Identity Header compression type The SNDCP PDUs. 3765 4321 8765432 Oct 1 NSAPI Oct 1 NSAPI DCOMP PCOMP PCOMP Segment # N-PDU # Data Segment N-PDU # (continued) SN-Data PDU format N-PDU # (extended) Data Segment Data compression Number of SN-Unidata PDU format segments in a N- PDU (0 to 16) N-PDU number (0 to 524,287) can isolate individual data flows when multiple mobile stations' input are multiplexed together on a single channel. These protocols were carefully planned to enable the interoperation among the various nodes in a GSM and GPRS architecture. 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 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. CHAPTER PCUSN-to- Interface (Gb) PCUSN-to-SGSN Interface (Gb) Chapter 9 Objectives Upon completion of this chapter, you should be able to Describe the PCUSN interface. Discuss the way that Frame Relay works. Understand the way GPRS uses the Frame Relay services at the Gb interface. Combine the benefits of Frame Relay and the advantages of GPRS. Understand why ETSI chose Frame Relay as the transport for the PCUSN. High-Level Characteristics of the Gb Interface In contrast to the A interface, where a single user has sole use of a dedicated physical resource throughout the lifetime of a call irrespective of informa- tion flow, the Gb interface enables many users to be multiplexed over a com- mon physical resource. GPRS signaling and user data may be sent on the same physical resources. Access rates per user may vary from zero data to the maximum possible bandwidth (for example, the available bit rate of an E1). Position of BSSGP Within the Protocol Stack on the Gb Interface The following peer prot