Nortel Networks 553-3001-211 manual Frame structure

Page 890 of 894 Appendix A: LAPB Data Link Control protocol

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 275 on page 891. 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.

553-3001-211 Standard 2.00 September 2004