TABLE OF CONTENTS Broadcast/multicast control is a layer 2 sublayer that exists only in the U-plane. The necessary control information is received from the RRC, just as in the PDCP sublayer. This layer handles only downlink broadcast/multicast transmission. See Figure 7.27.
The BMC task implements the transfer of cell broadcast messages. Cell broadcast service (CBS) is not a UMTS-only service, since it is also used in GSM, though not yet very widely. This service is specified for UMTS in [20]. Cell broadcast messages are SMS text messages (although they can be much longer than the normal SMS messages) that are broadcast to everybody in a cell (or in a set of cells). A CBS message consists of CBS pages. One page contains 82 octets, and if 7-bit characters are used, it is possible to send 93 characters in a page. A CBS message may contain up to 15 pages, which gives a maximum size of 1,395 characters for CBS messages. These messages can be received by all mobiles capable of receiving CBS. But the mobiles have to be in either the idle, the CELL_PCH, or the URA_PCH states. Cell broadcast messages are assigned a message class type, which can be used by the UE to filter and receive only those messages that are of interest to it. The categories to be subscribed to could include contents such as news, traffic information, and weather forecasts. The user can, of course, reject all cell broadcast messages.
The...
