GGSN

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 has access to the mobile subscriber data for GPRS. On the network side, GGSN has a GTP protocol based interface towards the roaming network. For a subscriber, it may have a diameter based interface or any other interface for accessing SIM card subscription.  

GPRS Network Registration:

For data services, a sim card first connects to the SGSN in the roaming network. SGSN sends the 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, the mobile device gets the authentication information.

After successful authentication, the sim does a GPRS location update.  During the location update, HLR sends the GPRS subscription data to the device. A GPRS subscription has 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 a GPRS location update, the data signal on the device is visible in the 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 the GTP protocol. This is called PDP context activation.  PDP Context activation setup a logical tunnel between GGSN and SGSN using GTP-C. The 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 use this protocol over ss7/sigtran.  The home network should have an 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 authentication, SGSN initiates an 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

GTP-C is the control plane 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.

GTP-U

This protocol carries the actual data or user plane data for the internet. IP packets are received over the tunnel from SGSN and send to PDN from GGSN. Ip packets received from PDN and sent back to the SGSN in the tunnel. GTP-U version 1 is used. 

UDP protocol :

GTP-C and GTU-U protocol use services of User Datagram Protocol. 

IP Protocol:

UDP uses the 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. The protocol between MME and HSS is the diameter.  S6a diameter interface is used. 

LTE uses GTP-C version 2 and for GTP-U the version is 1.

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