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  • Sneha Bisht


Conventionally, enterprises across the world use ISDN PRI lines to enable business communication. However, in recent times, businesses have turned to the SIP trunks for their enterprise telephony needs, due to its easy scalability and cost saving potential. A SIP trunk is an advanced network resource which enables voice calls on existing IP networks like internet connection or enterprise WAN.

While an E1 PRI line can support 30 simultaneous calls (channels) and about a 100 DID numbers, a single SIP trunk can support ‘n’ number of channels. Since the SIP trunk is a logical connection, the channels can be easily upgraded/ downgraded any time as per the business need without additional physical infrastructure.

How does it fare in India?

Telecom licensing guidelines in India significantly differ from the rest of the world. The Internet Telephony guidelines from the Department of Telecom allow telecom service providers to carry voice traffic on public internet, but with the following restrictions:

  • PC to PC; within or outside India

  • PC in India to Telephone outside India

  • IP based H.323/SIP Terminals connected directly to ISP nodes to similar Terminals; within or outside India.

Due to such regulatory requirements, telecom service providers in India provide a hybrid ‘SIP over PRI’ setup where SIP trunks are delivered on private IP networks of the enterprise with physical termination of the circuit at the customer premise. This ‘SIP over PRI’ differs from traditional SIP trunk across the world. However, it comes with a minimum of 10 channels which can be upgraded/downgraded any time, like its traditional counterpart.

SIP Trunks in India

SIP Trunks globally

Delivered over enterprise IP network

Delivered over the public internet network

Requires physical termination on the customer premise via a telephone cable line or an ethernet cable

Logical circuit, requires no physical termination

​IP PABX is required

IP PABX is not required

SIP Trunks for international calling

While enterprises are not allowed to use pure SIP trunking for nation-wide calls within India due to regulatory restrictions, it is ok to use it for international calls. VoIP based SIP trunk over high-speed internet connection or enterprise WAN network can be used to make international calls, without any regulatory challenge.

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