Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1999-07-09
2002-12-31
Pham, Chi (Department: 2631)
Pulse or digital communications
Transceivers
Modems
C375S220000
Reexamination Certificate
active
06501790
ABSTRACT:
COPYRIGHT NOTICE
Copyright 1997 ViaDSP, Inc. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method for providing communication between modems over digital networks, and more specifically, the present invention is directed to methods and apparatus for providing high speed modem relay using locally connecting modems.
BACKGROUND OF THE INVENTION
A number of standards exist for defining communication protocols between modems coupled together for communication over the Public Switched Telephone Network (PSTN) or for communication over dedicated lines. For example, these standards include the V.34, V.32, and V.32bis standards among other standards promulgated by the International Telecommunications Union (ITU). A number of problems arise when modems implementing one of the above standards, or some similar standard, are coupled together over a digital link as shown in FIG.
1
and described below.
FIG. 1
shows a communication system
10
for providing full-duplex communication between modems
12
and
14
. The communication system includes, in addition to modems
12
and
14
, a first PSTN
16
, a second PSTN
18
, a first switch
20
, a second switch
22
, and a digital channel
24
connecting the first switch to the second switch. As understood by those skilled in the art, either or both of the PSTNs
16
and
18
could be replaced by dedicated lines. The digital channel may be implemented in one of a number of different ways such as through packet switched or synchronous transmission networks examples of which are the internet and a private satellite network respectively. Each of the first switch
20
and the second switch
22
includes a modem, which may be similar to modems
12
and
14
. The use of the modems in the switches minimizes the bandwidth needed to pass data over the digital network. In addition, each of the switches includes circuitry for coupling to the digital channel
24
.
Several problems arise when attempting to use standard high-speed modems as the modems
12
and
14
in the communication system
10
. These problems are due primarily to the relatively long network dependent propagation delays between switches
20
and
22
, which make it difficult for the system to support features of high speed modems defined in the V.34 and V.32bis standards. These features include: automoding, a feature which allows a high-speed modem, to recognize and communicate with a “slower” modem such as a V.22 or V.22bis modem; and “training”, including retraining, and “rate negotiation”, including renegotiation, which allow connected modems to train their equalizers and dynamically alter the data rate between the modems (while in data phase) based on continuous analysis of line conditions.
Another problem that can arise when using high speed modems in the communication system
10
is that differences in clock speeds may result in unacceptable bit error rates. For example, typical modem standards require that the clock offset of the clock signal used to transmit data be less than ±0.01% of the baud rate. If in the system
10
, the clock rate for sending data from modem
12
is 0.01% faster than nominal and the corresponding clock rate within switch
22
is 0.01% slower than nominal, then there will be a periodic inherent data loss in the communication system. In some prior art systems, this clock problem is hidden by error correction protocols negotiated by the end modems
12
and
14
that enable retransmission of lost data. This solution, however, results in an undesirable reduction in the effective data rate between modem
12
and modem
14
.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide methods and apparatus that overcome the problems and drawbacks discussed above associated with operating modems over digital channels.
In one general aspect, the invention features an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes a modem module that couples to the first modem over the first network. The modem module provides data to the first modem at a data rate determined in part by a modulation rate of the modem module. The apparatus further includes a digital channel interface module coupled to the modem module, the digital channel interface module including a buffer that receives data from the digital channel and provides data to the modem module, and a control circuit coupled to the buffer and the modem module, the control circuit being constructed and arranged to detect a level of data in the buffer and to modify the modulation rate of the modem module based on the level of data detected.
The digital channel can be coupled to a second apparatus, and the digital channel interface module can be constructed and arranged to communicate with the second apparatus over the digital channel. The modem module can be adapted to receive automoding signals from the first modem and to transfer the automoding signals to the digital channel interface module, and the digital channel interface module can be adapted to send data corresponding to the automoding signals to the second apparatus over the digital channel. The digital channel interface module can be adapted to receive automoding signals from the other apparatus over the digital channel and to transfer the automoding signals to the modem interface module, and the modem interface module can be adapted to send data corresponding to the automoding signals to the first modem. The modem interface module can be adapted to receive rate renegotiation signals from the first modem and to transfer the rate renegotiation signals to the digital channel interface module, and the digital channel interface module can be adapted to send data corresponding to the rate renegotiation signals to the second apparatus over the digital channel. The digital channel interface module can be adapted to receive rate renegotiation signals from the other apparatus over the digital channel and to transfer the rate renegotiation signals to the modem interface module, and the modem interface module can be adapted to send data corresponding to the rate renegotiation signals to the first modem. The first network can be a public switched telephone network, and the modem interface module can be constructed and arranged to communicate with the first modem over the public switched telephone network. The modem interface module can include modems of the type defined by V.34, V.32 and V.22 families of ITU specifications.
A second aspect of the present invention is directed to an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes first means for operatively coupling to the first modem over the first network to provide a data signal having a data modulation rate to the first modem, second means for transmitting data to and for receiving data from the digital channel, data storage means for storing data received from the digital channel, and control means, coupled to the first means, the second means and the data storage means, for detecting a level of data in the data storage means and for modifying the modulation rate based on the level of data detected.
The first means can include means for receiving automoding signals from the first modem, and means for transferring the automoding signals to the second means, and the second means can include means for sending data corresponding to the automoding signals to a second apparatus over the digital channel. The second means can include means for receiving automodin
Bayard Emmanuel
Mintz Levin Cohn Ferris Glovsky & Popeo P.C.
NMS Communications Corporation
Pham Chi
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