How Does VoIP Connect To Landlines?

Posted on: 2015-09-28 | Categories:VoIP VoIP Hardware VoIP Phones VoIP Services VoIP Technology

Do you want to know how VoIP connects to landlines? In this short article you will learn all about it.

VoIP is a substantial upgrade to the phone call as we know it. Even though the user experience remains the same, there are a lot of differences between VoIP and the old PSTN system.

VoIP is the basis on which future voice communication tools will be built and most of the world will switch over to VoIP over the next couple of decades.

There is a fundamental difference between the landline phones that use copper lines to transmit phone calls and VoIP which delivers voice calls over the Internet.

The PSTN relies on circuit switching technology that has remained largely unchanged for the better part of a century. Although there have been improvements and efficiencies, the underlying basics remain the same.

PSTN – TDM Circuit Switching

When a call is made from a phone number using PSTN, circuits along the way connect the 2 people involved in the call. The connection has to be maintained for the entire duration of the call Regardless of whether it is a few miles apart or thousands of kilometers.

It is for this reason users have to pay high prices for long-distance or international calls. In addition, various operators charge interconnection fees when competitors terminate calls on their network that can vary substantially for international calls.

In a sense, the end-user is renting a portion of the phone infrastructure for the particular time period. No wonder long-distance calls are so expensive!

Phone carriers invest a lot of capital laying down lines even to remote corners and thus, distance has a big impact on how calls are charged. This is the biggest reason for area codes – operators use it as a basis to determine how to charge for a particular call.

VoIP – Data Packet Switching

On the other hand, VoIP relies on the same packet switching technology that powers the Internet. Voice signals are turned into data packets – each of which contains a part of the content as well as the address of the final destination.

These individual packets are then sent through multiple hops across different servers until they reach the device at the other end. They are then reassembled according to the packet instructions, converted into voice signals which are then heard as words by the other person.

Since these packets are transported individually – and each may take a different route to the destination – there is no need to maintain a complete connection between the two ends. Fundamentally this makes VoIP much cheaper when compared to a traditional phone call, especially over large distances.

Why Connect VoIP and PSTN Networks?

As we can see, the underlying technology for VoIP differs substantially from PSTN. Calls from a VoIP number to another VoIP number are easy enough to make, irrespective of the actual device used for the call.

VoIP calls can be made from a computer to another computer, computer to smartphone/tablet and vice versa as well as from an IP phone to a computer/mobile device. All these calls will be either free or very inexpensive as they do not travel over the PSTN at any point.

However given the number of landlines still operational around the world, people who use VoIP will have to make calls to landlines quite often. Not all members of a family or a group of friends will be using VoIP and so one person will have to call another on a landline.

The same is true for businesses that have to contact customers or suppliers who do not use VoIP. Even if the other party is using VoIP, they may be traveling to a location where landline offers the only means of access. Such situations are not uncommon even in countries where VoIP usage is extremely high (and there are very few of those at present).

How to Connect Different Technologies

When a VoIP call is made to a landline number, the call travels for a portion of the time over the PSTN. The amount of time the call spends on the PSTN usually determines the price of the call (apart from the base charges for any VoIP to VoIP call).

At the point where it enters the PSTN, a process called address translation takes place. It means that the IP address is translated to the identifying phone number of the called party to complete the call. It is similar to the process used to convert email IDs and website links to IP addresses on the Internet.

Since VoIP utilizes packet switching technology, every VoIP device that is connected to the Internet is assigned its own IP address. When a call is made from a VoIP end point to another, there is no need for address translation as both devices can be identified by their IP addresses. However when a call is made to/from a landline, address translation is needed to act as a bridge between IP addresses and phone numbers.

Different Rates for VoIP – VoIP and VoIP – Landline Calls

The most popular VoIP services for consumers such as Skype generally offer free calls to other users on the same network, as long as they are using the computer or mobile device to make the VoIP call.

Calls made to landlines are generally charged more and billed separately to the customer. The reason for this is because a portion of the call travels over the PSTN, incurring charges from phone operators.

As VoIP adoption increases, the number of calls that have to be terminated on the PSTN is falling by the day. Even in areas where people still use landlines, phone operators are switching out the underlying infrastructure over to VoIP.

It relieves them of the burden of maintaining aging copper networks that can often require expensive repairs. Combined with the growing popularity of mobile VoIP applications and services, fewer calls are made to normal landlines on a regular basis.

Nevertheless, it will be sometime before all PSTN networks are phased out in every country and VoIP becomes the standard.