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Definitive Guide to SIP Trunk

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SIP Trunk is a fabulous technology. However, in India, VoIP and SIP Trunking have legal restrictions. VoIP phone systems work on SIP Trunking. However, in India, it is used very differently as compared to the rest of the world.

The right way to build a call centre requires a bit of planning. Apart from hardware/software & agents, the most critical part for call centre setup is the selection of the right telephone line.

A Telephone line is the backbone of any business for handling their customer service effectively.
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What is SIP Trunking

A SIP trunk allows your IPPBX to make calls over IP. One is private & other is public. Usually, SIP trunks provided over Public internet & not required physical termination at an organisation. That means the SIP trunk is a virtual connection.

It is one of the best phone lines to make & receive the calls from an organisation. It uses well-known industry standard protocol known as Session Initiation protocol SIP based on VoIP or Voice over Internet Protocol technology. The main advantage over the telephone line is handling the capacity of more simultaneous caller with scalability & cost-effectiveness.

SIP Trunking is a fabulous technology. However, in India, VoIP and SIP Trunking have legal restrictions. Voice over IP works on SIP Trunking.
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How does SIP Trunking work?

In India, due to TRAI or Telephone Regulatory Authority of India regulation, it is provided over private IP network & requires physical termination at the organisation.

Let’s talk about How SIP trunking works in India vs SIP trunk Globally.

SIP Trunk in India SIP Trunk Globally
It’s over a private IP network.It’s over public internet connection.
It is also known as PRI over SIP.Known as VoIP based SIP trunk or VoIP line.
It’s terminated as a physical telephone cable or Ethernet cable in an organisation.It is virtual. There is no physical termination required.
IP PBX is required to connect SIP trunk.IP PBX is not compulsory to connect SIP trunk.
Internet is not requiredHigh speed Internet is required
You can’t use it from anywhere. It can be used in your organization only.You can use it from anywhere as it is over the internet.
Common MYTH. In India, most of the people believe that they require a high-speed internet connection to setup IP PBX u0026amp; SIP trunk. This is entirely wrong in India.
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PSTN (Landline)

What we generally refer to as Landline is technically known as the Public switched telephone network PSTN. Only one simultaneous call is possible with regular PSTN Line. PSTN lines also have only one number. Homes and small offices generally use PSTN lines.

PRI Line

Medium size offices and call centres use PRI (Primary Rate Interface). A regular PRI line offers 30 simultaneous calls (channels) and 100 numbers (generally). The phone numbers that come with a PRI line are also known as DID (direct inward dialling) numbers.

PRI lines are more suitable for SME because it’s cost effective and very technologically advanced. If the requirement of simultaneous calls is more than 30 channels, then the company has to go for multiple PRI lines.

SIP Trunk

India, many Telecom providers, have also started to provide SIP over PRI. PRI-SIP is a kind of SIP trunk. However, the best part is that it comes with a minimum of 10 channels. It provides flexibility, which is not available in PRI lines.

It is becoming popular over PRI in India at a very rapid pace.

The most significant advantage of SIP trunk over PRI is that the number of channels can be increased or decreased without changing physical lines.
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SIP Trunk versus Traditional PRI lines

SIP trunk has various benefits over the regular traditional

SIP TrunkTraditional PRI Line
Simultaneous call capacity can be upgraded or downgraded on single SIP trunk.PRI line has 30 channel. Multiple physical line required to increase the simultaneous call capacity.
It’s connected to Ethernet port or LAN port of IP PBX, which is cheaper.It’s connected to PRI port of IP PBX or EPBX , which is costlier. To connect multiple PRI lines, multiple PRI port is required on IP PBX or PABX which turns costlier.
Easily scalable.Not easily scalable.

Using SIP Trunk to call outside India

VoIP based SIP trunk is used to make international calls from India. It require high-speed internet. Vonage, RingCentral, Mitel etc. are the VoIP based SIP trunk providers. Here is a list of VoIP based providers for International Calling.

While pure SIP trunking is not allowed in India for Local Calls (within India), It is perfectly legal to use it for International Calls.
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SIP Trunk Setup

Setting up is more straightforward and cost-effective. However, since it is based on IP & digital, to get the ROI or Return of Investment of every component in telephony infrastructure should be digital.

There are mainly three components required to setup SIP Trunk effectively.

  1. IP PBX or Internet Protocol-based Private Branch Exchange.
    1. SIP trunk required to terminated to IP PBX. IP PBX is a critical element of telephony infrastructure. IP PBX must have features like IVR, ACD & CRM integration to get the benefits of SIP trunk. Don’t use IP to Analog converter to stick with old PBX.
  2. IP Phone or Softphone
    1. Use IP Phone & softphone to get the best sound quality with SIP trunk. A softphone is a software used to make & receive calls from a computer. Headsets required to communicate using a softphone. Don’t use the analogue phone by using IP to analogue converter or FXS Gateway or Foreign Exchange Station Gateway.
  3. Local Area Network (LAN)
    1. Proper planning of computer networks is required to get the benefits of IP telephony infrastructure along with sip trunk.
    2. Security devices like Firewall is a must to secure your IP Telephony infrastructure & data network.
When digital transformation is done right, it’s like a caterpillar turning into a butterfly, but when done wrong, all you have is a really fast caterpillar. – George Westerman
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Benefits of SIP Trunk

  • Scalability
    • SIP trunk starts with minimum ten channel & can go to up to 1500 channel without any hardware changes. Scaling up or scaling down is easy
  • Cost Savings
    • SIP Trunk saves money in two ways.
      • Buy what we need. SIP Trunk plans are always very flexible. Not like PRI. SIP trunk does not require costly gateway device, like PRI. (PRI lines need PRI Card or PRI gateway, which is an extra cost).
  • No Special Cable Required
    • A SIP trunk (outside India) is a virtual connection and does not require any Physical cable termination at office premises.
  • ACD or Automatic Call Distribution & IVR or Interactive Voice Response
    • ACD works well with SIP trunk due to multiple channel & multiple DID (Direct Inward Dialing) IVR played on SIP trunk is different customer experience than played on PSTN analogue line due to its crystal clear voice quality.
  • DID (Direct Inward Dialing) & DOD (Direct Outward Dialing)
    • Different telephone numbers for various departments or people in the organisation. SIP trunk provides 100 DID/DOD & you can upgrade that by request. DID refer to inbound number & DOD refers to an outbound number.
  • Digital Voice Quality
    • It is provided over an IP network or digital network, and voice quality is crystal clear compared to PSTN (Public Switched Telephone Network) line or analogue line.
  • Lightning Fast Dialing.
    • IT has a faster call connection time compared to PSTN & GSM line, which turns into higher productivity.
  • Easier Maintenance
    • No need for separate telephone wiring for multiple PSTN analogue line & analogue phones. Voice & Data network combined, with a single one.

SIP Trunk Providers

In India, there are more than a few operators providing sip trunking service. Services offered by these providers include lots of other telephony offerings. Here is a non-comprehensive list.

  1. For India Calling (Local – PRI SIP)
    1. Tata Teleservices
    2. Vodafone
  2. For International Dialling (Native SIP Trunk)
    1. Twilio
    2. Vonage
    3. voxbone
Unified Communications or UC deployed in combination with IP PBX, CRM or Customer Relationship Management and u003cstrongu003eSIP Trunku003c/strongu003e takes customer experience CX to a different level.
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Comments Rating 5 (1 review)


  1. Milind Natu November 28, 2020
    • Kimaya Patil December 4, 2020

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