We have 100 people working as an IT service company for mainly software development and maintenance projects. We want to have Requirements Management processes in place such that we can comply with CMMi level 2 and then gradually to level 3.
Could you provide some guidance on how we should proceed?
Entire books have been writeen on this subject so I won't try to replicate that information here. The short answer is: start by looking at what you ALREADY do today and perform a gap analysis between that and the CMMI practices for Requirements Management (REQM).
REQM is what is required for ML2. Requirements Development is part of ML3. For REQM, there are three key areas you need to focus on: developing a shared understanding of what the requirements mean, understanding how they impact the rest of the project (if they're new or changed), and gaining an appropriate level of committment from all key stakeholders.
Understanding what they mean includes ensuring they are even valid to begin with, that they come from the right source, the constraints, the issues, the risks, and that the amount of work to implement them is understood.
Understanding how they impact the project includes conducting a "traceability" exercise to determine the related changes that have to take place, reconciling the other project work with the new or changed requirement, and ensuring the team is working on the right things as the requirements change.
And finally, gaining committment on the requirement(s) is more than a "sign off." It means that all parties (customer, team, management, etc) are committed to all doing what it takes (as identified in the prior paragraph) to implement the new or changed requirement.
Focus on those three things (as opposed to the practices in the model) and you'll be fully compliant (and more importantly, successful). Good luck!