Voice over IP: Systems and Solutions
Provides an extensive look at Voice over Internet Protocol (VoIP) and its effects on the communications industry.
TABLE OF CONTENTS Voice over IP: Systems and Solutions
5.2: Interface Requirements
5.2 Interface Requirements
The way in which global telephony applications are structured presents a need for international standards to be specified for two kinds of interface.
The first kind is a more general case of the inter-domain example given above, called the 'horizontal interface'. The second is the set of interfaces between technologies that are 'stacked' on top of one another in a series of layers, to provide an overall 'service stack'. These can be referred to as 'vertical interfaces', as shown in Fig 5.1.
Figure 5.1: Horizontal and vertical interfaces.
5.2.1 Horizontal Interfaces
5.2.1.1 Inter-Domain Interworking
The simple example given above referred to the interface between the domains of different service providers. To request, connect, maintain and terminate a call across two or more domains, the data necessary for these operations has to be passed between the domains concerned. Both the format of the data and the way in which it is passed between domains have to be standardised. To date, VoIP solutions deployed in the market have relied upon the existence and capabilities of the public switched telephone network (PSTN) to provide these functions. It is apparent that these issues will have to be resolved for VoIP-based protocols in order for them to supplant the existing PSTN circuit-switching technology.
5.2.1.2 Inter-Technology Interworking
As well as the need for standardised interfaces between domains under the control of different service providers, the requirements for interworking between the different technologies, which each of these domains could be using, have to be...
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