Transcript Introduction to Packet Voice Technologies

Voice Over Internet Protocol
(VoIP)
Basic Components of a Telephony Network
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.
Analog-to-Digital Voice Encoding
Compression Bandwidth Requirements
Supervisory Signaling
Basic Call Setup
What Is a PBX?
Packetized Telephony Networks
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

Distributed Call Control
Centralized Call Control
Packet Telephony Components
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).

T1 Interface


A US T1 with 1.54MB of bandwidth and 24-channels, can
handle 23 voice calls at 64kbps each. One of the
channels is dedicated for Data or T1 control.
In comparison, a US T3 with 45MB of bandwidth can
handle 672 voice calls at 64kbps each.
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
Requirements of
Voice in an IP Internetwork
IP Internetwork


IP is a connectionless protocol
IP provides multiple paths from source to
destination
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.
Reordering of Packets
c
A
B


IP assumes packet-ordering problems will occur
RTP reorders packets into their original form
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
Major VoIP Protocols
VoIP Protocols and the OSI Model