3Com NBX 100 Installation Manual page 44

44 C 1: I
HAPTER NTRODUCTION
NBX 100 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 100 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 100 supports IP Precedence, also called IP Type Of
Service (ToS, to specify the class of service for each packet. The NBX 100
also supports and allows you to configure settings for the emerging
Differentiated Services technology, which defines prioritizing over the
WAN.
Low-bandwidth Connections
You can configure a telephone to function as a low-bandwidth device or
to use ADPCM Audio Only so that it can operate over links that have
bandwidth as low as 56 Kbps, such as a single B channel of a PRI ISDN
line. A low-bandwidth telephone offers a minimum feature set. For
example, paging, conferencing, and music-on-hold are not available over
a low-bandwidth link.