3Com SuperStack 3 NBX, Руководство администратора

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H.323 G
ATEWAY
Bandwidth
Bandwidth is the capacity to carry information. By using H.323, the same
bandwidth that supports one uncompressed G.711 voice connection can,
instead, support several compressed G.723 conversations with little
noticeable difference in quality.
Networks differ in the age of their equipment and in the quality of their
service. Traffic can form a bottleneck if network loads force a wide area
service provider to route traffic through old equipment.
Congestion
Users notice congestion when voice “breaks up” during a call.
Congestion can occur anywhere on the network, for example, at an
overloaded LAN (local or remote), at an overloaded router or firewall, or
within an overloaded internet. Because voice packets are only significant
during a conversation, IP networks respond to congestion by discarding
the data packets they can’t accommodate. Resending or delaying packets
is not an effective solution.
At the local level, congestion symptoms can be subtle. For example,
routers from different vendors can respond differently to congestion
because of the way they prioritize their response to packet congestion.
When considering communications problems, it is important to maintain
reserve capacity and to use a systematic approach that considers the
entire, end-to-end, connection.
Connections
Sometimes packet loss is caused by a poor physical connection. This type
of packet loss is more likely to occur in a LAN than in a WAN. Typical
causes are faulty wiring, connectors, and termination. High-bandwidth
LANs (100BASE-T) are more likely to have termination problems than
low-bandwidth (10BASE-T) LANs.
Packet Delay
Latency and jitter delays affect the Quality of Service.
Latency
Latency is the sum of all the fixed delays in an end-to-end connection.
Latency prevents a caller from responding immediately to another caller’s
remarks.