McDewey

Understanding Delay in Packet Voice Networks Contents Introduction
Basic Voice Flow
How Voice Compression Works
Standards for Delay Limits
Sources of Delay
Coder (Processing) Delay
Packetization Delay
Serialization Delay
Queuing/Buffering Delay
Network Switching Delay
De-Jitter Delay
Build the Delay Budget
Single-Hop Connection
Two Hops on a Public Network with a C7200 that Acts as a Tandem Switch
Two-Hop Connection over a Public Network with a PBX Tandem Switch
Two-Hop Connection over a Private Network with a PBX Tandem Switch
Effects of Multiple Compression Cycles
Considerations for High-Delay Connections
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Related Information
Introduction
When you design networks that transport voice over packet, frame, or cell infrastructures, it is important to understand and account for the delay components in the network. If you account correctly for all potential delays, it ensures that overall network performance is acceptable. Overall voice quality is a function of many factors that include the compression algorithm, errors and frame loss, echo cancellation, and delay. This paper explains the sources of delay when you use Cisco router/gateways over packet networks. Though the examples are geared to Frame Relay, the concepts are applicable to Voice over IP (VoIP) and Voice over ATM (VoATM) networks as well.
Basic Voice Flow
The flow of a compressed voice circuit is shown in this diagram. The analog signal from the telephone is digitized into pulse code modulation (PCM) signals by the voice coder-decoder (codec). TAC Notice: What's Changing on TAC Web

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