PDF of this tutorialATM, from the start, was designed to be a multimedia, multiservice technology. Although ATM has been accepted by service providers for its ability to deliver high-speed data services, until recently its potential for deploying voice services was overlooked. With the competitiveness of today's market though, network operators and service providers have been continuously striving to reduce operating costs and lift network efficiency and have turned to the ATM network to achieve these goals.
With hundreds of millions of dollars of ATM equipment infrastructure in the United States alone, service providers have recognized that significant economies of scale can be achieved if the data traffic and voice traffic are integrated onto a single network. In order to achieve this, service providers have started to use the circuit emulation services (CESs) of ATM switches to carry full or fractional E-1/T-1 circuits between end points. These CES mechanisms treat voice as a constant stream of traffic encoded as a constant bit rate (CBR) stream. In actuality though, voice is a combination of bursts of speech and silence and this increases the complexity of VoP.
The ATM Forum and International Telecommunications Union (ITU) came up with several advanced mechanisms to improve the efficiencies of transporting voice traffic, including:
- ATM trunking using AAL–1 for narrowband services
- ATM trunking using AAL–2 for narrowband services
- IP over ATM (AAL–5)
- Loop emulation service using AAL–2
Table 1 summarizes the benefits of utilizing the different methods for transporting VoATM.
| Standards | Voice Compression | Silence Removal | Channel Suppression | Switched Concentration |
| CES | No | No | No | No |
| BD–CES | No | No | Yes | No |
| ATM trunking using AAL–1 | No | No | Yes | Yes |
| VoIP over ATM | Yes | Yes | No | No |
| AAL–2 | Yes | Yes | Yes | Yes |
