Software C# Engineer | Mission Critical Communications

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

• C# / .NET Framework / .NET Core Mastery: 3+ years of professional experience with a deep focus on asynchronous network programming.
• .NET Frameworks Experience: WCF, SignalR, EF, ASP.NET, WebAPI
• Protocol Expertise: A solid understanding of the SIP Protocol Stack (INVITE, PUBLISH, SUBSCRIBE, etc.) and experience with RTP/RTCP stacks.
• Data Handling: Proficiency in parsing complex XML schemas (XSD) and handling multipart/mixed MIME bodies.
• Software Engineering Principles: Strong grasp of OOP, SOLID principles, and modern CI/CD workflows (Git, Pull Requests, Agile).

Preferred (The "Nice to Haves")

• 3GPP Standards: Familiarity with TS 24.379 (MCPTT) or related MCX standards.
• Security: Experience with SRTP, TLS, or Key Management lifecycles (KMS).
• Domain Knowledge: Previous experience with UK Police Control Room environments or the Emergency Services Network (ESN)

In return for your expertise, we'll support you in this new challenge with coaching & development every step of the way. Also, to reward your hard work you'll get:

• Competitive salary and bonus schemes
• Two weeks of additional pay per year (holiday bonus)
• 25 days holiday entitlement + bank holidays
• Attractive defined contribution pension scheme
• Private medical insurance
• Employee stock purchase plan
• Flexible working options
• Life assurance
• Enhanced maternity and paternity pay
• Career development support and wide-ranging learning opportunities
• Employee health and wellbeing support EAP, wellbeing guidance etc
• Carbon neutral initiatives/goals
• Corporate social responsibility initiatives including support for volunteering days
• Well-known companies discount scheme

We are an equal opportunities employer and we want you to have every opportunity to shine and show us your talents, please let us know if there is anything we can do to make sure the process works for you. We celebrate diversity and are committed to creating an inclusive environment for all employees

At Motorola Solutions, we believe that everything starts with our people. We're a global close-knit community, united by the relentless pursuit to help keep people safer everywhere. We build and connect technologies to help protect people, property and places. Our solutions foster the collaboration that's critical for safer communities, safer schools, safer hospitals, safer businesses, and ultimately, safer nations. Connect with a career that matters, and help us build a safer future. 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 hubs in Glasgow, Leicester, Hemel and Krakow. 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. Our daily work is remote and often asynchronous, with workflows managed via Google Chat & collaborative documents in G-Suite. However, you'll also have the opportunity to join us for frequent in person work & social events like post-work pints, Flight Club darts, or our annual all-hands. As a Software Engineer within our Agile delivery team, you will move beyond standard CRUD applications to solve complex network and real-time communication challenges. You will lead the development of expansion products that interface with 3GPP-compliant User Equipment (UE).