Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Mobile Station to SGSN Interface Mobile Station to SGSN Interface SNDC Primitive Network Layer SNDC Primitive Figure 8-11 The SNDCP layer. Compression Decompression Application IP/X.25 SNDCP SNDCP SNDC Layer Segmentation Reassembly BSSGP BSSGP GSMRF GSMRF l1bis l1bis Gb SGSN LLC Primitive LLC Layer LLC Primitive SNDCP Service Functions The following functions are performed by the SNDCP and are shown in Figure 8-12: Transmission and reception of N-PDUs in acknowledged or unacknowledged LLC mode. In acknowledged mode, the receipt of data is confirmed at the LLC layer and the data is transmitted and received in order per NSAPI. In unacknowledged mode, the receipt of data is not confirmed at the SNDCP layer or the LLC layer. Transmission and reception of variable-length N-PDUs between the mobile station and the SGSN. Transmission and reception of N-PDUs between the SGSN and mobile station according to the negotiated QoS profile. Segmentation and reassembly of the data to a maximum-length PDU. The output of the compression function is segmented to the length of the PDU as determined by the mode selected. This is independent of the particular network layer protocol being used. Transfer of the minimum amount of data possible between the SGSN and the mobile station through the use of compression techniques. Compression of redundant protocol information (TCP/IP headers) at the transmitter and decompression at the receiver. Compression may be performed independently for each QoS delay class and precedence class. If several network layers use the same QoS delay class and Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Mobile Station 