DS from FOLDOC

DS0

The zeroth DS level, having a transmission rate of 64,000 bits per second (64 kb/s), intended to carry one voice channel (a phone call).

Last updated: 2001-03-18

DS1

<communications>

A DS level and framing specification for synchronous digital streams, over circuits in the North American digital transmission hierarchy, at the T1 transmission rate of 1,544,000 bits per second (baud).

DS1 is commonly used to multiplex 24 DS0 channels. Each DS0 channel, originally a digitised voice-grade telephone signal, carries 8000 bytes per second (64,000 bits per second). A DS1 frame includes one byte from each of the 24 DS0 channels and adds one framing bit, making a total of 193 bits per frame at 8000 frames per second. The result is 193*8000 = 1,544,000 bits per second.

In the original standard, the successive framing bits continuously repeated the 12-bit sequence 110111001000, and such a 12-frame unit is called a super-frame. In voice telephony, errors are acceptable (early standards allowed as much as one frame in six to be missing entirely), so the least significant bit in two of the 24 streams was used for signaling between network equipments. This is called robbed-bit signaling.

To promote error-free transmission, an alternative called the extended super-frame (ESF) of 24 frames was developed. In this standard, six of the 24 framing bits provide a six bit cyclic redundancy check (CRC-6), and six provide the actual framing. The other 12 form a virtual circuit of 4000 bits per second for use by the transmission equipment, for call progress signals such as busy, idle and ringing. DS1 signals using ESF equipment are nearly error-free, because the CRC detects errors and allows automatic re-routing of connections.

Compare T-carrier systems.

[Kenneth Sherman, "Data Communications : a user's guide", third edition (1990), Reston/Prentice-Hall/Simon & Schuster].

Last updated: 1996-03-30

DS1C

<communications>

A DS level and framing specification for digital signals in the North American digital transmission hierarchy. A DS1C signal uses 48 PCM channels and has a transmission rate of 3.15 Megabits per second, twice that of DS1.

DS1C uses two DS1 signals combined and sent on a 3.152 megabit per second carrier which allows 64 kilobits per second for synchronisation and framing using "pulse stuffing". The channel 2 signal is logically inverted, and a framing bit is stuffed in two out of three code words, resulting in 26-bit information units. The channels are interleaved and then scrambled by the addition modulo 2 of the signal with the previous bit. Finally the bit stream is combined with a control bit sequence that permits the demultiplexor to function by preceding each 52 bits with one DS1C framing bit. A series of 24 such 53-bit frames forms a 1272-bit "M-frame".

Last updated: 1995-02-07

DS2

<communications>

A DS level and framing specification for digital signals in the North American digital transmission hierarchy. A DS2 signal uses 96 PCM channels and has a transmission rate of 6.31 Megabits per second, twice that of DS1C.

Last updated: 1995-02-07

DS3

<communications>

The third DS level, a framing specification for digital signals in the North American digital transmission hierarchy. A DS3 signal has a transmission rate of 44.736 Megabits per second.

DS3 is used, for example, on T3 synchronous Integrated Services Digital Network lines.

Last updated: 1995-01-12

DSA

Directory System Agent

DSDM

Dynamic Systems Development Method

DSE

1. Display Screen Equipment. See Visual Display Unit.

2. Data Structure Editor.

Last updated: 2002-11-09

DSEE

Domain Software Engineering Environment

D-shell connector

<hardware>

One of the family of connectors: DA-15, DB-25, DC-37, DD-50, DE-9, and DEH-15 [VGA]. The "D" is the shape of the shell, the next letter determines connector size, and the number is the maximum pin count.

Last updated: 1999-12-08

DSI

Delivered Source Instruction

DSL

<communications>

1. Digital Subscriber Line.

<language>

2. Digital Simulation Language.

<language>

3. Denotational Semantics Language.

Last updated: 1996-10-13

DSLAM

Digital Subscriber Line Access Module

DS level

<communications>

(Digital Signal or Data Service level) Originally an AT&T classification of transmitting one or more voice conversations in one digital data stream. The best known DS levels are DS0 (a single conversation), DS1 (24 conversations multiplexed), DS1C, DS2, and DS3.

By extension, the DS level can refer to the raw data rate necessary for transmission:

 DS0      64 Kb/s
 DS1   1.544 Mb/s
 DS1C  3.15  Mb/s
 DS2   6.31  Mb/s
 DS3  44.736 Mb/s
 DS4 274.1   Mb/s

(where K and M signify multiplication by 1000 and 1000000, rather than powers of two). In this sense it can be used to measure of data service rates classifying the user access rates for various point-to-point WAN technologies or standards (e.g. X.25, SMDS, ISDN, ATM, PDH).

Japan uses the US standards for DS0 through DS2 but Japanese DS5 has roughly the circuit capacity of US DS4, while the European standards are rather different (see E1). In the US all of the transmission rates are integral multiples of 8000 bits per second but rates above DS1 are not necessarily integral multiples of 1,544 kb/s.

Last updated: 1998-05-18

DSM

1. Data Structure Manager.

An object-oriented language by J.E. Rumbaugh and M.E. Loomis of GE, similar to C++. It is used in implementation of CAD/CAE software. DSM is written in DSM and C and produces C as output.

["DSM: An Object-Relationship Modeling Language", A. Shah et al, SIGPLAN Notices 24(10):191-202 (OOPSLA '89) (Oct 1989)].

2. DIGITAL Standard MUMPS.

Last updated: 1995-01-10