VoIP Rob Fama
What Is VoIP? • VoIP stands for Voice Over Internet Protocol • Delivers voice communications over existing internet infrastructure and protocols. • Effectively VoIP is a substitution for telephone. • VoIP uses one of several application protocols (like HTTP), however it is transmitting audio rather than text. • The audio is encoded into bytes, sent to a destination, and then decoded on the other end. • This contrasts telephone, which just transmits an analog transmission – no encoding or decoding necessary.
Classic Telephone • Classic telephone consists of a PSTN – public switched telephone network. • The PTSN is a public backbone network • A central hub would make a direct connection between two end points. • We often see this in old movies, when a telephone user requests to an operator in front of a switchboard to be connected to a specific person. • An analog transmission gets sent over a copper wire. • There is a hard cap in the number of conversations that happen at a time – it is not possible for two conversations over the same line.
VoIP Connectivity • A user can use a VoIP system to connect to a user on a classic telephone 3 different ways: • An Analog Telephone Converter (ATA), which connects a broadband network to an analog telephone line • VoIP phone (most popular one is by Cisco) which is special hardware that looks like a phone but works over IP • A softphone – software to install on a computer to simulate a phone.
Benefits of VoIP • Everything is moving towards IP networks, so development and money efforts are already focused in that direction. • Internet is cheaper than telephone, being billed by the byte is cheaper than being billed by the minute. • Scalability – Multiple discussions can happen simultaneously over one line, where with a classic phone there is a hard cap as there is a dedicated line.
Benefits of VoIP • Software provides many existing phone features for free (redial, caller ID) and also allows for video conferencing, white board, etc which is usually bundled with VoIP. Faxes are also supported. • Can make a call anywhere there is an internet connection – in a coffee shop, airport, etc. • VoIP device to VoIP device (usually in the form of software) is free in most cases (Skype).
Disadvantages of VoIP • Susceptible to latency and jitter, just as any normal IP application. • This is untrue with an analog phone line as it is a dedicated line. • Susceptible to DoS attacks, or eavesdroppers • Eavesdropping is also possible with a classic telephone line. • When the power goes out, analog phones continue to run but VoIP depends on power of connectivity devices and the VoIP device itself (usually a PC).
Disadvantages of VoIP (cont) • On a regular phone, emergency calls can be traced to a home address. • With VoIP calls they cannot be traced to any particular location other than the ISP. • If there is a power outage, emergency calls cannot be made.
VoIP Protocols • VoIP is not a protocol itself, it is a term that describes a variety of protocols, some open and some proprietary. Some protocols: • H.323 • IP Multimedia Subsystem (IMS) • Skype (propriatery)
H.323 • Supports both audio and video transmission, used most often in video conferencing software. • Has a fairly complex stack consisting of terminals, multipoint control units, gateways, gatekeepers, and border elements. • Contains a “gateway” which enables communication with older analog encoded networks.
IP Multimedia Subsystem (IMS) • Framework for providing voice, video, and other multimedia services over IP. • Developed by same forum who worked to further integration of 3G wireless (called 3G.P). • Geared to further wireless past GSM networks. • Can connect to network in a variety of ways, only hard requirement is that it is over IP.
Bibliography • “Voice over IP”; Varshney, Snow, McGivern, Howard; Communications of the ACM, vol 45, pp 89 – 96; 2002 • “Voice over Internet Protocol. Definition and Overview". International Engineering Consortium. 2007. http://www.iec.org/online/tutorials/int_tele/index.asp • “Voice Over Internet Protocol”. Wikipediahttp://en.wikipedia.org/wiki/Voice_over_Internet_Protocol • “H.323”. Wikipedia. http://en.wikipedia.org/wiki/H.323 • “IP Multimedia Subsystem”. Wikipedia http://en.wikipedia.org/wiki/IP_Multimedia_Subsystem