GPRS technology introduce few network elements and nodes to the existing PLMN (phase 2) network which had been welly serving the circuit switch barrier services which are voice and short message service.
Network Element that support GPRS service
- PCU (Packet Control Unit)
- SGSN (Serving GPRS Support Node)
- GGSN (Gateway GPRS Support Node)
- BG (Border Gateway)
New Interface that introduced in GPRS service
- Gb (Interface between PCU and SGSN)
- Gd (Interface between SGSN and SMS-Gateway MSC (SMS-GMSC))
- Gf (Interface between SGSN and EIR for enquired IMEI)
- Gn (Interface between SGSN and local PLMN)
- Gp (Interface between SGSN and other PLMN when roaming - inbound roaming)
- Gs (Interface between SGSN and VLR for cordinating conventional GSM network when operating in GSM mode and GPRS Mode) - backward compatible
- Gr (Interface between SGSN and HLR for exchange subscriber information)
- Gc(Interface between GGSN and HLR for exchange location information)
- Gi (Interface between GGSN with external packet network element or service provider)
PCU - Packet Control Unit
- It can be located at SGSN, BSC or at BTS side depending on the vendor that implementing it.
- Conversion of Packet Data into PCU-Frames ( packet switched data and also TRAU-Frame from circuit switch data). PCU route both traffic types, circuit-switched and packet switched for all downstream. While upstream, PCU fraems converted and sent to SGSN via frame relay / ATM networks.
- Responsible for all radio control in GPRS which is Radio Link Control and Medium Access Control.
- Routing of data packets between GGSN and packet switched service.
- Mobility management that update the HLR via GPRSLocationUpdate operations whenever there is changes of Routing Area ( smaller than Location Area in conventional GSM 2G network). Besides, the SGSN will also inter operate with VLR via BSSMAP+ to update location area if there is changes compare to the previous location area.
- PDP / GPRS Session Management for maintaining the Packet Data Protocol session
- Resolve the APN ( Access Point Name ) via DNS liked service to indentify which GGSN should it to refer to. GTP (GPRS Tunnel Protocol is used for the SGSN and GGSN communications)
- SGSN would need to have huge tempory buffer of the packet data in case there is changes of cell during packet data transfer, the earlier SGSN would need to transfer the unacknowledged packet to the newly roam SGSN.
- Data compression also be part of the SGSN role to optimized the air-interface transferring of bursty traffic.
- Domestic charging can be applied here.
- Interconnection of the PLMN network towards external packet data network service provider.
- If Internet Protocol is chosen as the PDP context, the mapping of IP address that obtain during the session management and the mobile station identification will be kept here.
- International GPRS roaming charging can be applied here as the SGSN can be a foreign PLMN.
- takes care of all inter-PLMN GPRS traffic. It is important for roaming mobile stations.
Class A,B and C GPRS mobile station
- Class A - Simultaneous Operation of Circuit Switch and Packet Switch (both operate at the same time)
- Class B - Simultaneous Monitoring only, if the Packet Switch is active ( e.g. surfing WAP ) there is a traffic activity on Circuit Switch ( e.g. SMS ) the Packet Switch GPRS session will be suspend and resume after the circuit switch activity finish.
- Class C - Only support Circuit Switch or Packet Switch network only.