Digital Signal 1

DS1 instance evidence

Record whether identification rests on configuration, a service record or an observed signal.

1. What evidence identifies this instance as a DS1 signal rather than merely a service sold as T1? definition
2. Which port, transport path and service records refer to this same signal instance? boundary

Profile agreement

Record the applicable profile explicitly, including regional distinctions; DS1 and J1 share a nominal rate but have differences in alarm behaviour. [RFC 4805](https://www.rfc-editor.org/rfc/rfc4805.html)

1. Which specification revision and equipment documentation define the endpoint profile? provenance
2. What evidence distinguishes this profile from J1 or an E1 interface represented by the same management interface type? boundary

Framing mode agreement

Distinguish D4/SF, ESF and intentionally unframed operation, recording receiver alignment separately from configuration.

1. What framing mode is configured and what mode is actually detected in each direction? measurement
2. Does absent frame alignment indicate a fault or intentional unframed operation? boundary

Channel allocation consistency

Record assignment of the 24 eight-bit payload positions or their aggregate use; conventional framing provides 1,536,000 payload bit/s before service-specific deductions.

1. Which positions carry each service, and which are idle, reserved or unavailable? measurement
2. Do channel numbering and grouping agree at both terminations and intermediate cross-connects? boundary
3. What usable service rate remains after signalling reservations and protocol overhead? measurement

Signalling reservations

Record robbed-bit use and any dedicated signalling channel without assuming that every DS1 carries telephone calls.

1. Which channels, if any, use robbed-bit signalling, and under which framing arrangement? definition
2. Does the intended service require every payload bit to be preserved? boundary

Line-code compatibility

DS1 electrical interfaces commonly offer AMI and B8ZS; record the selected mode at each applicable termination. [Cisco DS1 interface specifications](https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/ons-15454-sonet-56-port-ds-1-e1-card/product_data_sheet0900aecd8031a1de.html)

1. Which line code is configured and detected at each electrical termination? measurement
2. What documented pulse-density or zero-suppression restrictions constrain this payload? boundary
3. What coordinated configuration changes are needed to satisfy the service's bit-transparency requirement? action

Timing plan consistency

Require an explicit clock-source chain and evidence of timing stability.

1. What clock drives each transmit direction, and which upstream reference ultimately supplies it? provenance
2. What measured slips or clock-source changes suggest a timing loop or reference mismatch? measurement

Adaptation preservation

Record what each adaptation preserves, regenerates or terminates, including framing, timing and alarm information.

1. Where is this DS1 multiplexed, encapsulated or regenerated along its path? boundary
2. Which payload, timing and alarm behaviours does each adaptation promise to preserve? provenance
3. What evidence is required before substituting a different bearer? action

Alarm and counter interpretation

Record local and remote indications separately, with applicable counter definitions, interval validity and unavailable-time treatment. [RFC 4805](https://www.rfc-editor.org/rfc/rfc4805.html)

1. Which endpoint and receive direction report LOS, LOF, AIS or remote alarm, and when did each indication begin? measurement
2. Which error counters are valid for this framing mode, and over what complete observation interval? measurement
3. What additional observation would distinguish framing mismatch, timing impairment and bearer failure? action

Bounded diagnostic test

Record loopback location, test direction, pattern, duration, expected result and restoration evidence.

1. Which DS1 segment will this loopback and test pattern exercise, and which faults remain outside its reach? boundary
2. Which services will the test interrupt, and what authorisation covers that interruption? action
3. What observations will confirm loopback removal, restored configuration and acceptable service performance? action

Check these first

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these check these first hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Kinds and varieties

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these kinds and varieties hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Identifiers and schemes

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these identifiers and schemes hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Standards and regulation

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these standards and regulation hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Real-world use

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these real-world use hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Typical measurements

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these typical measurements hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Failure modes and hazards

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these failure modes and hazards hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Regional variation

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these regional variation hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance

Neighbouring kinds and how to tell them apart

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these neighbouring kinds and how to tell them apart hold for the sense of Digital Signal 1 this model covers, and on what evidence? provenance