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Different network components of the GPRS are connected together by well
defined interfaces. Some new interfaces to GSM have been added in GPRS to
support packet switched data mainly between GGSNs, SGSNs and other network
components. The following interfaces have been defined:
- Um interface between MS and BTS is very similar to GSM and defines
the modulation type, error correction/detection technique, power control
information etc.
- A interface between BTS and BSC defines the channel allocation,
power measurement information etc.
- Gb interface connects BSCs to SGSN.
- Gn interface is used between GSNs of same PLMN to exchange user
profile when the user moves from one SGSN to another.
- Gp interface is defined between two GSNs of different PLMN for
exchanging the user profile and other signaling information between a
SGSN and GGSN of another area.
- Gf interface is used between SGSN and EIR to query the IMEI
information if a MS tries to register with the network.
- Gr interface between SGSN and HLR is used to get the user profile,
the current SGSN address and the PDP address(es) for each user in PLMN.
- Gc interface between GGSN and HLR is used by GGSN to query user's
location and profile to update its location register.
- Gi interface connects GGSN to external PDN (e.g. X.25 or IP).
- Gs interface between SGSN and MSC/VLR is used to perform paging
request of circuit switched GSM call for combined attachment procedure.
- Gd interface between SMS-Gateway (SMS-GMSC) and SGSN is used to
exchange short message service (SMS) messages.
All GSNs are connected over a GPRS backbone network over IP. Within this
backbone the GSNs encapsulate and transmit PDN packets by using GPRS
Tunneling Protocol (GTP). This backbone network is of two types:
- Intra-PLMN backbone connects the GSNs of same PLMN and are therefore
private IP based networks of the service provider.
- Inter-PLMN backbone connects the GSNs of different PLMNs if there is
a roaming agreement is between them. The gateways between these PLMNS are
called border gateways and perform security functions apart from regular
functions to protect the private information against unauthorized usage.
Next: Services
Up: System Architecture
Previous: GPRS System Architecture
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2002-10-12