Voice Over Internet Protocol (VoIP). Basic Components of a Telephony Network.

Voice Over Internet Protocol

(VoIP)

Basic Components of a Telephony Network

Central Office SwitchesClasses 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

IP assumes packet-ordering problems will occur RTP reorders packets into their original form

A

c

B

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