PDU Transmission The BSSGP layer manages two kinds of buffers, as shown in Figure 9-21: Mobile station buffers One for each user BVC buffer One for each BVC When receiving an LLC packet, BSSGP puts it into the mobile station buffer corresponding to the Temporary Logical Link Identity (TLLI). Mes- 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. PCUSN-to-SGSN Interface (Gb) PCUSN-to-SGSN Interface (Gb) TLLI User Data Figure 9-21 The PDU transmission. BSSGP Buffer Buffer BVCI=1 BVCI=2 BVCI=1 NSEI 1 NSEI 2 sages for the same cell are multiplexed onto the same BVC, and a buffer is dedicated to it. BSSGP Virtual Connection Identifier (BVCI) BVCs provide communication paths between BSSGP entities. Each BVC is used in the transport of BSSGP PDUs between peer PTP functional enti- ties, peer point-to-multipoint (PTM) functional entities, and peer signaling functional entities. The BVCI is used to enable the lower NS layer to effi- ciently route the BSSGP PDU to the peer entity. This parameter is not part of the BSSGP PDU across the Gb interface, but is used by the NSE across the Gb. Any BSSGP PDU received by the BSS or the SGSN containing a PDU type that does not fit (according to the definitions) with the functional entity identified by the BVCI provided by the NSE is discarded and a STA- TUS PDU with a cause value set to Protocol error-unspecified is sent. PTP functional entity Responsible for PTP user data transmission. One PTP functional entity exists per cell. PTM functional entity Responsible for PTM user data transmission. One or more PTM functional entities exist per BSS. 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. PCUSN-to-SGSN Interface (Gb) Chapter 9 Signaling func