Applied Communications Technology Voice Over IP (VOIP) nas1, April 2012 How does VOIP work? Why are we interested? What components does it have? What standards make it work in practice? What does it add to business capabilities? How good is the quality for people using it? How do we measure and monitor quality? How can we use VOIP in our software projects?

Applied Communications Technology Advantages More efficient use of bandwidth and equipment Lower transmission costs Consolidated network expenses – one network, not two Software-based and wireless phones offer flexibility, customisation Access to new communications devices (such as wifi-enabled smartphones, cable set-top boxes)

Applied Communications Technology Advantages Improved employee productivity through features provided by IP telephony: – IP phones are complete business communication devices – Directory lookups and database applications (XML) – Integration of telephony into any business application Improved features – Conferencing, call by name, contextual data – Message recording, logging

Applied Communications Technology How it works 1. Convert the Analogue voice to digital data (ADC) 2. Compress the digital ready for transport (CODEC) 3. A number of different codecs are used depending on the scenario 1.G.711, G.722 or G List of which software supports which standard Place packets on the network for transport 5. A signaling protocol to call users, e.g. H323 or SIP. 6. Receiver converts packet back to analogue information to listen to

Applied Communications Technology Voice Encoding Sample, quantise and compress audio Packetise and transmit data Decompress, convert to analogue, play audio

Applied Communications Technology VOIP network components Telephones provide telephony features to users. can be IP phones, software-based telephones operated on PCs, or traditional telephones (analog or ISDN). Gateways interconnect the VoIP network with traditional telephony devices. These can be analog or ISDN telephones, faxes, circuit- switched PBX systems, or public switched telephone network (PSTN) switches. Multipoint control units required for conferences. If more than two parties are involved in a call, all members of the conference send their media to the MCU. The MCU mixes the media and then sends the media to all participants. Application servers provide XML-based services to IP phones. IP phone users have access to directories and databases through XML applications.

Applied Communications Technology VOIP network components Gatekeepers provide Call Admission Control (CAC) to prevent the network from being over subscribed. As well, CAC translates telephone numbers or names to IP addresses for call routing in an H.323 network. Call agents provide call control, CAC, bandwidth control, and address translation services to IP phones or Media Gateway Control Protocol (MGCP) gateways. Video endpoints provide video telephony features to users. As with audio-only calls, video calls need a multipoint control unit for conferences. For videoconferences, the multipoint control unit has to be capable of mixing video and audio streams.

Applied Communications Technology VOIP network components

Applied Communications Technology Session Initiation Protocol Open standard Text based protocol, similar to HTTP Support voice, video, chat, interactive game, virtual reality The SIP address is identified by a SIP URL: Examples of SIP URLs:

Applied Communications Technology H.323 vs SIP SIPH.323 PHILOSOPHY "New World" - a relative of Internet protocols - simple, open and horizontal "Old World" - complex, deterministic and vertical IETF ITU Carrier-class solution addressing the wide area Borne of the LAN - focusing on enterprise conferencing priorities STATUS Industry endorsed Popularity due to the fact that it was the first set of agreed-upon standards Many vendors developing products The majority of existing IP telephony products rely on the H.323 suite

Applied Communications Technology Protocols and Standards

Applied Communications Technology Establishing a Connection: H.323

Applied Communications Technology Establishing a Connection: SIP proxy

Applied Communications Technology Establishing a Connection: SIP

Applied Communications Technology Key Issues Quality of Service (QoS) – IPv4 has no standard built-in QoS support, yet very important Scalability Interoperability – inter-networking and PSTN, too Security Emergency services – e.g. 999 services Integration with PSTN for end-to-end services

Applied Communications Technology VOIP is a big topic There is a business case for VOIP in all levels of enterprise This University is rolling out VOIP devices to staff There is a high-level networking view that helps us understand how VOIP works Underneath that there are many details – packet structures, real-time networking protocols, router and LAN tuning for efficient deployment And human considerations – sound quality, jitter, lag, added services