hat are provided by the various services from the upper and lower layers. Notifications are passed from layer to layer to ensure that the information has been properly formatted, transmitted, and received. These primitives make the process complete. Several discussions center on the chart of protocols, as shown in Fig- ure 1-20. Refer to this chart for the next block of protocol stack discussions. Mobile Station Protocols The signaling protocol in GSM is structured into three general layers, depending on the interface. Layer 1 is the physical layer, which uses the channel structures discussed above over the air interface. Layer 2 is the data-link layer. Across the Um interface, the data-link layer is a modified version of the Link Access Procedure for the D Channel (LAPD) protocol used in ISDN, called Link Access Protocol on Dm Channel (LAPDm). Across the A interface, the Message Transfer Part (MTP) Layer 2 of Signaling Sys- tem Number 7 is used. Layer 3 of the GSM signaling protocol is divided into three sublayers: radio resources management (RR), mobility management (MM), and connection management (CM). Figure 1-20 The protocol stacks. BSSMAP BSSMAP /DTAP MTP 3 MTP 3 LAPDm LAP D LAP D MTP 2 MTP 2 GSM RF GSM RF Layer 1 Layer 1 MTP 1 MTP 1 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. Introduction to GSM Chapter 1 The Mobile Station to BTS Protocols The radio resources (RR) management layer oversees the establishment of a link, both radio and fixed, between the mobile station and the MSC. The main functional components involved are the mobile station, the Base Station Subsystem, and the MSC. The RR layer is concerned with the man- agement of an RR-session, which is the time that a mobile is in dedicated mode, as well as the configuration of radio channels including the allocation of dedicated channels. The mobility management (MM) layer is