
Related features: SIP transports and ports, Voice host selection by the edge, Public and private edge addresses (NAT).
SIP transports and ports
The edge listens for SIP over UDP, TCP and TLS on published ports and uses a separate internal port toward the voice hosts.
For: Integrators, Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelPro environment(SIP_PORT, SIPS_PORT, SIP_TLS_PORT, INTERNAL_SIP_PORT, SIP_PORT_INTERNAL, TLS_ENABLED) | TelPro variables |
Read more:
- Reference: Signaling transports and availability
- Reference: Network ports
Related features: SIP over TLS at the edge, Network ports, allowed sources and firewall, SIP edge proxy.
Supported SIP methods
The edge accepts the SIP requests needed for calls, transfers and keepalives and answers other methods with a defined rejection.
For: Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | SIP edge routing (no customer setting)(INVITE, ACK, BYE, CANCEL, OPTIONS, REFER, NOTIFY, UPDATE, PRACK, INFO) | SIP methods |
Read more:
- Reference: SIP methods
- Reference: Limits
Related features: Responses generated by the edge, OPTIONS keepalive, Reliable provisional responses (100rel and PRACK).
Responses generated by the edge
Some requests are answered by the edge itself, for example keepalives, unknown trunks or blocked admission, so carriers can tell an edge decision from a voice service answer.
For: Integrators, Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | SIP edge routing (no customer setting)(sl_send_reply) | Responses generated by the edge |
Read more:
- Reference: Responses generated by the edge
- Troubleshoot: Identify a routing response first
- Troubleshoot: Recognize unknown-trunk rejections
Related features: Supported SIP methods, Number lookup and routing responses, Rejected and unknown SIP traffic.
OPTIONS keepalive
The edge answers SIP OPTIONS pings from carriers so their trunk health checks see the platform as reachable.
For: Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | SIP edge routing (no customer setting)(OPTIONS) | Request handling and trunk health |
Read more:
- Reference: Request handling and trunk health
Related features: Supported SIP methods, Trunk health probes.
Reliable provisional responses (100rel and PRACK)
Provisional responses can be sent reliably and acknowledged with PRACK when a carrier requires it, with the mode chosen per voice deployment.
For: Integrators, Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelSys environment(SIP_100REL_MODE) | Voice variables |
Read more:
- Reference: Reliable provisional responses (100rel / PRACK)
- Troubleshoot: Investigate a 100rel configuration mismatch
Related features: Supported SIP methods.
SIP transaction and dialog timers
Fixed edge timers limit how long a request waits for an answer, how long a call may ring and how long an established dialog is kept.
For: Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | SIP edge configuration (no customer setting)(fr_timer, fr_inv_timer) | Timers and retransmission |
Read more:
- Reference: Timers and retransmission
Related features: Maximum call duration, Supported SIP methods.
SDP, codecs and number format at the edge
The edge and voice hosts negotiate a defined codec set and SDP shape and expect numbers in a stated format, which carriers need to match during onboarding.
For: Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | Voice and edge media configuration (no customer setting) | Codecs and DTMF |
Read more:
- Reference: Codecs and DTMF
- Reference: SDP and media security
- Reference: Called-number format
- Reference: RTCP and acceptance checks
- Reference: Interoperability requirements and limits
Related features: Voice codecs on SIP calls, Public and private edge addresses (NAT), Supported SIP methods.
Public and private edge addresses (NAT)
The edge advertises its public address in SIP and SDP while using private addresses inside the platform, so media flows correctly across NAT.
For: Deployment operators, Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelPro environment(PUBLIC_IP, PRIVATE_IP, EXTERNAL_IP, HOST_LAN_IP) | TelPro variables |
Read more:
- Reference: NAT and media addresses
- Reference: TelPro variables
Related features: SIP edge proxy, Media floating address.
SIP termination headers
When the platform ends or transfers a call it adds a Reason header with a cause and short text, plus a transfer reason on transfer INVITEs, so the carrier side can log why.
For: Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | Voice runtime (format fixed; limits per app)(Reason, X-Transfer-Reason) | Diagnostic header formats |
Read more:
- Reference: Diagnostic header formats
- Reference: Default optional-header limits
- Reference: Protected headers and normalization
- Reference: Proxy-compatible header names
- Troubleshoot: If optional termination headers are invalid
- Troubleshoot: 2. Distinguish header preparation from publication
Related features: Platform termination causes and SIP mapping, Hang up from a flow or a bot, Final SIP response for calls that never connect, Transfer reason on the new call leg, Optional SIP header budget.
Voice host selection by the edge
The edge sends each new call to a healthy voice host chosen by a balancing method and skips hosts whose heartbeat is missing or that are draining.
For: Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Platform settings | Admin Settings › Server Groups › Load Balancing Method(lbMethod) | Configure a server group |
| Services and containers | TelPro environment(TELSYS_LB_METHOD) | TelPro variables |
Read more:
- How it works: Follow the request path
- Reference: Heartbeat and call admission
- Set it up: Configure a server group
Related features: Load balancing across voice instances, Instance heartbeats and usage reports, Draining an edge.
Voice service control interface (ARI and AMI)
The voice runtime controls calls on the telephony hosts through their REST and manager interfaces, with session limits that cap how many calls one host can carry.
For: Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelSys and TelPhi environment(ARI_URL, ARI_USER, ARI_PASSWORD, ARIAPP, ARIENABLED, ARIBINDMASK, ARIHTTPSESSIONLIMIT, AMI_HOST, AMI_PORT, AMI_USER, AMI_SECRET) | Voice variables |
Read more:
- How it works: Roles and the ARI connection
- Reference: ARI session limits
- Troubleshoot: Read Voice logs
Related features: Voice service operation, Voice host selection by the edge, Concurrent call limit per voice instance and group, Voice service and media diagnostic logs.
Handoff of an inbound call to the voice runtime
After the edge forwards an INVITE, the telephony host passes the channel to the voice runtime, which looks up the number and starts the flow.
For: Deployment operators, Integrators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | Voice runtime (no customer setting)(StasisStart) | Follow the request path |
Read more:
- How it works: Follow the request path
- Troubleshoot: Follow an action from intent to observed
Related features: Voice service control interface (ARI and AMI), Number lookup and routing responses.
Rejected and unknown SIP traffic
Requests from unknown sources or matching no trunk are rejected and tagged in the logs, so scanning traffic is visible without reaching a voice host.
For: Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | SIP edge routing (no customer setting) | Rejected calls and security tagging |
Read more:
- Reference: Rejected calls and security tagging
- Reference: Rejects without a structured record
- Troubleshoot: Recognize unknown-trunk rejections
Related features: Responses generated by the edge, Trunk identification and allowed IPs, SIP edge log records, Edge source verification and call token checks.
SIP edge health
Each edge reports whether it is up and accepting calls, which operators check before and after changes.
For: Deployment operators
| Level | Where to change it | Owner section |
|---|---|---|
| Services and containers | TelPro health endpoint | Check edge health |
Read more:
- Set it up: Check edge health
- Set it up: Verify the edge
Related features: Draining an edge, Edge instance overview.