Nortel Networks 2000 Manual De Usuario
Chapter 4 Policy-enabled networks 277
Using the Business Policy Switch 2000 Version 1.2
DiffServ Concepts
DiffServ is described in IETF RFCs 2474 and 2475. This architecture is flexible
and allows for either end-to-end QoS or intradomain QoS by implementing
complex classification and mapping functions at the network boundary or access
points. Within a DiffServ domain, the packet treatment is regulated by this
classification and mapping.
and allows for either end-to-end QoS or intradomain QoS by implementing
complex classification and mapping functions at the network boundary or access
points. Within a DiffServ domain, the packet treatment is regulated by this
classification and mapping.
The DiffServ basic elements are implemented within the network and include:
•
Packet classification functions
•
A small set of per-hop forwarding behaviors
•
Traffic metering, marking, and policing
Traffic is classified as it enters the DS network and is then assigned the
appropriate PHB based on that classification. Within the IP packet, the 6 bits in
the DSCP are marked to identify how the packet should be treated at each
subsequent network node. This mapping of DS codepoints to per-hop behavior
(PHB) is configurable, and the DSCP may be re-marked as it passes through a
DiffServ network. Re-marking the DSCP allows for the treatment of packets to be
reset based on new network specifications or desired levels of service.
appropriate PHB based on that classification. Within the IP packet, the 6 bits in
the DSCP are marked to identify how the packet should be treated at each
subsequent network node. This mapping of DS codepoints to per-hop behavior
(PHB) is configurable, and the DSCP may be re-marked as it passes through a
DiffServ network. Re-marking the DSCP allows for the treatment of packets to be
reset based on new network specifications or desired levels of service.
DiffServ assumes the existence of a Service Level Agreement (SLA) between DS
domains that share a border. The SLA defines the profile for the aggregate traffic
flowing from one network to the other based on policy criteria. As the traffic
moves within the DiffServ network, policies ensure that traffic marked by the
different DSCPs is treated according to that marking.
domains that share a border. The SLA defines the profile for the aggregate traffic
flowing from one network to the other based on policy criteria. As the traffic
moves within the DiffServ network, policies ensure that traffic marked by the
different DSCPs is treated according to that marking.
QoS classes
The BPS 2000 supports the following Nortel Networks QoS classes:
•
Critical and Network classes have the highest priority over all other traffic.
•
Premium class is an end-to-end service functioning similarly to a virtual
leased line. Traffic in this service class is normally guaranteed an agreed-upon
peak bandwidth. This service class is suitable for real-time applications like
video and voice over IP. The recommended PHB for this service is the
Expedited Forwarding (EF) PHB.
leased line. Traffic in this service class is normally guaranteed an agreed-upon
peak bandwidth. This service class is suitable for real-time applications like
video and voice over IP. The recommended PHB for this service is the
Expedited Forwarding (EF) PHB.