Finally we look at choosing a VoIP provider.

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Carrier Services Infrastructure (CSI) is the foundation of telephony communications. It carries both public and private communications for all VoIP providers. When a business chooses a VoIP solution, it will then have its own sub-network of a larger CSI.

There are 5 different canada telegram CSI types: PSTN, DS, OC, HFC and Wireless. Here we take a look at what characterises these 5 types and how they are owned.


Public Switched Telephone Network (PSTN)
In 1876 Alexander Graham Bell made the world’s first voice transmission over a physical wire. When combined with switches and telephone exchanges, the PSTN began to grow as bundles of wire running between exchanges. PSTN supports VoIP over a Primary Rate Interface (PRI) line or over broadband DSL.

Digital Service Network (DS)
DS is a dedicated network dating from 1964. When a business took out a DS line, it had its own dedicated line – known as type T1 or T3. A T3 line would carry high-speed data, voice and video at 45 Mbps. DS carries VoIP over private dedicated network (PDN) channels.

Optical carriers (OC)
OCs are another type of dedicated network, introduced in the 1980s using fibre optic cable. Like DS, they support VoIP using PDN channels, but with OC3 or OC12 transports – OC12 carries 622 Mbps.

Hybrid fibre-cable (HFC)
HFCs were also introduced in the 1980s, using a mix of optical and coaxial cable to carry broadband content. HFCs support VoIP using broadband cable modems over dedicated networks.