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Introduction to VoIP 3UET Session 3 Introduction Lesson objectives • Explain difference between Circuit Switched and Packet Switched • Explain advantages of VoIP • Define what are Codecs Analogue Systems • Traditional broadcast media such as radio, television, and PSTN use analogue technology, • Represented as a series of varying sine waves. • The term analogue can be traced to the similarity between the actual fluctuations of the human voice and the “analogous,” or comparable, modulation of a carrier wave. Introduction to VoIP • Analogue electromagnetic signals that continuously vary in their strength and speed. • e.g. voice Analogue Systems • The human voice occupies the 20Hz to 20KHz range, with most energy in the 300–3300Hz range Basic Telephone System Operation • Telephone systems use analogue-switched lines to provide voice communications by converting sound waves, vibrations that move in the air, into electrical signals. • When a person speaks into a telephone handset, acoustical energy vibrations caused by the person’s voice apply varying amounts of pressure to the diaphragm. Basic Telephone System Operation • In response to the natural rise and fall of human speech, the diaphragm in turn converts this pressure into different amounts of current or electrical energy. • This variation in the current is in effect an electrical representation of the human voice • The resulting output of this process is an analogue electrical signal PSTN • The job of the Public Switched Telephone Network (PSTN) is to reliably facilitate telephone conversations at anytime • PSTN combines analogue, digital, and electromechanical data links to make sure every time you pick up a phone receiver you hear a dial-tone PSTN • The PSTN is a switched network • In switched networks links between endpoints don’t need to be permanent because they aren’t needed constantly • The only time a link between two endpoints is needed is when a call is in progress between them. • The rest of the time is idle • Switching is a method whereby links are established and removed as needed. SS7 • Signaling System 7 (SS7) is the PSTN’s signaling component • A second network that runs alongside the PSTN • It’s purpose is coordinating communication between switches, telephone company databases and billing systems • Toll-free calling and long distance call routing are both functions of SS7 Circuit Switched vs Packet Switched Circuit Switching • Circuit switching used by telephone networks for more than 100 years • Connection is made for the duration of the call • When the dialled party answers the call, a circuit is established connecting the two phones together via a series of switches • Circuit is dedicated to that call for the duration – Until 1960 or so, every call a dedicated wire stretching from one end of the call to the other for the duration of the call Circuit Switched vs Packet Switched • Today your voice is digitized and combined with others onto a single fiber optic cable for much of the journey • There's still a dedicated piece of copper wire going into your house • An exchange/switch with 50 circuits can only handle 50 calls at any one time – Limits capacity – Expensive Circuit Switched vs Packet Switched • Think about... • Voice is transmitted at a fixed rate of 64Kbps in each direction • Translates to 16 KB each second (960 KB every minute) • 10-minute conversation, the total transmission is 9,600 KB (roughly 10 megabytes) • In a typical phone conversation, much of this data is waste Circuit Switched vs Packet Switched • Silence – While you are talking, the other party is listening, generally means that only half of the connection is in use at any given time – Dead Air where neither party talks • If we could remove the silence, we transmit less data • Instead of sending a continuous stream of bytes (both silent and noisy), what if we sent the bits? • Hence we arrive at packet switching, i.e. non-dedicated resources Circuit Switched vs Packet Switched Packet Switching • On the internet a dedicated connection is not maintained between client and server • Data networks send/receive as required • The sending computer chops data into small chunks (known as packets) and adds an address to each one telling the network devices where to send them Circuit Switched vs Packet Switched • A router picks it up and moves it a little closer to its destination • Another router does the same and so forth until it reaches its destination • Instructions contained within the packets are used to reassemble the data into its