Voice over Internet protocol - VoIP

  1. 1
    What is the Internet Protocol - IP?

    The Internet Protocol (IP) is a protocol that enables information to be routed, in the form of packets, from a personal computer (PC) to another, over the Internet.

    In general, when a user establishes a connection to the Internet, the Internet Service Provider (ISP) assigns a public IP address to the computer (e.g.:, which identifies it in a unique way throughout the whole Internetwork.

    Thus, when a user sends an email message or a file, the information is divided in small packets (IP packets) which include both the receiver’s address and its own.

    IP packets go through a quite complex route until they reach their destination, as the receiver’s address is analysed by several intermediate machines before reaching the computer to which the email message or file is being conveyed.

    The various IP packages that comprise the information may take different Internet courses and, according to the period of time they take to do so, they reach their destination in a different order from that initially routed.

    Thus, the IP protocol merely delivers packets, and as a result, the support of a different protocol (of a higher level) is necessary to reorganize them - the Transmission Control Protocol (TCP).

  2. 2
    What is VoIP?

    The Voice over Internet Protocol (VoIP) is a technology that allows the user to make telephone calls over a data network like the Internet, by converting an analogue voice signal into a set of digital signals, in the form of packets with IP addressing, which may be routed, namely, over an Internet connection (preferably a broadband connection).

    You need for this purpose a personal computer (PC) equipped with a microphone and headphones, an IP telephone or a traditional telephone connected to an IP adaptor (Analogue Telephone Adapter - ATA).

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    What types of VoIP calls can I make?

    According to the available equipment, the following types of telephone calls can be made:

    • PC-to-PC - a VoIP provider software needs to be installed in the personal computer (PC) and the caller must know the IP address of the called party to make the connection.


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    • PC-to-telephone - as in the previous case, a software must be installed in the computer, enabling the caller to dial the telephone number of the called party, or to use an IP telephone or a traditional telephone (public service telephony network - PSTN) with ATA (Analogue Telephone Adapter).


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    • Telephone-to-telephone - the advantage of this type of call is that you don’t need to connect the computer, as the call made through the phone is established in a regular way.


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  4. 4
    What kind of equipment do I need to make a VoIP call?

    For any type of call, the user needs to conclude a contract with the Internet Service Provider (ISP) which preferably provides broadband Internet access through an ADSL or cable modem.

    As regards PC-to-PC calls (between personal computers) or PC-to-telephone calls (between a personal computer and an analogue telephone), you need a personal computer with the minimum recommended configuration and a microphone, headphones being likewise advisable in order to avoid feed-back which occurs when you use both microphone and speakers.

    As far as telephone-to-telephone calls are concerned, the user needs to have a router/switch to which the modem and the IP telephone must be connected. If you only have an analogue telephone, you need an adaptor to connect it to the router/switch.

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    How can the use of a VoIP terminal be characterized?

    The use of a VoIP terminal may be:

    1. Fixed, where it is at the same location or address at all times;

    2. Nomadic, where it is possible to connect it in different locations in the country (different geographic areas) or even abroad; or

    3. Mobile, where it is possible to maintain an active moving voice session throughout the national territory. Certain IP technologies which facilitate this type of use are currently under a development process (for example, WiMAX and 3G).

  6. 6
    Where can I get information on the necessary software to make VoIP calls?

    You may request information on the necessary software to make VoIP calls from providers, who frequently make such information available also at the respective websites.

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    If I have VoIP service, who can I call?

    Depending upon your VoIP provider, you can be limited to communicate with a group of users, or you may be free to make any type of calls (local, national or international calls, and calls to fixed or mobile networks).

  8. 8
    What Are Some Advantages of VoIP?

    The implementation of VoIP services is acknowledged as being very important, not only to increase competition and the development of the electronic communications market, but also for the direct and significant benefits users derive from it (including the provision of additional innovative services at competitive prices), essential targets in the Community regulatory framework.

    Because VoIP is a digital service, it may offer a number of features (such as the possibility of nomadism) and services that are not available with traditional phone services. Moreover, if you have always-on broadband access, you need not maintain a telephone line just to make telephone calls.

  9. 9
    Does VoIP have potential disadvantages?

    The disadvantages presented by the VoIP service relatively to the traditional telephone service should be analysed as regards the user’s communication equipment.

    If the user has a telephone line, mobile phone and broadband Internet access through a cable modem, and intends to disconnect the telephone line, the VoIP service may present the following potential disadvantages:

    1. Although call forwarding to emergency services should be ensured by VoIP service providers, there are some technical problems in determining the precise location of the VoIP terminal in nomadic use;

    2. The VoIP services do not work during power outages and the service provider may not offer backup power (you should make sure of this by consulting the information supplied by the service provider). However, this disadvantage may be rectified if you are provided with an uninterrupted power source, duly dimensioned; and

    3. VoIP providers may not offer white page listings and directory assistance.

  10. 10
    Can I use my computer while I talk on the phone?

