Yealink VC400 Administrator's Manual

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Configuring Network95modern IP networks. Differentiated Services Code Point (DSCP) is used to define DiffServ classesand is stored in the first six bits of the ToS (Type of Service) field. Each router on the network canprovide QoS simply based on the DiffServ class. The DSCP value ranges from 0 to 63 with eachDSCP specifying a particular per-hop behavior (PHB) applicable to a packet. A PHB refers to thepacket 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 codepoints are of the form “xxx000”. The first three bits are the IP precedence bits. These classselector PHBs retain almost the same forwarding behavior as nodes that implement IPprecedence-based classification and forwarding. Expedited Forwarding PHB – the key ingredient in DiffServ model for providing alow-loss, low-latency, low-jitter and assured bandwidth service. Assured Forwarding PHB – defines a method by which BAs (Bandwidth Allocations) canbe given different forwarding assurances. Default PHB – specifies that a packet marked with a DSCP value of “000000” gets thetraditional 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 tointerference from other lower priority traffic. VoIP can guarantee high-quality QoS only if thevoice, video and data packets are given priority over other kinds of network traffic. Yealink videoconferencing systems support the DiffServ model of QoS. DSCPs for voice, video and datapackets that can be specified respectively.Voice QoSTo 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-qualityvoice transmission when the voice packets are configured to a higher DSCP value.Video QoSTo ensure acceptable visual quality for video, video packets emanated from the system shouldbe configured with a high transmission priority.