Line Modules of Digital Telephone Switching Systems


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Document Category Engineering
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5.15 Memories
Processor memories, other than mass storage (tapes, disks, etc.), shall consist of nonvolatile solid-state integrated circuits. The system shall provide for the protection of information stored in the memories during conventional power failures. Disk and/or tape units can be used for back-up storage.
With regards to the common control equipment unit(s), the system shall have a full redundancy capability.

5.16 Programs

All software dedicated to call processing and basic diagnostics shall be on-line in main memory at all times. Backup programs shall be available from overlay programs in secondary storage, when required.

Line Modules of Digital Telephone Switching Systems

The line units shall comply with the following specified characteristics:
5.17.1 The maximum allowed loss within any single local exchange, for local-to-local connection must be 0.5 dB from MDF to MDF (Main Distribution Frame).

5.17.2 Functions performed by the line units for the analog subscriber line (when required) shall include BORSCHT. {Battery feed (for subscriber terminals), Overvoltage protection, Ringing (ringing voltage source), Signaling [subscriber loop supervision (on-hook, off-hook)], Coding (A/D and D/A conversion to/from PCM format), Hybrid (two-wire to four-wire conversion), and Test}.
5.17.3 Digital analysis can be performed at the peripheral equipment.
5.17.4 The Pulse Code Modulation (PCM) filters and CODECs shall meet D3 and D4 format. CODECs shall use 8 kHz sampling, 8 bit/sample encoding, μ255-15 segment and A-13 segment compounding for encoding and decoding in accordance with ITU-T G.711 “PCM of voice frequencies;” and ITU-T G.732 “characteristics of primary PCM multiplex equipment operating at 2048 kb/s.” The digital switch shall support ONLY the 32 channel A-law trunking protocol.

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