Technical data

Features

EN4442EN00EN_0001

Siemens

noise and “silence“ are transmitted. Voice activity detection makes use of this knowledge,

interrupts the data transmission and drastically reduces the data rate as soon as silence is

detected. As soon as voice activity is detected again, transmission for that direction is

immediately re-established (with full bandwidth).

The resulting bandwidth reduction is in the range of 50% to 75% which is very significant.

The VAD classmark is deactivated by default, but can be activated at any time for voice

connections.

4.10 Comfort Noise Generation (CNG)

While using VAD, the DSP at the destination emulates background noise from the source side,

preventing the perception that a call is disconnected.

4.11 Echo Cancellation

The HG 3500 integrated gateway supports on board echo cancellation for up to 60/120

channels (performed on the on-board DSP modules) compliant with the ITU-T G.168 standard.

Given the relatively long delays inherent to IP telephony, (echo becomes more noticeable the

longer the delays) echo needs to be removed prior to transmission.

4.12 QOS Support

VLAN-tagging according IEEE 802.1p/q on Layer 2 as well as DiffServ (defined in RFC 2474)

on the IP Layer have been implemented in order to provide the best possible voice quality using

an IP network.

Of course all switches and routers in the customer’s IP network must support IEEE 802.1p/q

and/or DiffServ prioritization in order to take advantage of these mechanisms.

4.12.1 Real Time Port Monitoring

The HiPath 4000 system monitors a number of network parameters that can affect QoS

between IP line gateways and phones. These parameters are used to troubleshoot and quickly

locate IP network problems

The following parameters are monitored

● Delay for VoIP payload connections between IP clients and IP gateways.

VAD must not be activated in the case of fax, modem and digital data connections!