computer science

VoIP phone

VoIP phone is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand VoIP phone rather than just read about it. In short: A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network (PSTN).

Key takeaways

VoIP phone belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect VoIP phone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of VoIP phone from memory before moving on to harder problems.

Reference excerpt

A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network (PSTN). Digital IP-based telephone service uses control protocols such as the Session Initiation Protocol (SIP), Skinny Client Control Protocol (SCCP) or various other proprietary protocols.

Types VoIP phones can be simple software-based softphones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone. Traditional PSTN phones can be used as VoIP phones with analog telephone adapters (ATA). A VoIP phone or application may have many features an analog phone doesn't support, such as e-mail-like IDs for contacts that may be easier to remember than names or phone numbers, or easy sharing of contact lists among multiple accounts. Generally the features of VoIP phones follow those of Skype and other PC-based phone services, which have richer feature sets but may experience latency-related problems, because they rely on mainstream operating systems' IP and audio support. As mainstream operating systems became better at voice applications with appropriate quality of service (QoS) guarantees, and 5G handoff (IEEE 802.21 etc.) becomes available from wireless carriers, tablets and smartphones became the dominant interfaces. iPhone, Android and the QNX OS used in 2012-and-later BlackBerry phones are widely capable of VoIP performance. Besides wireless, they also typically support USB, but not Ethernet or Power over Ethernet interfaces. The smartphone became the dominant VoIP phone because it works both indoors and outdoors, and shifts base stations/protocols easily. It achieves this by accepting higher access costs and call clarity, and other factors personal to the user. The PoE/USB VoIP phone was thus relegated to the role of a transitional device, except in traditional business office, where it is still widely used as a desk phone.

Components and software

A VoIP telephone consists of the hardware and software components. The software requires standard networking components such as a TCP/IP network stack, client implementation for DHCP, and the Domain Name System (DNS). In addition, a VoIP signalling protocol stack, such as for the Session Initiation Protocol (SIP), H.323, Skinny Client Control Protocol (Cisco), and/or Skype, is needed. For media streams, the Real-time Transport Protocol (RTP) is used in most VoIP systems. For voice and media encoding, a variety of codecs are available, such as for audio: G.711, GSM, iLBC, Speex, G.729, G.722, G.722.2 (AMR-WB), other audio codecs, and for video H.263, H.263+, H.264. User interface software controls the operation of the hardware components, and may respond to user actions with messages to a display screen.

STUN client To enable the VoIP communications, the SIP/RTP packets should be utilised and STUN client would be the key component for VoIP communications with management of the SIP/RTP packets. A Session Traversal Utilities for NAT (STUN) client is used on some SIP-based VoIP phones as firewalls on network interface sometimes block SIP/RTP packets. Some special mechanism is required in this case to enable routing of SIP packets from one network to other. STUN is used in some of the sip phones to enable the SIP/RTP packets to cross boundaries of two different IP networks. A packet becomes unroutable between two sip elements if one of the networks uses private IP address range and other is in public IP address range. Stun is a mechanism to enable this border traversal. There are alternate mechanisms for traversal of NAT, STUN is just one of them. STUN or any other NAT traversal mechanism is not required when the two SIP phones connecting are routable from each other and no firewall exists in between.

DHCP client DHCP client software simplifies connection of a device to an IP network. The software automatically configures the network and VoIP service parameters.

Hardware

The overall hardware may look like a telephone or mobile phone. A VoIP phone has the following hardware components

A handset with a headphone and a microphone, unless the whole telephone is a hand-held device containing these A loudspeaker to act as a speakerphone Keypad or touchpad to enter phone number and text Display hardware to feedback user input and show caller-id/messages General-purpose microprocessor (GPP) to control the device A voice engine or a digital signal processor (DSP) to process RTP messages. Some IC manufacturers provides GPP and DSP in single chip AD and DA converters: To convert voice to digital data and vice versa Ethernet or wireless network hardware to send and receive messages on data network Power source - a battery or DC/AC source; some VoIP phones receive electricity from Power over Ethernet Some VoIP phones include an RJ-11 port to connect the phone to the PSTN

Other devices There are several Wi-Fi enabled mobile phones and PDAs that have pre-installed SIP client software, or are capable of running IP telephony clients, including most smartphones. Analog telephone adapters provide an interface for traditional analog telephones to a voice-over-IP network. They connect to the Internet or local area network using an Ethernet port and have jacks that provide a standard RJ11 interface that can accommodate a standard analog telephone. Another type of gateway device acts as a simple cellular base station. Regular mobile phones can connect to this device, and make VoIP calls. While a license is required to run a cellular base station in most countries, these can be useful on ships, or in remote areas where a low-powered gateway transmitting on unused frequencies is likely to go unnoticed. Some VoIP phones and ATAs also support PSTN phone lines directly.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with VoIP phone

Start with the simplest possible case. Write down what VoIP phone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to VoIP phone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about VoIP phone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of VoIP phone

In research: VoIP phone appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses VoIP phone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: VoIP phone is common in secondary-school and first-year university syllabi. It links to neighbouring topics Network appliances, Voice over IP, so understanding it makes those chapters shorter.
In everyday life: Look for VoIP phone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study VoIP phone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what VoIP phone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain VoIP phone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is VoIP phone in simple terms?

Why does VoIP phone matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study VoIP phone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on VoIP phone.