国庆，旅游等等杂事让我荒废了接近3个月，现在还是要重新开始努力了，不管结局如何。

GSM0408RR部分阅读的选取部分
Two service access points are defined on signalling layer 2 which are discriminated by their Service
Access Point Identifiers (SAPI) (see GSM 04.06):
i) SAPI 0: supports the transfer of signalling information including user-user information;
ii) SAPI 3: supports the transfer of user short messages.

The general purpose of Radio Resource procedures is to establish, maintain and release RR connections
that allow a point-to-point dialogue between the network and a mobile station. This includes the cell
selection/reselection and the handover procedures. Moreover, Radio Resource management procedures
include the reception of the uni-directional BCCH and CCCH when no RR connection is established. This
permits automatic cell selection/reselection.
A RR connection is a physical connection used by the two peer entities to support the upper layers’
exchange of information flows.

In idle mode no RR connection exists.
In Idle mode, upper layers can require the establishment of an RR connection

In dedicated mode, the RR connection is a physical point-to-point bi-directional connection, and includes a
SAPI 0 data link connection operating in multiframe mode on the main DCCH. If dedicated mode is
established, RR procedures provide the following services:
- establishment/release of multiframe mode on data link layer connections other than SAPI 0, on the
main DCCH or on the SACCH associated with the channel carrying the main signalling link;
- transfer of messages on any data link layer connection;
- indication of temporary unavailability of transmission (suspension, resuming);
- indication of loss of RR connection;
- automatic cell reselection and handover to maintain the RR connection;
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- setting/change of the transmission mode on the physical channels, including change of type of
channel, change of the coding/decoding/transcoding mode and setting of ciphering;
- allocation/release of an additional channel (for the TCH/H + TCH/H configuration);
- allocation/release of additional channels for multislot operation;
- release of an RR connection.

In case a change of dedicated channels is required using a dedicated assignment and handover
procedure, respectively, the RR sublayer will request the data link layer to suspend multiple frame
operation before the mobile station leaves the old channel. When the channel change has been
completed, layer 3 will request the data link layer to resume multiple frame operation again.

For SAPIs other than 0, the data link procedures described in GSM 04.06 do not provide any guarantee
against message loss or duplication.