User guide

TD 92422GB

18 February 2010 / Ver. E

System Planning

Ascom IP-DECT System

2 Wired LAN/Backbone Requirement

It is highly recommended that a Network Assessment of the LAN is carried out before an

installation or when new applications and/or user density is added to secure the voice

quality.

There are several things to consider when designing a network:

• In order to achieve optimal performance the infrastructure should be connected to a

switched network (no hubs or repeaters).

• When setting up a network supporting both voice and data it is recommended that

voice and data are separated on different VLANs.

• Maximum capacity of the VoIP traffic may not exceed 25% of the capacity of the

network.

• Maximum capacity of the network may not exceed 75% of the total capacity of the

network, including the VoIP traffic.

• No firewalls should be used in the network. If they are anyway, tunneling or application

aware firewalls should be used.

• Depending on network size, a backbone of at least 100 Mbps should be used.

Figure 1.

In a switched network the transmission delay should not be an issue but if voice traffic is

routed a significant transmission delay could be added. If the transmission delay is too

long an echo will appear in the voice path impacting the systems voice quality. The

transmission delay will also add to the speech delay.

Jitter in voice packages will also add to the speech delay since the IPBS/IPBL will adjust the

jitter buffer size.

Note: There are several tools from third-party vendors that is used to provide detailed and

useful information when performing site surveys.

2.1 End-to-End QoS

To achieve QoS for a phone call, it is important that QoS is enabled or managed all the

way between the two end points. By following a speech packet as it travels along the path

between the end points, it is possible to identify all network segments and transitions

where QoS needs to be managed.