About VoIP

Revision as of 12:36, 21 August 2013

VoIP is an acronym that stands for Voice Over Internet Protocol, or, as the common user would name it, phone service over the Internet. It is a technique that brings communications at another level, allowing you to use an Internet broad-band connection to make calls instead of using Plain Old Telephony System (POTS). Service providers may allow you to call only the persons that are under the same network and some may allow you to make a call to anyone who has a analog or digital telephone line, no matter if we are talking about a local, long distance, mobile or international call.

There are two ways of using this technology: either by replacing your old phone with a new one that supports VoIP or by using an adaptor to connect the present phone to the VoIP network. No matter what solution you consider, there is also the possibility to disconnect it from the present network and making a new contract with the VoIP service provider or to keep them both. We will see later why anyone would choose an option or the other. VoIP converts the voice signal into digital signal that goes through the Internet until it reaches the called party. Then it is reconverted and outputs into the telephone as normal voice. This is convenient because you can speak using a telephone. The need of replacing the telephone with another type of hardware does not exist.

Why use VoIP?

This is the first question that comes when migrating to another service. The main advantages of using this new technology are:

• lower costs
• increased functionality.

Lower costs

But how low are the costs? It depends on the provider that you choose. There are different ways of charging. In some cases, phone calls are free within the local network. This is used when a provider already has the network system (e.g. is a Internet ISP) and the overall consumption of the bandwidth supports this feature. Notice that a local network it is not defined by a geographical area, but rather by your options. To explain this better, I will use an example: let’s say you belong to the X VoIP provider’s network. But you go in vacation somewhere else, possibly in another country. If you have an Internet connection, all people calling you from your city will not be charged and all the people you call and are in the city too. Another way you could be charged is a monthly flat fee that also may include free minutes in your network, another network or with some telephone numbers. You don’t have to use a telephone to speak over the Internet. An alternative is a headset and a microphone plugged into your computer and specialized software.

Increased functionality

The telephone only needs an Internet connection to work. This means that you can take the phone anywhere with you and still be able to make and receive calls. You may also have some advantages like saving a conversation to listen later, check the availability of a person. Practically, these are just of a few because VoIP’s functionality is software, depends on protocols and therefore can be easily changed or updated without the need of purchasing a new hardware every time you want a new service.

You will have an idea of how IP telephony works after reading the following example. Let’s assume that George wants to call Mary. They are subscribers of the same telephony network. George’s phone has the address 192.168.101.5 and Mary’s 192.168.101.6. These are the IP addresses and every phone of the two knows about each others address. George picks up the phone and calls Mary, as usual by dialing her number. Mary’s phone starts ringing and, when she answers, her telephone sends a connect message to George’s phone. Once the connection has been established, packets containing data (voice) are sent from one phone to the other. When they are finished talking, George puts down the phone. In that moment, a disconnect message is sent to Mary’s phone which responds with a release message. This is the basic idea of a VoIP phone call. Of course, things are a little more complicated when a gatekeeper is used, or the users calling are not in the same network as the ones that they call. But there is nothing to worry. It is all being taken care of by the data network, that is the Internet and by the service provider. For a typical user, things will work this way every time you make a call.

IP telephony is also known as packet-switched telephony. Instead of the normal circuit-switched voice lines used in analogue connections, VoIP packets are sent from phone to phone. In the Internet, packages may not come in the same order that they are sent, but they are numbered, helping the application to easily reconstruct the message. But in voice and video calls this is very important. Messages have to come in the same order or at least the section that handles the reconstruction of package order has to work in real-time. This can cause an effect called increased latency. For this not to happen special protocols for VoIP have been developed. These are used to carry data over the Internet, handle the way the two terminals understand and communicate with each other. Although these protocols help, the latency problem still remains. In networks with 256kps or more bandwidth, there is no problem, but if you have less it is very difficult to ensure minimum latency and time order of the packets. VoIP is designed to totally replace PSTN (Public Switched Telephony Network). Originally, these lines were analogue, nowadays they are almost entirely digital.

