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Chapter 2
Getting Started
Establishing Connectivity
This section describes how to connect the SPA900 Series IP phone hardware. It includes the
following topics:
•
•
Bandwidth Requirements
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 900 Series 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
Codec
G.711
G.726-40 87 kbps
G.726-32 79 kbps
G.726-24 71 kbps
G.726-16 63 kbps
G.729
This table is based on the following assumptions:
•
•
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
Document Version 3.0
Bandwidth Requirements, page 2-9
Installing the SPA900 Series IP Phone, page 2-10
Table 2-1
illustrates the bandwidth budget using different codecs.
Ethernet Bandwidth Budget for Off-Net VoIP Calling
Approximate bandwidth budget for
each side of conversation
110 kbps
55 kbps
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.
2 calls
4 calls
220 kbps 440 kbps 660 kbps 880 kbps
174 kbps 348 kbps 522 kbps 696 kbps
158 kbps 316 kbps 474 kbps 632 kbps
142 kbps 284 kbps 426 kbps 568 kbps
126 kbps 252 kbps 378 kbps 504 kbps
110 kbps 220 kbps 330 kbps 440 kbps
Linksys 900 Series IP Phone Administrator Guide
Establishing Connectivity
6 calls
8 calls
2-9
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