    Yes, provided that you are using a ISDN or broadband access (namely ADSL or cable).

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    Can I make/receive calls, if my computer is turned off?

    Yes, if you are making calls with a VoIP phone or a traditional phone with an adaptor. Nevertheless, your broadband Internet connection needs to be active.

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    Can I tell a VoIP call apart from a traditional call by the ringtone?

    No, as the ringtone for both cases is similar, unless you configure different ringtones for each type of call.

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    If I have a webcamera connected to the computer can I make a personal videoconference?

    Yes, if you have installed software (duly configured) that enables the videoconference to take place, and the called party is also provided with a webcamera.

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    Are there IP video and “videoless” phones?

    There are several types of IP phones or IP video phones which may be purchased in the national market or through the Internet. Provided that the called party also has a video phone similar to yours, both of you may establish a videoconference regardless of whether the computer is turned on or not.

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    If I am a client of a VoIP service provider, am I entitled to receive detailed billing?

    Yes. Users of publicly available networks and services are entitled to receive detailed billing. For additional information, please consult your VoIP service provider.

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    If I am a client of a VoIP service provider, can I make calls to the 112 emergency service?

    Yes. VoIP service providers should ensure call forwarding to emergency services. However, there are currently some technical problems in determining the precise location of the VoIP terminal in nomadic use, and therefore providers of this type of services may not have the conditions to ensure full access to the 112 service. For additional information, please consult your VoIP service provider.

  17. 17
    If I am a client of a VoIP service provider, can I identify the caller line – CLI (caller line identification) of a call I receive? And in a call I make, can the called party see the CLI?

    The concern in generating and transporting the CLI that reliably presents the call source aims at enabling the return thereof. As regards access to emergency services, this facility is quite important to the proper operation of the service.

    The CLI generation and accuracy confirmation in its source are incumbent upon the operator of the network wherein the call is originated. Nevertheless, the correctness of the information comprised in the CLI may not be, for the time being, ensured in an Internet environment.

    For additional information, please consult your VoIP service provider.

  18. 18
    The quality of service provided by VoIP service providers is different from that provided by providers of the traditional fixed telephony?

    Companies that provide publicly available electronic communications services, such as the providers of VoIP services, are bound to publish and make available to end users comparable, comprehensive and up-to-date information on the quality of service provided.

    Moreover, companies that provide the service of access to the public telephone network at a fixed location and telephone service at a fixed location are bound to the provision of information on quality of service, pursuant to Regulation no. 46/2005, published on 14 of Junehttps://www.anacom.pt/render.jsp?contentId=975357. Providers of VoIP services at a fixed location are also bound to comply with the provisions of this Regulation.

    The quality of VoIP services perceived by users depends generally on three aspects:

    • Network topology - the delays in establishing VoIP calls, as well as in delivering IP packets, may affect the quality thereof. These delays depend on the number of knots between endpoints in communication and on potential multiple conversions between the Commuted Public Telephony Network - CPTN and the IP network, which depend on the topology of the network used;
    • Interconnection congestion - current IP networks, particularly in the Internet environment, have as a basic concept the so-called best effort, which means one more communication will always be possible, but at the expense of the quality of communications existent in the network; and
    • Codecs used - The VoIP service usually uses codecs that compress the voice signal, which may reduce the voice quality (digitalized) or delay the communication. On the other hand, some codecs have a remedial effect on transmission problems, namely, by minimizing the impact of packet loss. However, they have the disadvantage of needing higher computer processing.

    The quality of service provided by VoIP service providers is different from that supplied by providers of the traditional fixed telephony and should be assessed on a case-by-case basis.

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    If I subscribe the services of a VoIP service provider, can I access call selection and pre-selection through a different provider?

    The activation of selection and pre-selection is incumbent upon a direct access provider, and thus that will only be possible if the VoIP service provider integrates this category. On this matter, please consult also the Selection and Pre-Selection Draft Regulationhttps://www.anacom.pt/render.jsp?contentId=444206.

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    If I subscribe the services of a VoIP service provider, can I port my current number to that provider?

    The providers of VoIP services provided at a fixed location are subject to the obligation to implement number portability, that is, they have portability rights and obligations.

    ANACOM is currently assessing the application of number portability obligations/rights to providers of nomadic VoIP service.

    Considering that number portability is allowed only in the scope of the same service, is it not permitted between the geographic numbering range “2” and the non-geographic numbering range “30”.

    For additional information, please consult your VoIP service provider.