VoIP White Paper
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© 2006 InSciTek Microsystems, Inc. All rights reserved. Allworx is a registered trademark of InSciTek Microsystems. All other names may be
trademarks or registered trademarks of their respective owners.
Revised: February 8, 2007
Page 10
7 Bandwidth Calculations
This section provides details for a technical foundation of bandwidth calculations in Allworx-supported VoIP
applications across the LAN and WAN. Also included are deployment recommendations that may help
resellers and end-users with their application rollouts.
• In a VoIP telephone call, the caller’s voice is converted to electrical signals which are then coded into
data network packets or traffic. The coding/decoding (codec) scheme and the packet transmit interval
collectively determine the amount of bandwidth consumed per call.
• G.711 calls send and receive a stream of Ethernet frames, each 214 bytes long, at a rate of 50 per
second (20ms interval). The bandwidth required is 85.6kbps in each direction of the call. Calls that
traverse Frame Relay, ATM/DSL, PPPoE, or VPN links will consume more bandwidth due to the
additional encapsulation of the transport protocol(s).
• G.729A calls send and receive a stream of Ethernet frames, each 74 bytes long, at a rate of 50 per
second (20ms interval). The bandwidth required is 29.6kbps in each direction of the call. Calls that
traverse Frame Relay, ATM, or VPN links will consume more bandwidth due to the additional
encapsulation of the transport protocol(s).
• Both G.711 and G.729A codecs may be used for VoIP calls through the Allworx. This typically involves a
call from a VoIP phone through the Allworx server to another VoIP phone or soft-phone. Codec
preference settings at each endpoint will determine which is used. For Allworx IP phones, this setting is
configured on the handset’s pages for each particular station.
• Only the G.711 codec is supported for calls in which the Allworx server is an endpoint. This typically
involves a call from an Allworx-attached analog phone to another phone (VoIP or analog), a call from a
VoIP phone to the Allworx voicemail system or auto attendant, or a call from a VoIP phone to an external
user over analog public telephone network connections
.
7.1 Codec Support Matrix
Calling/Called Endpoint Codec Supported
Cisco 7905 G711
Cisco 7912 G711
Cisco 7940 G711 & G729A *
Cisco 7960 G711 & G729A *
Allworx 9102 G711 & G729A *
Allworx 9112 G711 & G729A *
Analog set
Analog telephone line
G711
3
rd
party gateways G711 & G729A **
Auto Attendant G711
On-Hold Music G711
Voicemail G711
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