Introduction To Diffserv - ZyXEL Communications Prestige 652H series User Manual

Prestige 652H/HW Series User's Guide
LABEL
Scheduler Select either Priority-Based or Fairness-Based from the drop-down menu to control
the traffic flow.
Select Priority-Based to give preference to bandwidth classes with higher priorities.
Select Fairness-Based to treat all bandwidth classes equally. See section 20.5.
Maximize Select this check box to have the Prestige divide up all of the interface's unallocated
Bandwidth and/or unused bandwidth among the bandwidth classes that require bandwidth. Do not
Usage select this if you want to reserve bandwidth for traffic that does not match a bandwidth
class (see section 20.6.1) or you want to limit the speed of this interface (see the
Speed field description).
Back Click Back to go to the main BW Manager screen.
Apply Click Apply to save your settings back to the Prestige.
Cancel Click Cancel to begin configuring this screen afresh.

20.9 Introduction to DiffServ

Quality of Service (QOS) mechanisms provide the best service on a per-flow guarantee. To fine-tune the
levels of services on the priority of the traffic flow using QoS places a heavy burden on the network
infrastructure.
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.
20.9.1 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.
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.
20-10
Table 20-9 Bandwidth Manager: Summary
DESCRIPTION
Bandwidth Management