D Guidance for VoIP Installation
D.1 VoIP Requirements
Bandwidth Assessment
When using IP-CSs, you must ensure that the IP network in use has enough bandwidth to support VoIP
communications. If the amount of bandwidth required for VoIP communications is more than the network can
accommodate, speech quality will be compromised. In addition, there may be an adverse effect on the
performance of other applications (e.g., email or web applications) that use the same network. Therefore, care
must be taken when assessing bandwidth requirements.
Inform your network administrator of the required bandwidth, and make sure that the network can support VoIP
communications even under conditions of maximum network traffic.
Required Bandwidth for a Call via an IP-CS
The required bandwidth depends on what combination of codecs and packet sending intervals is used. Keep
in mind the following points about the type of codecs and packet sending intervals, in terms of speech quality:
•
The speech quality of the codecs varies as follows: G.711 (High), G.729A (Low)
*1
•
The shorter the packet sending interval, the higher the speech quality.
•
The higher the speech quality the IP-CSs provide, the more bandwidth the IP-CSs require.
*1
When the preferred codec of each party differs, the call will be established using the lower codec. For example, if the caller prefers
G.711 while the called party prefers G.729A, the call will be established using G.729A.
Codec
Packet Sending Interval
20 ms
30 ms
40 ms
60 ms
G.711
87.2 kbps
79.5 kbps
—
—
G.729A
31.2 kbps
23.5 kbps
19.6 kbps
15.7 kbps
Required Bandwidth for Each Virtual IP-CS Card
To allow all IP-CSs to handle calls simultaneously, it is necessary to keep available the bandwidth required by
a virtual IP-CS card with the maximum number of IP-CSs connected.
Provided below is the formula to calculate the amount of bandwidth required for each virtual IP-CS card.
Required Bandwidth
= (Bandwidth for a call via an IP-CS
´
4)
Network Configuration
You must evaluate the structure of the existing network to see if a VoIP network can be implemented. Below
are the points that should be evaluated.
Is the IP network a managed network?
A VoIP network should be implemented on a managed IP network such as Frame Relay, Leased Line, or
IP-VPN (Virtual Private Network).
An unmanaged network, such as the Internet (including an Internet VPN), cannot be used to employ a VoIP
network because delays and loss in data transmission can cause huge degradation in speech quality.
Is it possible to have static IP addressing?
IP-CSs on the network always perform VoIP communications through the PBX. Therefore, the PBX must be
assigned static IP addresses, which must be programmed to each IP-CS on the network.
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Quick Installation Guide
Document Version 2009-12
D Guidance for VoIP Installation
