Voice over Internet Protocol (VoIP) uses digital compression techniques and packet switching to transmit voice conversations over the Internet or other IP-based networks. There are two main types of call setup in telephony networks - centralized call control where one device controls the call, and distributed call control where devices collaborate to control the call. For VoIP to work effectively, quality of service measures must be implemented to guarantee delivery, minimize packet loss and jitter, and ensure calls can tolerate delays of up to 150ms.

1. Voice Over Internet Protocol
(VoIP)

2. Basic Components of a Telephony Network

3. Central Office Switches
Classes of CO Switches
 Class 5: (C5)
-End office Switches
 Class 4: (C4)
-Tandem Switches
• C5’s are considered
the higher layer
switches at the core
of the switching
network.
• C4’s are more local
switches and closer
to the CO.

4. Analog-to-Digital Voice Encoding

5. Compression Bandwidth Requirements

6. Supervisory Signaling

7. Basic Call Setup

8. What Is a PBX?

9. Packetized Telephony Networks

10. Packet-Switched Telephony
vs.
Circuit-Switched Telephony
 More efficient use of bandwidth and
equipment
 Lower transmission costs
 Consolidate network expenses
 Increased revenue from new services
 Service innovation

11. Distributed Call Control

12. Centralized Call Control

13. Packet Telephony Components

14. Real-Time vs. Best-Effort Traffic
 Real-time traffic needs guaranteed delay
and timing.
 IP networks are best-effort with no
guarantees of delivery, delay, or timing.
 The Solution is end-to-end quality of
service (QOS).

15. E1 Interface
 A US E1 with 2.048MB of bandwidth and 32-channels,
can handle 30 voice calls at 64kbps each. Two of the
channels is dedicated for Data or E1 control.
 In comparison, a US T3 with 45MB of bandwidth can
handle 672 voice calls at 64kbps each. E3!!!

16. Today’s PSTN
So why can’t our current PSTN handle the emergence of
VoiP, video, and data services all on the same circuits of
the original PSTN network?
=Because, you can’t run a converged network on what is
primarily a network that was designed for just VOICE.
Many US carriers and private companies have large data
buildings just to ride VOICE traffic over a data network.
Equation VOICE + VIDEO + DATA OVER A
DATA NETWORK= CONVERGENCE

17. Requirements of
Voice in an IP Internetwork

18. IP Internetwork
 IP is a connectionless protocol
 IP provides multiple paths from source to
destination

19. Packet Loss, Delay, and Jitter
 Packet loss
 Loss of packets severely degrades the voice
application.
 Delay
 VoIP typically tolerates delays up to 150 ms before
the quality of the call degrades.
 Jitter
 Instantaneous buffer use causes delay variation in
the same voice stream.

20. Reordering of Packets
 IP assumes packet-ordering problems will occur
 RTP reorders packets into their original form
A
c
B

21. Reliability and Availability
 Traditional telephony networks claim 99.999%
uptime.
 Data networks must consider reliability and
availability requirements when incorporating
voice.
 Methods to improve reliability and availability
include:
 - Redundant hardware
 - Redundant links
 - UPS Power Systems
 - Proactive network management/monitoring

22. Major VoIP Protocols

23. VoIP Protocols and the OSI Model