Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1999-01-29
2002-09-17
Chin, Stephen (Department: 2634)
Pulse or digital communications
Transceivers
Modems
C375S219000
Reexamination Certificate
active
06452963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to modems and a method for connecting the modems with an improved connection speed.
2. Background of the Related Art
Recent developments in communication have sharply increased the use of modems. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) has promulgated various recommendations and standards for data communication. There is consequently a need to improve the connection speed and rate between modems. According to ITU-T recommendations, which pertains to a connection speed of up to 28800 bps on a telephone line, modems are designed to connect through 4 phases of handshaking. These phases include a first phase of network interaction, a second phase of probing and ranging, a third phase of equalizing and echo canceler training, and a fourth phase of final training. A description of each phase, separately describing the call modem and the answer modem, is presented below.
For better understanding, a glossary of signal and sequence is provided. Additional details can be found in ITU-T Recommendation V.34.
ANS: Answer Tone, 2100 Hz
ANSAM: Amplitude modulated answer tone, 2100 Hz
CI: Call indicator signal, 300 bps, V.21(L) modulation
CM: Call menu signal, 300 bps, V.21(L) modulation, indicates modulation mode available in call modem.
CJ: CM Terminator, acknowledges detection of JM and indicates the end of CM, 300 bps, V.21(L) modulation.
JM: Joint menu signal, indicates modulation mode available jointly in call/answer modem, 300 bps, V.21(H) modulation.
Tone A: 2400 Hz, used by answer modem
Tone/A: Phase shifted Tone A
Tone B: 1200 Hz, used by call modem
Tone/B: Phase shifted Tone B
INFO sequence: Used to exchange modem capability, result of line probing, data mode modulation parameter.
Call modem: INFO
0
c
, INFO
1
c
Answer modem: INFO
0
a
, INFO
1
a
Modulation: DPSK, 600 bps
Carrier frequency: call modem—1200 Hz, answer modem—2400 Hz
INFOMARKSa: signal transmitted by answer modem by applying binary ones to the DPSK modulator.
INFOMARKSc: signal transmitted by call modem by applying binary ones to the DPSK modulator.
Line probing signal: L
1
, L
2
L
1
: A set of tones spaced 150 Hz apart at frequency from 150 Hz to 3750 Hz (900 Hz, 1200 Hz, 1800 Hz and 2400 Hz are omitted), transmitted for 160 ms at a level 6 dB higher than a nominal power level.
L
2
: Same as L
1
but is transmitted for no longer than 550 ms plus round trip delay at nominal power level.
B
1
: One data frame of scrambled binary one.
E: 20 bit sequence of binary ones
J: Whole number of repetitions of one of two 16 bit patterns.
Constellation size
Bit 0~ 15
4 point
0000100110010001
16 point
0000110110010001
J′: Used to terminate J, Bit 0~15=1111100110010001
MD: Manufacturer defined signal determined at INFO
1
.
PP: Used to train equalizer.
TRN: Scrambled binary one
MP: Modulation parameter sequence
Type 0: Contains maximum call-to-answer modem rates, maximum answer-to-call rates, amount of constellation shaping, encoder choice, nonlinear encoder parameter, auxiliary channel enable.
Type 1: Type 0 +precoder coefficient
MP′: MP sequence with acknowledge bit set to 1
DSR: Data Set Ready
RXD: Received Data
RLSD: Data Channel Received Line Signal Detector
T: Symbol Interval; thus for 28,000 bps, T=1/28,800 sec
16T=16/28,000 sec
128T=128/28,000 sec
512T=512/28,800 sec
Modem connection is accomplished in four phases, each of which will now be described.
FIRST PHASE
Referring to
FIG. 1
, the call modem initially transmits CI (call indicator signal, 300 bps, V.21(L) modulation), CJ (CM terminator, acknowledgment of JM detection) or CNG, and becomes ready to detect either of ANS/ANSAM. If the call modem detects ANSAM, it stops transmission for a prescribed time period Te. After this time period, the call modem is ready to detect JM, and also transmits CM. When two identical JM signals are detected, the modem transits CI and the process proceeds to the second phase after transmitting silence for 75 ms.
