Centralized Cloud Connector Edition for multi-branch Enterprises


In an earlier blog post, I spoke about the Sonus Cloud Link solution and how customers can leverage the simplicity of install and management of Cloud Connector Edition (CCE) embedded within the SBC 1000/2000 for remote offices.

Depending on the size of your business, there can be value in having CCE instances at remote offices, especially to reduce latency associated with users connecting to a Skype for Business Mediation server role within the CCE. In this blog, I’ll focus on what an enterprise should think about doing as the business grows or perhaps is already large enough that the CAPEX of deploying a CCE at every location, especially for smaller locations starts to look cost prohibitive.

The good news is that while Microsoft doesn’t support their PSTN access across geographic boundaries (e.g. you can’t get a UK number for an office in the US for an additional customer service line, etc.), there are ways of solving this issue in a cost effective manner using hybrid. In addition, the approach outlined below will customers a more robust telephony network without downside.

A few things to consider when deploying remote sites such as does the office have:

  1. ExpressRoute or access to a similar QoS guaranteed link?
  2. A Software Defined Wide Area Network (SD-WAN) Solution?
  3. SIP trunking or traditional PSTN trunking?
  4. Requirements for legacy TDM infrastructure, whether that’s a fax machine, overhead paging or connectivity to an on-premise PBX?

Before I get into how best to approach this, talking about the best topology is in order. In Diagram 1, we have 3 distinct areas, edge, core and service.

Diagram 1:

We see on the bottom (edge), 3 distinct offices in the United States (San Francisco, Chicago, and New York), but they are fairly spread out across the USA. Each of the locations are equipped with a qualified SBC or Gateway. If the offices are in locations with TDM, you can go with a product that provides gateway functions (many times an SBC provides Analog/BRI/PRI embedded as does the SBC 1000/2000), if the location also offers SIP trunking, an SBC will work just fine too and doesn’t need the TDM ports unless you’re connecting to a legacy infrastructure.

In the core, we see redundant SBCs as well as redundant CCE instances which are called PSTN sites. Each PSTN calling site can support up to 1,500 simultaneous calls and are distributed across CCE pools (500 calls each) in an n+1 fashion (in this case, 3 with 1 to spare). The SBCs should have the ability to scale to the number of simultaneous calls. While the diagram shows physical SBCs, these could just as easily be software based ones like the Sonus SWe. Each business may have different types of calling patterns, which may necessitate a traffic study (e.g. an analysis of CDRs). As your enterprise goes from a legacy infrastructure to a UC one, these parameters can vary. Also if deploying Cloud PBX, the PSTN Conferencing is included with the E5 license which could vastly reduce the number of channels required if your enterprise is used to a lot of collaboration.

Now let’s dig into the inbound and outbound call flows:

Inbound (Centralized Trunking)

  1. External User Calls 415-555-1234 and calls come into centralized core SBC via Service Provider via SIP trunking
  2. SBC routes 415-555-1234 to the PSTN Site 1 with the CCE as it’s determined that the user is a Cloud PBX user
  3. CCE routes the signaling up to the Cloud PBX service and determines that the user is in San Francisco
  4. CCE tells the Core SBC to route to route media to the Skype for Business user on wide area network (WAN)

Inbound (Distributed Trunking)

  1. External User Calls 415-555-1234 and calls come into edge SBC/gateway via Service Provider
  2. Edge SBC routes signaling to PSTN Site 1 with the CCE as it’s determined that the user is a Cloud PBX user
  3. CCE routes the signaling up to the Cloud PBX service and determines that the user is in San Francisco
  4. CCE tells the edge SBC to route media to the Skype for Business client on local area network (LAN)

Outbound (Centralized or Distributed Trunking)

  1. Internal User Dials 510-555-1234 and signaling is routed to PSTN Site 1 with the CCE
  2. CCE determines that this is not a Cloud PBX User and routes the call to the core SBC
  3. Core SBC uses Least Cost Routing (LCR) to determine if the calls should go out the centralized SIP trunks or the edge SBC/Gateway
  4. User is routed out appropriate trunk


  1. User in San Francisco dials 911
  2. Signaling is sent to CCE which then asks the core SBC where to route the call
  3. Core SBC tells CCE to route calls out of the Edge SBC in San Francisco so it hits the appropriate PSAP (Public Service Answering Point) with any additional ELIN information as required (and if supported by Gateway).

Deploying your enterprise hybrid telephony in this fashion has considerable advantages

Centralized Core SBCs that scale and that support multiple service providers allows for tremendous cost savings over having POTS or fractional T1s at the remote locations.

Some service providers are not even allowing for new TDM circuits, which means that offices that are required to get SIP trunking which then would require MPLS as well. Leveraging deterministic routing and SD-WAN solutions over an internal network could provide significant savings (see VellOS)

Centralized CCE (especially if factoring in redundancy) means fewer CCEs. If you’re a company that has hundreds of branch locations, imagine the patching, maintenance and power requirements of all of these Windows Server 2012 R2 operating systems and COTS (Commercial Off The Shelf) server or appliances. Also as Cloud PBX updates, CCEs in turn will be updated and that will take additional bandwidth, but more importantly more updates on more CCEs equates to additional monitoring (likely at different times) to ensure that an updates go smoothly.

Edge SBCs whether physical or virtual not only secure those remote sites, but often serve as a way to retire older PBX and key systems while still providing support for analog devices.

That’s a lot of advantages for an enterprise that may still be “on the fence” about Cloud PBX. Sonus core and edge SBCs (and Gateways) with their robust embedded routing engines can really turbo charge your Microsoft Cloud PBX environments. Check out our documentation for specific configuration examples how to accomplish the 4 scenarios described above.


  • MathWorks estimates that through the automated provisioning and call routing features of the Sonus solution, the company has freed up more than 250 IT staff hours per week for more important projects.

    MathWorks is the leading developer of mathematical computing software for engineers and scientists. Founded in 1984, MathWorks employs 2800 people in 15 countries, with headquarters in Natick, Massachusetts, U.S.A.
  • The industry-leading performance and scale of Sonus' SBC 5100 allows us to maintain a competitive edge in the market while delivering exceptional customer service. 

    Smart Tel is a major player in the Singapore telecommunications industry and aims to develop its global presence with new offices in Australia, Thailand, Indonesia, Philippines, India, South Africa, the US and the UK, with cost effective, easy-to-use and scalable telephony solutions.
  • We wanted to work with an industry-leading SBC vendor and our market analysis indicated that Sonus was the clear choice for this partnership.

    (GCS) is a software company founded in 2006 by Neal Axelrad and Jay Meranchik. GCS' goal is to be the best company in the marketplace. We are privately held and have offices in New York & New Jersey USA.
  • Sonus made the deployment, integration and migration to Microsoft Lync easy. 

    We are experts in identifying and delivering flexible communication solutions that scale and adapt to your business demands, empowering your business to do more, faster and with less effort and cost.