Zte ZXG10 OB06, Technical Manual

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ZXG10 OB06 ZTE Integrated Outdoor GSM Base Station Technical Manual
36 Confidential and Proprietary Information of ZTE CORPORATION
The I frame structure of LapDm is shown in Figure 19.
F
I G U R E
1 9 I F
R A M E
S
T R U C T U R E O F
L
A P
D
M
SAPI N(S) N(R)
Address
Control Information
The I-frame in LapDm consists of the address field, control field and
information field.
The address field contains the SAPI. On the radio interface, LapDm
supports two types of messages: signaling and short message service,
distinguished by the SAPI. SAPI=0 represents the signaling link, and
SAPI=3 represents the short message link.
The maximum length of a LapDm frame on the TCH is 23 bytes, and
21 bytes on the SACCH. The reason for this difference is that there are
two special-purpose bytes in each SACCH block: Since the maximal
length of the frame on the radio interface is of 21 or 23 bytes which
cannot meet the need of most pieces of signaling, segmentation and
regrouping are required to be defined in LapDm. Thus an “additional”
bit is used to distinguish the last packet frame from other frames.
Thanks to this mechanism, there will be no restriction to fix the packet
length on the radio path, with the only exception when these messages
must be transmitted on other interfaces, namely, 260 bytes mentioned
in the radio interface specification.
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.
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 flow
control or error recovering mechanism.