Riverstone Networks Network Device SSG - Manual (Page 7)

Number Pooling
Local exchange carriers require a central office
(CO) code per rate center. As a result, there is
an increasing incidence of CO code exhaustion
requiring the associated numbering plan area
(NPA) splits and overlays. Currently, the CO
codes, NPA-NXX, are assigned to carriers at the
10,000-block level. At this level, the telephone
number utilization tends to be inefficient in
sparsely populated rate centers or in switches
that do not have many subscribers. As a result,
area codes are split even though numbers
remain unused. The goal of Number Pooling is
to promote better number utilization, thereby
avoiding additional area code splits. Number
Pooling addresses this use by using 1000-block-
level Number Pooling to avoid NPA splits.
The Number Pooling feature provides for
the assignment of numbers in blocks of 1,000.
These 1,000 numbers are considered pooled.
The owner of the 1,000 number block is called
the block holder, and the owner of the NPA-
NXX is called the code holder. A code holder
surrenders unused blocks to the pool, which
may then be assigned to another service
provider. The service provider owning the block
assigns a location routing number (LRN) for
all numbers within that block. The LRN is
used to route the call to the service provider
(destination). Any number within a pooled
block can port to another service provider.
Therefore, any given 10-digit telephone number
can be ported, pooled, both ported and pooled,
or neither ported nor pooled.
Table 1 shows some examples of ALR routing.
Table 1 - Types of ALR
Type of ALR Used for
ALR for HLRs HLR routing
ALR for SMSCs SMSC routing
ALR for VMSs VMS routing
A L C AT E L 5 >
ALR routing locates and
routes customer service
queries, facilitating
communication across
the network to all
wireless service nodes.