Serwis


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v.34 & v.8 Explained

I. Description of v.8 and v.34

v.8

  • Allows GSTN equipment to identify data equipment (Echo Canceling, V.25)
  • Allows modems (and other data communication equipment) to handshake quickly.
  • Allows data calls to be passed to DCE(Data Communication Equipment) automatically.
    (similar to CNG tones and faxing)
  • Uses 300 bps, V.21 modulation to transmit CI, CM, and JM.

v.34

  • ITU-T recommendation for 2400 through 28800 bps.
  • Multiple symbol rates
  • 2 carriers, one selectable, except at 3429 symbol rate.
  • Other features for optimum throughput for line conditions
  • 200 bps, auxiliary data channel

II. Terms related to v.8 and v.34

v.8

  • CI Call indicate * optional
  • ANSam Modified Answer Tone
  • CM Call Menu - Modulation, Protocol, GSTN
  • JM Joint Menu
  • S54=128 Disable v.8
  • S54=64 Disable CI

v.34

  • Negotiation
  • Symbol rates
  • ATI11
  • ATY11
  • S Registers S54 - S57

ATI11

USRobotics Courier HST Dual Standard V.34 Fax Link Diagnostics.
Modulation V.34
Carrier Freq (Hz) 1920/1920
Symbol Rate 3200/3200
Trellis Code 32S-2D/32S-2D
Nonlinear Encoding OFF
Precoding ON
Shaping OFF
Preemphasis (-dB) 3/3
Recv/Xmit Level (-dB) 7/8
Roundtrip Delay (msec) 2

ATY11

Freq Level
1000 22
3000 25
3300 25
3350 27
3450 31
3600 37

S54 Bit Mapped

    1 = Disable 2400 symbol rate
    2 = Disable 2743 symbol rate
    4 = Disable 2800 symbol rate
    8 = Disable 3000 symbol rate
    16 = Disable 3200 symbol rate
    32 = Disable 3429 symbol rate
    64 = Disable Call Indicate
    128 = Disable v.8 Mode

S55 Bit Mapped

    1 = Disable 8S-2D trellis code
    2 = Disable 16S-4D trellis code
    4 = Disable 32S-2D trellis code
    8 = Disable 64S-4D trellis code
    16 = Reserved
    32 = Reserved
    64 = Reserved
    128 = Reserved

S56 Bit Mapped

    1 = Disable Non linear coding
    2 = Disable TX level deviation
    4 = Disable Pre-emphasis
    8 = Disable Pre-coding
    16 = Disable Shaping
    32 = Reserved
    64 = Disable V.34
    128 = Disable V.FC

GSTN General Switched Telephone Network (PSTN)

Bandwidth The difference, expressed in hertz, between two limited frequencies of a band.

Throughput Effective data transmission rate over time, usually expressed in bits per second.

Constellation Quadrature Amplitude Modulation bit mapping diagram.

QAM Quadrature Amplitude Modulation - modulating or changing an analog by adjusting its amplitude, and its phase.

Carrier An analog signal which carriers no information, but is used as a reference point.

Symbol Rate Number of symbols represented over a given period of time. A symbol is an analog sample which represents a given number of data bits.

TCM Trellis Coded Modulation. A special method of QAM which allows for many invalid bit combinations, therefore making error detecting easier.

Non Linear Encoding A method for improving distortion immunity near the perimeter of a signal constellation by introducing a non-uniform two dimensional signal point spacing.

Precoding Pre-coding is a non-linear equalization method for reducing equalizer noise enhanced caused by amplitude distortion. Equalization is performed at the transmitter using pre-coding coefficients provided by the remote modem. Certain parts of the bandwidth can be boosted to accommodate roll off and other drops in amplitude. Analogous to a graphic equalizer on a stereo.

Shaping A method for improving noise immunity by introducing a non-uniform two dimensional probability distribution for transmitted signal points. The degree of constellation shaping is a function of the amount of constellation expansion. Essentially, the QAM constellation is modified to accommodate noise.

Preemphasis A linear equalization method where the transmit signal spectrum is shaped to compensate for amplitude distortion. The pre-emphasis filter is selected using a filter index provided by the remote modem. The analog signal is boosted linearly to accommodate a weak signal.

TX Level Deviation The transmit level can be automatically adjusted to accommodate the telephone lines. If you turn it off, the modem may think the lines are better than they are.

III. V.34 INFORMATION CHART

Symbol Rate Min Bit Rate Max Bit Rt Carrier Frq.** Bandwidth Req.
2400
2400
21600
1600
400-2800
1800
600-3000
2743*
4800
24000
1646
274-3018
1829
457-3200
2800*
4800
24000
1680
280-3080
1867
467-3267
3000
4800
26400
1800
300-3300
2000
500-3500
3200
4800
28800
1829
229-3429
1920
320-3520
3429*
4800
28000
1959
244-3674

^Optional symbol rates under the V.34 specification. We implement all of the optional symbol rates.

** Each symbol rate supports two carrier frequencies and two bandwidth ranges. During negotiation, the modems will decide which to use.

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