In this model, a packet radio channel of GPRS is mapped
into a VC in the serving OVPN. The links between edge
GGSNs and PEs devices (AC links) are non-optical links.
Therefore, no much change is required for Gi interfaces in the
edge GGSNs. The roles of PE devices are to establish tunnels
through the core optical network, multiplex packet radio
channels from GGSNs into tunnels, maintain the tunnels, and
demultiplex the packet radio channels from the tunnels to
other GPRS partners.
Data packets of a GPRS can change their packet radio
channels while their terminals roam. This can require some
changes of VCs in the serving OVPN, or even a new serving
OVPN must be established. Problems arise on how the GPRS
roaming impacts on the management and maintenance of the
serving OVPN and how the serving OVPN changes to adapt
to the GPRS roaming.
Changes of the serving OVPN is caused by changes of the
access points of the GPRS that it supports. If changes of the
packet radio channel do not make any change on the edge
GGSNs (which participate in the current serving OVPN), no
change is required for the serving OVPN. However, in cases
where some edge GGSNs are replaced by others, the serving
OVPN must be reconfigured.
The reconfiguration of a serving OVPN normally requires a
delay, which can cause a considerable loss for data over the
serving OVPN. To reduce this loss, predictions about possible
changes for a GPRS before providing a serving OVPN are
needed. However, in some case, the reconfiguration of the
serving OVPN is required.