Write a short note on following

Write a short note on following
(a) Videoconferencing (b) Voice Mail
Answer the following
(a) Which telecommunication is used for two way audio and video transmission?
(b) If someone is not answering your call and you will have to convey a message. What you can use in this context?

(a) Video Conferencing It is the conduct of video conference by a set of telecommunication technologies which allow two or more location to communicate by a simultaneous two way video and audio transmission.
(b) Voice Mail It was introduced in the late 1970s. These are essentially digital recordings of outgoing and incoming voice messages that are managed by either an on-site or off-site system.