Pankaj K.

I build and fix production voice systems: AI voice agents, contact center platforms, and multi-tenant VoIP/PBX, from SIP signaling to the SaaS around it. Top Rated on Upwork with 100% Job Success, 4.9 stars, and 2,200+ hours delivered. Recent clients specifically praised production voice-AI stabilization, clean asynchronous architecture, and working barge-in. Many of my projects start where a prototype or an existing platform breaks under real call traffic. WHAT I DELIVER 1- AI voice agents: STT + LLM + TTS pipelines on LiveKit, Pipecat, Vapi, Retell and ElevenLabs, using OpenAI, Claude or local LLMs, with RAG, tool calling, MCP/agent tooling, barge-in handling, and warm transfer to a human. 2- Contact center and dialer platforms: CCaaS, UCaaS and CPaaS builds, power, preview and predictive dialers, queues, agent desktops, call recording, reporting, and CRM/ERP integration. 3- FreeSWITCH, FusionPBX and Asterisk: hosted and multi-tenant PBX, SIP trunks, IVR, dial plans, routing, provisioning, WebRTC, and high availability. 4- Production troubleshooting: one-way audio, SIP/RTP failures, trunk and routing problems, latency, security hardening, migrations, and stability under load. 5- Full-stack SaaS around the voice layer: NestJS, Node.js, Laravel, CodeIgniter, Python (FastAPI, Flask), Go (Gin), React/Next.js/Vue, PostgreSQL, Redis, Docker, Kubernetes, and AWS/GCP/Azure, including APIs, admin portals, and mobile apps. 6-Telephony providers: Twilio, Telnyx, Plivo. PROJECTS 1. AI Voice Agent+Telephony Integration (STT, LLM, TTS) Description: Clients’ voice agents often sound fine in a demo and fall apart on real phone calls. I designed an architecture that connects FreeSWITCH/Asterisk to speech-to-text, an LLM and text-to-speech, with barge-in (callers can interrupt), audio-format compatibility between telephony and AI providers, and a provider cost comparison. Warm transfer to a human agent is part of the design. The same approach is behind my production voice-AI stabilization work for clients. Skills: Voice AI, FreeSWITCH, Asterisk, OpenAI API, Speech-to-Text, Text-to-Speech, Node.js, VoIP, SIP 2. UnifiedPBX: Multi-Tenant VoIP and Contact Center Platform Description: A multi-tenant PBX and CCaaS platform built on FreeSWITCH and FusionPBX, with a modern web layer on top. It covers SIP routing, IVR, queues, DIDs, call recordings, CDR reporting and WebRTC calling, all under one architecture. Built for providers and MSPs who want to host many customers on one platform. Live at unifiedpbx.in. Skills: FreeSWITCH, FusionPBX, CCaaS, Multi-tenant SaaS, WebRTC, NestJS, Node.js, PostgreSQL, React, SIP 3. NinjaDialer: Outbound Dialer and Contact Center Description: Outbound dialing platform for call centers: dialing workflows, SIP and telephony integration, agent screens, backend APIs and reporting. Designed to keep agents on live calls and give managers visibility into campaign performance. Covers power, preview and predictive dialing approaches. Skills: Dialer, Call Center Software, VoIP, SIP, FreeSWITCH, Asterisk, REST API, Reporting 4. React SIP/WebRTC Diagnostic Lab (Live Tool) Description: A browser-based tool for diagnosing one-way audio, no audio and connectivity problems between a browser and a FreeSWITCH/FusionPBX server. It lets you test the audio path and see where WebRTC calls break (ICE, codecs, media), without digging through server logs first. Open the live tool from the link. Skills: WebRTC, SIP, React, FreeSWITCH, FusionPBX, Troubleshooting, VoIP, JavaScript 5. Full-Stack SaaS, API and Infrastructure Engineering Description: Backend and frontend engineering for SaaS products: React/Next.js frontends, Node.js/NestJS services, PostgreSQL, Docker deployment and monitoring with Prometheus and Grafana. PORTFOLIO: FreeSWITCH, FusionPBX, Asterisk: UnifiedPBX, SIP/WebRTC Diagnostic Lab, NinjaDialer AI voice agents, conversational AI: AI Voice Agents, UnifiedPBX, Parent IVR Twilio, Telnyx, CPaaS: Parent IVR, SandeshX, UnifiedPBX SaaS / full-stack development: UnifiedPBX, SandeshX, Full-Stack SaaS Engineering ERP / CRM transformation: Insurance ERP, Telecom ERP, School Management AI automation / analytics: AI Voice Agents, Foliolytics, Predictive Behavior eXchange Web application / React development: SIP/WebRTC Diagnostic Lab, UnifiedPBX, VirtualMentor Cloud / DevOps / architecture: UnifiedPBX, Full-Stack SaaS Engineering, AI Voice Agents HOW I WORK - End-to-end delivery, from architecture to deployment and monitoring - Strong debugging on live systems, with clear written findings - Long-term support after launch - Live demo of similar work on request - AI-assisted development (Claude Code, Codex, Cursor) to move faster without skipping testing TO GET STARTED Send me three things: the platform you run, what is failing or missing, and the outcome you need. I'll reply with a scoped plan, whether that is a quick audit, a targeted fix, or a full build.