GPRS Network Node Dimensioning

Among the nodes that
need to be dimensioned for GPRS traffic are the BSC, the SGSN, and the
GGSN. Generally, the capacity of a BSC is limited by the number of cells,
the number of BTS sites (or interfaces to BTS sites), the number of transceivers
(regardless of whether those transceivers are used for voice or data),
and the number of simultaneous PDCHs. In addition, one needs to dimension
the Gb interface, which is related to the number of Gb ports (T1 or E1)
supported by the BSC. In most implementations, one finds that the number
of supported PDCHs is sufficiently large so that other limitations, such
as the maximum number of transceivers, will be reached first, particularly
in a combined GSM/GPRS network.
An SGSN has a number of capacity limitations—the number of attached
subscribers, the number of cells, the number of routing areas, the number of Gb ports, and the total throughput capacity. Typically, one finds that the key
capacity limitations are the number of attached subscribers and the total
throughput, as these limits are likely to be met before any of the others.
For the GGSN, the key limitations are the number of simultaneous PDP
contexts and the total throughput. These key dimensioning factors are
listed in Table 5-3.