# didlogic Learning Center

> This scope covers evergreen educational resources under /learn/ for understanding voice infrastructure, SIP, phone numbers, call quality, AI voice connectivity, and business messaging.

Use this file to find explanatory material. For didlogic product selection, use the relevant product scope; for API and configuration instructions, use the developer portal.

## Start here

- [Learning Center](https://didlogic.com/learn/): Index of didlogic explainers on voice infrastructure and messaging.
- [What is SIP trunking?](https://didlogic.com/wp-content/uploads/llms_md/what-is-sip-trunking.md): How SIP trunks connect a PBX, contact center, or voice application to the public phone network.
- [What is a DID number?](https://didlogic.com/wp-content/uploads/llms_md/what-is-a-did.md): Direct inward dialing and virtual-number fundamentals.
- [Virtual phone numbers explained](https://didlogic.com/wp-content/uploads/llms_md/virtual-phone-numbers-explained.md): How virtual numbers work, their main types, and common regulatory considerations.
- [What is the PSTN?](https://didlogic.com/wp-content/uploads/llms_md/what-is-the-pstn.md): The public phone network and its role in connecting telephone numbers.

## SIP and call media

- [What is SIP?](https://didlogic.com/wp-content/uploads/llms_md/sip-protocol-explained.md): The Session Initiation Protocol and its role in setting up and ending calls.
- [What is RTP?](https://didlogic.com/learn/what-is-rtp/): How real-time transport carries voice media during a call.
- [SIP response codes](https://didlogic.com/wp-content/uploads/llms_md/sip-response-codes.md): Reference guide to 1xx–6xx SIP responses and how to interpret them in multi-hop calls.
- [SIP ALG explained](https://didlogic.com/wp-content/uploads/llms_md/sip-alg-explained.md): Why SIP ALG can cause registration, call, and audio problems, and how to diagnose it.

## Quality and security

- [VoIP latency, jitter, and packet loss](https://didlogic.com/wp-content/uploads/llms_md/voip-latency-jitter-packet-loss.md): Network conditions that degrade call audio and the symptoms they produce.
- [Voice codecs](https://didlogic.com/learn/voice-codecs-g711-g729-opus-hd-voice/): G.711, G.729, Opus, and codec trade-offs for voice calls.
- [VoIP toll fraud and SIP security](https://didlogic.com/learn/voip-toll-fraud-sip-security/): Common SIP fraud patterns and practical security controls.

## AI voice and messaging

- [How AI voice agents connect to the phone network](https://didlogic.com/wp-content/uploads/llms_md/how-ai-voice-agents-connect-to-the-phone-network.md): The roles of phone numbers, SIP trunks, and carriers in AI voice calls.
- [Connecting AI voice platforms via SIP](https://didlogic.com/learn/connecting-ai-voice-platforms-via-sip-vapi-retell-livekit-and-elevenlabs/): Conceptual connection patterns for Vapi, Retell, LiveKit, and ElevenLabs.
- [What is A2P messaging?](https://didlogic.com/wp-content/uploads/llms_md/what-is-a2p-messaging.md): Application-to-person SMS concepts and common business-message types.