Configuring Security, Quality, and Network Features
Ensuring Voice Quality
Cisco SPA500 Series and WIP310 IP Phone Administration Guide
102
5
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.
Cisco recommends using the Cisco IP phones with QoS-capable networking
equipment that can prioritize the VoIP application traffic. QoS features are
available on many data networking switches and routers. A QoS-enabled router
prioritizes the packets going upstream to the ISP.
The following table approximates the bandwidth budget for each side of the
conversation (in each direction) using different codecs and number of calls. This
table is based on the following assumptions:
•
Bandwidth calculated with no silence suppression
•
20 millisecond of payload per RTP packet
G.723.1
High complexity. Cisco IP phones support the use of
ITU G.723.1 audio codec at 6.4 kbps. Up to two
channels of G.723.1 can be used simultaneously. For
example, Line 1 and Line 2 can be using G.723.1
simultaneously, or Line 1 or Line 2 can initiate a three-
way conference with both call legs using G.723.1.
NOTE
G.723.1 is not supported on the 525G or
WIP310.
3.8
G.722
Only one G.722 call at a time is allowed. If a
conference call is placed, a SIP re-invite message is
sent to switch the calls to narrowband audio.
NOTE
Not supported on the WIP310.
4.3 (approx)
Codec (Voice
Compression
Algorithm)
Complexity and Description
MOS Score
