Glossary
Key terms and concepts used throughout the Vonage Client SDK documentation
- # answer webhook
An HTTP endpoint on the custom backend that the Vonage API calls when a call is initiated. The webhook must return a valid NCCO that instructs the Vonage API how to route the call.
- # APNs — Apple Push Notification service
Apple's push delivery infrastructure. PushKit VoIP pushes are delivered through APNs. A valid push certificate must be uploaded to the Vonage dashboard for inbound call delivery on iOS.
- # call
A voice communication session between two or more participants. A call is composed of one or more legs, one per participant.
- # callee
The participant who receives a call invite. The callee's client app receives the invite via the onCallInvite callback and can answer or reject it.
- # caller
The participant who initiates a call. The caller's client app uses serverCall() to start an outbound call.
- # CallKit
An Apple framework that presents the native system call UI on iOS. Apple mandates that every VoIP push handled via PushKit must result in a reportNewIncomingCall to CallKit.
- # Conversation Service
The Vonage backend service that manages conversations, sessions, and event delivery. In most documentation contexts, this can be understood as the Vonage API.
- # createSession
The SDK method used to establish an authenticated session with the Vonage API. Requires a valid JWT from the custom backend. Can optionally accept a previous session ID to recover pending events.
- # custom backend
A server built by the developer that mints JWTs for authentication, serves answer webhooks with NCCO instructions, and communicates with the Vonage API. Required for all call flows.
- # DTMF — Dual-Tone Multi-Frequency
Signaling tones sent during an active call to navigate IVR menus or transmit digit sequences. The SDK exposes sendDTMF() to emit tones and onDTMF to receive them.
- # FCM — Firebase Cloud Messaging
Google's push notification service for Android. The Vonage Client SDK uses FCM data messages to deliver inbound call invite payloads when the app is backgrounded or killed.
- # ICE — Interactive Connectivity Establishment
A protocol framework used by WebRTC to find the best path between two peers through NATs and firewalls. ICE candidates are gathered during call setup and reconnection.
- # JWT — JSON Web Token
A signed token minted by the custom backend using the Vonage application private key. Used to authenticate sessions with the Vonage API. Must include claims: sub, application_id, acl, and exp.
- # leg
A single participant's connection in a call. In most contexts, 'leg' and 'call' are interchangeable. The SDK API uses 'leg' in method names such as onLegStatusUpdate.
- # MOS — Mean Opinion Score
A numerical measure of voice call quality on a scale from 1.0 (bad) to 5.0 (excellent). The SDK reports MOS via onRTCStatsUpdate to help monitor call quality in real time.
- # NCCO — Nexmo Call Control Object
A JSON structure returned by the custom backend's answer webhook that instructs the Vonage API how to handle a call (e.g. connect, transfer, play audio).
- # PSTN — Public Switched Telephone Network
The traditional global telephone network. App-to-phone calls route through the PSTN via Vonage. Inbound PSTN calls appear with channelType 'phone' in onCallInvite.
- # PushKit
An Apple framework that delivers high-priority VoIP push notifications to iOS apps, waking them from a killed or suspended state. Required for reliable inbound call delivery on iOS.
- # SDP — Session Description Protocol
A format for describing multimedia session parameters (codecs, transport addresses, media types). WebRTC uses SDP in the offer/answer exchange to negotiate call media.
- # serverCall
The SDK method used to initiate an outbound call. Sends a context object to the Vonage API, which then calls the custom backend's answer webhook to retrieve NCCO routing instructions.
- # session
An authenticated connection between a client app and the Vonage API. Sessions have a 15-minute TTL and must be recreated by calling createSession again before expiry.
- # Vonage API
Vonage-owned servers that establish and manage calls, handle sessions, and communicate with custom backends via webhooks. This is the core service that the Vonage Client SDK interacts with.
- # Vonage Client SDK
The SDK embedded in client apps (Android, iOS, Web) that enables voice calling, session management, and real-time event handling. Also referred to as 'Client SDK'.
Also known as: Client SDK
- # WebRTC — Web Real-Time Communication
An open standard providing browsers and mobile applications with real-time peer-to-peer audio/video communication via simple APIs. The Vonage Client SDK uses WebRTC internally to establish and maintain voice call media streams.