original state Circuit Switched vs Packet Switched • Individual packets in a stream may travel entirely different routes from A to B • A brief connection is opened just long enough to send a small chunk of data • Very efficient - the network routes the packets along the least congested and cheapest lines Introduction to VoIP Introduction to VoIP • VoIP - Voice over Internet Protocol • Any technology that transmits a conversation over a data network Introduction to VoIP Analogue Signals • Digitised, chopped up into small pieces (packets) •Transmitted across a data network (e.g. the internet) Introduction to VoIP • Free phone calls? – Some VoIP providers offer free calls between customers or other VoIP providers – Not quite free - Cost of internet connection, possibly higher bandwidth than otherwise required • Cheaper Phone Calls? – NodePhone (13/5/07) • Free to other NodePhone customers • 18c untimed calls to fixed lines anywhere in Australia • From 5c/min International calls – Engin - “Engin National” Plan (13/5/07) • Free Engin to Engin • Free National Calls (fixed lines) • International calls from 3.5c/min Introduction to VoIP • Activity • Look up some other VoIP providers • What plans do they offer? • Lookup http://www.whirlpool.net.au > discussion forum > Voice over IP > Voice over IP (VoIP) Information Here – Look at the VoIP Providers Introduction to VoIP • Advantages of VoIP • Multiple Lines on a Physical Link - More than one call on a single broadband connection • Location Independence - Incoming calls find your phone regardless of where you are connected to the network • Staff can work from anywhere with a sufficiently fast and stable Internet connection • Many VoIP packages include features that most telcos charge extra for e.g. 3-way calling, call forwarding, automatic redial, and caller ID. • Integrate with other services - e.g. CRM Introduction to VoIP • VoIP Challenges • Routing VoIP traffic through firewalls and address translators • Network Traffic Issues - Delay/Network Latency, Packet loss, Jitter, Echo – The principal cause of packet loss is congestion, which can be controlled by congestion management and avoidance – Variation in delay is called jitter • Security – – – – Majority of consumer VoIP devices do not support encryption yet Easy to eavesdrop on VoIP calls and change their content Sniffing tools commonly available Skype uses encryption which is transparent to the user Introduction to VoIP • Reliability – Power supplied to analogue phones via phone company exchange – Back-up generators or batteries located at the telephone exchange – VoIP hardware powered by household electricity – PSTN has been matured over decades and extremely reliable – Broadband networks - even the best are still subject to intermittent outages – SLAs on ADSL Introduction to VoIP • Computer Hardware – Phone system is dependant on individual PCs of varying specifications and power. A call can be affected by processor drain • Difficulty Sending faxes/modem calls – Sending faxes over VoIP difficult – Voice codecs are not designed for fax transmission Introduction to VoIP • Emergency calls – – – – – – Unable to locate network geographically Fixed line phones - fixed location Mobile phones - triangulate based on cell towers Calls cannot easily be routed to a nearby call center 000 calls impossible on some VoIP systems In the event that the caller is unable to give an address, emergency services may be unable to locate them in any other way • One large VoIP carrier requires the registration of the physical address where the VoIP line will be used • Some also maintain their own emergency call center that will take emergency calls Introduction to VoIP VoIP Phones • Several types of phone • ATA (Analog Telephone Adapter) – Connects a standard phone for use with VoIP – Analog-to-digital converter – Some providers bundling ATAs free with their service – Ordinary Phone ---- ATA ---- Ethernet --- Router ---- Internet ---- VOIP Service Provider Introduction to VoIP Introduction to VoIP VoIP Phones • IP Phones – Look just like normal phones – IP phones have an Ethernet connector – Wired or WiFi – Onboard software handles IP calls – Also known as Hardphone – IP Phone ----- Ethernet ---- Router ---- Internet ---VOIP Service Provider Introduction to VoIP VoIP Phones • Softphones – Phone implemented in software running on a PC or PDA – Use PC speakers/microphone or headset – e.g. Skype, X-Lite, SJPhone Codecs • Codecs • Short for coder/decoder • Any technology for compressing and decompressing data • Can be implemented in software, hardware, or