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.

Channel data rate

64k

56k

56k

Telco

B8ZS must be used for 64k. Either B8ZS or AMI can be used with 56k, though AMI is more common.

Number of channels; channel map

1-24

Varies

Telco

Based on subscription level for fractional T1.

Channel order

Continuous

Alternating

Continuous

Telco

Alternating is used to ensure pulse density on non-B8ZS links. Half of the channels carry data, and the other half are used to maintain ones density. The bandwidth penalty is very high, so the alternating option is rarely used.

Data inversion

Do not invert

Invert

Do not invert

Telco

Assures ones density on some types of HDLC lines; generally not needed.

Bit stuffing

Do not stuff

Stuff

Disable

Telco

Required only when line does not ensure correct ones density; generally not used.