Nortel Networks 553-3001-211 manual Synchronous communication

QPC513 Enhanced Serial Data Interface card Page 843 of 894

The QPC513 ESDI card is an intelligent controller. The local micro-processor performs all of the overhead associated with synchronous data transfer. The system processor passes data to the ESDI card processor a byte at a time using conventional memory reads and writes. The ESDI card processor stores the data in a RAM cache on the ESDI card, and passes it to the synchronous communication chip in blocks using Direct Memory Access (DMA) techniques.

Synchronous communication

The ESDI cards supports LAPB, a subset of the HDLC synchronous protocol. A description of the LAPB protocol is shown in Appendix A, LAPB data link protocol on page 889.

The HDLC data link is a bit-oriented protocol. The information data bits are transmitted transparently across the link in packets. The maximum length of the information field for these packets is 128 octets, where an octet consists of 8 bits.

The characteristics of the synchronous communication ports are shown in Table 261.

Table 261

Characteristics of synchronous ports (Part 1 of 2)

Characteristics	Description
Duplex mode	half, (full)
Data rate (bps)	1200, 2400, (4800), 9600,
	19200, 48000, 56000, 64000
Clock	(internal), external
Data Link Level LAPB protocol	(1), 3
SL-1 address

Note 1: * See the Configuration Record (LD 17) in Software Input/Output: Administration (553-3001-311) to modify the link control system parameters and performance thresholds.

Note 2: The values in parentheses are the default.

Circuit Card Description and Installation