Page 97 - From GMS to LTE

General Packet Radio Service (GPRS) and EDGE 83

2.3.6 Network Mode of Operation
Similar to GSM, the data transferred over the GPRS network can be both user data and
signaling data. Signaling data is exchanged, for example, during the following procedures:

the network pages the mobile device to inform it of incoming packets;
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the mobile device accesses the network to request resources (PDTCHs) to send
●
packets;
modification of resources assigned to a subscriber;
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acknowledgment of correct reception of user data packets.
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This can be done in a number of ways.
In GPRS, NOM I signaling for packet‐ and circuit‐switched data is done via the GSM
PCH. To make sure that incoming voice calls are not missed by class B mobile devices
during an active data transfer, an interface between the circuit‐switched part (MSC)
and the packet‐switched part (Serving GPRS Support Node – SGSN) of the network is
used. This interface is called the Gs interface. Paging for incoming circuit‐switched calls
will be forwarded to the packet‐switched part and then sent to the mobile device as
shown in Figure 2.9. If a packet data transfer is in progress when paging needs to be
sent, the mobile device will be informed via the Packet‐Associated Control Channel
(PACCH), to which the circuit‐switched GSM part of the network does not have access.
Alternatively, the paging is done via the PCH. The Gs interface can also be used for
combined GSM/GPRS attach procedures and location updates (LU). As it is optional,
some, but not all, networks use the functionality today.
GPRS NOM II is simpler than NOM I and is the most commonly used network opera-
tion mode today. This is because there is no signaling connection between the circuit‐
switched and packet‐switched parts of the core network, that is, no Gs interface is used.
To overcome the shortcoming of not being able to signal incoming SMS and voice
calls during a GPRS data transfer between the circuit‐switched and packet‐switched
core network, a method has been defined for the BSC in the radio network to inform the

Figure 2.9 Paging for an incoming voice call via the
Gs interface.
PSTN

MSC
Gs Interface
SGSN

A-Interface Gb Interface

BSS