
Configuring Dial Services
4-4
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Figure 4-3. LAPD Frame
The fields in the LAPD frame are as follows:
•The opening flag and closing flag fields are High-level Data Link Control
(HDLC) flags that separate one frame from the next.
•The address field contains two kinds of information. It provides a data-link
layer entity; more specifically, a logical point that defines the data link
between the user and the network. This portion of the address is the service
access point identifier (SAPI). The address field also contains a number to
identify the terminal equipment connected to the ISDN network. This is the
terminal endpoint identifier (TEI). Either the network assigns a unique
number to each device or you set this number at the device.
•The control field identifies the type of frame. This field also contains
sequence numbering.
•The information field contains data to set up the link.
•The frame-check sequence is a cyclic redundancy check (CRC).
Opening flag
Address
Control
Information
Closing flag
Frame-check sequence
DS0009A
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