Download - 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