1. Voice over IP

2. IP Networking Overview
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IP assumes delay and packet ordering problems

3. Delay budget deals with one-way delay, not a round-trip!
Voice Delay with IP
One-Way, Mouth-to-Ear Delay
Description
1-150 ms
Suitable for most delay sensitive applications like voice. ms
Still acceptable, but starts to influence voice quality. Communication can be annoying if no actions are taken.
400 ms and greater
Unacceptable for most delay sensitive applications.
Delay budget deals with one-way delay, not a round-trip!
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4. Understanding VoIP
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5. Major VoIP Protocols Catatan : VoIP Protocol Description H.323
ITU standard protocol for interactive conferencing.
Evolved from H.320 ISDN standard.
Flexible, complex.
Media Gateway Control Protocol (MGCP)
Emerging standard for Public Switched Telephone Network (PSTN) gateway control, thin device control.
Session Initiation Protocol (SIP)
IETF protocol for interactive and non-interactive conferencing.
Simpler, but less mature, than H.323.
Real-Time Transport Protocol (RTP)
IETF standard media streaming protocol.
Real-Time Transport Control Protocol (RTCP)
Protocol that provides out-of-band control information for an RTP flow.
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Low Latency Queuing (LLQ)
Priority queuing technique that uses priority queuing-class-based weighted fair queuing (PQ-CBWFQ).

6. The PBX seizes a trunk line to the router, and forwards dial digits.
Signaling from PBX to the Router
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The PBX seizes a trunk line to the router, and forwards dial digits.

7. Signaling Between Routers
The Dial Plan Mapper reads the dial digits, and finds the address of the remote IP peer. The H.323 agent initiates a Q.931 call to the remote peer.
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8. Signaling from Router to PBX
The remote H.323 agent seizes a PBX trunk, returns a Q.931 acknowledgment to the origin, and forwards dial digits to the PBX
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9. VoIP Bandwidth Consumption
Coded Frame Size (bytes)
Voice Frames in VoIP Packet
IP+UDP+RTP Header Size (bytes)
Layer 2 Header Size (bytes)
Voice Bandwidth (Kbps)
Layer 2 Technology Used
Total Bandwidth Required
Coding Algorithm
G.711 64
160 2 40
Ethernet II 26
90.4
G.711 64
160 2 40
MLPPP 7
82.8
G.711 64
160 2
2 (cRTP)
MLPPP 7
67.6
Ethernet II (Cisco Default)
G.729 8 20 2 40 26
34.4
G.729 8 20 2 40
MLPPP 7
26.8
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G.729 8 20 2
2 (cRTP)
MLPPP 7
11.6

10. VoIP QoS Building Blocks
Devices Affected
IP Network Issue
Solutions
Backbone speed and scale
Backbone routers
High-performance routers
Packet classification
Edge routers
IP Precedence
Bandwidth management and admission control
Edge routers
Voice compression
Real-Time Transport Protocol (RTP) header compression
Gatekeepers
Congestion management
Edge routers
Backbone routers
Weighted Random Early Detection (WRED)
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Queue management
Edge routers
Backbone routers
Low Latency Queuing (LLQ)
Other queuing techniques

11. RTP Header Compression
RTP Headers are almost always 2 Bytes long when compressed.
RTP header compression saves bandwidth by compressing packet headers across WAN links.
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12. Low Latency Queuing
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13. Configuring IP Precedence
Precedence Definition
7 Network control
6 Internetwork control
5 Critical
4 Flash-override
3 Flash
2 Immediate
1 Priority
0 Routine
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14. Example: VoIP over PPP Configuration
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