## Supported Protocols The following protocols are supported: | Protocol | Supported Functionality | | --- | --- | | SIP | SIP signaling, as specified in [IETF RFC 3261](https://datatracker.ietf.org/doc/html/rfc3261). | | TLS | The Transport Layer Security (TLS) is a cryptographic protocol that provides secure communication over a network. Voice Gateway supports TLS 1.2 and later versions. TLS 1.3 is preferred for optimal security. | | SIP over TLS | Partially encrypted SIP, as specified in [IETF RFC 3261](https://datatracker.ietf.org/doc/html/rfc3261). Some servers may communicate unencrypted, depending on specific requirements. | | SIPS | Fully encrypted SIP, as specified in [IETF RFC 3261](https://datatracker.ietf.org/doc/html/rfc3261). All servers in the communication chain use TLS for encrypted communication. | | SIP over WebSockets | SIP over secure WebSockets, as specified in [RFC 7118](https://datatracker.ietf.org/doc/html/rfc7118). | | RTP | The Real-time Transport Protocol as specified in [RFC 3550](https://datatracker.ietf.org/doc/html/rfc3550). | | SRTP | Encrypted media using the Secure Real-time Transport Protocol (SRTP), as specified in [RFC 3711](https://datatracker.ietf.org/doc/html/rfc3711). | | RTCP | The RTP Control Protocol (RTCP) provides quality of service (QoS) statistics for RTP media streams. | | Session Description Protocol (SDP) | The Session Description Protocol (SDP), as specified in [RFC 4566](https://datatracker.ietf.org/doc/html/rfc4566). | | Offer/Answer Model with the Session Description Protocol (SDP) | The offer or answer model for negotiating SIP sessions, as specified in [RFC 3264](https://datatracker.ietf.org/doc/html/rfc3264). | | DTMF | The use of RTP payloads to carry DTMF events, as specified in [RFC 2833](https://datatracker.ietf.org/doc/html/rfc2833). | | SIP Digest Authentication | SIP Digest Authentication challenges and authenticates SIP devices, as specified in [RFC 8760](https://datatracker.ietf.org/doc/html/rfc8760). | | SIPREC | Acting as a SIPREC client or server to accomplish call recording, as specified in [RFC 7866](https://datatracker.ietf.org/doc/html/rfc7866). | | WebRTC clients | Receiving calls from WebRTC clients, such as web browsers or native mobile apps. | | DTMF - SIP INFO | Receiving DTMF via SIP INFO, as specified in [RFC 2976](https://www.rfc-editor.org/rfc/rfc2976). | | SIP OPTIONS | OPTIONS pings to allow remote SIP gateways and Session Border Controllers (SBCs) to test the health of the Voice Gateway SBCs. | | Session timers | SIP session timers, as specified in [RFC 4028](https://datatracker.ietf.org/doc/html/rfc4028). | | SIP UPDATE | The SIP UPDATE method to refresh SIP session. | | STUN | Session Traversal Utilities for NAT (STUN), as specified in [RFC 5389](https://datatracker.ietf.org/doc/html/rfc5389). | | Diversion Indication in SIP | The Diversion header, as specified in [RFC 5806](https://datatracker.ietf.org/doc/html/rfc5806). | | SIP REFER | Sending the SIP REFER method to transfer calls, as specified in [RFC 3515](https://datatracker.ietf.org/doc/html/rfc3515). Receiving SIP REFER is not supported. | ## Supported Codecs The following audio codecs are supported: - `G.711`(preferred): - `A-law`. - `U-law`. - `OPUS`. - `G.722`. ## Features ### Trunk management and Routing - Transferring calls via [SIP REFER](https://datatracker.ietf.org/doc/html/rfc3515) or [SIP INVITE](https://datatracker.ietf.org/doc/html/rfc3261). - Multiple SIP trunks per customer. - Configuring SIP trunks with options like tech prefix, SIP Diversion header, Outbound authentication (including `REGISTER`). - Routing calls based on trunk group, Direct Inward Dialing (DID), or DID range. - Least-cost routing selection of outbound trunk. ### Call Features - Custom SIP headers on inbound and outbound calls. - Mid-call SIP INFO requests. - P-Asserted-Identity header to identify caller. - Receiving compact SIP headers. - Receiving re-INVITE with no Session Description Protocol (SDP). - [Answering machine detection](https://docs.cognigy.com/voice-gateway/references/verbs/amd). - Configurable music on hold. - Configurable [Atmosphere Sounds](https://docs.cognigy.com/ai/agents/develop/node-reference/voice/voice-gateway/parameter-details) playing in the background of the conversation. - Configurable [Silence Overlay](https://docs.cognigy.com/ai/agents/develop/node-reference/voice/voice-gateway/parameter-details) playing background sounds when there’s a long pause in a call. - [TTS streaming](https://docs.cognigy.com/voice-gateway/streaming) to reduce latency. ### Call Management - [Creating outbound calls via REST API](https://docs.cognigy.com/voice-gateway/creating-outbound-calls). - Performing operations on calls in progress via REST API. ### STT and TTS providers - Many cloud-based and on-premises [speech providers](https://docs.cognigy.com/voice-gateway/references/tts-and-stt-vendors) are available, along with the option to integrate [custom speech API](https://docs.cognigy.com/voice-gateway/webapp/speech-services#add-custom-speech-vendors) tailored to your needs. - [Fallback speech configuration](https://docs.cognigy.com/voice-gateway/webapp/applications#add-additional-tts-and-stt-vendor) if the primary vendor fails. ### Call Recording and Storage - [Call recording](https://docs.cognigy.com/voice-gateway/webapp/recent-calls#call-recordings) via integration with a third-party SIPREC server. - Pausing or resuming transcription and recording to avoid the collection of Personally Identifiable Information (PII). - Call recording with no third-party components, [recordings streamed to the preferred cloud storage](https://docs.cognigy.com/voice-gateway/webapp/recent-calls#call-recordings). ### Call Quality Monitoring and Optimization - Observability features include [tracing call events with open telemetry](https://docs.cognigy.com/voice-gateway/webapp/recent-calls). - Visual view of [speech latency](https://docs.cognigy.com/voice-gateway/webapp/recent-calls#call-recordings) (TTS and STT) on each call. - [Caching of TTS audio](https://docs.cognigy.com/voice-gateway/webapp/accounts#tts-prompt-caching) when possible to reduce costs. ## Technical Support For any further or more specific questions about the Voice Gateway technical capabilities, contact [Cognigy technical support](https://docs.cognigy.com/help/get-help). Last modified on July 6, 2026.