Software Engineer c#

Department Description
Guardian is a call taking & dispatching platform used by emergency service operators across the UK & Europe. We help 999 or 112 operators answer calls from the public and dispatch out nearby responders, enabling the right response when every second counts, and ultimately helping our customers save lives.

As our solution has grown from a small startup to one of the leading offerings for Fire & Police agencies, our customers now trust us to solve more of their problems. You will help us innovate across the Guardian portfolio by working under our senior product leads to refine our core call taking & dispatching offerings, while also getting the chance to carve your own path by leading development for an expansion product.

The Guardian team is distributed across the UK & Poland, with offices in Kraków and Glasgow. We currently have around 150 employees. We have a relaxed but hard working environment where jeans and t-shirts are the norm and good ideas and debate are encouraged.

Core Responsibilities:
• Develop C# components for high-concurrency SIP sessions, managing complex headers and MIME bodies to support features like "First-to-Answer" and Group Regroups.
• Implement RTP/RTCP media handling for Mission Critical Voice (MCPTT) and Video (MCVideo), ensuring seamless floor control (transmission rights) in half-duplex environments.
• Build handlers for MCData services (SDS, File Distribution) using HTTP and SIP MESSAGE requests, and manage XCAP retrieval logic for XML configuration documents.
• Integrate OIDC authentication flows and MIKEY-SAKKE encryption to ensure media transport remains secure and resilient.

Basic Requirements
• 2+ years of professional experience with a deep focus on asynchro\ous network programming (C# / .NET Framework / .NET Core )
• WCF, SignalR, EF, ASP.NET, WebAPI
• Understanding of the SIP Protocol Stack (INVITE, PUBLISH, SUBSCRIBE, etc.) and experience with RTP/RTCP stacks.
• Proficiency in parsing complex XML schemas (XSD) and handling multipart/mixed MIME bodies.
• Strong grasp of OOP, SOLID principles, and modern CI/CD workflows (Git, Pull Requests, Agile).

Preferred:
• Familiarity with TS 24.379 (MCPTT) or related MCX standards.
• Experience with SRTP, TLS, or Key Management lifecycles (KMS).

In return for your expertise, we’ll support you in this new challenge with coaching & development on every step of your way.  Also, to reward your work you’ll get the following:
• Private medical coverage, Multisport
• Life insurance (two annual incomes), 
• Employee Stock Purchase Plan – 15% discount for buying Motorola’s Stock units, 
• Employee Pension Plan – 3,5 % of the month’s gross salary, which goes to the retirement account
• IP Tax Relief (up to 80%)
• Yearly salary increase (depends on individual performance)
• Annual bonus (depends on company performance)
• Flexible working hours (usually the day starts between 8-10), 
• 8 hours working day (30 minutes lunch break included).
• Hybrid work