both in combination • Audio Codecs - WAV, MP3, AAC, WMA Codecs Discussion • Have you ever compressed files with zip or rar? • What happens? • Compression - Smaller file size • When you decompress the file do you get your original document back? • Yes - lossless compression • Do some files compress better than others? • Yes - internal redundancy Codecs Discussion • Have you ever created a jpeg image using a tool that allows you to set the quality? • What happens to the image at lower quality settings? • Smaller file size, becomes blurry (information loss) • Have you ever ripped CDs? • Do you use MP3, AAC, WMA, or Ogg? • Why? • Some are proprietary formats, limited playback options • Ogg is open but not well supported • Differences in quality on the resultant output • What happens when ripping CDs? • Translation from one codec to another • Compression Codecs • • • • • • • • Does your ripping program let you change the bit rate? What effect does that have? File size, perceived quality Does music ripped in AAC or WMA sound better/worse than MP3? Yes, different psycoacoustic modelling If you burn MP3s to an Audio CD and rip it again does it sound the same? No, data loss every time there's a lossy encode When authoring audio/video use lossless formats for masters, lossy for final distribution Codecs • Compression/Encoding – Different codecs use different methods to encode data – Generally incompatible with each other – Different codecs are used for different tasks, a video codec can't be used for Audio – All things being equal, different codecs will deliver differences in audio/video quality Codecs • Bit rate – – – – Information per unit of time Usually expressed as bits per second Higher numbers = more data Bit rate is often an indicator of sound/video quality, however different codecs will achieve different perceived quality at different bit rates • e.g. 64Kbps WMA would sound similar to 128Kbps MP3 – Higher bit rates - more information, more effort to decode, more disk space required – Some devices will require lower bit rates, e.g. hand held's Codecs Loss • Two main approaches to compression • Lossless – Compresses data, and the decompressed version is identical to the original – Often used for documents, program files and other data where “similar to the original” won't do – Lossless algorithms are usually generic, can compress anything – Often less space saved – e.g. zip, rar Codecs • Lossy – If we accept there's data in the original file that we don't need, we can throw it away – e.g. sounds we don't hear, shades of colours don't see – Terms like • psychoacoustic (“the way the brain interprets sound”) and • psycovisual used to describe techniques which determine what we can see/hear and removing everything else – e.g. shout and tap fingers at the same time, will hear shouting but not finger tapping Codecs – Video - 20+ frames per second often little change between frames – Locating and cutting out unchanged segments called “statistical data redundancy” – Slightly corrupt video files and digital TV often pixelate in areas with movement – Every time you save your file in a lossy file format, it discards more of the data – Move to a lossy format only as the very final step in your project. Codecs • Quality Factors for VoIP • Bandwidth - More bandwidth, higher bitrates=better sound quality • Codec - Different codecs have different audio characteristics • Hardware - Better hardware in general results in higher quality sound • Network Factors - Better networking = better sound VoIP Codecs • • • • • • • • • • • ULAW - Best sound for big connections ALAW - Supposedly good for Fax. G726.1 (g726) - Compromise ILBC - Often a default for Softphones (Xten etc). G729 - Quite lossy, good for low bandwidth connections GSM - Slightly better quality then g729 Recommended Speeds 1.5/256 or Higher = ULAW or ALAW 512/128 = g726.1 or ULAW (If your connection is of good quality) 256/64 = ILBC, GSM or G729 Note: If you are on a higher speed you can use the lower speed codecs. This will allow you to make more simultaneous calls. • The following table shows bandwidth requirements for many common codecs. Codec.................Bandwidth Usage (Up/Down) G.711 (64 Kbps).......87.2 Kbps G.729 (8 Kbps)........31.2 Kbps G.723.1 (6.3 Kbps)....21.9 Kbps G.723.1 (5.3 Kbps)....20.8 Kbps G.726 (32 Kbps).......55.2 Kbps G.726 (24 Kbps).......47.2 Kbps G.728 (16 Kbps).......31.5 Kbps GSM (7 or kbps).......low ILBC (low)............low More Information: compare.ozvoip.com/codecs.php VoIP Codecs Review • http://www.ozvoip.com/frequently-asked-questions/#codec