01.- introduction to packet voice technologies

© 2008 Cisco Systems, Inc. All rights reserved. Cisco PublicPresentation_ID 11

Fundamentos de Telefonía IP

Introduction to Packet Voice Technologies

© 2008 Cisco Systems, Inc. All rights reserved. Cisco PublicULg VoIP 2

Basic Components of a Telephony Network


Basis Components of a Telephony Network

PSTN: Public switched telephone network

Analog telephone: Able to connect directly to the PSTN and is the most common device on the PSTN. Converts audio into electrical signals.

Digital telephone: Typically connects to a PBX system. Converts audio into binary 1s and 0s, which allows more efficient communication than analog.

Private switch: Allows a business to operate a “miniature PSTN” inside its company. This provides efficiency and cost savings because each phone in the company does not require a direct connection to the CO switch.


Basis Components of a Telephony Network

Central office (CO) switch: Provides services to the devices on the local loop. These services include signaling, digit collection, call routing, setup, and teardown.

Trunk: Provides a connection between switches. These switches could be CO or private.

Local loop: The link between the customer premises (such as a home or business) and the telecommunications service provider


Local Loops, Trunks, and Interswitch Communication

The communication path between several central office switches is known as a trunk. Just as it is not cost-effective to place a physical wire between your house and every other house you want to call, it is also not cost-effective to place a physical wire between every central office switch.


Local Loops, Trunks, and Interswitch Communication

Meshed Network Versus Hierarchical Network


Circuit-Switching Hierarchy

Switches are currently deployed in hierarchies. End office switches (or central office switches) interconnect through trunks to tandem switches (also referred to as Class 4 switches). Higher-layer tandem switches connect local tandem switches


PSTN Services and Applications



• Call blocking Blocks specific incoming numbers so that callers are greeted with a message saying the call is not accepted.

• Calling line ID blocking Blocks the outgoing directory number from being shown on someone else's display. (This does not work when calling 800-numbers or certain other numbers.)

• Automatic callback Enables you to put a hold on the last number dialed if a busy signal is received and then automatically place the call to the initiator's line once the destination is free. This is sometimes also called camp on.



• Circuit-switched long distance Basic long-distance services (normally at a steeply discounted rate).

• Calling cards Pre-paid and post-paid calling cards.


Central Office Switches


What is a PBX?

PBX: Private Branch Exchange


What is a PBX?

Control complex: Provides the intelligence behind the PBX system; all call setup,routing, and management functions are contained in the control complex.

Line cards: Provide the connection between telephone handsets and the PBX system.

Trunk cards: Provide connections from the PBX system to the PSTN or other PBX systems.


What is a Key System?


Comparing Key Systems with PBXs


Basic Call Setup


Loop (Local or Station) +

48v48v–

Station PBX or Central Office

Switch

Loop Start Signaling (FXS)

TR

On-hook,open loop

BELL

+–

DC Current Switch48v48v

Off-hook,close loop

BELL

+–

AC

Ringing Switch

BELL !!BELL !!

48v48vBELL

Ring on-hookAns off-hook

Current sense


On-HookOpen Circuit

On-HookOpen Circuit

Basic Call Progress: Idle

TelephoneSwitch

LocalLoop48v48v

LocalLoop

On-HookOpen Circuit

On-HookOpen Circuit


DC CurrentDC Current

Dialed DigitsPulses or Tones

Dialed DigitsPulses or Tones

Off-HookClosed Circuit


Basic Call Progress: Dialing

TelephoneSwitch

LocalLoop48v48v

dialtone

On-HookOpen Circuit

On-HookOpen Circuit


LocalLoop



Basic Call Progress: Switching

Addressto

PortTranslation

TelephoneSwitch

48v48v

?

On-HookOpen Circuit

On-HookOpen Circuit


LocalLoop

LocalLoop

Basic Call Progress: Ringing

Ring BackTone

Ring BackTone



TelephoneSwitch

On-HookOpen Circuit

On-HookOpen Circuit

90V ACRing Signal

90V ACRing Signal

48v48v

RG


Voice EnergyDC Current

Voice EnergyDC Current

LocalLoop

LocalLoop



Basic Call Progress: Talking

TelephoneSwitch

Voice Energy

DC Current

Voice Energy

DC Current



48v48v

RGXX


Address Signaling


Informational Signaling


Digital vs Analog Connections


Sending Multiple Calls over a Single Line

The original problems of analog connections:

• The signal degrades over long distances.

• You can’t send multiple calls over a single line (resulting in massive cabling requirements).

Digitizing voice solves the first problem because you can easily transmit a numeric value any distance a cable can run without any degradation or line noise. Time-division multiplexing (TDM) solves the second problem.


Time-Division Multiplexing


Frequency-Division Multiplexing


Drawbacks to the PSTN

• Data has overtaken voice as the primary traffic on many networks built for voice.

• The PSTN cannot create and deploy features quickly enough.

• Data/Voice/Video (D/V/V) cannot converge on the PSTN as currently built.

• The architecture built for voice is not flexible enough to carry data.


VoIP Overview

VoIP is the family of technologies that allows IP networks to be used for voice applications, such as telephony, voice instant messaging, and teleconferencing. VoIP defines a way to carry voice calls over an IP network, including the digitization and packetization of the voice streams. IP Telephony VoIP standards create a telephony system where higher-level features such as advanced call routing, voice mail, and contact centers can be utilized.


VoIP Overview

VoIP services convert your voice into a digital signal that travels over an IP-based network.

If you are calling a traditional phone number, the signal is converted to a traditional telephone signal before it reaches its destination. VoIP allows you to make a call directly from a computer, a VoIP phone, or a traditional analog phone connected to a special adapter. In addition, wireless “hot spots” in locations such as airports, parks, and cafes that allow you to connect to the Internet might enable you to use VoIP services.


VoIP Advantages


Packet Telephony vs. Circuit Switched


Circuit Switching vs Packet Switching


Call Control


Distributed Call Control


Centralized Call Control


Packet Telephony Components



Gatekeeper: Provides Call Admission Control (CAC), bandwidth control and management, and address translation.

Gateway: Provides translation between VoIP and non-VoIP networks, such as the PSTN.

Multipoint Control Unit (MCU): Provides real-time connectivity for participants in multiple locations to attend the same videoconference or meeting.



Call agent: Provides call control for IP phones, CAC, bandwidth control and management, and address translation. Unlike a gatekeeper, which in a Cisco environment typically runs on a router, a call agent typically runs on a server platform.

Application servers: Provide services such as voice mail, unified messaging, and Cisco Communications Manager Attendant Console.


Real-Time vs. Best-Effort Traffic


Physical Connectivity Options


Connections to the PSTN


Trunks

Trunks are used to interconnect gateways or PBX systems to other gateways, PBX systems, or the PSTN. A trunk is a single physical or logical interface that contains several physical interfaces and connects to a single destination.

This could be a single FXO port that provides a single line connection between a Cisco gateway and a FXS port of smallPBX system, a POTS device, or several T1 interfaces with 24 lines each in a Cisco gateway providing PSTN lines to several hundred subscribers.

Trunk ports can be analog or digital and use a variety of signaling protocols


Foreign Exchange Station (FXS) Interface


Foreign Exchange Office (FXO) Interface


E&M Interface


Analog Trunks


T1 Interface


E1 Interface


BRI Interface


Connectivity Options


Campus LAN Environment


Centralized Call Processing Environment


Distributed Call Processing Environment


Service Provider Environment

01.- introduction to packet voice technologies

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