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412 AIR INTERFACE SIGNALING IN CDMA NETWORKSFigure 13.3-2. Protocol stack and physical and logical channels for cdma2000w.Physical channels are always denoted by uppercase acronyms, while logicalchannels use lowercase acronyms. The acronyms are based on simple rules: F/ffor forward, R/r for reverse, D/d for dedicated, C/c for common, CH/ch forchannel, t for traffic and s for signaling. The type and number of channels actuallyused in a system, out of all the ones defined in the standard, depend on radio configurationsand spreading rates.Channels, both physical and logical, can be common or dedicated. A commonchannel is shared by all MSs in a cell and is used to send and receive informationto/from MSs before they have been assigned a traffic channel, for example,during initialization, idle, and system access states.Dedicated channels are used by individual MSs to exchange signaling and userdata with the BS, and they are assigned by the BS. The BS can assign multiple dedicatedchannels to the same MS to form a Traffic Channel.A significant difference with IS-95 is found in the Reverse CDMA Channel,which can be configured (in RC 3 and higher) with Reverse Pilot Channels. The synchronizationmade possible by Reverse Pilot Channels allows the use of Walshcodes in the reverse direction.Power Control. In the Reverse CDMA Channel, power control with RC 1 andRC 2 works the same way as for IS-95. With RC 3 through RC 7 the operation isalmost the same, with open loop and closed loop, but there are some differencesin the way the power control subchannel is derived. A Common Power ControlChannel (see next section) may also be used.In the Forward Channel, power control with RC 1 and RC 2 works exactly as forIS-95, while RC 3 through RC 10 use a full closed loop operation with inner andouter loop, both controlled by the MS via the Reverse Power Control Subchannel.13.3.2 cdma2000 SignalingProtocol Stack. The communication protocol for the cdma2000 air interface isstructured with three layers and several sublayers (Fig. 13.3-2):. Layer 1, or physical layer. Layer 2, or data link layer, subdivided into two sublayers: medium accesscontrol (MAC) and link access control (LAC). Layer 3, or upper layer signaling (ULS)