Linksys VOICE SYSTEM SPA 900 SERIES - Manual (Page 33)

2-10
Linksys IP Phone Administrator Guide
Firmware Version 5.1
Chapter 2 Getting Started
Establishing Connectivity
• Installing the SPA900 Series IP Phone, page 2-10
Bandwidth Requirements1
Depending on how you have your IP phones configured, each call requires 55 to 110 kbps in each
direction. Therefore, using G.729 as the voice codec setting, and with an average business-grade
broadband Internet connection supporting 1.5 Mbps downstream and 384 kbps upstream, a total of seven
(7) simultaneous conversations can be reliably supported with adequate bandwidth available for file
downloads.
Linksys recommends using the Linksys IP phone with QoS-capable networking equipment that can
prioritize the VoIP application traffic. QoS features are available on many Linksys data networking
switches and routers. A QoS-enabled router prioritizes the packets going upstream to the ISP.
Table 2-1
illustrates the bandwidth budget using different codecs.
This table is based on the following assumptions:
• Bandwidth Calculated with No Silence Suppression
• 20 Millisecond of payload per RTP packet
Note The use of silence suppression can reduce the average bandwidth budget by 30% or more.
For more information about bandwidth calculation, refer to the following websites:
http://www.erlang.com/calculator/lipb/
http://www.packetizer.com/voip/diagnostics/bandcalc.html
Installing the SPA900 Series IP Phone
This section describes how to install and verify operation of SPA900 Series IP phones.
Check to make sure that you have the following package contents:
• Linksys 900 Series phone
• Ethernet cable
• Power adapter (must be ordered separately for PoE units: SPA922, SPA942, and SPA962)
Table 2-1 Ethernet Bandwidth Budget for Off-Net VoIP Calling
Codec
Approximate bandwidth budget for
each side of conversation
2 calls 4 calls 6 calls 8 calls
G.711 110 kbps 220 kbps 440 kbps 660 kbps 880 kbps
G.726-40 87 kbps 174 kbps 348 kbps 522 kbps 696 kbps
G.726-32 79 kbps 158 kbps 316 kbps 474 kbps 632 kbps
G.726-24 71 kbps 142 kbps 284 kbps 426 kbps 568 kbps
G.726-16 63 kbps 126 kbps 252 kbps 378 kbps 504 kbps
G.729 55 kbps 110 kbps 220 kbps 330 kbps 440 kbps