GGSN - What GGSN stands for
GGSN full form is, GPRS support Node. A mobile network operator deploys GGSN , in home PLMN as a gateway to provide internet service to a mobile subscriber. GGSN have access to the mobile subscriber data for GPRS. On network side , GGSN have GTP protocol based interface towards the roaming network. For subscriber , it may have diameter based interface or any another interface for accessing SIM card subscription.
GPRS Network Registration:
For data services a sim card first connects to the SGSN in roaming network. SGSN sends authentication request to the HLR located in home network with the IMSI. HLR sends the request to the AuC (authentication center , holding sim card information for generating authentication information), If subscriber or IMSI is provisioned on HLR and Auc, mobile device gets the authentication information.
After successful authentication, sim does a gprs location update. During location update, HLR sends the grps subscription data to the device. A gprs subscription have APN and QoS or Quality Of Service profile. Values received in QoS, used by the sgsn for setting a bearer channel with the device. After update location, the data signal on device is visible in case of 3G. In LTE after registration with HSS (in lte HSS holds the subscription ). For gateway in place of GGSN have PGW in lte.
Data Session Creation:
After registration, sgsn creates a data session with the GGSN over GTP protocol. This is called pdp context activation. PDP Context activation setup a logical tunnel between GGSN and SGSN using GTP-C . Following shows create pdp call flow along with gprs registration.
Protocols for data services in 3g and 2g:
GSM MAP over SS7 :
SGSN and HLR/AuC uses this protocol over ss7/sigtran. Home network should have agreement with the roaming network.
To authenticate a user or IMSI, sgsn sends Send Authentication Info (SAI) gsm map message to the HLR/AuC. HLR sends SAI response to sgsn. In response based on apn , sgsn drives the ggsn address.
After successful authetication , sgsn initiates update gprs location procedure with HLR. Sgsn sends Update GPRS Location map operation over ss7 to the HLR, on success hlr returns GPRS data in Insert Subscriber Data map operation.
GTP-C is the control plain protocol used between SGSN and GGSN for creating up a PDP context. After pdp context setup a tunnel is formed between sgsn and ggsn. GTP-C protocol version 0 and version 1 is used in 2g and 3g data.
This protocol carries the actual data or a user plane data for internet. IP packets are received over tunnel from sgsn and send to PDN from GGSN. Ip packets received from PDN and sent back to the sgsn in tunnel. GTP-U version 1 is used.
UDP protocol :
GTP-C and GTU-U protocol uses services of User Datagram Protocol.
UDP uses services of Internet Protocol.
Protocols for data service in LTE:
In LTE, in place of HLR , HSS is used and in place to SGSN , MME is used. Protocol between MME and HSS is diameter. S6a diameter interface is used.
LTE is uses GTP-C version 2 and for GTP-U the version is 1.