Yealink CP969, Administrator'S Manual

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Administrator’s Guide for SIP-T5 Series Smart Media Phones
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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,
regarding how to guarantee that packet traffic not be delayed or dropped due to interference
from other lower priority traffic. VoIP can guarantee high-quality QoS only if the voice and the
SIP packets are given priority over other kinds of network traffic. IP phones support the DiffServ
model of QoS.
Voice QoS
In order 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 IP phones
should be configured with a high transmission priority. It is not applicable to CP960 IP phones.
SIP QoS
SIP protocol is used for creating, modifying and terminating two-party or multi-party sessions.
To ensure good voice quality, SIP packets emanated from IP phones should be configured with
a high transmission priority.
DSCPs for voice and SIP packets can be specified respectively.
Wi-Fi QoS
Wi-Fi Multimedia (WMM) is based on the IEEE 802.11e standard and provides basic Quality of
service (QoS) features to wireless networks. QoS enables Wi-Fi access points to prioritize traffic
and optimizes the way shared network resources are allocated among different applications.
Note
For voice and SIP packets, the IP phone obtains DSCP info from the network policy if LLDP
feature is enabled, which takes precedence over manual settings. For more information on LLDP,
refer to
LLDP on page 54 .