October 06, 2005
VoIP architecture
VoIP systems can be divided into three major groups that include systems that have been developed from the traditional PBX platforms, systems evolved from the traditional data-switching networks, and VoIP systems that have been developed from scratch. Each system has its own merits, cost and implementation implications and can be used to achieve 99.999% availability.
The traditional PBX systems have consistently delivered 99.999% reliability that is now being used as a standard for VoIP systems. However, these legacy PBX systems operate independently of one another and cannot back each other up. Each PBX at a given site is in effect isolated from the rest of the network and is a single point of failure. It is a fragmented and centralized architecture.
Data-optimized switch platforms can also be used to transmit voice; however even though the bandwidth requirement of voice is small, it has a very low tolerance of delay. To develop a VoIP platform, a call control is implemented in a centralized server which is a single point of failure. The installation of multiple call servers can help to mitigate the risk of server failure but the call servers depend upon the availability of the IP network that connects remote offices. In the event of a WAN outage, survival mode features can be used to connect the IP phones. These features are optional and the voice quality is reduced. Setting up voice capabilities in a data network can lead to complexities that increase the difficulties in providing a high level of availability. Also, the reliability at every stage such as design and operation becomes difficult as several devices have to be integrated before one can achieve a decent level of voice quality using VoIP.
A voice platform created from scratch can leverage the inherent resilience of IP networks. IP voice switches can be used to distribute a voice system that runs on a peer-to-peer architecture, with more than one point of failure ensuring greater availability. A switch can also act as a standalone PBX capable of making best-effort calls using a failover PSTN trunk, in case the IP backbone is down. The switches work in tandem and are capable of providing PSTN access to a site that has its own switch out of order. This means that a native VoIP system can provide 99.999% of availability; the network will go down only in the event of a WAN outage or all the switches going down at the same time.
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