VoIP SIP Trunk and its application


With increase in average broadband speed and its usage, VoIP has become preferred medium of communication for large enterprises. As the communication happen in digital form via IP, you can use IP communication for text, voice and video communication, well in that case name will change from “Voice over IP” to “Video over IP”.

Let’s check the technology, its usage, benefits and its limitations.
To setup a basic VoIP communication, businesses need an IP PBX, LAN Setup, IP phone or SIP phone. An IP PBX(private branch exchange) is local telephone switching with an enterprise that switches calls between the users with the help of extension line. Few IP PBX also have capability of a VoIP gateway, they can also switch calls between a VoIP call and a PSTN call, or between two traditional telephone users in the same way that a conventional PBX does. Note – In many countries mixing of PSTN and VoIP is not permitted

What is SIP – SIP (Session Initiation Protocol) is a signaling protocol widely used in multimedia communication sessions such as voice and video calls. SIP is one the protocol to enable VoIP. It defines how messages can be send between two endpoints and controls the call initiation, termination and signaling. It is also used for other data applications like video conferencing, instant messaging, media distribution. SIP was developed and standardized by Internet Engineering Task Force (IETF).

A typical call flow in VoIP & role of SIP and SIP trunk How VoIP , SIP and SIP trunk works


What is SIP Trunking – In analog communication “trunks” means a dedicated line analog line from the service provider to the enterprise. In IP communication, A SIP trunk is a service offered by an ITSP (internet service provider) to use SIP to provide a unified communication to the enterprises, the customer just need to have a SIP enabled PBX or IP PBX.
Note – VoIP gateway and SIP gateway is not permitted in India and few middle east countries (check details)

Why people prefer SIP trunk?
  • As call happens over VoIP, it saves money on long distance service
  • As SIP trunks connect directly to your ITSP without traversing to PSTN, you can completely eliminate IP-PSTN gateways. Few ITSPs also host a PBX for customers, so substantial cost is saved.
  • Eliminate a PRI connection - With a SIP trunk, you don’t have to to buy PRI line. Instead, you can just buy the bandwidth from ITSP
  • Multiple mode of communication You can use it for audio & video conference, instant messages etc.
    Limitations of VoIP calling
  • 1. In few countries like India the interconnection of PSTN & VoIP calls is not permitted, you can VoIP only for internal communication (check details)
  • 2. For small and medium enterprise, who just need voice calling or call center setup the SIP call is not advisable as initial setup cost be too high.
Solution of small and mid-sized business
In India and middle east countries, where interconnection of VoIP and PSTN is not permitted, PSTN based Cloud Telephony is a best solution. Businesses just have to pay monthly charges and they can start a full-fledged contact center within 24 hrs.

What are the major differences between a PRI and SIP Trunk
PRI SIP Trunk
PRI (Primary Rate Interface) is a physical connection to the PSTN over a dedicated line that only serves voice transmission. SIP (Session Initiating Protocol) Trunk is a connection between ITSP and enterprise, it can be used for voice, chat and video
It uses circuit switched model for making voice connections between people Uses a packet switched model for making communication
Number of simultaneous call depend on number of channels. Typically, PRI comes with 30/ 23 channels based upon E1/T1 Number of simultaneous call depend on bandwidth, just need take extra bandwidth if you want to increase number of calls
Number of simultaneous call depend on bandwidth, just need take extra bandwidth if you want to increase number of calls QoS depend on bandwidth and number of users
    About Us
  • Ozonetel is a pioneer of cloud telephony in India and a multichannel cloud contact center solution provider. Our solution is deployed across industry, few of our trusted customers are Bigbasket, Shaadi.com, Zomato, HUL, Abhibus.