3Com NBX, Руководство по установке

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Before You Begin Installation 85
NBX System Quality of Service
Quality of Service (QoS) is a way to allocate resources in data switches
and routers so that data can be prioritized, with the most time-critical
data receiving higher priority. At Layer 2, the NBX system supports
Ethernet 802.1Q, “Standard for Virtual Bridged Local Area Networks,”
and its associated specification, 802.1P, “Standard for Local and
Metropolitan Area Networks, Supplement to Media Access Control
(MAC) Bridges: Traffic Class Expediting and Dynamic Multicast Filtering.”
These IEEE Ethernet standards define how Ethernet packets can be
prioritized.
At Layer 3, the NBX supports IP Precedence, also called IP Type Of Service
(ToS), to specify the class of service for each packet. The default
hexadecimal value for NBX system IP ToS settings is 0xb8.
Low-bandwidth Connections
You can configure a telephone to operate in lower-bandwidth
environments such as a single B channel of a BRI ISDN line or other links
with bandwidth as low as 56 Kbps.
■
The preferred method for enabling a low-bandwidth connection is to
select G729 audio, forcing the device to use lower-bandwidth
compressed audio when communicating with other system devices.
■
Alternatively, you can configure the telephone as a low-bandwidth
device by disabling some of the internal features such as paging,
conferencing, and music-on-hold. A check box in the NBX NetSet
device configuration screen (
Telephone Configuration > Telephones )
automatically selects the best parameters for low-bandwidth
connections.
You can also connect an NBX Telephone to the system over a broadband
connection and that is not considered a low-bandwidth connection. See
the
NBX Administrator’s Guide for information about connecting a
remote telephone over a broadband connection.
Before You Begin
Installation
Before you install the NBX system hardware:
■
Complete the system plan. See the System Planning Guide on the
NBX Resource Pack .
■
Verify that the external telephone lines are active and present at the
installation location.