AudioCodes MP-26 series, Руководство пользователя

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User's Manual 11. Quality of Service
Version 4.4.0 135 MP26x/MP27x
11 Quality of Service
Network-based applications and traffic are growing at a high rate, producing an ever-
increasing demand for bandwidth and network capacity. For obvious reasons, bandwidth
and capacity cannot be expanded infinitely, requiring that bandwidth-demanding services
be delivered over existing infrastructure, without incurring additional, expansive
investments.
The next logical means of ensuring optimal use of existing resources are Quality of Service
(QoS) mechanisms for congestion management and avoidance. QoS refers to the
capability of a network device to provide better service to selected network traffic. This is
achieved by shaping the traffic and processing higher priority traffic before lower priority
traffic.
As QoS is dependent on the "weakest link in the chain", failure of but a single component
along the data path to assure priority packet transmission can easily cause a VoIP call or a
Video on Demand (VoD) broadcast to fail miserably. QoS must therefore obviously be
addressed end-to-end.
The following are the potential bottleneck areas that need be taken into consideration when
implementing an end-to-end QoS-enabled service.

The Local Area Network: LANs have finite bandwidth, and are typically limited to 100
Mbps. When given the chance, some applications consume all available network
bandwidth. In business networks, a large number of network-attached devices can
lead to congestion. The need for QoS mechanisms is more apparent in wireless LANs,
where bandwidth is even more limited (typically no more than 20 Mbps on 802.11g
networks).

The Broadband Router: All network traffic passes through and is processed by the
broadband router. It is therefore a natural focal point for QoS implementation. Lack of
sufficient buffer space, memory or processing power, and poor integration among
system components can result in highly undesirable real-time service performance.
The only way to assure high QoS is the use of proper and tightly-integrated router
operating system software and applications, which can effectively handle multiple real-
time services simultaneously.

The Broadband Connection: Typically, the most significant bottleneck of the
network, this is where the high speed LAN meets limited broadband bandwidth.
Special QoS mechanisms must be built into routers to ensure that this sudden drop in
connectivity speed is taken into account when prioritizing and transmitting real-time
service-related data packets.

The Internet: Internet routers typically have a limited amount of memory and
bandwidth available to them, so that congestions may easily occur when links are
over-utilized, and routers attempt to queue packets and schedule them for
retransmission. One must also consider the fact that while Internet backbone routers
take some prioritization into account when making routing decisions, all data packets
are treated equally under congested conditions.
Note: For recommended QoS configuration see Section 11.7 on page 151 .