ZXG10-BTS (V2.9) Technical Manual
50
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The address field contains SAPI and TEI. It performs addressing for
different units via TEI in the Abis interface link. Generally, a unit has
multiple functional entities, and the logical physical links between
different functional entities are identified by the functional address
SAPI. LapD supports three kinds of information: Signaling (including
short messages), O&M and LapD layer management information. Links
of the three kinds of information are distinguished by SAPI.SAPI=0
represents the signaling link, SAPI=62 represents the O&M link, and
SAPI=63 represents the management link of the LapD layer.
In the control field, N (S) represents the sending serial number and the
I frame’s serial number currently sent by the sending end; N (R)
represents the receiving serial number, the expected sending serial
number of the next I frame. N (R) is used to predict the instruction
from the receiving end.
FCS (Frame Check Sequence) is used for error code detection.
Flag is the beginning and the end token of a frame, namely, an 8-bit
font containing six consecutive 1s.
2. UI frame operation
The L3 message is sent in the no-serial-number frame mode, and the
receiver is not required to send the received confirmation after
receiving the UI frame. This operation mode does not provide a flow
control or error recovering mechanism.
The UI frame structure is shown in Figure 26. It is made up of the
address field, control field and information field.
F
I G U R E
2 6
U I F
R A M E
S
T R U C T U R E O F
L
A P
D
Address
Control
Information
000
P
0011
TEI
SAPI
The address field contains SAPI and TEI. In the address field, P
represents the query bit, and if this bit is set to 1, it means requiring
the response frame from the opposite-end peer entity.
LapDm Protocol
In GSM, LapDm is a data link protocol for signaling transmission between
MS and BTS (V2.9), with the purpose of using the Dm channel to transmit
messages for respective entities of Layer 3 via the radio interface. LapDm
is based on LapD, with some simplification and modification.
In the ZXG10-BTS(V2.9), LapDm implements the following functions:
Summary of Contents for ZXG10-BTS
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