Senior Software Engineer – Core VoIP / SIP Backbone

Practice By Numbers, Inc.; Bellevue (WA); Hybrid; USD 150,000 - 180,000; Full time

Benefits offered by this job

Competitive base salary + equity

Medical/dental/vision insurance

401(k) with company match

Flexible PTO and paid holidays

Job summary

Practice by Numbers, Inc. in Bellevue, WA is seeking a Senior Software Engineer to own the core VoIP/SIP backbone.

You will design and implement Golang-based services, integrate with Kamailio/OpenSIPS and FreeSWITCH, and ensure scalable, secure telephony for thousands of dental practices.

This hybrid role offers a competitive salary, equity, and benefits as part of a high-impact SaaS platform.

Qualifications

• 7–10 years of software development with 4–5 years in large-scale VoIP/SIP systems.
• Strong Golang skills with production-grade networked services and APIs.
• Hands‑on experience with Kamailio/OpenSIPS and FreeSWITCH or Asterisk.
• Deep understanding of SIP, RTP, NAT traversal, and SBC concepts.
• Experience designing highly available telephony backbones with clustering and load balancing.

Responsibilities

• Design and implement a carrier-grade SIP/VoIP core using Kamailio/OpenSIPS for signaling and FreeSWITCH for media.
• Build Golang-based SIP services (registrar, routing, monitoring) and internal APIs.
• Configure SIP load balancing, failover, and multi-node high-availability setups.
• Implement dial plans, least-cost routing, DID management, and PSTN gateway integration.
• Own security and robustness of the VoIP stack (TLS/SRTP, rate limiting, fraud controls).
• Integrate telephony backbone with PBN's SaaS platform via internal APIs and webhooks.
• Define monitoring, alerting, logging, and capacity planning for SIP signaling and RTP.
• Collaborate with product/ops to translate requirements into VoIP designs.

Skills

Golang

VoIP/SIP

Linux networking

REST APIs

TCP/UDP networking

SIP signaling

High availability

Tools

Kamailio/OpenSIPS

FreeSWITCH/Asterisk

tcpdump/Wireshark

PostgreSQL/MySQL

Job description

Senior Software Engineer – Core VoIP / SIP Backbone

Location: Hybrid, Bellevue WA

Employment Type: Full-Time

Compensation: $150K-180K base salary, depending on experience + equity + benefits

About Practice by Numbers

Practice by Numbers (PBN) is a leading dental practice management SaaS platform serving over 5,000 dental practices across North America. Our platform delivers practice management, VoIP telephony, payments, and advanced analytics. We are evolving into an AI-first product, adding conversational automation and intelligent communication workflows for patients and front-office teams.

About the Role

This role owns the design and implementation of the core VoIP/SIP telephony backbone for PBN, including SIP routing, media handling, scalability, and reliability. You will architect and build Golang-based SIP services and control planes on top of open-source components such as Kamailio (or similar SIP server), FreeSWITCH/OpenSIPS, and related media/RTP proxies. This is a senior individual contributor role with high ownership and direct impact on a product used by thousands of dental practices daily.

Key Responsibilities

• Design and implement a carrier-grade SIP/VoIP core using components like Kamailio/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 (multi-node SIP proxies, distributed media servers, RTP proxies).
• Implement and maintain dial plans, least-cost routing, DID management, class-4/class-5 style switching logic, and integration with upstream carriers and PSTN gateways.
• Own security and robustness of the VoIP stack: TLS/SRTP, authentication/authorization, rate limiting, fraud detection hooks, and abuse controls.
• Integrate the telephony backbone with PBN's SaaS platform (user accounts, billing, analytics, AI/automation flows) via well-defined internal APIs and webhooks.
• Define monitoring, alerting, logging, and capacity planning for SIP signaling, RTP/media, and VoIP quality (MOS, jitter, packet loss).
• Collaborate with product and operations teams to translate business requirements (IVRs, call queues, routing rules, AI agents) into resilient VoIP and backend designs.

Required Qualifications

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

Nice to Have

• Experience with WebRTC, SIP over WebSockets, and browser/mobile softphone integrations.
• 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/FreeSWITCH clusters on AWS/GCP, Kubernetes, service meshes).
• Prior work building call center or CPaaS-style platforms, including programmable IVRs, queues, and analytics.

What Success Looks Like

• A robust, observable VoIP backbone that sustains high call volumes with low failure rates and predictable call quality across geographies.
• Rapid rollout of new telephony features (IVRs, routing rules, AI agents) through clean APIs and configuration-driven behavior rather than manual changes.
• Demonstrated reduction in telephony incidents and MTTR through automation, strong monitoring, and clear runbooks.

Benefits & Perks

• Competitive base salary (Salary range) + equity
• Comprehensive medical, dental, and vision insurance
• 401(k) with company match
• Flexible PTO and paid holidays