Future Networks

A centerpiece for voice infrastructures

If companies switch to SIP trunks, they should acquire a PBX as well. It is a decision that will save them more than just voice channels.

Many companies operate their voice infrastructure locally per site. An IP changeover is the best reason to centralize this infrastructure and reduce the number of voice channels.  

"Central" is the magic word when it comes to operating e-mail servers and business applications in big companies. But when you talk about voice infrastructures, many IT departments still think "locally". In the ISDN age, there was usually a PBX (private branch exchange) at every company site that was connected via one or more ISDN (Integrated Services Digital Network) lines with the old telephone network (PSTN). As a result, it cost a lot of money to operate it: the IT department had to maintain each PBX individually. New connections had to be booked and installed at each site. "These drawbacks are magnified when you are talking about inhomogeneous architectures", Jörg Fischer and Christian Sailer write in their book "VoIP Praxisleitfaden" (VoIP Practical Guide). With this, they mean either different systems, different system versions or differently configured systems.
Entry into the All-IP age now provides companies with the best opportunity to switch their voice infrastructure, because voice no longer requires special hardware. It runs like e-mail as an application on servers and communicates via data networks. It also makes absolutely no difference where the server for this application is located.

Company networks already use standard IP

Big companies have been using the basis for centralized IP telephony for a long time now. The cross-site network (Wide Area Network, WAN) uses the IP protocol anyway, thanks to MPLS technology. And many already use Voice over IP (VoIP) via their LAN (Local Area Network) locally as well. A study conducted by the German technology publication Computerwoche found that 64 percent of big companies in Germany, Austria and Switzerland use IP-enabled PBXs. What is more: for IP-based lines, companies usually have to upgrade or even replace their local IP PBXs. An option here would then be to implement one large, central IP PBX right away, per continent, for example. Or even better: two in a redundant structure to provide back-up support.  
The benefits of central voice infrastructures are clear: companies can significantly reduce the operating costs for their telephony. Firstly, fewer systems are easier to maintain. Secondly, the IT department manages all communication services and devices company-wide via an online portal. Finally, the company requires fewer voice channels for simultaneous telephone calls.

"Channel-sharing" for sites

There are two reasons for this: first, a local PBX connects external calls to the public network directly at the company site. With an ISDN primary rate interface, for example, there are 30 voice channels available to do this job (although they may never be needed). Any number of channels can actually be booked on IP-based PBX lines or SIP trunks, but the IT department will also factor in a certain buffer here.
A central IP-based PBX, on the other hand, communicates via the existing company data network with the on-site devices and connects calls centrally via an SIP gateway to the carrier's IP network. This means that the company sites share the central voice channels and, therefore, the "buffer". The number of channels required decreases.

Internal telephony in the internal network

The second reason involves the internal calls between the company's own sites. Local PBXs send these calls just like a normal call via the carrier network. If a WAN is used to make calls, the central PBX actually connects the internal calls, but the devices communicate with one another directly via the company network. For this reason, internal calls do not require a gateway to the public network. The number of voice channels required also declines as a result. In turn, the required bandwidth in the company network will increase – for both internal and external calls. The total costs fall nonetheless.  
VoIP switch: on-site becomes central voice infrastructure
Centralized voice infrastructures offer an additional benefit: unlike local SIP trunks, special products for central SIP gateways make it possible to port the numbers of all ISDN and analog lines – regardless of the line type and regardless of whether the primary rate interfaces use their own call number blocks or a single shared block. As a result, employees can take not just their personal extension number with them when they change their local workstation. They can now do it anywhere in the company.

Unknown potential

Companies can either operate their central PBXs themselves and let a service provider handle the management. Or they can procure a "hosted PBX," a complete system from an external private or public cloud. According to Computerwoche, however, only every 10th big company in Germany, Austria and Switzerland makes calls via the cloud. The situation is similar worldwide. In The SIP Survey 2015, only 5.5 percent of surveyed companies (mainly larger companies) said they used cloud-based voice services.
One key reason for this hesitancy: security concerns. However, voice infrastructure centralization can actually boost IT security. Companies simply need session border controllers set up upstream of the central PBXs, instead of numerous local ones. You can read more on this and IT security with Voice over IP in the next article from our Future Networks Perspective.

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