Nortel Networks Circuit Card - Manual (Page 902)

Page 902 of 906 Appendix A: LAPB Data Link Control protocol
553-3001-211 Standard 3.00 August 2005
LAPB subset of the HDLC protocol and transmitted serially to the line at a
rate determined by the downloaded parameters.
The QPC513 card receives data serially from the line, packaged in LAPB
information frames. After determining that a block is error free the data is
supplied to the Circuit Switch Equipment as a block.
Frame structure
All transmissions are in frames and each frame conforms to the format shown
in Table 280 on
page 903 . In particular, frame elements for applications using
a port on the QPC513 follow these LAPB conventions:
• Zero information field is permitted.
• Inter-frame time fill is accomplished by transmitting contiguous flags.
This is compatible with AT&T Technical Requirement BX.25 and
ADCCP standards.
• Extensions for the address field or the control field are not permitted.
This requirement imposes constraints to satellite operations.
• Individual station addresses are assigned in service change for balanced
configuration. The default ESDI address is 10000000. The far-end
default address is 11000000.
• The LAPB basic control field (modules 8) format is implemented.
• Frame check sequence is implemented in accordance with LAPB
procedures.