Chapter 3 - Interfaces and Protocols
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•
The second layer (middle) is the data link layer with the LAPDm
adopted. It comprises of various data transmission structures and
controls data transmission.
•
The third layer is the highest layer. It comprises of various messages
and programs and provides service control. Layer 3 further consists of
three sub-layers:
•
Radio-resource Management (RR)
•
Mobility Management (MM)
•
Connection Management (CM)
Relevant protocols of Um interface are as follows:
•
GSM 04.03 describes the channel structure and access capability
•
GSM 04.04 specifies the physical layer structure
•
GSM 04.05 defines the data link layer protocol
•
GSM 04.08 stipulates the layer-3 protocols
Abis Interface
Abis interface is the standard interface between OB06 and BSC.
Abis interface sends the signals from BSC to OB06. These signals are
generally the standard PCM 2 MHz E1 signals, transmitted physically in
one of the following ways:
•
Over 75
Ω
coaxial cable in unbalanced mode
•
Over 120
Ω
cable in balanced mode
•
Through digital microwaves, fiber transmission (SDH/PDH) or satellite
link.
