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SWITCHING,ROUTING,ANDSIGNALING 781Table 3TMN ArchitectureLogical layer Functional responsibilitiesBusiness management Provides an enterprise view that incorporates high-level, business planning
and supports setting goals, establishing budgets, tracking financial
metrics, and managing resources such as products and people.
Service management Provides the basic contact point for customers (provisioning, billing and
accounting, troubleshooting, quality monitoring, etc.) as well as for
service providers and other administrative domains.
Network management Provides an overall view of the network resources, end to end, based on
the information from below about network elements and links.
Coordinates activities at the network level and supports the functional
requirements of service management.
Element management Provides a view of individual network elements or groupings into
subnetworks. Element managers (OSs) are responsible for subsets of all
network elements, from the perspective of TMN-manageable information
such as element data, event logs, and activity. Mediation devices belong
in this layer, communicating with OSs via the Q3 interface.
Network elements Presents the TMN-manageable information of individual network resources
(e.g., switches, routers, Q-adapters).there may be no or a limited choice of carriers. Other
countries have begun to deregulate, so that multiple car-
riers compete for subscriber business, often creating more
choices in technology and services, as well as better pric-
ing. In either case, service availability may differ from one
location to another: DSL access might be easily obtained
in greater Boston, but not be available in a rural area; T1
service might be acquired readily in Singapore but per-
haps not everywhere in New York City.
Do not make the mistake, however, of assuming that
more highly developed areas or countries always have bet-
ter service options than developing ones. An established
metropolitan area experiencing rapid growth in demand
for telecommunications may be less able to adapt or ex-
pand existing cable and switching capacity to meet new
orders than a new suburban business park where there
is plenty of room to install new cables and switches to
provide higher-speed services. Similarly, developing coun-
tries that have very little investment in old infrastructure
may be able to skip generations of technology, installing
the latest where there was previously none. Economics
tend to dictate that this does not happen uniformly, but
rather emphasizes locations more likely to provide rapid
payback for the particular technology investment (e.g.,
urban rather than rural, business rather than residential,
and high-density population areas). Often it is the access
infrastructure that lags behind, because the upgrade costs
cannot be amortized across multiple subscribers the way
backbone investments can. This is especially true where
the end-points are individuals with more limited budgets
than business or organizational enterprises.SWITCHING, ROUTING,
AND SIGNALING
Network Architecture
MANs and WANs are usually divided into three logical seg-
ments (Figure 5).Accesstypically includes the customerpremises equipment (CPE) located in a subscriber’s build-
ing or office area and the link that physically connects
from there to the service provider’s point of presence. This
link is connected to a device at theedgeof the service
provider’s network, and the edge device is connected to
devices that compose thecore(also called the backbone)
of the service provider’s network. Different technologies
are often used in the access and core portions, with the
edge required to translate between the two. The ratio of
the aggregate input capacity from all subscriber connec-
tions to an edge device to the output capacity from the
edge into the core describes the degree of oversubscrip-
tion. For example, if the sum of all access links is 200 Mbps
and the core link is 100 Mbps, then the oversubscription
ratio is 2:1. A ratio less than or equal to 1 is called non-
blocking; the network performance for values greater than
1 depends on the bursty nature of data traffic to minimize
the probability that traffic will be delayed excessively (by
buffering) or discarded (when buffers become full).MAN or WANBAaccessedgecoreFigure 5: WAN/MAN architecture.