Nortel BCM 3.7, Manual

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796 Policy configuration overview
N0008589 3.3
Business Communications Manager uses DiffServ to manage network traffic and resources. The
information that is required to support DiffServ and multi-field classification is transferred using
the Common Open Policy Services (COPS) protocol. COPS is a query and response protocol that
exchanges policy information messages using the Transmission Control Protocol (TCP). All
configuration can be performed using SNMP and Unified Manager.
DiffServ IP Quality of Service (QoS) architecture
DiffServ uses a simple mechanism that relies on a special encoding of the first 6 bits of the
DiffServ byte in the IP header. This byte is the IPv4 Type of Service (ToS) byte; for IPv6, is the
Traffic Class byte. The first 6 bits of this byte are called the DiffServ Code Point (DSCP).
In the packet forwarding path, differentiated services are processed by mapping the packet DSCP
to a particular forwarding treatment, or per hop behavior (PHB), at each network node along its
path. The code points may be chosen from a set of 32 standard values, a set of 16 recommended
values to be used in the future, or a set of 16 values reserved for experimentation and local use. Of
the 32 standard values, there are 8 Class Selector code points that are used primarily (but not
exclusively) for backward compatibility with existing definitions of the ToS byte.
Business Communications Manager is a DiffServ node that can support DiffServ functions and
behavior. DiffServ architecture defines a DiffServ-capable domain as a contiguous set of
DiffServ-compliant nodes that operate with a common set of service provisioning policies and
PHB definitions. The DiffServ domain is an autonomous system or network such as an internet
service provider (ISP) network or campus LAN.
DiffServ assumes the existence of a service level agreement (SLA) between DiffServ 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. In a given traffic direction, the traffic is expected to be shaped at
the egress point of the upstream network and policed at the ingress point of the downstream
network.
End-to-end QoS is enabled, typically through bilateral agreements (an agreement between two
DiffServ domains), between all the domains from the sender to the receiver. These agreements aid
in consistent PHB and QoS performance across all domains.
Typically, there are three types of edge devices in a DiffServ domain:
• Edge node (EN) — the switch or router connected directly to the desktop end station (ES)
(Business Communications Manager is an edge node in the DiffServ domain)
Ingress border node (IBN) — the ingress router at the boundary between two DiffServ
domains
• Egress border node (EBN) — the egress router at the boundary between two DiffServ domains
The following figure shows the bandwidth broker and various DiffServ nodes in two DiffServ
domains.