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Voice Over IP - Per Call Bandwidth Consumption
Document ID: 7934
Interactive: This document offers customized voice bandwidth calculations with theTAC Voice Bandwidth Codec Calculator (registered customers only) tool.
Contents
Introduction
Prerequisites
Requirements
Components Used
Conventions
VoIP – Per Call Bandwidth
Explanation of Terms
Bandwidth Calculation Formulas
Sample Calculation
Configuring Voice Payload Sizes in Cisco CallManager and IOS Gateways
Impact of Changing Voice Payload Sizes
Voice Activity Detection
RTP Header-Compression or Compressed RTP (cRTP)
Heuristics for Compression
NetPro Discussion Forums - Featured Conversations
Related Information
One of the most important factors to consider when you build packet voice networks is proper capacity planning. Within capacity planning, bandwidth calculation is an important factor to consider when designing and troubleshooting packet voice networks for good voice quality.
This document explains voice codec bandwidth calculations and features to modify or conserve bandwidth when Voice over IP (VoIP) is used.
Note: As a complement to this document, we recommend theTAC Voice Bandwidth Codec Calculator (registered customers only) tool. This tool provides information on how to calculate the bandwidth required for packet voice calls.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware versions.
For more information on document conventions, refer to theCisco Technical Tips Conventions.
The following protocol header assumptions are used for the calculations:
40 bytes for IP (20 bytes) / User Datagram Protocol (UDP) (8 bytes) / Real-Time Transport Protocol (RTP) (12 bytes) headers.
Compressed Real-Time Protocol (cRTP) reduces the IP/UDP/RTP headers to 2or 4bytes (cRTP is not available over Ethernet).
6 bytes for Multilink Point-to-Point Protocol (MP) or Frame Relay Forum (FRF).12 Layer 2 (L2) header.
1 byte for the end-of-frame flag on MP and Frame Relay frames.
18 bytes for Ethernet L2 headers, including 4 bytes of Frame Check Sequence (FCS) or Cyclic Redundancy Check (CRC).
Note: The following table only contains calculations for the default voice payload sizes in Cisco CallManager or Cisco IOS?Software H.323 gateways. For additional calculations, including different voice payload sizes and other protocols such as Voice over Frame Relay (VoFR) and Voice over ATM (VoATM), use theTAC Voice Bandwidth Codec Calculator (registered customers only) tool.