cisco vo ip

VoIPVoice Over Internet Protocol

Benefits of Packet Telephony Networks

• More efficient use of bandwidth and equipment

• Lower transmission costs

• Consolidated network expenses

• Improved employee productivity through features provided by IP telephony:

– IP phones are complete business communication devices

• Directory lookups and database applications (XML)

• Integration of telephony into any business application

– Software-based and wireless phones offer mobility

• Access to new communications devices (such as, PDAs and cable set-top boxes)

Packet Telephony Components

Two Basic Methods for Voice over IP

Analog Interfaces

Analog Interfaces

Analog Interface Type Description

FXS Used by the PSTN or PBX side of an FXS–FXO connection

FXO Used by the end device (phone) side of an FXS–FXO connection

E&M Trunk, used between switches

Digital Interfaces

Digital Interfaces

Interface Voice Channels (64 kbps Each) Signaling Framing

OverheadTotal Bandwidth

BRI 2 1 channel (16 kbps)

48 kbps 192 kbps

T1 23 1 channel (64 kbps)

8 kbps 1544 kbps

E1 30 64 kbps 64 kbps 2048 kbps

Stages of a Phone Call

Stages of a Phone Call

Voice Packets

Basic Voice Encoding:Converting Analog to Digital

Voice Codec Characteristics

Standard Bandwidth per Voice Channel

G.711 64

G.726 16, 24, 32

G.729 8

Describe Cisco VoIP Implementations

•Encapsulating Voice Packets for Transport

Voice Encapsulation Examples

• Digitized voice is encapsulated into RTP, UDP, and IP.

• By default, 20 ms of voice is packetized into a single IP packet.

IP Telephony

Auxiliary VLANs

Cisco IP Phone

• Voice traffic tagged for voice VLAN

Power over Ethernet

Power over Ethernet (PoE)

• Sending operating power over Ethernet Category 5 cable • Power-sourcing equipment (PSE)

– Switches, power injector• Powered devices

– IP phones, Access points

• Distances up to 100 meters• Alternative: AC power adapter

Midspan Power Injection

• Uses pairs 4,5 and 7,8

• Requires eight-wire cabling

• Does not extend 100-m total length limit

• Not possible for 1000TX

Power-Sourcing Equipment

•Power injector• AIR-PWRINJ3/AIR-PWRINJ-FIB

•Powering switch• Cisco Catalyst 3560-PS/3750-PS

• Cisco Catalyst 4500/6500 switch

with inline power line cards

• Router module NM-16ESW-PWR

• Router card HWIC-4ESW-POE

• Router with PoE support