Senior Software Developer

OPR Ltd; Guildford; Hybrid; GBP 55,000 - 65,000; Full time

Job summary

A UK technology company is seeking an experienced Senior Software Developer in Guildford to enhance SIP platforms and contribute to a collaborative engineering culture. The ideal candidate should have expertise in SIP/VoIP protocols, Python, and secure systems development. This hybrid role offers up to £65,000 based on experience along with a supportive work environment and attractive benefits including annual leave, pension, and private medical insurance.

Benefits

24 days annual leave plus bank holidays

Pension scheme

Life insurance

Private medical insurance

Birthday and volunteering day off

High street discount vouchers

Qualifications

• 5+ years of experience in Python or another object-oriented language.
• Strong understanding of SIP / VoIP and related protocols.
• Experience in secure systems design at both software and network levels.

Responsibilities

• Design and enhance enterprise SIP platform and support services.
• Develop integrations with third-party systems including AI services.
• Troubleshoot and resolve SIP / RTP platform-level issues.

Skills

SIP / VoIP and related protocols

Python or another object‑oriented language

Object‑oriented design principles

HTTP / RESTful APIs

Flask or Django

Secure systems design and development

SIP / RTP troubleshooting

Git / GitHub

Docker containerisation

Linux (Ubuntu-based) environments

Full driving licence

Tools

Wireshark

MongoDB

MySQL

Kubernetes

ArgoCD

FreeSWITCH

Job description

Senior / Experienced Software Developer

Location: Guildford (Hybrid – must be UK-based and within a two-hour commute)

Contract: Full-time, Permanent

Salary: 55,000–65,000 (depending on experience)

The Opportunity

An established UK technology company is expanding its Software Development Team and is looking for an experienced Senior Software Developer to help evolve a large‑scale, enterprise‑grade SIP platform and its associated REST APIs.

This is an excellent opportunity to work on complex, real‑world systems in a collaborative, technically strong environment. You’ll contribute to the ongoing development of a mission‑critical communications platform, build value‑added services, and work with modern AI‑driven integrations.

The organisation is known for its strong engineering culture, long‑term customer partnerships, and commitment to professional development. You’ll be joining a supportive, innovation‑led environment where your ideas and expertise will have a real impact.

Role Summary

• Designing, developing, and enhancing an existing enterprise SIP platform and supporting services
• Building new value‑added services and capabilities around the core platform
• Developing integrations with third‑party systems, including AI‑based voice recognition, transcription, and sentiment analysis services
• Ensuring secure software design and development at both application and network levels
• Analysing, troubleshooting, and resolving SIP / RTP and platform‑level issues
• Contributing to secure development processes, policies, and compliance with standards such as ISO 27001 and PCI-DSS
• Collaborating closely with other developers and stakeholders to deliver high‑quality, scalable solutions

Essential Skills & Experience

• SIP / VoIP and related protocols (SDP, RTP, RFC2833 / RFC4733, etc.)
• Python or another object‑oriented language (5+ years)
• Object‑oriented design principles
• HTTP / RESTful APIs
• Flask or Django, including Jinja, Pytest, SQLAlchemy, and Marshmallow
• Secure systems design and development (software and network level)
• SIP / RTP troubleshooting using tools such as Wireshark
• Git / GitHub (or similar version control systems)
• Docker containerisation
• Linux (Ubuntu-based) environments
• A full driving licence and car due to the client’s location

Desirable Skills

• FreeSWITCH (configuration and, ideally, source code)
• C / C++ (for open‑source troubleshooting or minor code changes)
• Kamailio
• Auth0 / OAuth 2.0
• MongoDB and / or MySQL
• CI / CD pipelines (e.g. GitHub Actions)
• Kubernetes / ArgoCD
• WebRTC

Benefits

• 24 days annual leave plus bank holidays
• Pension scheme
• Life insurance
• Private medical insurance
• Birthday and volunteering day off
• High street discount vouchers

Thank you for taking the time to apply

to OPR Resourcing Specialists. If your application is successful you will be contacted within 7 days. We apologize but due to the high volume of applications we receive we are unable to provide feedback on individual CVs.

Regrettably, we are unable to offer Right to Work Sponsorship.

If you do not currently have the Right to Work in the UK or will need additional support to extend your current Right to Work status, your application cannot be considered.

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