| Date post: | 12-Jan-2016 |
| Category: |
Documents |
| Upload: | janis-terry |
| View: | 216 times |
| Download: | 0 times |
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
AdvantagesMore 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
AdvantagesImproved 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 works1. 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.723
2. List of which software supports which standard - http://compare.ozvoip.com/codecsupport.php
4. 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 componentsTelephones 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 componentsGatekeepers 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 ProtocolOpen standard
Text based protocol, similar to HTTP
Support voice, video, chat, interactive game , virtual reality
The SIP address is identified by a SIP URL: user@host.
Examples of SIP URLs:
Applied Communications Technology
H.323 vs SIPSIP H.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 topicThere 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
