Yealink VC Series, Руководство администратора

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Administrator‘s Guide for Yealink Video Conferencing Systems
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The Best-Effort service is the default QoS model in the IP networks. It provides no
guarantees for data delivery, which means delay, jitter, packet loss and bandwidth
allocation are unpredictable. Differentiated Services (DiffServ or DS) is the most widely
used QoS model. It provides a simple and scalable mechanism for classifying and
managing network traffic and providing QoS on modern IP networks. Differentiated
Services Code Point (DSCP) is used to define DiffServ classes and is stored in the first six
bits of the ToS (Type of Service) field. Each router on the network can provide QoS
simply based on the DiffServ class. The DSCP value ranges from 0 to 63 with each DSCP
specifying a particular per-hop behavior (PHB) applicable to a packet. A PHB refers to
the packet scheduling, queuing, policing, or shaping behavior of a node on any given
packet.
Four standard PHBs available to construct a DiffServ-enabled network and achieve
QoS:

Class Selector PHB – backwards compatible with IP precedence. Class Selector
code points are of the form ―xxx000‖. The first three bits are the IP precedence bits.
These class selector PHBs retain almost the same forwarding behavior as nodes
that implement IP precedence-based classification and forwarding.

Expedited Forwarding PHB – the key ingredient in DiffServ model for providing a
low-loss, low-latency, low-jitter and assured bandwidth service.

Assured Forwarding PHB – defines a method by which BAs (Bandwidth Allocations)
can be given different forwarding assurances.

Default PHB – specifies that a packet marked with a DSCP value of ―000000‖ gets
the traditional best effort service from a DS-compliant node.
VoIP is extremely bandwidth and delay-sensitive. QoS is a major issue in VoIP
implementations, , with regard to guaranteeing how that packet traffic is not delayed or
dropped due to interference from other lower priority traffic. VoIP can guarantee
high-quality QoS only if the voice, video and data packets are given priority over other
kinds of network traffic. Yealink video conferencing systems support the DiffServ model
of QoS. DSCPs for voice, video and data packets that can be specified respectively.
Voice QoS
To make VoIP transmissions intelligible to receivers, voice packets should not be
dropped, excessively delayed, or made to suffer varying delay. DiffServ model can
guarantee high-quality voice transmission when the voice packets are configured to a
higher DSCP value.
Video QoS
To ensure acceptable visual quality for video, video packets emanated from the system
should be configured with a high transmission priority.