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Grandmetric LLC
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Grandmetric LTD
Office 584b
182-184 High Street North
E6 2JA
+44 20 3321 5276

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  • Case Study

    Global VoIP/PSTN interconnection transformation towards Global SIP Service Provider 

    Migration of VoIP interconnection to SIP trunk operator 

    When a lack of standards in voice communication causes excessive costs of infrastructure maintenance and, as result, blocks its development, migration of VoIP and PSTN interconnections towards a global SIP operator is in fact a step towards the digital transformation of the entire organization.  

    Grandmetric case study

    Our goal was to prepare for the migration of voice services to a single global operator providing local PSTN interconnections. We also combined Microsoft Teams, Cisco Voice, and Session Border Controllers (SBC) into one, scalable structure. 

    Piotr Potargowicz, Senior Systems Engineer | Voice & Collaboration Architect at Grandmetric 


    • A global producer of medical articles 
    • 15000+ employees, 250 sites, global presence 


    • Grandmetric Advanced Services
    • Audit of Voice systems and of Contact Center  
    • Design of voice communication 
    • Tech Consulting  

    Our engagement

    • 3 Voice & Collaboration engineers 
    • Technical Account Manager 
    • A 20-month-long project 

    Challenges of global organizations

    A manufacturer of medical and orthopedic equipment with 250 sites spread across all continents faced a situation when each geographical region ordered, designed, and maintained voice services on its own

    The distribution of operators and providers hurts financial and operational efficiency.  It was especially painful when incidents occurred and there was no easy way to discover who was responsible for a particular area of voice transmission. On top of that, the company lacked a comprehensive standard of documenting and carrying out an inventory of hardware, which, in turn, led to higher operational costs

    Challenges in the project of migrating PSTN interconnections to a global SIP operator

    Results of IP and PSTN interconnection migration 

    Implementation of coherent standards in voice systems

    One global telecom operator for the entire organization

    System management from one dashboard  

    Leverage to win better prices and lead times reserved for global clients

    Ability to configure and manage an unlimited number of numbers  

    Solution – implementation of voice communication standards and migration to global operator 

    Once we got to know our client’s challenges and objectives, we proposed to deal with them in a four-step process.  

    1. First, we built the inventory of the infrastructure to obtain a thorough knowledge of existing voice systems and Contact Centers in all locations.  
    1. Then, we did High-Level Design Planning with client’s representatives, to work out the rules their new voice communication needs to follow.  
    1. Having the HLD in place, we moved to Low-Level Design (LLD) to describe in detail the configuration of clients’ future Call Manager, addressing, partitions, and other parts of the infrastructure.  
    1. Finally, we conducted the migration to a global SIP trunk operator, taking care of change management, testing, documentation, and knowledge transfer.  

    Considering the global character of the project and its strategic meaning to the client, we applied each step in a diligent manner.  

    Audit of voice infrastructure

    The biggest challenge of this step came from the fact that each region in the company was independent. It meant that each could use different telecom operators, different voice systems providers, etc. As a result, the communication structure across regions varied heavily.  

    The lack of documentation and schemes of logical connections made our inventory an investigation. However, thanks to using adequate tools and experience, our engineers created thorough documentation that became a starting point for choosing a telecom operator to support our client in the transformation of their IP telephony and Call Center.

    Our audit documentation comprised the elements below.  

    1. The architecture of Unified Communications, including the analysis of UCUX clusters and Cisco CUCM, as well as the architecture of the virtualization platform.  
    1. Description of problems and issues detected in each of examined architectures.  
    1. Inventory of versions of all used systems.
    1. Used licenses. 
    1. Upgrades suggestions for systems and licenses.
    1. Dial plan
    1. Call Center environment. 
    Cisco Unified Communication Project - audyt of voice systems
    Cisco Unified Communication Deployment Audit

    High-Level Design 

    After we obtained full information about the infrastructure, we moved to a High-Level Design. Due to a significant number of sites, and various levels of proposed transformation at each site, the size of the working group on the client’s end reached 30 people at its peak.  

    The key factor at the planning level was to collect the business requirements from the management board as well as from the telecom operator that was supposed to become a global operator. 

    We used to meet regularly with the client’s representatives distributed across all continents, to work out the functional principles for the new telephone network.  

    We planned the numbering and the Callflow.

    Example of a Callflow of voice services

    Low-Level Design

    Once the High-Level Design was accepted, we started to prepare configurations. The goal of such an approach was to have a detailed plan before moving to the migration phase.  

    When working on Low-Level Design, we designed the addressing and Cisco CUCM, including:  

    • A detailed inventory containing the bill of materials essential for the migration; 
    • CSS;
    • Partitions; 
    • Route lists; 
    • Short numbering; 
    • DID; 
    • Schemes. 

    Take a look below to see one of the schemes we created.  


    Due to the strategic meaning of the project, we kept on meeting regularly with business representatives to present our solutions, answer all their questions, and have our work approved. 

    Migration of VoIP and PSTN interconnections 

    The final step was the migration itself. Business indicated 66 locations in which we migrated the voice system according to the prepared plan. The migration was made in a few steps described below:  

    1. Discovery – is understood as acknowledging business objectives and the proposed solution for each location.  
    2. Setup of Cisco Gateway and Call Managers. 
    1. Regular meetings with business reps to accept the solution.  
    1. Testing and troubleshooting in a single location. 
    1. Preparation of technical documentation.  
    1. Intense support on the day of launch (NBD Hyper-care). 
    1. Transfer of documentation and of knowledge to the client’s technical teams (Knowledge transfer).  

    How to migrate voice systems – a practical guide

    1. Learn about the limitations of used technologies

    The freedom to choose whatever technology you want for your organization becomes a burden at some stage of growth. Especially when every region has the right to do so. Different standards in every region make it impossible to introduce best tech practices across the organization. It also corrupts the possibility to compare the efficiency of regions. The Global SIP solution allows to standardize communication and provides the whole organization with comparable quality of voice services. To fit its purpose though, the system needs to be properly designed and configured. 

    2. Take care of all stakeholders  

    One of the requirements we mentioned was to switch to a global operator’s infrastructure. The operator has already had a business relationship with our client as well as their own vision for the migration. The operator’s vision, however, did not fulfill all business objectives of our client’s, and therefore, had to be reviewed. When proposing our solution, Grandmetric engineers had to win not only the client but also take care of their relationship with the operator who was one of the stakeholders. 

    3. Take time to design the missing link  

    Global SIP is a link between the IP network and the PSTN infrastructure. To use the potential of this connection, one needs to design it with the tiniest detail. We started our project with a High-Level Design in which we presented a high-level architecture of the system. Only after it was acknowledged, did we move further to building detailed schemes and configurations. For this reason, the conceptual phase and planning took much longer than the implementation phase. We knew that solid preparation and documentation will save us and our client a lot of stress down the road.  

    4. Run post-implementation tests!  

    After migrating all test locations, we made sure that the communication worked as expected. We also provided our client with intense post-implementation support.  

    Wondering if the transformation of voice systems or migration to a global operator could benefit your organization?

    Take a free pre-consultation with our Voice engineer and learn about your options! 

      Talk to our expert


      Marcin Biały Grandmetric

      Migration projects of legacy systems are not only a change from the technology standpoint. They’re also demanding planning and execution-wise. I’m pleased we managed to successfully work with a tight timeline as well as high technical demands both on the client, and on the operator side.

      Marcin Biały, Board Member at Grandmetric

      See also