The answer modem initially transmits ANSAM remains silent for 200 ms, and then stands ready to detect CM. If two identical CMs are detected, the modem transmits JM, and becomes ready to detect CJ. When CJ is detected, the process proceeds to the second phase after transmitting silence for 75 ms.
SECOND PHASE
Referring to
FIG. 2
, the call modem initially receives INFO
0
a
and Tone A from the answer modem, and transmits INFO
0
c
and Tone B. Then, after receiving Tone/A for 40 ms, the call modem transmits Tone/B. The call modem then transmits silence and awaits reception of a second Tone/A. Upon detecting the second Tone/A the call modem calculates the RTD (Round Trip Delay). The RTD is the time interval between the appearance of the Tone/B and receiving the second Tone/A minus 40 ms.
The call modem then receives signal L
1
from the answer modem. After receiving the L
1
signal for 160 ms, the call modem receives the L
2
signal for 500 ms, and subsequently transmits Tone B. Next, when the call modem detects Tone A and Tone//A, it transmits Tone/B for 10 ms, and becomes ready to detect Tone A again, while transmitting L
1
and L
2
. Upon detection of Tone A, the call modem transmits INFO
1
c
followed by transmission of silence. If the call modem subsequently receives INFO
1
a
, the process proceeds to the third phase.
The answer modem initially transmits INFO
a
after the 75 ms silence from phase one. It becomes ready to detect INFO
0
c
and Tone B. Upon detection of Tone B, the answer modem becomes ready to detect Tone/B, while transmitting Tone A followed by Tone/A. When Tone/B is detected, the answer modem calculates RTD. The RTD is the time interval between sending the Tone/A and receiving the Tone/B minus 40 ms.
After detecting Tone/B, the modem is ready to detect Tone B, and transmits Tone A, L
1
and L
2
. After detection of Tone B, the answer modem transmits Tone/A, and then transmits silence. Next, after detecting Tone/B, the answer modem receives L
1
and L
2
. After receiving L
1
and L
2
, the answer modem becomes ready to detect INFO
1
c
, and transmits Tone A. After detecting INFO
1
c
, the answer modem transmits INFO
1
a
. The process then proceeds to the third phase.
THIRD PHASE
Referring to
FIG. 3
, the call modem initially detects S and /S, and, after the duration of signal MD, detects S and /S again. If S and /S are detected, the call modem trains its own equalizer using the PP sequence followed by the TRN sequence. After detecting the J sequence for 500 ms, the call modem transmits S and /S. If the duration of signal MD is zero, PP is transmitted; otherwise S, /S and PP are transmitted. The call modem then transmits the TRN sequence after transmission of the PP sequence. Next, the call modem becomes ready to detect S, and transmits the J sequence. When S is detected, the process proceeds to the fourth phase.
The answer modem, after transmitting INFO
1
a
, transmits silence for 70 ms, followed by transmission of S and /S. If the duration of signal MD is as indicated in INFO
1
a
, the answer modem transmits the PP sequence; otherwise, S, /S and PP are transmitted. Next, the answer modem transmits the TRN and j sequences, and becomes ready to detect S. After detecting after S and /S, the answer modem transmits silence and trains its equalizer with PP and TRN sequences if MD is zero. If, however, the duration of signal MD is not zero, the answer modem trains its equalizer with PP and TRN sequences after first detecting S and /S. Next, after detecting the J sequence for 50 ms, the answer modem transmits the S sequence, and the process proceeds to the fourth phase.
FOURTH PHASE
Referring to
FIG. 4
, if the call modem detects the S sequence followed by the /S sequence, it ceases transmission of J and commences transmission of /J. At the transition from J to /J, circuit
107
(DSR) is enabled to receive and train TRN. Next, after /J transmission, TRN is transmitted and trained
Chin Stephen
Fan Chieh M.
Fleshner & Kim LLP
Hyundai Electronics Industries Co,. Ltd.
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