Description: This variable describes the variety of Zero Code Suppression used on the link, which in turn affects a number of its characteristics.

ds1JammedBit refers the Jammed bit Zero Encoding, in which the AT&T specification of at least one pulse every 8 bit periods is literally implemented by forcing a pulse in bit 8 of each channel. Thus, only seven bits per channel, or 1.344 Mbps, is available for data.

ds1B8ZS refers to the use of a specified pattern of normal bits and bipolar violations which are used to replace a sequence of eight zero bits (see [14]). In this context, all eight bits in a channel are technically available for data, but care must be taken with D4 encoded data to avoid having HDLC Flag streams imitate spurious Yellow Alarm conditions. Typically, one bit per frame is ignored to force flag streams to rotate, thereby avoiding this error type. CCITT Recommendation G.703 [11] may be referred to for further definition of these.

ds1InvertedHDLC refers to the practice, common on HDLC encoded DS1 data links, of inverting the data between the serial interface chip and the CSU. Since HDLC guarantees one zero every 6 bits in the worst case, while the standards call for (in effect) at least one pulse every eight, inverted HDLC enjoys 4/24 one's density on the line, which may improve the effective clock stability of a DS1 line. As with B8ZS, all eight bits in a channel are technically available for data, but care must be taken with D4 encoded data to avoid having HDLC Flag streams imitate spurious Yellow Alarm conditions. Typically, one bit per frame is ignored to force flag streams to rotate, thereby avoiding this error type.

ANSI Clear Channels may use ds1ZBTSI, or Zero Byte Time Slot Interchange (see [14]).

G.704 links, with or without CRC, use ds1HDB3 (see [11]).