The Challenges of Centralized
Call Flow with SIP Trunking

For many organizations, the ability to centralize call flow provides many benefits.  There can be significant cost savings reducing monthly costs by up to 50%.  And, it can also reduce the amount of hardware deployed at remote locations.  But, like with any technology, there are some special considerations needing to be addressed before final solutions can be designed.


  • E911 – When centralizing call flow at a primary location, remote sites no longer have local telephone lines which have traditionally been utilized for e911 services. Instead, the call trunks are located at another site.  Calls for help can send emergency services to the wrong physical site if not addressed.  Not only do e911 services need to be set up correctly out of the centralized trunk, but the enterprise telephone system must also be able to send out accurate information to complete the solution.  This can be especially challenging for organizations with users traveling between sites.  It can easily be set up, but some planning needs to be addressed.


  • Redundancy – Centralizing call flow can generate many benefits, but it also puts all your eggs in one basket. If the central site hosting the call flow for the enterprise goes down, all the remote sites can be impacted.  Therefore, a business continuity plan needs to be included in this solution to ensure there is a plan B should something catastrophic occur.  Most SIP carriers do provide such solutions, but they can differ significantly from design and cost standpoints.


  • Bandwidth – It is critical there is available bandwidth between the central site and the respective remote sites to be able to support this additional call flow. For most organizations, it can be assumed that each concurrent call path will consume 100 kbps of bandwidth to deliver the voice call.  If this bandwidth is NOT available, it can cause inadequate voice quality.  It is also recommended there is substantial up and download speeds to support the voice calls.


  • Class/Quality of Service – Along with having enough bandwidth to deliver the voice calls, it is also highly recommended CoS/QoS is established between the sites. This ensures the voice traffic will take priority over other applications, especially when the bandwidth becomes congested.  You do not want a large file download to consume too much bandwidth leaving little bandwidth for the voice traffic.


  • Telephone Number Porting – It has been our experience most telephone numbers can be ported to a centralized trunk, but there have been circumstances where this is not the case. The one reoccurring theme for telephone number porting issues is with smaller, independent telephone companies often located in very rural areas.  It is important to verify telephone numbers can be ported prior to going too far down the path of designing your solution.  There are secondary options if telephone numbers cannot be ported, but these can provide some limitations.

For many organizations, centralizing call flow can deliver a series of benefits including the reduction of CAPEX/OPEX, increasing productivity and increasing the customer experience.  But, there are special circumstances needing to be addressed early in the process to ensure such a solution will work for your organization.  If you feel such a solution may be beneficial to explore, maybe it is time to reach out to Orion Communications.  You can also find many positive examples of the outcomes in case studies posted on our website BLOG.