SGSN: |
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The SGSN or Serving GPRS Support Node is one of the
new network elements that need to be introduced for GPRS. The SGSN is part of the GPRS
core network. Together with the GGSN, the SGSN forms the GPRS core network (figure 1).
Note that the standard allows for the physical integration of SGSN and GGSN.
Figure 1: The SGSN controls a number of BSS's The SGSN is basically a packet switch that can route incoming data packets in uplink and downlink direction. In uplink direction, the SGSN is connected to the GGSN via the IP-based intra-PLMN-backbone. In downlink direction, the SGSN interconnects a number of BSS's to the GPRS core network. Therefore, each SGSN serves a limited geographic area as illustrated in figure 2, comparable to the MSC in plain GSM.
Figure 2: The geographic dedication of the SGSN Important Functions of the SGSN:
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Parameter | Description | Type (Mandatory / Optional - Fixed (Unchangeable) / Variable |
IMSI | Subscriber Identity | M/F |
MM State | The respective GPRS Mobility Management State (e.g. IDLE, STANDBY, READY) | M/V |
P-TMSI | The GPRS Counterpart for the GSM TMSI. Temporary Subscriber Identity | M/V |
P-TMSI Signature | M/V | |
IMEI | Equipment Identity Number | O/F |
MSISDN | Telephone Number | M/F |
Routeing Area | Current routeing Area | M/V |
Cell Identity | Current Cell in READY State | M/V |
Cell Identity Age | The time that elapsed since the last received LLC PDU from the Mobile Station at the SGSN | M/V |
VLR Number | The number of the current VLR/MSC | M/V |
New SGSN Address | IP-Address of the SGSN to which not sent N-PDUs should be forwarded to | O/V |
Authentication Triplets | Authentication and ciphering Parameters | M/V |
Kc | The currently used Ciphering Key | M/V |
CKSN | Ciphering Key Sequence Number of the Kc | M/V |
Ciphering Algorithm | Currently selected Ciphering Algorithm | M/V |
MS Radio Access Capability | The Radio access capabilities of the Mobile Station |
M/V |
MS Network Capability | The Network Capabilities of the Mobile Station | M/V |
DRX Parameters | The Parameters for the Discontinuous reception | M/V |
MNRG | Shall activity from the MS be reported to the HLR or not | M/V |
NGAF | Shall activity from the MS be reported to the VLR/MSC or not | M/V |
PPF | PS or CS services | M/V |
Subscribed Charging Characteristics | The Charging Characteristics of the Subscriber | M/V |
OMC Identity | Contains Identity of the OMC that shall receive the recorded trace | O/V |
SMS Parameters | The SMS related Parameters | O/V |
Recovery | Indicates if HLR or VLR is performing database recovery | M/V |
Radio Priority SMS | Parameters for SMS tramnsmission | O/V |
PDP Context Identifier | The Index of the PDP context | O/V |
PDP State | PDP state ACTIVE or INACTIVE | O/V |
PDP Type | IP or PPP | O/V |
PDP Address | The fixed
PDP-address of the mobile station (empty if dynamic IP-addressing is used) The mnemonic address of the serving GGSN (e.g. www.abcd.d2.gprs) applying to the DNS-rules. |
O/V |
APN Subscribed | The APN received from the HLR | O/V |
APN in Use | Indicates the APN Network Identifier | O/V |
NSAPI | Network Service Access Point Identifier | O/F |
TI | Transaction Identifier | O/F |
GGSN Address in Use | The IP Address of the currently serving GGSN | O/V |
VPLMN allowed | May the MS use only the HPLMN or the VPLMN too? | O/V |
QoS Profile Subscribed | Quality of Service Profile that a subscriber is paying for (one per PDP-context) | O/F |
Table 1: Information Storage within the SGSN
[2GTS 02.60 / 3GTS 23.060 / 3GTS 29.060]