ZyXEL Communications IP PBX X6004 - Manual (Page 185)

X6004 User’s Guide
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H A P T E R
8
QoS
8.1 Overview
This chapter shows you how to configure the X6004’s Quality of Service (QoS)
settings in the Configuration > PBX > Server Configuration > QoS screen.
Quality of Service (QoS) refers to both a network's ability to deliver data with
minimum delay, and the networking methods used to control the use of
bandwidth. Without QoS, all traffic data is equally likely to be dropped when the
network is congested. This can cause a reduction in network performance and
make the network inadequate for time-critical applications such as VoIP.
The following problems can occur on a congested network with poor QoS settings:
• Latency - delay of packet delivery. This can cause echoes during a
conversation.
• Jitter - variations in delay of packet delivery. This could cause strange sound
effects. The X6004 utilizes a jitter buffer to minimize the effects of jitter.
• Packet Loss - packets are dropped due to an overwhelming amount of traffic
on the network. Some degree of packet loss will not be noticeable to the end
user, but as packet loss increases the quality of sound degrades.
The X6004 can be configured to change the priority field of IP packets for all
outgoing RTP (Real Time Protocol) packets. The X6004 supports Type of Service
(ToS) and Differentiated Services (Diffserv) for implementing QoS. Configure the
X6004 with the QoS settings that your network uses for VoIP.
8.1.1 What You Can Do in this Chapter
Use the QoS screen to configure the type of QoS you want to use, and to specify
the level of service you want to use for the X6004’s traffic on your network. See
Section 8.2 on page 187 .
8.1.2 What You Need to Know
The following terms and concepts may help you as you read through the chapter.