Zyxel V301-T1 [108/240] Dscp and per hop behavior

Zyxel V301-T1 [108/240] Dscp and per hop behavior
Chapter 10 SIP Account Setup
V300 Series User’s Guide
108
Quality of Service (QoS)
Quality of Service (QoS) refers to both a network's ability to deliver data with
minimum delay and the networking methods used to provide bandwidth for real-
time multimedia applications.
Type Of Service (ToS)
Network traffic can be classified by setting the ToS (Type Of Service) values at the
data source (for example, at the V300) so a server can decide the best method of
delivery, that is the least cost, fastest route and so on.
DiffServ
DiffServ is a class of service (CoS) model that marks packets so that they receive
specific per-hop treatment at DiffServ-compliant network devices along the route
based on the application types and traffic flow. Packets are marked with DiffServ
Code Points (DSCPs) indicating the level of service desired. This allows the
intermediary DiffServ-compliant network devices to handle the packets differently
depending on the code points without the need to negotiate paths or remember
state information for every flow. In addition, applications do not have to request a
particular service or give advanced notice of where the traffic is going.
DSCP and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of
Service (TOS) field in the IP header. The DS field contains a 2-bit unused field and
a 6-bit DSCP field which can define up to 64 service levels. The following figure
illustrates the DS field.
Figure 88 DiffServ: Differentiated Service Field
DSCP is backward compatible with the three precedence bits in the ToS octet so
that non-DiffServ compliant, ToS-enabled network device will not conflict with the
DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior),
that each packet gets across the DiffServ network. Based on the marking rule,
different kinds of traffic can be marked for different priorities of forwarding.
Resources can then be allocated according to the DSCP values and the configured
policies.
DSCP
(6-bit)
Unused
(2-bit)

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