NEC SL1100, Сетевое руководство

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Networking Manual 6 - 1
Netw
or
k Design Consider
at
ions
6
Network Design Considerations
S
ECTION
1
I
NTRODUCTION
This chapter explains some issues that should be considered when
planning a NEC SL1100 VoIP installation. This is a generalized
explanation and therefore does not discuss vendor-specific issues and
solutions. Typically, different solutions are implemented by different
manufacturers.
S
ECTION
2
Q
O
S
Quality of Service (QoS) is one of the most important factors for VoIP.
This refers to the perceived quality of speech and the methods used to
provide good quality speech transmission. Several factors that affect
speech quality and several mechanisms can be used to ensure QoS.
This chapter also describes the problems that can occur and some
possible solutions. Each network equipment manufacturer (NEC, 3Com,
Cisco, etc.) has slightly different methods of implementing QoS and these
are not discussed in this document. This chapter provides an overview to
classify voice traffic on the NEC SL1100 so that the network equipment
can impose QoS.
2.1 QoS Definitions
This section lists common definitions used with QoS for VoIP.
Latency (Delay):
If at any point the usage on the network exceeds the available
bandwidth, the user experiences delay, also called latency. In more
traditional uses of an IP data network, the applications can deal with
this latency. If a person is waiting for a web page to download, they
can accept a certain amount of wait time. This is not so for voice
traffic. Voice is a real time application, which is sensitive to latency. If
the end-to-end voice latency becomes too long (150ms, for example),