23.1213GPPArchitectural requirements for Release 1999Release 1999TS
4.8.1 Functional role of SNDCP / PDCP
Out of the functions devoted to SNDCP in 2G network, only header compression and XID negotiation functions need to be considered in UMTS. Hence the term Packet Data Convergence Protocol (PDCP) is introduced.
4.8.2 Position for header compression
RNC position for header compression is the best place because:
– differential header compression algorithms work better if they are located in the place where packets are more likely to be discarded (after having discarded packets the compression algorithm can send a packet with full header). This place is the RNC (where the queues for downstream packets waiting for radio resources are located);
– the compression entity is as close as possible to the reliable link (as in 2G) which in this case is the RLC. Therefore it can be stated that a faster recovery of packets is possible after loss of packets in the radio interface and this solution will therefore minimize the amount of buffering in the UE and network;
– the compression can be 50ignallin for the used RAN.
– it increases the possible data rates that can be achieved: Locating the compression function in the RAN defers the SGSN from the task of opening and processing packets;
– efficient inter-system hand-over can be supported.
4.8.3 Implied protocol stack
Figure 4.44: User Plane Protocol Architecture with header compression mechanisms