Voice over IP Online Course
Lesson 3 - How Does VoIP Work?
Review: How Does VoIP Work?
This module looked at the mechanics of transmitting voice over a packet switching IP network.
Section A: Call control
This section introduced the concept of call control and the functions required to setup and
manage a call. SS7 is the system used to manage calls on the public system telephone network
and it is examined first to see which functions will need to be emulated on a VoIP system.
Section B: Call manager
This section examines how the call manager functions are handles on a VoIP system. Examined
in great detail are H.323 and SIP.
Section C: Transmitting voice
This section looks at how voice is transmitted over a VoIP system. The four steps are
sampling, quantizing, encoding and packetizing.
Exercise 3-1: How Does VoIP Work?
1. How does VoIP use SS7?
a) It maps the name to the IP address in the call database
b) It provides the out of band call setup for VoIP
c) It provides the SSP, SCP and STP for VoIP
d) Because it provides call control for the PSTN, SS7 is not used by VoIP directly
2. Which one of the following functions does the call manager not provide to a VoIP
system?
a) Encoding and compression
b) Admissions control
c) Zone management
d) Bandwidth control
3. Why can SIP integrate easily into Internet services?
a) It is controlled by the IETF
b) It uses a request-response protocol similar to HTTP
c) It uses the TCP/IP protocol
d) It supports audio, video and instant messaging
4. An H.323 zone is defined as
a) All the IP telephones and terminals on a subnet
b) All the IP telephones and terminals in a company
c) All the IP telephones and terminals which register with the H.323 gatekeeper
d) All the IP telephones and terminals on a network
5. Which one of the following encoding schemes would allow you to carry the most telephone
conversations for a fixed bandwidth?
a) G.723.1
b) G.711
c) G.729A
d) G.726
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