Senior Software Engineer – VoIP / SIP

Recrew AI; Kolkata District; On-site; INR 3,500,000 - 5,200,000; Full time

Job summary

Recrew AI in Kolkata is seeking a Senior Software Engineer - VoIP/SIP to own design and implementation of the core telephony backbone. You will build carrier-grade SIP services in Golang, integrate with our AI-first SaaS platform, and drive reliability for thousands of dental practices.

The role requires deep VoIP expertise, experience with Kamailio/OpenSIPS/Asterisk, and strong Linux networking. You will collaborate across product, engineering, and operations to deliver scalable, secure calling

Qualifications

• 7-10 years of software development experience with 4-5 years building or operating large-scale VoIP/SIP systems in production.
• Strong Golang skills with high-performance networked services and production-grade APIs.
• Hand-on experience with Kamailio, OpenSIPS, or Asterisk including configuration and routing.
• Deep understanding of SIP, RTP, SDP, NAT traversal, registrar/registration, B2BUA vs proxy, SBC concepts.
• Experience designing highly available telephony backbones: clustering, health checks, load balancing, failover.
• Strong Linux and networking fundamentals; iptables, firewalls, TCP/UDP, QoS; packet debugging with tcpdump/Wireshark.
• Experience integrating VoIP platforms with RESTful backends, databases (PostgreSQL or MySQL) and message queues for control and billing.

Responsibilities

• Design and implement a carrier-grade SIP/VoIP core using Kamailio or OpenSIPS for SIP signaling and FreeSWITCH or similar for media and application services.
• Build Golang-based SIP services — registrar, SBC-like components, routing logic, monitoring daemons — and internal APIs to control routing, policies, and provisioning.
• Configure and operate SIP load balancing, failover, and high-availability setups across multi-node SIP proxies, distributed media servers, and RTP proxies.
• Implement and maintain dial plans, least-cost routing, DID management, class-4/class-5 switching logic, and integrations with upstream carriers and PSTN gateways.
• Own security and robustness of the VoIP stack: TLS/SRTP, authentication, rate limiting, fraud detection hooks, and abuse controls.
• Integrate the telephony backbone with the company's SaaS platform via well-defined internal APIs and webhooks, covering user accounts, billing, analytics, and AI/automation flows.
• Define and own monitoring, alerting, logging, and capacity planning for SIP signaling, RTP/media, and VoIP quality metrics (MOS, jitter, packet loss).

Skills

Golang

VoIP/SIP

Linux

Networking

tcpdump/Wireshark

RESTful APIs

PostgreSQL/MySQL

Tools

Kamailio

OpenSIPS

Asterisk

FreeSWITCH

Kubernetes

AWS

GCP

Job description

Role: Senior Software Engineer - VoIP / SIP

Function: Software Engineering / Telephony Infrastructure

Location: Kolkata / Gurugram

Type: Full-time

Industry: AI, Medical SaaS, Dental Medical SaaS

About Company

The company builds medical AI SaaS for the U.S. dental market.

Thousands of dental practices across North America rely on its platform daily. It unifies analytics, scheduling, communications, payments, and marketing automation into one system.

The platform automates admin work and gives teams real-time visibility into revenue and retention. Founded in 2015 by a practicing dentist, a data strategist, and a PhD technologist.

The company is mission-driven, execution-oriented, and moving fast in a large, under-digitized healthcare vertical.

Position Overview

This role owns the design and implementation of the company's core VoIP/SIP telephony backbone — the infrastructure layer that powers calling, routing, and communication workflows for thousands of dental practices. The engineer will architect and build carrier-grade SIP services in Golang on top of open-source components, and integrate the telephony stack with the company's broader AI-first SaaS platform. The role reports to the Engineering India Head and sits at the intersection of deep infrastructure work and product-facing impact.

Role & Responsibilities

• Design and implement a carrier-grade SIP/VoIP core using Kamailio or OpenSIPS for SIP signaling and FreeSWITCH or similar for media and application services.
• Build Golang-based SIP services — registrar, SBC-like components, routing logic, monitoring daemons — and internal APIs to control routing, policies, and provisioning.
• Configure and operate SIP load balancing, failover, and high-availability setups across multi-node SIP proxies, distributed media servers, and RTP proxies.
• Implement and maintain dial plans, least-cost routing, DID management, class-4/class-5 switching logic, and integrations with upstream carriers and PSTN gateways.
• Own security and robustness of the VoIP stack: TLS/SRTP, authentication, rate limiting, fraud detection hooks, and abuse controls.
• Integrate the telephony backbone with the company's SaaS platform via well-defined internal APIs and webhooks, covering user accounts, billing, analytics, and AI/automation flows.
• Define and own monitoring, alerting, logging, and capacity planning for SIP signaling, RTP/media, and VoIP quality metrics (MOS, jitter, packet loss).

Must Have Criteria

• 7-10 years of software development experience with at least 4-5 years building or operating large-scale VoIP/SIP systems in production.
• Strong Golang skills including high-performance networked services, concurrent processing, and production-grade APIs.
• Hands-on experience with at least one open-source SIP server — Kamailio, OpenSIPS, or Asterisk — including configuration, routing logic, and packet-level troubleshooting.
• Deep understanding of SIP, RTP, SDP, NAT traversal, registrar/registration flows, B2BUA vs. proxy behavior, and SBC concepts.
• Proven ability to design and operate highly available telephony backbones: clustering, health checks, load balancing, and graceful failover.
• Strong Linux and networking fundamentals — iptables, firewalls, TCP/UDP, QoS — with comfort debugging at packet level using tcpdump or Wireshark.
• Experience integrating VoIP platforms with RESTful backends and databases (PostgreSQL or MariaDB/MySQL) and message queues for control and billing workflows.

Nice to Have

• Familiarity with VoIP billing, rating engines, CDR processing, and reseller hierarchies (class-4/class-5 softswitch products or similar).
• Cloud-native deployment of VoIP stacks — containerized Kamailio or FreeSWITCH clusters on AWS or GCP, Kubernetes, service meshes.
• Prior work building call center or CPaaS-style platforms including programmable IVRs, call queues, and analytics.

What We Offer

• End-to-end ownership of a mission-critical infrastructure layer powering thousands of live dental practices across North America.
• Direct exposure to AI-first product evolution — conversational automation, intelligent call routing, and front-office workflow integration.
• High-autonomy environment with tight cross-functional collaboration across product, engineering, and operations.
• Flexible scheduling within a fast-moving, execution-oriented team with real, measurable impact.