VoIP protocols

The PSTN is designed after a lot of standards. This applies to VoIP protocols as well. Below you will find a list with the most common protocols:

• H.323
• SIP (Session Initiation Protocol)
• Megaco (H.248) and MGCP (Media Gateway Control Protocol)
• Skinny Client Control Protocol
• MiNET
• IAX
• Skype

Network reliability

Another issue about VoIP is its’ reliability. A normal PSTN telephone is powered by the phone company. In case you need to make an urgent call and the power in your home is down you could make a phone call without any problems. This is not the case of VoIP. Usually separated power sources are not provided, so, when the power fails, your telephone will stop, too. Also, if the network congestion happens to very high at some time packets will be lost and this will a cause a momentary voice-drop. If you are in a network with a small bandwidth that is highly used, you may consider upgrading it.

The integration with the global numbers format is not an obligation. Some providers may give local numbers to the users. This is a bad thing because you might not be able to receive or make calls outside your network. A problem that still has to be resolved is the emergency calls, like 911 or 112. Normally, over a PSTN network these would redirect you to the nearest police/hospital section. But with VoIP this is not yet possible, because it cannot estimate distances. Using a pure VoIP network would bring some more advantages: Web, instant messaging, email, presence and video conferencing. Companies, in order to reduce costs, can also buy their own gateways, which, in some situations, is worth it.

Pro's and Con's of using VoIP

As VoIP rapidly extends, it now offers:

• a simple setup and use (almost the same as with old phones)
• voice storage (you can save your conversations and replay them any time you want, check voice mail.

Some of the risks that come with this technology are:

• theft: this includes also taking control of a server and listening to private stored conversations or even conversations taking place at that moment and also making phone calls from a number registered to that server.
• A new way of promoting products through telephone could became more popular. It may lead to system overhead if too many products are being promoted at a time.
• There is also the danger of someone stealing your number and making a call that was suppose to come from a trusted source to obtain some secret information.

How to protect yourself from all these possible attacks?

• The use of a junction-box. This is a hardware equipment that allows VoIP to come directly to your phone, without the need of a computer.
• Keep the passwords as private and as complicated as possible. This way it will be vary hard for someone to find out the password and steal your number/stored conversations
• If you do use a computer to connect to VoIP, make sure it is well guarded against attacks of any kind by purchasing and installing antivirus, firewalls and spyware programs.

As a short brief of VoIP, here are some things that you should now:

• VoIP refers to transporting voice (telephone calls) over a data network (e.g. Internet)
• An Internet high-speed connections is needed.
• There are different types of charging, depending on the provider
• You can call anywhere in the world, depending on the type of service you choose
• As an advantage, if you already have an Internet connection, it is not necessary to pay for the PSTN type telephone also
• Disadvantages: they are powered from inside the house, emergency calls cannot be easily redirected
• You can also use your PC while talking on the phone
• You may take the phone with you on a trip and still be able to receive and make calls where you go

Typical setups and applications

VoIP-PSTN gateway

A gateway is a device used for connecting two different types of networks. In this case, one network is the VoIP network and the other the PSTN. The gateway’s main task is to provide signaling interworking and to transform the information it receives on one side in information compatible with the other side. A gateway can consist of only one piece or it can be distributed into more components. These are:

• a Signaling Gateway - provides transparent interworking of signaling between switched circuit, in this case, PSTN, and the VoIP networks
• a Media Gateway - is responsible for extracting audio from the PSTN network, encode it and transport it over the Internet. This component carries the data
• a Media Gateway Controller - is used for controlling the call. It is also known as “Call Agent”.

SIP SBC

A typical session border controller is used to overcome some of the problems that may appear in a VoIP communication by integrating it between the caller and the called party signaling path. Such problems can be of various types. The more important ones are like it follows:

• The traversal of signal and media across a NAT or firewall border device can fail for various reasons. Let’s take them piece-by-piece. First, there is a firewall problem, even it doesn’t apply every time and for every firewall. It is about the probability that the dynamically opening and closing of ports on incoming calls might just not work. The main problem is the Network Address Translation (NAT) one. Here is about the IP addresses that are inserted in the packets by the VoIP clients, which addresses belong to the private network behind the NAT server, and consequently can’t be routed outside it. The session border controller is positioned between the clients with these problems and solves them so that the traffic can be possible. There aren’t only the signaling packets the ones that are passing through the border controller but the media ones too.

• Another reason to use a session border controller is due to different service providers for the clients, which states for a connection usually passing through many different codec hops. Here fits the border controller as a cheaper way to provide media translation and in addition also accounting information and security services.

• A use for a session border controller is also to collect usage information for each session. This can be used to create Charge Detail Records (CDRs) based on various factors as media type, bandwidth used, account information, etc.