03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS
The packet routeing and transfer function:
– routes and transfers packets between a mobile TE and an external network, i.e., between reference point R and reference point Gi;
– routes and transfers packets between mobile TE and other GPRS PLMN, i.e., between reference point R and reference point Gi via interface Gp; and
– routes and transfers packets between TEs, i.e., between the R reference point in different MSs.
The PDP PDUs shall be routed and transferred between the MS and the GGSN as N‑PDUs. In case of PDP type PPP, the maximum size of each N‑PDU shall be 1 502 octets. In other cases, the maximum size of each N‑PDU shall be 1 500 octets. When the MS or the GGSN receives a PDP PDU that results in an N‑PDU that is not larger than the maximum N‑PDU size, then the PDP PDU shall be routed and transferred as one N‑PDU. When the MS or the GGSN receives a PDP PDU that results in an N‑PDU that is larger than the maximum N‑PDU size, then the PDP PDU shall be segmented, discarded or rejected, depending on the PDP type and the implementation. The packet data protocol in the MS may limit the maximum size of the PDP PDUs that are routed and transferred, e.g., due to MS memory limitations.
Between the SGSN and the MS, PDP PDUs are transferred with the SNDCP.
Between the SGSN and the GGSN, PDP PDUs are routed and transferred with either the TCP/IP or the UDP/IP protocols. The GPRS Tunnelling Protocol transfers data through tunnels. A tunnel is identified by a tunnel identifier (TID) and a GSN address.
To support roaming GPRS subscribers, and for forward compatibility, the SGSN is not required to know the tunnelled PDP. Every SGSN shall have the capability to transfer PDUs belonging to PDPs not supported in the PLMN of the SGSN.