What is SIP Trunking? SIM trunking all details with examples.

Sip Trunking

With the growth of many business across glob. SIP trunking in Voip is the new and convenient method of communication. Almost every business requires large calling volume. Sip trunking is the technology which makes VoIP suitable for business. This leads to the need of a PBX and a high capacity connection for voice, fax etc.

SIP trunking have two parts one is SIP and other is trunking. To explain better we will explain each part in detail.

The full form of SIP, is session initiation protocol. It is a signaling protocol. What is signaling protocol ? There are two types of channels/paths are in communication. One is signaling channel and other is media or voice channel. SIP does signaling for setup a media session. A media session can be for voice, video fax etc.

For setup a session , sip messages carries , media end point information in session description protocol (SDP).

SIP Uses , service of underlying TCP/IP or UDP/IP.

Trunk is a very common term in telecom. You have heard about in olden days a long distance call was called a trunk call. A group of communication lines is trunk, lines can be shared by many callers or agents. For example in call center, all customers dials a same customer support number. But at the same time multiple customers can be served. Because for each call a line is allocated from the trunk. The telephone line in our home for PSTN is a trunk with one line only.

Next step is, to configured trunking details in the IP PBX.

Now call from an extension to the external phone number. IP-PBX , do the SIP signaling with the trunk provider. As a result VoIp call is setup with the external phone number. The external phone number may be a voip number, pstn or a mobile phone number. If not a voip number then there will be conversion from VoIP to PSTN. You do not need to worry about this conversion. Trunking provider take care of all the necessary conversion.

From the name it looks that only SIP protocol is sufficient. But it is not true. SIP alone can do only signaling, for a complete call other VoIP technologies works together. This includes streaming of media over IP network.

The first question comes here what is pri? We all have seen traditional phone lines coming to our office or home. These lines are called Primary Rate Interface (PRI) lines. On one end a line connects to the handset and other side it connects a telephone box. Following is a comparison of Pri lines with the SIP lines i tabular form.

SIP Trunk PRI Relatively a new . Old and traditional lines. No special hardware is required. Ethernet or Wifi connectivity is only required for SIP trunk. Special hardware required. The hardware is a PRI card. The system using card, also needs to install the software or driver for the card. There is no type all connections uses same IP lines for communications. There is no limitations on channels. A pri line can be of T1 or E1 type. T1 have 24 channels and E1 have 31 channels. Maximum bandwidth for T1 is 1.544 Mbps and for E1 2.048 Mbps. Same IP network, there is nothing like voice and data channels. Signaling and actual voice data flows on separate channels. Bandwidth is not guaranteed. Speed depends on underlying IP network speed. Bandwidth is guaranteed. Low cost and need no dedicated lines. High in cost and need to maintain separate lines. Easy to scale, when concurrent calls increases. Not easy , as scaling requires to add more physical lines. SIP trunk provider can provide redundancy by rerouting traffic in case on failure to another SIP server for VoIP calls. There is only a single switching center which connects to the PRI line and calls can not reroute , so not redundant.

Setup Fee: Initially moving to new providers need to setup connections , this may take some significant time. The user might not be expert in technical stuff for setup voip. This may lead to hire for an expert or the sip trunking company will setup and charge an amount.

Concurrent Calls: Capacity is always a major factor for deciding cost. SIP trunking comes with the advantage , where capacity is not limited and easy to scale.

Business needs advantages of flexibility and cost. With Voip, no limit on channels as PRI lines have. A business can choose option on usage basis. Can pay minimum for only one channel and on needs on can pay for 1000 channels.

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