From 2.5 seconds of silence to replies in under 350 ms
How we made a phone agent fast enough for natural conversation, and kept each caller locked to their own data.
1. Cascaded Streaming vs. Speech-to-Speech Black Boxes
While end-to-end speech-to-speech models offer expressive prosody, enterprise logistics deployments require deterministic tool execution guards and strict database multi-tenancy. However, naive sequential pipelines (Twilio PSTN → STT → RAG → LLM → TTS) routinely exceed 2.5 seconds of silence per turn.
2. Sub-350ms TTFT via Clause-Boundary Piping & Redis Pruning
By orchestrating Deepgram streaming ASR events into an asynchronous FastAPI pipeline with pre-warmed connection pools, we execute collection-level Qdrant HNSW lookups in under 50ms. Simultaneously, Redis active session memory prunes stale multi-turn passages, cutting median prompt token volume by 40% and bringing LLM Time-to-First-Token (TTFT) below 350ms. Token streams are segmented at clause boundaries and piped immediately into streaming TTS.
3. Zero-Trust Retrieval Outside the Prompt
Prompt instructions like 'Only answer questions for customer X' are trivially bypassed via prompt injection. We bind verified caller session claims (org_id, customer_id, order_scope) directly into Qdrant mandatory payload filters and tool-call execution middleware—achieving zero cross-tenant unauthorized exposures in production.