03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS
The relay function of a network node transfers the PDP PDUs received from the incoming link to the appropriate outgoing link. At SGSN and GGSN the relay function stores all valid PDP PDUs until they are forwarded to the next network node or until the maximum holding time of the PDP PDUs is reached. The PDP PDUs are discarded when buffering is longer than their maximum holding time. This maximum holding time is implementation dependent and can be influenced by the PDP type, the QoS of the PDP PDU, the resource load status, and by buffer conditions. The discarding protects resources from useless transfer attempts, especially the radio resource. Impacts on user protocol operation by too short holding time shall be avoided.
The SGSN and GGSN relay functions add sequence numbers to PDP PDUs received from SNDCP and from the Gi reference point, respectively. The SGSN relay function may perform re-sequencing of PDP PDUs before passing the PDP PDUs to SNDCP. The GGSN relay function may perform re-sequencing of PDP PDUs before passing the PDP PDUs to the Gi reference point.