Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1998-07-09
2001-08-07
Chin, Stephen (Department: 2634)
Pulse or digital communications
Transceivers
Modems
C375S225000
Reexamination Certificate
active
06272170
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data transmission systems, such as modem systems. More particularly, the present invention relates to start-up, training, and device capability exchange procedures associated with modem systems.
BACKGROUND OF THE INVENTION
Modem systems are widely used to communicate data over the public switched telephone network (“PSTN”) and other telecommunication networks. A general block diagram of a typical modem system
100
is illustrated in
FIG. 1. A
first modem
102
may be operatively associated with any suitable data source, e.g., a first personal computer (“PC”)
104
. Similarly, a second modem
106
may be operatively associated with a second PC
108
. Although not shown in
FIG. 1
, modem
102
or modem
106
may be integrated with PC
104
or PC
108
, respectively.
When a data communication session is initiated, a data communication channel
110
is established between modems
102
and
106
. Digital data from PC
104
may be processed by modem
102
in accordance with any number of well-known protocols, then transmitted over data communication channel
110
to modem
106
. Upon receipt of the transmit signal, modem
106
processes the received signal to extract the original digital data, then presents the data to PC
108
.
The broad functional overview set forth above applies to virtually all modem systems. However, the detailed operation of modem systems is often governed by national or international standards. For example, certain modem systems may be governed by ITU-T Recommendation VO.34, published September 1994 (“VO.34”), the entire content of which is hereby incorporated by reference. To ensure that individual modem devices are compatible with one another, VO.34 specifies: transmission data rates; encoding and decoding techniques; signals and sequences utilized during start-up, training, and other modes; line probing methodologies; electrical characteristics; and other operating parameters.
Once a communication session is established between the modem
102
and modem
106
, the Phase 1 procedure set forth in VO.34 is performed. The Phase 1 procedure generally relates to the identification and selection of operating features supported by modems
102
and
106
; this procedure is often referred to as the modem capabilities exchange procedure. For example, different modem devices may be configured to operate in accordance with any number of standardized (but not mandatory) functional protocols. Prior to entering the data mode, the modem devices exchange and/or negotiate their operating capabilities and select one or more protocols to be followed during the current communication session. Phase 1 is governed by ITU-T Recommendation VO.8, published 1994 (“VO.8”), and ITU-T Recommendation VO.8 bis, published August 1996 (“VO.8 bis”). The entire contents of VO.8 and VO.8 bis are hereby incorporated by reference. VO.8 bis dictates how modems
102
and
106
perform the identification and selection of operating protocols.
Following Phase 1, modems
102
and
106
enter Phase 2 to conduct line probing and ranging in accordance with VO.34. The receiver associated with modem
106
is trained for optimized performance at the designated data rate during Phase 3. Phase 4, which follows the Phase 3 training, is performed to enable modems
102
and
106
to exchange data rates and modulation capabilities, e.g., the enabling of shaping, non-linear mapping, and trellis code type. After Phase 4 is complete, the modem system may enter the data transmission mode.
Due to the various start-up routines and procedures, an undesirably long time may pass between the initialization of the communication session and the beginning of the data mode. This delay (i.e., start-up latency) is due in part to the large amount of data transmission and processing that is performed during capabilities exchanging, training, and other VO.34 start-up procedures. Furthermore, VO.8 and/or VO.8 bis is performed at a relatively slow data rate, e.g., 300 bps, rather than the relatively high data rates typically associated with the data mode. Accordingly, the exchange and processing of data during VO.8 and VO.8 bis has the side effect of delaying the data mode.
In prior art VO.34 modem systems, the Phase 3 training is performed in response to the primary data rate selected for use during the data mode. Training the modem system at the primary data rate utilizes a relatively large number of training parameters designed to assess the line conditions and tune the equalizers resident at the receive modem, e.g., modem
106
. In addition, training for the primary data rate may also be more prone to errors; redundant transmission of training sequences may be required to reduce the likelihood of such errors. As a result, the rather long sequences transmitted during conventional Phase 3 training may exacerbate the problem of start-up latency in the modem system.
SUMMARY OF THE INVENTION
Accordingly, it is an advantage of the present invention that an improved modem system is provided that has a reduced start-up latency time associated therewith.
Another advantage of the present invention is that information associated with the exchange of modem operating capabilities is transmitted at a relatively high data rate compared to prior art systems.
Another advantage is that information associated with the exchange of modem operating capabilities is transmitted after the training of the receive modem.
A further advantage of the present invention is that it provides a method for reducing the time required to perform the procedures set forth in VO.8 bis.
Another advantage is that the modem system performs receiver training in two stages associated with different data rates to reduce the time required to effectively complete such training.
The above and other advantages of the present invention may be carried out in one form by a data transmission system having a first device and a second device, each being configured to communicate with one another over at least one communication channel, a transmitter configured to send initial capabilities exchange data at an initial data rate from the first device to the second device, and a rate negotiation element for changing the initial data rate to an intermediate data rate supported by the data transmission system. The transmitter is also configured to communicate operational capabilities data at the intermediate data rate from the first device to the second device.
REFERENCES:
patent: 5509050 (1996-04-01), Berland
patent: 5812281 (1998-09-01), Mukai et al.
patent: 5903603 (1999-05-01), Kennedy et al.
patent: 0601260A1 (1994-06-01), None
patent: 0711060A1 (1996-05-01), None
patent: WO 97/49228 (1997-12-01), None
Chin Stephen
Conexant Systems Inc.
Fan Chieh M.
Snell & Wilmer L.L.
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