T1: A Survival Guide

Summary of Settings

Table 6-4 summarizes the most common CSU/DSU configuration options, along with available settings, common industry defaults, and additional remarks.

Table 6-4. T1 CSU/DSU configuration options

Option name	Possible settings	Common CSU/DSU default	Who sets this option?	Remarks
Framing	Superframe (also SF or D4) Extended superframe (ESF)	Equipment defaults to SF; most lines are ESF Some equipment can autoselect	Telco
Line code	AMI B8ZS	Equipment defaults to AMI; lines are usually B8ZS	Telco
Transmit clock source	Network (also looped timed): transmit clock derived from receive clock DTE Internal CSU/DSU oscillator	Varies	DTE vendor; the network setting is generally safest	There is a wide variation in terminology. Consult the manual.
DTE clocking	Internal CSU/DSU oscillator Inverted signal from oscillator Supplied by DTE (also called external)	Internal Sometimes can be automatically selected	DTE vendor	Generally internal. Long cables may require inverting the internal clock signal.
Line build out	0 dB 7.5 dB 15 dB 22.5 dB	0 dB Some equipment can autoselect	Telco	Usually 0 dB when connected to a smart jack, though it could be anything.
Transmit FDL performance reports	Transmit Do not transmit	Transmit	Telco	Performance reports exist only on ESF links.
Transmit yellow alarm	Transmit Do not transmit	Transmit	Telco/ISP
Inband signaling	Yes No	No	Telco	Steal 8 kbps from channel 1 for signaling.